Publications

2026

• Static and dynamic Monte Carlo simulations of phonon drag effects on thermoelectric properties in silicon nanostructures
  
  • Ghanem Mohammad
  • Dollfus Philippe
  • Sen Raja
  • Sjakste Jelena
  • Saint-Martin Jérôme
  Computational Materials Science, Elsevier, 2026, 268, pp.114630. Thermoelectric transport in silicon nanofilms is investigated using a self-consistent electro-thermal Monte Carlo simulator that couples electron dynamics to a phonon bath with spatially varying temperature. A key novelty of this work is the explicit inclusion of the phonon-drag contribution, implemented by modifying the electron-phonon momentum exchange based on the local deviation of the phonon distribution from equilibrium. The method is validated against bulk silicon data and extended to incorporate rough boundary scattering for both electrons and phonons, yielding excellent agreement with experimental measurements on nanofilms. We also analyze the transient regime and show that a temperature bias produces a slower current response than a voltage bias, although the phonon-drag effect itself tends to accelerate the response. These results demonstrate that the proposed framework provides a powerful tool for predicting both steady-state and time-dependent thermoelectric behavior in semiconductor nanostructures. (10.1016/j.commatsci.2026.114630)
  DOI : 10.1016/j.commatsci.2026.114630
• Irradiation-resistant heterostructures based on monolayer MoS 2
  
  • Sangiorgi Emanuele
  • Migliore Francesca
  • Madonia Antonino
  • Alessi Antonino
  • Grasset Romain
  • Cavani Olivier
  • Panasci Salvatore Ethan
  • Schilirò Emanuela
  • Giannazzo Filippo
  • Seravalli Luca
  • Cannas Marco
  • Agnello Simonpietro
  Physica Status Solidi A (applications and materials science), Wiley, 2026. Monolayer molybdenum disulfide is a semiconducting 2D material presenting very appealing characteristics for its incorporation into electronic flexible devices. At present, atomic vacancies in its structure are known to significantly affect its properties. Nonetheless, the effects of electron irradiation on it are still under investigation. In this work, the structural, electronic, and optical properties of monolayer molybdenum disulfide are studied before and after electron irradiation. By analyzing samples either obtained via a mechanical exfoliation process or grown via chemical vapor deposition, we show that following irradiation no significant change is present. This result indicates a strong resistance to the effect of electron irradiation at energies able to induce the formation of sulfur vacancies. By comparing our results to the current literature, we hypothesize that previously reported effects of electron irradiation are either due to the formation of molybdenum vacancies or to ionization of the electronic shell of this material. The presented results help to shed light on the role of atomic vacancies on the properties of this 2D material from a fundamental point of view and on its usage in extreme environment applications. (10.1002/pssa.202500759)
  DOI : 10.1002/pssa.202500759
• Combined Temperature and Photobleaching Effects on P‐Doped Optical Fibers
  
  • Travailleur Allan
  • Roche Martin
  • Alessi Antonino
  • Ollier Nadège
  • de Noirfontaine Marie‐noëlle
  • Girard Sylvain
  Physica Status Solidi A (applications and materials science), Wiley, 2026, 223 (5). In this paper, we investigate the combined effects of temperature and photobleaching (PB) on multimode phosphorus‐doped (P‐doped) optical fibers (OFs) response under irradiation. To achieve this purpose, we investigate the kinetics of the radiation‐induced attenuation (RIA) in the visible spectral range (450–800 nm) under X‐ray irradiation up to 5Gy(SiO 2 ) with a dose rate of 10 mGy(SiO 2 )/s, varying the temperature of irradiation from −80°C to +80°C. This study is part of a recent series of investigations on the regeneration of these radiation‐sensitive optical fibers after they have served as dosimeters. The spectral range investigated allows us to study absorbing defects such as the metastable and stable phosphorus oxygen hole centers (POHC) and the P2 point defects. Our data suggests that thermally‐assisted bleaching has an impact during and after irradiation on the RIA. It is clear that thermal bleaching is relevant, especially for wavelengths below 580 nm; its contribution remains minor compared to that of the PB by 408 nm laser. Furthermore, thermal bleaching appears to be negligible for wavelengths above 580 nm. This work provides further understanding of the combined temperature and photobleaching effects on the regeneration of transmission capability of P‐doped fiber dosimeters in the visible range. (10.1002/pssa.202500774)
  DOI : 10.1002/pssa.202500774
• Near-field thermal radiation between deep subwavelength membranes driven by corner and edge modes
  
  • Ordonez-Miranda Jose
  • Anufriev Roman
  • Liñán-Abanto Rafael
  • Coral Maelie
  • Nomura Masahiro
  • Volz Sebastian
  Journal of Applied Physics, American Institute of Physics, 2026, 139 (8), pp.085108. We demonstrate that the thermal radiation between deep subwavelength membranes of silicon carbide (SiC) exhibits a maximum enhancement over that of infinite SiC surfaces separated by the same vacuum gap. Based on fluctuational electrodynamics, we show that this enhancement occurs at a separation distance of 200nm and increases for thinner and colder membranes. This peak arises from the dominant contribution of electromagnetic modes localized at the corner and vertical edges of sufficiently thin membranes, which enable a strong coupling of surface phonon-polaritons appearing along their top and bottom surfaces. These resonant corner and edge modes effectively extend the emission cross-sectional area of the membranes over their geometrical one and, therefore, amplify their thermal radiation. For 10-nm-thick membranes of SiC at 300 K, the thermal conductance reaches 54 pWK−1, which yields a maximum enhancement of 4.5 over the value for infinite SiC surfaces. Our findings, thus, reveal that the regime of near-field thermal radiation driven by corner and edge modes emerges and is optimized in deep subwavelength membranes separated by intermediate distances. (10.1063/5.0311645)
  DOI : 10.1063/5.0311645
• Experimental study of spin pumping and spin-to-charge conversion in superconductor/ferromagnet heterostructures
  
  • Hassan Hadi H.
  , 2026. Superconducting spintronics" aims to merge dissipationless superconducting correlations with the spin degree of freedom of spintronics. Superconductor/Ferromagnet (S/F) bilayers constitute a simple superconducting spintronic device, and have been under study for years. The main focus so far has been on s-wave superconductors, meanwhile, high-Tc d-wave superconductors are more easily accessible thanks to critical temperatures (Tc) exceeding the boiling point of liquid nitrogen (77K). In this thesis, we leverage two experimental techniques to study multiple S/F heterostructures: ferromagnetic resonance (FMR) -driven spin pumping and spintronic terahertz emission. The first technique relies on exciting the magnetization of the ferromagnet, producing a spin current that diffuses into the adjacent materials, and probing its effect through optical and electrical responses. The second technique is based on an ultrafast demagnetization which drives a current of superdiffusive spin polarized hot electrons; when these hot electrons propagate in a material with high spin Hall angle, a transverse charge current is produced, emitting a THz electromagnetic pulse. We use an s-wave superconductor (MoSi) and a d-wave cuprate (YBCO), with either an insulating ferrimagnet (YIG) or metallic ferromagnets (Py, LSMO, CoFeB). We started by comparing YIG/MoSi bilayers with a YBCO/Py: both systems show a drop of the Gilbert damping at the superconducting transition, consistent with the conventional picture stating that the opening of superconducting gap suppresses the quasiparticle spin sink in the superconductor. YBCO/Py shows nevertheless an upturn in the damping at low temperatures, as reported by S. J. Carreira et al. (2021), linked to the emergence of Andreev bound states at faceted interfaces. When we probe the electrical response of lithographically patterned bilayers of YIG/MoSi and YBCO/Py, both systems share a behavior that appears to be universal: transverse voltages, odd in magnetic field reversal, exhibit a large increase across the superconducting transition, with varying intensity as a function of the superconductor's thickness, reaching up to two orders of magnitude higher than the normal-state voltages. The evidenced decrease of spin pumping across the superconducting transition exclude spin Hall conversion as the mechanism behind the simultaneous voltage increase. We propose a theoretical explanation of the anomalous voltage peak based on the superconducting diode effect, in collaboration with A. Buzdin et al.. We pushed our FMR study into half-metallic ferromagnets in YBCO/LSMO bilayers, which exhibit an upturn in the damping below Tc instead of a drop. Thanks to the atomically abrupt interface of these bilayers, we interpret the damping increase as a successful access to unconventional superconducting spin sinking channels, notably interface-bound quasiparticles and spin triplet correlations. Finally, we demonstrated the feasibility of d-wave-superconductor/spintronic-terahertz-emitter (YBCO/Pt/CoFeB) heterostructures through a thin film structure optimization. Exploratory THz emission and transmission measurements show promising preliminary results of the superconducting proximity effect on the THz emission of superconducting terahertz emitters. Overall, this manuscript argues for a shift from bulk-material selection toward interface engineering as the primary lever in superconducting spintronic devices.
• A short derivation of Boltzmann distribution and Gibbs entropy formula from the fundamental postulate
  
  • Lairez Didier
  , 2022. Introducing the Boltzmann distribution very early in a statistical thermodynamics course (in the spirit of Feynmann) has many didactic advantages, in particular that of easily deriving the Gibbs entropy formula. In this note, a short derivation is proposed from the fundamental postulate of statistical mechanics and basics calculations accessible to undergraduate students. (10.48550/arXiv.2211.02455)
  DOI : 10.48550/arXiv.2211.02455
• Energy and Information:a Chronicle of Hesitations on the Role of the Observer in Physics
  
  • Lairez Didier
  , 2025. Energy has no definition, except that given by a conservation principle which essentially amounts to defining it as the elements of an open list of unknown cardinality. Entropy, identified by Shannon as information we lack, has too many definitions. This results in an unstable and hesitant interpretation of their link. Thermodynamics, the science of changes in form of energy, is phenomenological, all its laws are induced from observation. From the origin, the concept of energy is linked to the observer's knowledge, to the information he has: what and where to look and with what instruments. Thermodynamics only addresses the sensible world. It is Aristotelian. But this is disturbing if we consider that reason can give us access to Plato's intelligible world, the one that is beyond the sensible world and independent of us. This is disturbing if we consider that science can access to the intrinsic properties of things, those which are independent of us. This is disturbing if we have a purely Platonic conception of science. Hence the statistical mechanics approach ("The rational foundation of thermodynamics", J.W. Gibbs). This is the first pendulum movement of ideas, whose oscillations continue to this day, because unfortunately statistical mechanics introduces many inconsistencies, mainly due to the ergodic hypothesis. Luckily, these inconsistencies are all solved by Shannon's information theory. Sadly, information theory is too Aristotelian and too conceptual. Fortunately, Landauer principle makes it more \textquote{physical}. This is currently the latest attempt to bringing the notions of energy and information back to what is considered the right side of science, that of Plato. Landauer principle is now commonly regarded as a fundamental law of physics. Unpleasantly, it can be shown that this principle is not one. (10.20944/preprints202505.2245.v1)
  DOI : 10.20944/preprints202505.2245.v1
• Electron charge dynamics and charge separation: A response theory approach
  
  • Lacombe Lionel
  • Reining Lucia
  • Gorelov Vitaly
  SciPost Physics, SciPost Foundation, 2026, 20 (2), pp.035. This study applies response theory to investigate electron charge dynamics, with a particular focus on charge separation. We analytically assess the strengths and limitations of linear and quadratic response theories in describing charge density and current, illustrated by a model that simulates charge transfer systems. While linear response accurately captures optical properties, the quadratic response contains the minimal ingredients required to describe charge dynamics and separation. Notably, it closely matches exact time propagation results in some regime that we identify. We propose and test several approximations to the quadratic response and explore the influence of higher-order terms and the effect of on-site and nearest-neighbour interactions U U and V V . (10.21468/SciPostPhys.20.2.035)
  DOI : 10.21468/SciPostPhys.20.2.035
• Unraveling energy flow mechanisms in semiconductors by ultrafast spectroscopy: Germanium as a case study
  
  • Raciti Grazia
  • Abad Begoña
  • Dettori Riccardo
  • Sen Raja
  • K. Sivan Aswathi
  • Sojo-Gordillo Jose M
  • Vast Nathalie
  • Rurali Riccardo
  • Melis Claudio
  • Sjakste Jelena
  • Zardo Ilaria
  Advanced Science, Wiley Open Access, 2026, pp.e15470. Semiconductor materials are the foundation of modern electronics, and their functionality is dictated by the interactions between fundamental excitations occurring on (sub-)picosecond timescales. Using time-resolved Raman spectroscopy and transient reflectivity measurements, we shed light on the ultrafast dynamics in germanium. We observe an increase in the optical phonon temperature in the first few picoseconds, driven by the energy transfer from photoexcited holes, and the subsequent decay into acoustic phonons through anharmonic coupling. Moreover, the temperature, Raman frequency, and linewidth of this phonon mode show strikingly different decay dynamics. This difference was ascribed to the local thermal strain generated by the ultrafast excitation. We also observe Brillouin oscillations, given by a strain pulse traveling through germanium, whose damping is correlated to the optical phonon mode. These findings, supported by density functional theory and molecular dynamics simulations, provide a better understanding of the energy dissipation mechanisms in semiconductors. (10.1002/advs.202515470)
  DOI : 10.1002/advs.202515470
• Competing effects of charge-carrier and impurity scattering limiting phonon heat conduction in heavily-doped silicon
  
  • Sen Raja
  • Acosta Abanto Juan Carlos
  • Brouillard Mélanie
  • Gomès Séverine
  • Robillard Jean-François
  • Ciavatta Alessandro
  • Paulatto Lorenzo
  • Vast Nathalie
  • Saint-Martin Jérôme
  • Sjakste Jelena
  • Chapuis Pierre-Olivier
  , 2026. With respect to undoped semiconductors, thermal transport by phonons is limited by two additional mechanisms when doping increases: charge-carrier and impurity scattering. Previous works provided contradicting conclusions on the dominant doping-induced scattering mechanism in silicon. In this work, we clarify the competing roles of impurity and charge-carrier scatterings of phonons in the reduction of the lattice thermal conductivity in n-and p-doped silicon, by comparing experimental results obtained with the 3ω method and predictive DFT-based calculations for a large set of doping concentrations and a wide temperature range. The analysis allows delimiting the doping and temperature ranges where (i) extrinsic scattering surpasses intrinsic (phonon-phonon and phonon-isotope) one and (ii) one of the two doping-induced mechanisms plays the dominant role. We observe that the experimental setup impacts both the thermal conductivity value and the critical doping concentration at which the thermal conductivity is reduced by half.