P4F colloquium 2026

11 May 2026, 09:00 → 13 May 2026, 18:00 Europe/Prague

Slov - "Sál A. Kochanovské" - část A (podium) Solid/1.NP/P.23/1 (Slovanka)

We are pleased to invite you to the Physics For Future Colloquium 2026, taking place from May 11–13, 2026, at the Institute of Physics of the Czech Academy of Sciences in Prague (FZU).

Over the course of three days, you will have the opportunity to explore the research achievements of our fellows across various fields of physics. Presentations will follow a science café format to make cutting-edge physics accessible and engaging for a broad audience, including non-experts.

The programme also includes sessions dedicated to possible alternative careers after achieving the doctoral title, such as science diplomacy, research management or an editor of a research magazine.

Another session will be dedicated to a way of transition from lab to industry, where the speakers will speak about their careers.

P4F_Colloquium_2026_invitation.pdf

P4F_Colloquium_2026_Programme.pdf

Monday 11 May

09:00 → 09:15 Welcome session

09:00 Welcome

09:15 → 10:30 Division of Elementary Particle Physics & ELI: Part I

09:15 Silicon Carbide Detectors

This talk reviews the development of 4H-SiC Low Gain Avalanche Detectors as a next step in wide bandgap sensor technology. A central part of the contribution is the development and evaluation of the first segmented LGAD structures produced in 4H-SiC. The presentation will highlight progress on segmentation design, charge-sharing behaviour, and early timing studies, supported by initial TCT and testbeam campaigns. In parallel, the stability and uniformity of the implanted gain layer are being investigated across wafers and compared with TCAD predictions to understand the achievable control of internal multiplication in SiC. These results frame the current status of SiC LGAD development and define the next steps toward robust, radiation-tolerant timing detectors for future high energy physics applications.

Speaker: Peter Švihra

svihra_wide_bandgap_detectors.pdf

09:30 Radiation-hydrodynamics of star-disc collisions for quasi-periodic eruptions

Quasi-periodic eruptions (QPEs) are a recently discovered class of repeating X-ray flares from galactic nuclei hosting supermassive black holes. Their physical origin remains uncertain, but repeated collisions between a star and an accretion disc have emerged as a promising explanation. In this scenario, each disc crossing drives shocks, launches dense outflows, and produces radiation that may power the observed flares. We use three-dimensional radiation-hydrodynamics simulations to study the collision dynamics, the outflow properties, and the resulting radiative signatures. The simulations show that the interaction is naturally asymmetric: energy and momentum are redistributed preferentially along the star’s direction of motion, producing forward and backward outflows with different masses, velocities, and luminosities. The outflow and emission also depend on the stellar velocity and size, the disc density profile, and the inclination of the stellar orbit relative to the disc. Overall, these results support star-disc collisions as a promising framework for explaining the main observed features of QPE sources.

Speaker: Dr Taj Jankovič (Institute of Physics of the Czech Academy of Sciences)

jankovic_taj.pdf

jankovic_taj.pptx

09:45 Entanglement through topological interfaces in CFT revisited

Present theoretical predictions for the entanglement entropy through topological defects are violated in numerical simulations of critical systems. In this talk, I introduce a new formalism for the preparation of reduced density matrices in the presence of topological defects, and emphasize the role of defect networks with which they can be dressed. Grouplike and duality defects are considered in detail for the Ising model, establishing agreement with numerically found entanglement entropies. Since this new construction functions at the level of reduced density matrices, it accounts for topological defects beyond the entanglement entropy to other entanglement measures. The framework employs boundary conformal field theory techniques to implement the factorization of Hilbert space, which I recapitulate at the beginning of the talk and discuss its relation with the entanglement spectrum.

Speaker: Christian Northe (Czech Academy of Sciences)

KolloquiumMai26.pdf

10:00 Study of stray radiation at a laser-driven ion beamline

Laser-driven ion accelerators are an emerging technology capable of producing ultra-short, high-intensity particle beams with broad energy spectra, opening new opportunities in physics, materials science, and medical applications. Within this context, the ELIMAIA–ELIMED beamline is designed to transport, shape, and deliver laser-accelerated ion beams with controlled parameters for multidisciplinary research and radiobiology.

Stray radiation generated both at the laser–target interaction and along the beamline was characterized and investigated. This radiation—including neutrons and photons—originates from the primary laser-plasma interaction as well as from subsequent beam interactions with matter, posing challenges for diagnostics and radiation protection. Monte Carlo simulations, benchmarked against experimental measurements, were used to study the origin and spatial distribution of these fields, supported by dedicated radiation monitoring systems.

This presentation reports the main outcomes of this work, including improved understanding of radiation sources and their spatial distribution, and demonstrates approaches for reducing background radiation in laser-driven ion beamlines.

Speaker: Helena Lefebvre (Extreme Light Infrastructure Beamlines)

HLefebvre_P4F_presentation.pdf

10:15 Quo vadis Single-Mirror Small-Size Telescope

An important method in gamma-ray astronomy is observation using Imaging Atmospheric Cherenkov Telescopes (IACTs). IACTs are large-diameter, ground-based reflective telescopes equipped with sensitive cameras. The telescopes detect the faint flashes of Cherenkov light emitted during the development of extensive air showers, which are initiated by high-energy cosmic gamma-ray photons interacting with the atmosphere.
The Single-Mirror Small-Sized Telescope (SST-1M) is an IACT prototype developed by a consortium of institutions from the Czech Republic, Poland, and Switzerland. An array of two SST-1M telescopes was constructed at the Ondřejov Observatory of the Czech Academy of Sciences and has been operational since 2022. The telescopes utilize an innovative camera system featuring a photodetection plane based on silicon photomultiplier technology and fully-digitized electronics. The SST-1M can perform joint observations in stereo mode, significantly improving sensitivity, angular resolution, energy resolution and gamma/hadron separation. Since their installation, the telescopes have successfully detected several galactic and extragalactic cosmic gamma-ray sources. The ongoing discussion regarding the relocation of the telescopes is currently centered on two potential future sites. The performance of the SST-1M telescopes at both locations will be presented. Moreover, recent results from a hybrid analysis incorporating data from surface detectors will be shared.

Speaker: Patrik Čechvala (Institute of Physics, Czech Academy of Sciences)

Colloquium_Fellows_Cechvala_2026.pdf

10:30 → 10:45 Coffee break

10:45 → 12:00 Division of Elementary Particle Physics & ELI: Part II

10:45 Numerical polology: next-generation model-building for precision cosmology

Particle dark matter, along with many ultraviolet scenarios, suggest that additional low-energy degrees of freedom remain to be discovered. Theories of new physics may be understood as statistical models, for which the Lagrangian couplings are model parameters. The net worth of a theory is determined by its Bayesian evidence: the likelihood of precision cosmology data is multiplied by the prior probability of the couplings, and integrated over the coupling-space. Precision cosmology has made great advances both in the collection of data and the efficient computation of likelihoods. But whilst the complementary programme of manufacturing candidate models is very active, it is far less systematic, and priors are seldom specified.

We present a framework for massively automating the construction of new physics models, designed to scale with the ever-increasing volume of data. Numerical polology uses nested sampling to identify unitary and technically natural regions in coupling-space. Such models form self-consistent effective field theories, which is essential since the predictivity of a model (the ability to compute a likelihood) is endowed by the systematics of QFT alone. The framework is adapted to bosonic theories of the dark sector: the phenomenological implications of arbitrary field content (field number, rank and index-symmetry) can be systematically explored with recourse to tools such as GetDist and Cobaya. The framework is inspired by the SOFTSUSY/SARAH tools for supersymmetric model-building, and builds directly on the PSALTer software for modified gravity. The latter is computer algebra software, which scales badly with complexity: numerical polology overcomes this technical hurdle and facilitates data-driven model-building.

We illustrate numerical polology with a Stueckelberg extension of massive gravity, and derive simple posterior reweightings from black hole superradiance, large scale structure, pulsar timing data and gravitational wave dispersion. We also discuss realistic prospects for more sophisticated likelihood plugins. We then perform a high-resolution survey of the coupling-space of symmetric rank-two fields, using high-performance computing. We discuss numerical challenges, and the benefits of migrating the present Julia implementation to JAX.

• List item

Speaker: William Barker (FZU)

PresentationLite.pdf

11:00 Understanding Closed-String Amplitudes in the Pure Spinor Approach

Scattering amplitudes in string theory describe how strings interact, but even the simplest cases can be subtle in modern formulations. In this talk, I will revisit the two-point function for closed strings in the pure spinor approach, where a naïve extension of open-string methods fails.

We will show how this issue can be resolved by carefully implementing BRST symmetry, leading to a consistent and essentially unique prescription based on an unconventional choice of variables. This completes the picture for this class of amplitudes and clarifies an important aspect of the formalism.

Speaker: Sitender Kashyap

11:15 Understanding initial stage effects in high energy collisions

Probing the earliest stages of high-energy collisions is essential for understanding the formation and evolution of strongly interacting matter. In this work, we investigate initial-state effects in relativistic collider environments through the interplay of parton energy loss (quenching) and diffraction. These results offer a novel pathway to constrain parton densities, saturation phenomena, and the early-time dynamics of quark–gluon matter in high-energy collisions.

Speaker: Souvik Priyam Adhya

public_P4F_spadhya_2026.pdf

12:00 → 13:00 Lunch

13:00 → 15:30 Alternative careers

15:30 → 16:00 Coffee break

Tuesday 12 May

09:00 → 10:00 Colloquium breakfast

10:00 → 12:00 Division of Optics and HiLASE: Part I

10:00 Metal Organic Frameworks-based Surface Enhanced Raman Scattering (SERS) for Water Pollution Monitoring

In response to growing environmental concerns, there is a need for accurate and efficient methods to detect water pollutants. This research focuses on developing an advanced microchannel-based Surface-Enhanced Raman Spectroscopy (SERS) substrate. This innovative platform aims to identify various water contaminants, including pharmaceutical residues like diclofenac, caffeine, and carbamazepine. The main objective is to design a microfluidic system incorporating customised SERS substrates to improve detection sensitivity and accuracy. The project is divided into phases, starting with the creation of a set of SERS substrates: lithography-derived gold nanoparticles and differently shaped gold nanoparticles. Different Metal- Organic Frameworks (MOFs) will be tested to trap pollutants on the substrates. The system's core is its structured microchannels, which allow the smooth flow of liquid samples. These channels integrate SERS substrates, forming a platform for pollutant detection. Water samples containing pollutants are introduced into the microchannels, where the porous MOFs grown on plasmonic nanostructures capture analytes, enabling enhanced Raman signals to be recorded. Spatial analysis of Raman spectra across the channels provides detailed insights into the detection process and interactions between pollutants and substrates, confirming system reliability and sensitivity. The combined use of diverse SERS substrates and precise microchannel design creates a platform capable of multi-pollutant detection, suitable for real-time, on-site monitoring. By integrating advanced technology into this design, this work showcases the transformative potential of microchannel-based SERS substrates in promoting cleaner, safer water resources amid environmental conservation efforts.

Speaker: Prasanth Asokan (Division of Optics)

10:20 Development of Fe-based medium entropy alloy for cryogenic applications

A cost-effective, Co-free Fe-based medium entropy alloy (MEA), was developed to achieve an exceptional combination of strength and ductility at both room and cryogenic temperatures. The Co-free design is strategically motivated by the high cost, supply risk, and density associated with Co-containing alloys, making the present system more economically and industrially viable without compromising performance. The alloy design prioritizes higher concentrations of low-cost elements (Fe, Mn, Si, and Al) while limiting expensive constituents, enabling a sustainable pathway for advanced structural materials. Thermodynamic phase calculations is used for the development of a predominantly face-centered cubic (FCC) matrix with precipitate formation, promoting multiple deformation mechanisms. The alloy was synthesized via vacuum casting followed by homogenisation, forging and hot rolling to obtain a refined microstructure. The compositional design, with higher Fe content, enables the activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), contributing to enhanced strain hardening and mechanical stability. The developed MEA exhibits superior strength–ductility synergy compared to conventionally processed hot-rolled 316L stainless steel and representative Co-containing medium and high entropy alloy. Notably, the alloy demonstrates improved tensile performance at both ambient and cryogenic temperatures, highlighting its suitability for demanding applications under cryogenic environments.

Speaker: Himanshu Kumar (HiLASE Centre, Institute of Physics of the Czech Academy of Sciences Dolní Břežany, Czech Republic)

10:40 Tuning Laser–Plasma Optical Emissivity via Advanced Spatial Beam Shaping

Laser-produced plasmas (LPPs) are widely used as light sources for laser-induced breakdown spectroscopy (LIBS) and for nanoparticle generation. The optical emission properties of LPPs are strongly governed by early laser–plasma interaction dynamics. In this study, advanced laser beam shaping was employed to control plasma formation and emission during laser ablation of metallic and non-metallic targets. Doughnut-shaped beams and diffractive beam-splitting configurations were investigated to examine their influence on plasma–target coupling, plume evolution, and optical emission behavior. Experiments were conducted using short and ultrashort laser pulses over a range of ambient pressures. Time-resolved diagnostics were employed including fast gated optical emission spectroscopy, nanosecond imaging of plume expansion, and Langmuir probe measurements. By tailoring the spatial intensity distribution of the incident laser beam, plasma dynamics and emission efficiency were systematically modified, resulting in enhanced optical emission compared to conventional Gaussian beam irradiation. This study bridges advanced beam shaping and high-precision analytical spectroscopy, seeking to push LIBS sensitivity limits.

Speaker: Dr Girum A. Beyene (FZU - INSTITUTE OF PHYSICS OF THE CZECH ACADEMY OF SCIENCES)

11:00 Optimized control of optoelectronic properties in CuCrO2 films fabricated by pulsed laser deposition

Transparent p–n junctions are essential for the next advancement in transparent electronics (displays, sensors, or solar cells). The challenges arise from the lack of high-quality p-type transparent conducting oxides. A promising candidate is CuCrO2, a wide-bandgap delafossite, which offers both p-type conductivity and strong transparency.
In this P4F project, pulsed laser deposition (PLD) was employed to systematically optimize p-type CuCrO₂ thin films. Using the third harmonic of a pulsed nanosecond Nd:YAG laser for target ablation, key deposition parameters, including oxygen partial pressure, substrate temperature and Cu/Cr ratio, were optimized. The optimized film, deposited at 700 °C and 2.3 mPa O₂, exhibited 64% average visible transmittance and an electrical conductivity of 62.5 S cm-1. These values correspond to a record Gordon figure of merit of 6150 µS and a Haacke figure of merit of 1.2 × 10-5 S, demonstrating substantial progress toward high-performance p-type transparent conducting films. XPS analysis revealed a high Cu/Cr ratio in the optimized film, suggesting Cu antisite defects as the origin of the enhanced conductivity.
Alternatively, to control the Cu concentration in the coatings, two KrF excimer laser beams simultaneously ablated CuO and Cr2O3 ceramics. This strategy enabled single-step deposition of films with Cu/Cr ratios from 0.6 to 1.4 across Cu-poor and Cu-rich regimes, without requiring separate targets for each composition. Structural and optoelectronic analyses showed polycrystalline, multiphase films containing CuCrO2, Cu2O, Cr2O3, Cu, and Cr, with CuCrO2 as the dominant phase. The films retained approximately 60% visible transparency and an optical bandgap of about 3.2 eV. Notably, the Cu-deficient film with Cu/Cr = 0.6 exhibited improved conductivity and a higher figure of merit, among synthesized samples, confirming Cu deficiency as an effective route to enhance conductivity while maintaining transparency.
Current efforts focus on fabricating high-performance plasmonic p-Cu1+xCr1-xO₂/n-AZO transparent p–n junctions. Based on the progress achieved, the project is on track to meet its planned milestones by the end of this year. Overall, this work establishes a clear pathway for developing high-performance p-type CuCrO2-based TCOs and integrating them into transparent p–n junctions for energy-efficient next-generation transparent electronics.

Speaker: Shahab Ahmed Abbasi (FZU – Institute of Physics of the Czech Academy of Sciences)

11:20 Shaping light to shape nanoparticles: toward controlled and productive pulsed laser ablation in liquid

Due to their size ranging from one nanometre to a few hundred nanometres, nanoparticles exhibit a high surface-to-volume ratio and specific light-matter interactions (plasmon effect) that benefit applications such as catalysis, optics, and medicine. Chemical synthesis methods dominate the market due to their strong reproducibility and tunable properties. However, these methods are highly material specific, requiring a dedicated protocol to be developed for each new composition. Moreover, the reagents involved – surfactants, reducing agents, and precursors – can persist as contaminants in the final product, raising concerns for sensitive applications. Therefore, offering a versatile, well controlled, and clean method for nanoparticle production would be a significant asset to the industry.
Pulsed laser ablation in liquid addresses some of these requirements. Briefly, a laser pulse is fired onto an immersed target, resulting in confined plasma generation and subsequent nanoparticle nucleation and growth. The method is highly versatile – it can, in principle, be applied to any bulk target – and clean, as only the target and solvent are required. However, nanoparticle growth follows diverse out-of-equilibrium mechanisms, which gives rise to several challenges. Notably, productivity remains limited, and more importantly, fine control of nanoparticle morphology is still restricted to broad size distributions and spherical particles.
To benefit from PLAL’s intrinsic cleanliness while tackling these limitations, the RAYLEIHLAB project investigates temporal and spatial beam shaping strategies. Productivity is addressed through fluence optimisation via a multiple-beam approach, while size control is pursued through finer laser-matter interaction tuning using double-pulse or donut-shaped beam configurations.

Speaker: Rémi Bérard (FZU)

11:40 Non-invasive plasma diagnostics for low temperature deposition of VO2-based thin film by magnetron sputtering

To regulate reactive HiPIMS processes of vanadium oxides, plasma diagnostics based on the RF Sobolewski probe theory has been carried out. In addition to the typical approach of using a probe inserted into the chamber at the substrate side, a novel non-invasive approach using the target as an in-situ probe has also been developed. The RF Sobolewski probe method enables the measurements of ion flux, plasma density, electron temperature, as well as the sheath impedance during the HiPIMS process. The plasma characterization reveals that the imaginary part of sheath impedance is the most promising parameter for future HiPIMS process regulation. Furthermore, from the HiPIMS discharge waveforms, it is found that the average cathode current per pulse proves to be more suitable than the peak current (density) for process regulation when constant HiPIMS average power is maintained.

Speaker: Xiao Li (Division of Optics, Department of Low-Temperature Plasma)

Colloquium_Xiao--2026.pptx

12:00 → 13:00 Lunch

13:00 → 15:00 From lab to industrial partners

15:00 → 15:30 Coffee break

Wednesday 13 May

09:00 → 10:30 Divisions of Solid State Physics and Condensed Matter Physics: Part I

09:00 Automated Serial Precession Electron Diffraction for highly dose-sensitive crystals

TEM-based Electron Diffraction (ED) has progressed from sample orientation or phase analysis to a reliable method for ab initio crystal structure determination at the nanoscale. Owing to the high interaction strength, the practical limits of ED applicability continue to be explored, but its limitations are apparent: only a finite dose budget can be spent on collecting diffraction patterns from a crystal before affecting its structure.

The last few years have seen the development of many approaches that can be used to mitigate radiation damage. Simply merging short 3D experiments alleviates the issue, but for highly sensitive samples, limiting exposure to the absolute minimum is crucial. Here, Serial ED provides a solution. It does bring its own drawback of diffraction-pattern sparsity and partiality, but these can in turn be addressed using beam precession.

Serial Precession Electron Diffraction (Serial PED) is a simple method that can be used to strongly mitigate beam-damage contributions while offering enough data for structure solution. As demonstrated in 2025 by Plana-Ruiz et al. (J. Appl. Crystallogr., 58, 1249), supplementing serial ED with rocking illumination largely averages out orientation-dependent dynamical effects while increasing reciprocal space coverage. This not only facilitates indexing but ultimately lowers the required number of patterns and thus both the length and complexity of the diffraction experiment.

During my contribution, I will demonstrate the first fully automated acquisition algorithm for Serial PED. Rather than relying on image recognition or human input, the approach skips the imaging altogether and systematically scans the entire accessible area for diffraction. Optimized for handling up to kHz frame rates, the implementation determines grid geometry and then performs long sweeps across it, evaluating incoming frames live using a multiprocessing dispatcher.

The presented algorithm is implemented entirely in the open-source Python package Instamatic. Experiment progress can be saved, reloaded, monitored, and adjusted via an intuitive graphical interface while enabling easy customization of the back-end. Notably, the implementation utilizes only simple stage motions and thus can work for any TEM that provides beam precession, a fast camera, and programmable sliding stage control.

Speaker: Daniel Tchoń (Institute of Physics of the Czech Academy of Sciences)

Colloquium2_presentation.pptx

09:15 SMART Heusler nanowires for sensing and actuation

This project builds a comprehensive understanding of Ni-Fe-Ga Heusler nanowires. These materials provide the means for transfer of the shape memory and magnetocaloric properties of Heusler alloys towards nanoscale. A single-step synthesis developed during the project and immediate functionality make the nanowires a suitable material in the field of microelectronics, cell-oriented biomedicine and smart-hyperthermia applications. The fabrication technology was transferred to the FZU and the materials undergo an investigation of their magnetic and functional properties in the field of the shape memory phenomena and martensitic transformation, guiding the understanding of Heusler alloys' behavior at the nanoscale. The acquired results are currently used to build a prototype of nanowire–based sensing device, employing the changes induced by a martensitic transformation.

Speaker: Michal Varga

09:30 Unlocking Altermagnetic Magnons through Electrical and Optical Methods

Magnonics — the study of spin waves — is a promising field for developing energy-efficient future information technologies. In this project, we explored magnon transport in altermagnetic materials, a novel class of collinear and compensated magnetic systems with unique spin symmetries that allow for many useful spintronic phenomena.
Our experiments confirmed the transfer of spin current across interfaces between a heavy metal and an altermagnet (Pt|Ba₂CoGe₂O₇), which is a critical process for all-electrical magnon excitation and detection. Notably, we observed anisotropy in this transfer, suggesting that magnon transport in altermagnets may also be anisotropic. We also successfully fabricated devices for all-electrical magnon excitation and detection and conducted preliminary measurements. However, further optimization of measurement techniques will be required to improve the signal-to-noise ratio.
Using THz spectroscopy, we also investigated coherent magnon propagation in α-Fe₂O₃, another altermagnetic candidate. Our results provided clear evidence of coherent magnons and their group velocity, offering new insights into their fundamental properties. These findings lay the groundwork for future studies on anisotropy, external field effects, and temperature dependence.
Overall, this work not only deepens our understanding of altermagnets but also opens new pathways for their application in spintronic devices.

Speaker: Miina Leiviskä

09:45 Decoherence enhanced effects in open quantum systems

Environmental interactions are usually associated with decoherence and the loss of quantum information. However, they also play an essential role in the measurement, control, and stabilisation of quantum devices. We theoretically investigate this dual role in two open quantum systems.

The first system is a singlet–triplet qubit in a double quantum dot monitored by a quantum point contact. Standard descriptions of Pauli-spin-blockade readout typically assume a single electronic level per dot [1–3]. In this regime, the quantum point contact (QPC) acts as a nearby charge sensor. The counting statistics of the QPC current provides a clear readout contrast: the singlet branch produces noisy, super-Poissonian current, while the Pauli-blocked triplet branch remains approximately Poissonian. We extend this model by including a higher-energy electronic level. This additional level opens a leakage pathway that allows the triplet state to bypass Pauli spin blockade, reducing the fidelity of spin-to-charge conversion. At high QPC bias or small level splitting, this leakage produces strong bunching and super-Poissonian fluctuations in the triplet signal, so that the triplet branch can become noisier than the singlet. For larger level splittings or lower bias, the leakage is suppressed and the conventional readout regime is recovered. These results identify higher-level leakage as an important error mechanism in QPC-based spin readout and provide guidance for optimising bias, tunnel couplings, and level structure in semiconductor quantum devices.

The second system consists of two bosonic modes, each coupled to its own
independent bath. Motivated by the weak-coupling limitations on bosonic
autonomous entanglement engines identified in Ref. [4], we study whether
stronger and more general system–bath coupling can generate steady-state
entanglement autonomously. Using a non-equilibrium Green’s function approach, we go beyond Markovian weak-coupling treatments and include non-Markovian noise, strong bath coupling, and counter-rotating interaction terms which are neglected in the weak-coupling theory. The resulting logarithmic negativity shows that tailored dissipative environments can generate and stabilise entanglement in regimes that are inaccessible to weak-coupling theory.

Together, these studies show that the environment is not only a source of decoherence. When modeled as part of the device, environmental interactions can reveal new error mechanisms, define useful operating regimes, and provide resources for quantum readout and autonomous entanglement generation.

References
[1] S. D. Barrett and T. M. Stace, Phys. Rev. B 73, 075324 (2006).
[2] Ł. Marcinowski, K. Roszak, P. Machnikowski, and M. Krzyżosiak, Phys. Rev. B 88, 125303 (2013).
[3] K. Roszak, Ł. Marcinowski, and P. Machnikowski, Phys. Rev. A 91, 032118 (2015).
[4] B. Longstaff, M. G. Jabbour, and J. B. Brask, Phys. Rev. A 108, 032209 (2023).

Speaker: Karol Kawa

colloquium2026.pptx

10:00 Engineering Atomic Size Mismatch in High-Entropy Garnets and Perovskites: A Novel Pathway to Enhance Functional Properties

Atomic size mismatch in oxide crystals has long been treated as a barrier, linked to phase instability, dopant segregation, and uncontrolled defect formation during melt growth. This project overturns that limitation by establishing ionic size mismatch and melt nonstoichiometry as controllable variables that define phase structure and functional properties in rare-earth aluminate high-entropy oxides. The central problem addressed is the absence of predictive composition-structure-property relationships in compositionally complex oxides, where conventional doping models fail and equilibrium phase diagrams provide no guidance for the multiphase and non-stoichiometric regimes that deliver the highest performance.
The work introduces a unified strategy based on three independently controlled mismatch parameters: (i) ionic-radius incompatibility on shared lattice sites, (ii) growth-rate-controlled phase partitioning, and (iii) melt-to-crystal stoichiometric deviation. These variables are accessed through micro-pulling-down ($\mu$-PD) crystal growth, directional solidification, and controlled melt chemistry, combined with synchrotron spectroscopy, electron paramagnetic resonance, thermoluminescence, and temperature-dependent luminescence. The $\mu$-PD method enables rapid exploration of off-equilibrium compositions and direct mapping of phase evolution beyond the limits of conventional Czochralski growth.
This approach yields direct control over phase architecture and functionality. In Ce$^{3+}$-doped YAG-YAP eutectics, growth rate defines lamellar spacing and dopant partitioning, enabling control of light propagation through the material by adjusting the microstructure. Large domains transmit blue light, while finer structures enhance scattering, enabling tuning of emission characteristics for high-power white laser diode operation. The same dual-phase structure enables ratiometric thermometry, with relative sensitivity up to $1.1\%~\mathrm{K}^{-1}$ under X-ray excitation, demonstrating self-activated optical temperature sensing under ionizing radiation.
A key advance is the use of strong cation size mismatch to engineer defect distributions and energy transfer. In Pr$^{3+}$-doped Lu$_3$(Al,Sc)$_5$O$_{12}$, Sc$^{3+}$ substitution introduces local lattice distortion that suppresses segregation, increases compositional uniformity, and localizes excitons. This directly enhances energy transfer to Pr$^{3+}$ centers, producing a six-fold increase in scintillation light yield ($11{,}200~\mathrm{ph/MeV}$). At higher Sc content, a critical threshold ($x \approx 1.5$) is reached where the garnet lattice destabilizes, generating a hypoeutectic garnet-perovskite structure. This transition arises from site instability under extreme size mismatch and produces a distinct defect configuration that further improves charge-carrier dynamics. At even higher mismatch, ferroelastic inclusions form that undergo symmetry changes under neutron irradiation, indicating potential for selective neutron radiation memory applications.
Melt nonstoichiometry provides an additional means of controlling phase composition and performance. In Ce$^{3+}$-doped (Tb,Y)$_3$Al$_5$O$_{12}$, moderate Y$_2$O$_3$ deficiency induces a garnet-Al$_2$O$_3$ dual-phase structure with improved thermal stability and luminous efficacy up to $158~\mathrm{lm/W}$, suitable for high-power white lighting based on laser diode excitation. At higher deficiency, a garnet--perovskite structure forms, increasing scintillation output by up to $80\%$ relative to the standard single-phase Y$_3$Al$_5$O$_{12}$:Ce scintillator through modified rare-earth partitioning and energy transfer.
The outcome is a predictive Crystal Phase Engineering framework in which mismatch is used to control phase formation, defect structure, and carrier dynamics from the atomic to the microstructural scale. This enables targeted design of materials with combined optical and radiation-detection properties. The resulting materials provide a pathway toward next-generation scintillators, high-power phosphors, self-activated thermometers operating in ionizing radiation fields, and ferroelastic materials for neutron-responsive memory in nuclear and space technologies.

Speaker: Dr Karol Bartosiewicz (Institute of Physics of the Czech Academy of Sciences)

Karol_Bartosiewicz_13.05.2026.pptx

10:15 High-Quality Stable Perovskite Quantum Dots Inks for Large Area Solar Cells

All-inorganic cesium lead iodide (CsPbI₃) perovskite quantum dots (PQDs) have emerged as promising candidates for next-generation photovoltaic and optoelectronic applications owing to their optoelectronic properties and solution processability.
However, the dynamic binding of intrinsic ligands (OA and OAm) to the PQD surface is easily disrupted in the polar environment of the purification process, leading to the formation of abundant surface defects, particularly (VI) and (VA) vacancies. This defect density is further amplified under ambient purification conditions, where moisture and oxygen accelerate phase instability and degrade the optoelectronic properties. Despite extensive efforts to improve the optoelectronic properties and stability of PQDs, effective strategies to suppress the defect formation during ambient purification are still lacking. We aim to develop a robust and scalable surface modification and purification strategy that mitigates surface defect generation under open-air conditions, enabling the production of high-quality PQDs suitable for subsequent formulation into quantum dot inks for large-area perovskite solar cells.
To achieve this, guanidinium trifluoroacetate was introduced during the final cooling stage (120–100 °C) of CsPbI₃ PQD preparation. We find that the surface modification with guanidinium cations effectively controls Ostwald ripening, as observed by in-situ PL measurements that reveal real-time emission peak shifts during cooling to enable insights into suppressed particle growth and ripening dynamics, passivates surface trap states, and enhances phase stability. As a result, the treated CsPbI₃ PQDs exhibit a significantly enhanced photoluminescence quantum yield (~80% relative to ~54% for the control sample), a narrower emission linewidth, and improved structural stability compared with their conventionally purified counterparts.
This work establishes a practical route for the reliable synthesis of high-quality CsPbI₃ PQDs under ambient conditions, offering a scalable strategy for the production of highly stable perovskite QDs. Importantly, these stable PQDs are well-suited for formulation into conductive quantum dot inks, enabling scalable fabrication of large-area perovskite solar cells and other optoelectronic devices.

Speaker: Jahangeer Khan (Thin Film and Nanostructures Department, FZU)

10:30 → 11:00 Coffee break

11:00 → 12:30 Divisions of Solid State Physics and Condensed Matter Physics: Part II

11:00 Optical creation and Electrical manipulation of non-trivial Magnetic Textures

Magnetic textures have recently attracted significant theoretical and experimental interest due to their rich and complex physical properties, making them potential candidates for new computational devices. Their feasibility as a data processing unit has also recently been demonstrated. However, the current developments in this regard are confined to a very small number of magnetic textures. In this presentation, we will explore ways to generate different types of textures, both in and out of equilibrium. This can be achieved through suitable material engineering or external stimulation. We will also demonstrate how to identify different configurations via their electrical response, exploiting the complex connection between their real and reciprocal space topology. These studies can therefore open new directions for designing texture-based computational devices.

Speaker: Sumit Ghosh

Colloquium_Ghosh_May26.pdf

11:15 GridFF: Efficient Simulation of Organic Molecules on Rigid Substrates

GridFF, an efficient method for simulating molecules on rigid substrates. The approach is inspired by techniques from techniques used in protein–ligand docking in biochemistry. By projecting molecule–substrate interactions onto precomputed spatial grids with tricubic B-spline interpolation, GridFF reduces the computational cost by orders of magnitude compared to traditional pairwise atomistic models, without compromising the accuracy of forces or trajectories. The CPU implementation of GridFF in the open-source FireCore package provides a 100–1000× speedup over all-atom simulations using LAMMPS, while the GPU implementation – running thousands of system replicas in parallel – samples millions of configurations per second, enabling an exhaustive exploration of the configuration space of small flexible molecules on surfaces within minutes. Furthermore, as demonstrated in our previous application of a similar technique to high-resolution scanning probe microscopy, GridFF can be extended beyond empirical pairwise potentials to those derived from ab initio electron densities. Altogether, this unlocks accurate high-throughput modeling of molecular self-assembly, adsorption, and scanning probe manipulation in surface science.

Speaker: Indranil Mal (FZU)

11:30 Tuning cooperativity of spin-crossover complexes on 2D surfaces and detecting spin-state transitions via magneto-transport studies

Despite demonstrating bistability, the absence of long-range magnetic order and poor electrical conductivity in spin-crossover (SCO) materials limit their prospects in spintronics. Here, we report easily processable Fe-based SCO nanostructures specifically [Fe(Htrz)2(trz)]BF4 grown on 2D reduced graphene oxide (rGO). X-ray photoelectron spectroscopy (XPS) reveals a new bonding state and interfacial charge transfer (CT) between rGO and the SCO nanoparticles. This CT promotes long-range magnetic exchange coupling among Fe(II) centers and induces magnetization within the rGO matrix.
The heterostructure exhibits enhanced cooperativity and magnetic ordering, which is manifested in the appearance of magnetic hysteresis loops. While pristine SCO nanostructures are paramagnetic with zero coercivity, the SCO-rGO hybrid displays a giant coercive field of ~3000 Oe. This induced magnetic order is further supported by temperature-dependent Mössbauer spectra analysis, which reveals the proportion of Fe(II) spin states and underscores how the 2D network enhances intermolecular interactions.
We addressed the typically insulating nature of SCO materials (conductance ~10-11 S) by embedding them on the conducting rGO template, which enhances conductance by six orders of magnitude (~10-5 S). This facilitates the detection of bistable spin states through conductance switching. Temperature-dependent transport data (I-V characteristics) demonstrate sharp spin-state transitions near room temperature, with the low-spin (LS) to high-spin (HS) transition resulting in significant conductance drops (up to 136%). Ab initio calculations corroborate these findings, confirming that interfacial charge transfer opens additional super-exchange pathways, thereby strengthening magnetic interactions in the hybrid architecture.

Speaker: Dr Shatabda Bhattacharya (FZU)

11:45 Probing perturbations in flexible molecular crystals employing 3D electron diffraction

Molecular crystals with macroscopic flexibility have shown tremendous potential for applications as flexible optical waveguides, fluorescent materials, piezo- and ferroelectrics, semiconductors and drug tablets in the last decade.[1 and references therein] μ-X-ray diffraction technique employing synchrotron radiation has been used to understand the underlying mechanisms of deformation.[2] However, inherent disadvantages of the method preclude quantification of underlying defects under strain.

3D electron diffraction is an emerging technique that has revolutionised nanocrystallography.[3] Exploiting the property of electrons that it interacts 104 times as compared to X-rays as well its ability to probe structures of submicron-sized crystalline samples, we have employed the technique to map deformations in mechanically deformed crystals of some molecular crystals.

In this contribution, we will demonstrate how 3D ED has aided in accurate atomic resolution studies by successfully performing structure solution and refinement against 3D ED data collected on mechanically deformed crystals. Furthermore, dynamical refinements reveal valuable physical information with respect to the variation of mosaicity of the different regions of a perturbed crystal.

This is the first demonstration of the enormous potential of 3D ED to probe atomic-scale perturbations in pliable molecular crystals. The implications of this study are enormous with respect to (i) use of laboratory-based TEM technique to complement large-scale facilities such as synchrotron and (ii) investigations of perturbations in pharmaceutical materials due to tabletting.

References:
[1] Z. Zhou et al. (2022) Chem. Eng J. 450, 138333.
[2] A. J. Thompson et al. (2021) CrystEngComm 23, 5731.
[3] M. Gemmi et al. (2019) ACS Cent. Sci. 5, 1315–1329.

Speaker: Somnath Dey (Electron Crystallography Group, Structural Analysis Department, Solid State Physics Section, FZU)

2026_Colloquium_Somnath.pdf

2026_Colloquium_Somnath.pptx

12:00 Broadband Charge Transport in 2D Ti₃C₂Tₓ MXene Thin Films: From D.C. to 80 THz

Probing charge carrier dynamics across a broad frequency range — from terahertz (THz) to infrared (IR) regimes — presents a powerful, contact-free procedure to investigate nanoscale transport phenomena in low-dimensional materials. Combining frequency dependent optical conductivity spectra with conventional d.c. electrical measurements enable a comprehensive picture of carrier transport mechanisms in morphologically complex systems such as solution processed 2D materials.
Here, we report a systematic investigation of charge transport in thin films of 2D Ti₃C₂Tₓ MXene over an exceptionally wide spectral range (d.c. + 0.3 - 80 THz). Films of varying thickness were fabricated by convection-assisted self-assembly at the liquid–air interface, yielding well-controlled 2D flake networks on semi-insulating Si substrates. Non-zero d.c. conductivity across all samples confirms a percolated network, validated by microstructure analysis via. optical and electron microscopy. Systematic increase of the real conductivity in the frequency range ~ 0.2 - 16 THz reveals partial carrier localization. Broadband fitting using the modified Drude-Smith model demonstrates a clear correlation between the localization rate and the characteristic MXene flake size. At higher frequencies, a crossover to intrinsic Drude behavior — marked by decreasing conductivity and increasing optical transparency — is observed. We further discuss the systematic evolution of transport parameters as a function of film thickness, providing design guidelines for MXene-based optoelectronic and electromagnetic applications.

Speaker: Kunal Tiwari (Department of Dielectrics, FZU Na Slovance)

Colloquim 13th May 2026_KT.pptx

12:15 Nitrogen doped Porous carbon spheres for energy storage application

Porous carbon materials are widely recognized as promising electrode candidates for supercapacitors due to their high specific surface area and tunable pore architecture, which facilitate efficient ion adsorption and enhance electric double-layer capacitance (EDLC). Furthermore, heteroatom doping, particularly nitrogen incorporation, can introduce additional pseudocapacitive contributions via faradaic reactions, thereby improving overall electrochemical performance. In this work, nitrogen-doped porous carbon spheres (NPCSs) were synthesized and evaluated as electrode materials for supercapacitor applications. Among the samples, NPCS-1 exhibits superior electrochemical performance in 1 M H₂SO₄ electrolyte compared to solid carbon spheres, demonstrating enhanced capacitance. This improvement is attributed to its high specific surface area (640 m² g⁻¹) and well-developed mesoporous structure (~7 nm), which promotes efficient ion transport and charge storage. These findings highlight the synergistic effect of nitrogen doping and hierarchical porosity, establishing NPCSs as promising candidates for next-generation high-performance supercapacitor electrodes.

Speaker: Dr Ranjithkumar Raju (Institute of Physics of the Czech Academy of Science)

Colloquium-2_Ranjithkumar Raju.1.pdf

12:30 → 13:30 Lunch