Other Condensed Matter · Cross-listed from physics.ins-det
Approximate resolution convolution function for fitting a dispersion gap measured on a triple-axis spectrometer
Emma Y. Lenander, Silas B. Schack, Kim Lefmann et al. (+1 more)
We present an analytic convoluted-gap function, eq. 11 in the manuscript, for fitting dispersion gaps measured on triple-axis spectrometers (TAS). At the gap, the instrumental resolution skews the signal, producing a high-energy tail that complicates fitting. Our function assumes an instrumental $Q$-resolution with two equal wide and one narrow direction (typical of focused TAS instruments), and a
parabolic dispersion at the gap, which is exact for quadratic and accurate for linear dispersions if the resolution is moderate. We demonstrate, that our function outperforms previous methods of fitting a gap, by giving a better fit and more accurate gap determination, seen in figure 4. Here, the anti-ferromagnetically gapped material; MnF$_2$ is simulated in a double-focusing TAS instrument. We also tested our function on experimental data on MnF$_2$ from a TAS-like instrument, where we reproduce the gap size from previous accurate experimentally determined measurements. The function is simple to implement, converges reliably, and we recommend its use for future gap fitting on TAS data.
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All authors Emma Y. Lenander, Silas B. Schack, Kim Lefmann, Henrik M. Rønnow
Mesoscale and Nanoscale Physics
Dispersive detection of single microwave photons with quantum dots
Stephanie Matern, Alberto Biella, Pasquale Scarlino et al. (+2 more)
Within a
circuit quantum electrodynamics architecture, we theoretically investigate the detection of a single propagating microwave
photon traveling through a resonant microwave cavity dispersively interacting with a double
quantum dot tunnel-coupled to a lead. Under suitable conditions, a single
photon in the cavity can induce a measurable change in the electronic occupation of the charge states. We develop a
quantum cascade approach that enables a time-resolved description of a single-
photon wave packet impinging on the cavity. We make use of a simple model of charge detector to assess the efficiency of our photo-detection configuration as functions of key parameters such as coupling strength, tunneling rate, temperature, and
photon resonance linewidth. We finally highlight a measurement-induced backaction effect on the cavity mode associated with the dispersive, non-absorptive detection process.
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All authors Stephanie Matern, Alberto Biella, Pasquale Scarlino, Iacopo Carusotto, Gianluca Rastelli
Statistical Mechanics
Fate of diffusion under integrability breaking of classical integrable magnets
Jiaozi Wang, Sourav Nandy, Markus Kraft et al. (+2 more)
Diffusive transport is a ubiquitous phenomenon, yet the microscopic origin of
diffusion in interacting physical systems remains a challenging question, irrespective of whether
quantum effects are dominant or not. In this work, we study infinite temperature
spin diffusion in a classical integrable, space-time discrete version of anisotropic Landau-Lifshitz magnet in the easy-axis regime, subjected to integrability-breaking perturbations. Our numerical results based on large-scale simulations reveal i) a sharp change in the
spin diffusion constant as a function of perturbation strength in the thermodynamic limit and ii) a crossover from non-Gaussian to Gaussian statistics of magnetization transfer reflected in higher order cumulants under integrability breaking. Both our observations hint to the presence of non-trivial
diffusion mechanism inherent to integrable systems.
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All authors Jiaozi Wang, Sourav Nandy, Markus Kraft, Tomaž Prosen, Robin Steinigeweg
Materials Science
Micrometer thick single crystal iron-garnet films on a diamagnetic buffer layer for cryogenic applications
A.N. Kuzmichev, P.M. Vetoshko, E.I. Pavluk et al. (+8 more)
This work advances the frontier of low-damping
magnetic materials, directly addressing the demand for ultra-low-loss components in
quantum computing and cryogenic electronics. Here we demonstrate a new approach to get single
crystal micrometer-thick yttrium iron garnet (YIG) films with low damping through isolating and mitigating interfacial paramagnetic contributions of a paramagnetic substrate by a buffer-layer. The YIG films with the diamagnetic yttrium scandium gallium garnet buffer layer grown by
liquid phase epitaxy on a gadolinium gallium substrate demonstrate homogeneity unprecedented for the thin planar YIG structures, yielding
ferromagnetic resonance linewidths of 4.9 MHz at 4 K and 5.9 MHz at 16 mK, the lowest values reported to date. These results underscore the critical role of interfacial engineering in overcoming intrinsic material limitations, opening avenues for further optimization in
spin-based technologies.
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All authors A.N. Kuzmichev, P.M. Vetoshko, E.I. Pavluk, A.A. Holin, G.A. Knyazev, A.S. Kaminskiy, S.S. Demirchan, R. Tyumenev, D.S. Kalashnikov, V.S. Stolyarov, V.I. Belotelov
Materials Science
Observation of a phonon bottleneck effect on the thermal depopulation from a photoexcited shallow defect in silicon
Sergio Revuelta, Hai I. Wang, Mischa Bonn et al. (+1 more)
We report the observation of a
phonon bottleneck effect impacting the thermal depopulation of photoexcited shallow defects in high-resistivity silicon. Using time-resolved terahertz (THz) spectroscopy, near-band-gap excitation produces a pronounced temporal delay in photoconductivity, indicating that a fraction of photogenerated charge carriers is temporarily trapped immediately after excitation. By analyzing the frequency-resolved complex photoconductivity as a function of pump-probe delay and
photon energy, we attribute this delay to the presence of a localized shallow state situated approximately 40 meV from the band edge, which competes with silicon's indirect band-to-band absorption. The zero-order kinetic profile of the temporal delay, its invariance with respect to
photon flux, and its temperature dependence collectively support the existence of a
phonon bottleneck that hinders the thermal release of electrons from this shallow trap. this represents experimental evidence of a
phonon bottleneck effect associated with the thermal activation of shallow traps in photoexcited silicon. These findings provide microscopic insight into carrier relaxation dynamics in silicon and highlight the significance of electron-
phonon interactions in the ultrafast processes governing materials used in optoelectronic applications.
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All authors Sergio Revuelta, Hai I. Wang, Mischa Bonn, Enrique Canovas
Statistical Mechanics
Phase Diagrams of the YK Surface-Reaction Model on 2D lattices with Exchange Diffusion
Henrique A. Fernandes, Roberto da Silva and Paulo F. Gomes
In this work, we investigate the phase diagrams of the Yaldram and Khan catalytic surface model on square and hexagonal
lattices when exchange
diffusion is allowed for carbon monoxide (CO) and nitrogen (N) atoms. To reach our goal, we carried out steady-state Monte Carlo (MC) simulations over $4\times 10^5$ points, for both
lattices, in order to obtain a framework of the steady reactive state of the model for different values of the nitric
oxide dissociation rate, $r_{NO}$. The results show the emergence of steady reactive state for certain values of $r_{NO}$ and of exchange
diffusion rate $x$ when the simulations take place on square
lattices. Our findings on the hexagonal
lattice also show that the
diffusion of these species favors the appearance of the active phase for values of $r_{NO}$ lower than that found for the standard model. In addition, we observed that the system possesses a continuous phase transition and a discontinuous one separating the active phase from absorbing states for both
lattices, except for $r_{NO}=1$ in which the continuous phase transition is destroyed and a steady reactive state emerges from the beginning since very small values of $x$.
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Materials Science
Atomistic Origin of Photoluminescence Quenching in Colloidal MoS2 and WS2 Nanoplatelets
Surender Kumar, Markus Fröhlich, Stefan Velja et al. (+8 more)
Large chemical tunability and strong light-matter interactions make colloidal transition metal dichalcogenide (TMD) nanostructures particularly suitable for light-emitting applications. However, ultrafast
exciton decay and quenched photoluminescence (PL) limit their potential. Combining femtosecond transient absorption spectroscopy with first-principles calculations on MoS2 and WS2 nanoplatelets, we reveal that the observed sub-picosecond
exciton decay originates from edge-located optically bright hole traps. These intrinsic trap states stem from the metal d-orbitals and persist even when the sulfur-terminated edges are hydrogen-passivated. Notably, WS2 nanostructures show more localized and optically active edge states than their MoS2 counterparts, and zigzag edges exhibit a higher trap density than armchair edges. The nanoplatelet size dictates the competition between ultrafast edge-trapping and slower core-
exciton recombination, and the states responsible for
exciton quenching enhance catalytic activity. Our work represents an important step forward in understanding
exciton quenching in TMD nanoplatelets and stimulates additional research to refine physicochemical protocols for enhanced PL.
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All authors Surender Kumar, Markus Fröhlich, Stefan Velja, Marco Kögel, Onno Strolka, André Niebur, Samuell Ginzburg, Muhammad Sufyan Ramzan, Jannik C. Meyer, Jannika Lauth, Caterina Cocchi
Superconductivity
Expansion of Momentum Space and Full 2$\pi$ Solid Angle Photoelectron Collection in Laser-Based Angle-Resolved Photoemission Spectroscopy by Applying Sample Bias
Taimin Miao, Yu Xu, Bo Liang et al. (+18 more)
Angle-resolved photoemission spectroscopy (ARPES) directly probes the energy and momentum of electrons in
quantum materials, but conventional setups capture only a small fraction of the full 2$\pi$ solid angle. This limitation is acute in
laser-based ARPES, where the low
photon energy restricts momentum space despite ultrahigh resolution. Here we present systematic studies of bias ARPES, where applying a sample bias expands the accessible momentum range and enables full 2$\pi$ solid angle collection in two dimension using our 6.994 eV
laser source. An analytical conversion relation is established and validated to accurately map the detector angle to the emission angle and the electron momentum in two dimensions. A precise approach is developed to determine the sample work function which is critical in the angle-momentum conversion of the bias ARPES experiments. Energy and angular resolutions are preserved under biases up to 100 V, and minimizing beam size is shown to be crucial. The technique is effective both near normal and off-normal geometries, allowing flexible Brillouin zone access with lower biases. Bias ARPES thus elevates
laser ARPES to a new level, extending momentum coverage while retaining high resolution, and is applicable across a broad
photon-energy range.
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All authors Taimin Miao, Yu Xu, Bo Liang, Wenpei Zhu, Neng Cai, Mingkai Xu, Di Wu, Hongze Gu, Wenjin Mao, Shenjin Zhang, Fengfeng Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Zuyan Xu, Zhihai Zhu, Xintong Li, Hanqing Mao, Lin Zhao, Guodong Liu, X. J. Zhou
Materials Science
A Combined Theoretical and Experimental Study of Oxygen Vacancies in Co$_3$O$_4$ for Liquid-Phase Oxidation Catalysis
Amir Omranpour, Lea Kämmerer, Catalina Leiva-Leroy et al. (+12 more)
In the present work, we investigate oxygen vacancies (V$_\mathrm{O}$) in Co$_3$O$_4$, both in the bulk phase and under
liquid-phase ethylene glycol oxidation, by combining theoretical and experimental techniques. Density functional theory calculations for bulk Co$_3$O$_4$ show that introducing an oxygen vacancy reduces two adjacent Co$^{3+}$ ions to Co$^{2+}$ and narrows the band gap. The newly formed Co$^{2+}$ ions adopt high-
spin configurations in distorted octahedral sites and remain stable in this state in ab initio molecular dynamics simulations at $300$ K. Computed O and Co K-edge X-ray absorption spectra for ideal and vacancy-containing Co$_3$O$_4$ show excellent agreement with the experimental data and serve as references to analyze the
liquid-phase ethylene glycol oxidation. The comparison with experimental O K-edge spectra of fresh and post-reaction catalysts shows that fresh samples resemble the vacancy-containing reference, whereas post-reaction spectra shift toward the ideal reference. These results suggest that under
liquid-phase ethylene glycol oxidation conditions, Co$_3$O$_4$ becomes more oxidized rather than reduced, by refilling preexisting oxygen vacancies. This is further supported by the observation that higher O$_2$ pressures increase the conversion and that the catalyst remains stable and active over several cycles.
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All authors Amir Omranpour, Lea Kämmerer, Catalina Leiva-Leroy, Anna Rabe, Takuma Sato, Soma Salamon, Joachim Landers, Benedikt Eggert, Eugen Weschke, Jean Pascal Fandré, Ashwani Kumar, Harun Tüysüz, Martin Muhler, Heiko Wende, Jörg Behler
Superconductivity
Increase of critical current density in FeSe superconductor by strain effect
Han Luo, Xinyue Wang, Xin Zhou et al. (+6 more)
Conventional $J_c$-enhancement methods like doping and irradiation often introduce extrinsic elements or defects, altering intrinsic properties. Here, we report a significant $J_c$ enhancement in FeSe single
crystals through compressive strain applied using a glass-fiber-reinforced plastic substrate with anisotropic thermal contraction during cooling. Under zero field at 2 K, $J_{\text{c}}$ increases by a factor of $\sim$4 from $\sim 2.3 \times 10^{4}$ to $\sim 8.7 \times 10^{4}$ A cm$^{-2}$; at 5 T, it achieves an order-of-magnitude enhancement, rising from $\sim 1.0 \times 10^{3}$ to $\sim 1.0 \times 10^{4}$ A cm$^{-2}$. Analysis based on the Dew-Hughes model of the $f_{\text{p}}$(h) relationship shows that strain strengthens
vortex pinning, and shifts the pinning mechanism from point-like pinning to combined point and surface pinnings. This work offers an effective method to enhance FeSe's current-carrying limitation, deepens understanding of iron-based
superconductors' pinning mechanisms, and highlights strain engineering's potential for optimizing superconducting performance.
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All authors Han Luo, Xinyue Wang, Xin Zhou, Longfei Sun, Mengqin Liu, Ran Guo, Sheng Li, Yue Sun, Zhixiang Shi
Superconductivity
Depairing critical current density and the vortex-free state in FeSe nanobridges
Yue Sun, Yuling Xiang, Zhixiang Shi et al. (+1 more)
The depairing limit and the
vortex-free state in a
superconductor is crucial for both the study of supercurrent related physics and the application eliminating noise linked to
vortex motion. In this work, we report the evidence of depairing limit and the
vortex-free state achieved by
geometric constraint in FeSe
superconductors. A series of narrow bridges with varying widths at the same location of a single
crystal were prepared by the \textquotedblleft pickup\textquotedblright method using successive focused ion beam millings. By simply reducing the width of bridge, the magnitude of critical current density ($J_{\rm{c}}$) is enhanced more than one order, evidence the achievement of depairing limit. Moreover, in the bridge with a width smaller than the penetration depth ($\lambda$), $J_{\rm{c}}$ is found to be robust against
magnetic field up to 1 kOe. The field-robust $J_{\rm{c}}$ is a strong piece of evidence for
vortex-free state, which is created by the enhancement of lower critical fields due to
geometric constraint.
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All authors Yue Sun, Yuling Xiang, Zhixiang Shi, Tsuyoshi Tamegai
Materials Science
Fostering Innovation: Streamlining Magnetocaloric Materials Research by Digitalization
Simon Bekemeier, Moritz Blum, Luana Caron et al. (+15 more)
Refrigeration based on the magnetocaloric effect (MCE) can contribute to energysaving, environmentally friendly cooling in private households, or industrial application. The cooling is based on the reversible heat release or uptake during a phase-transformation of the materials that can be controlled by a
magnetic field. This process could replace conventional compression-based refrigeration, which often relies on environmentally harmful refrigerants. Here we show, how to digitalize the process chain for the synthesis, theoretical and experimental characterization, and prototypical application of magnetocaloric
alloy. Different Heusler
alloys are examined experimentally as model systems for potential application in
magnetic cooling. OTTR templates are used for the acquisition and semantic representation of knowledge in the development of an ontology. The ontology, when combined with unstructured data, can be exploited to train a model that can then be used to predict missing facts, which can help to gain new insights and to generate new hypotheses. Furthermore, tools are developed that automate data acquisition into ontological structures and workflows are implemented that provide an easy-to-use theoretical and experimental evaluation of the MCE from first principles and raw data.
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All authors Simon Bekemeier, Moritz Blum, Luana Caron, Alisa Chirkova, Philipp Cimiano, Basil Ell, Inga Ennen, Michael Feige, Maik Gaerner, Thomas Hilbig, Andreas Hütten, Günter Reiss, Tapas Samanta, Sonja Schöning, Christian Schröder, Lennart Schwan, Chris Taake, Martin Wortmann
Superconductivity
Boost of critical current density near quantum critical points in FeSe-Based superconductors with two superconducting domes
Wei Wei, Qiang Hou, Jiajia Feng et al. (+10 more)
Recent studies have identified two superconducting domes in FeSe-based
superconductors. It was discovered that each dome is accompanied by a distinct nematic
quantum critical point (QCP): one associated with a pure nematic QCP, and the other with a nematic QCP entangled with antiferromagnetism (AFM). In this study, we delve into the
evolution of the critical current density ($J_{\rm{c}}$) with doping in FeSe${_{1-x}}$(Te/S)${_{x}}$ single
crystals, focusing on the behavior within the two superconducting domes. Surprisingly, three maxima of $J_{\rm{c}}$ were found in the two superconducting domes, with two sharp peaks in $J_{\rm{c}}$ observed precisely at the endpoints of the nematic phases, at $x$(Te) $\sim$ 0.5 for Te-doped and $x$(S) $\sim$ 0.17 for S-doped FeSe. The mechanisms of
vortex pinning and the influence of
quantum critical fluctuations have been extensively explored, emphasizing the contribution of
quantum critical fluctuations in modulating $J_{\rm{c}}$. Additionally, an increase in $J_{\rm{c}}$ was also noted near FeSe$_{0.1}$Te$_{0.9}$, where its origin has been explored and discussed. This finding provides crucial clues about the existence of an ordered phase endpoint beneath the superconducting dome, offering an initial basis for further investigation into the potential presence of a QCP beneath it.
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All authors Wei Wei, Qiang Hou, Jiajia Feng, Xinyue Wang, Xin Zhou, Nan Zhou, Yan Meng, Wei Zhou, Wenjie Li, Xiangzhuo Xing, Tsuyoshi Tamegai, Yue Sun, Zhixiang Shi
Superconductivity
Temperature-Induced Superconductivity Enhancement under Large Exchange Field
Xusheng Wang, Lianyi He and Shuai-hua Ji
Through a comprehensive free energy analysis, we demonstrate that finite temperature can simultaneously weaken superconductivity and mitigate
spin polarization induced depairing, leading to potential non-monotonic temperature-dependent behaviors in
superconductors subjected to large exchange fields. Remarkably, superconductivity can be counterintuitively enhanced by temperature when the Zeeman energy exceeds the superconducting order parameter, owing to the competition between thermal and
magnetic effects. We propose that multiband effect offers one possible microscopic route for this temperature-induced enhancement and demonstrate it explicitly within a two-band superconducting model. A detailed parameter analysis identifies the conditions under which this phenomenon emerges, suggesting that temperature-enhanced superconductivity may be observable in materials such as MgB2 and FeSe through transport and tunneling measurements.
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Materials Science
Light-induced photomechanical patterning of ferroelectric polarization
Alban Degezelle, Jonas Strobelt, Sarah Loebner et al. (+10 more)
Tailoring at will polar textures in ferroelectrics is critical for the development of nanoscale electronics and functional
oxide technologies. Freestanding ferroelectric membranes have enabled studies of strain-induced polarization responses, but the control over membrane shape and local polarization typically remains limited to spontaneous buckling or uniaxial mechanical deformations. In this work, we employ a versatile photosensitive-
polymer patterning approach to impose programmable bending strain profiles in ferroelectric membranes. Using BaTiO3 as a model system, we demonstrate deterministic 90{\deg} polarization rotation driven by engineered in-plane strain, and 180{\deg} polarization reversal arising from flexoelectric coupling through a controlled strain gradient. These results establish this programmable bending as a powerful approach to investigate strain-dependent domain structures, leverage flexoelectric effects, and engineer custom ferroelectric landscapes across a wide range of
oxide membranes.
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All authors Alban Degezelle, Jonas Strobelt, Sarah Loebner, Moussa Mebarki, Stephane Fusil, Vincent Garcia, Bruno Berini, Vincent Polewczyk, Yves Dumont, Sylvia Matzen, Philippe Lecoeur, Svetlana Santer, Thomas Maroutian
Materials Science
Growth driven phase transitions in Zinc Oxide nanoparticles through machine-learning assisted simulations
Quentin Gromoff, Magali Benoit, Jacek Goniakowski et al. (+2 more)
This study investigates the formation of zinc
oxide (ZnO) nanoparticles, a material of significant technological interest with complex structural properties, through atom-by-atom deposition modeling a process common in bottom-up synthesis. Our findings demonstrate that, although the body-centered tetragonal (BCT) structure is thermodynamically stable at
equilibrium for small particle sizes, the deposition process induces a
crystal-to-
crystal phase transition into the more stable wurtzite (WRZ) phase. This transformation is facilitated by a specific redistribution of the nanoparticle ions, which effectively compensates the emerging polar facets at the moment of transition. These insights offer a deeper understanding of
oxide nanoparticle formation, which should ultimately help the design of materials with targeted structural features.
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All authors Quentin Gromoff, Magali Benoit, Jacek Goniakowski, Carlos R. Salazar, Julien Lam
Superconductivity
Anomalous phase shift and superconducting diode effect in Josephson junctions via thin films of rare-earth intermetallic magnets
G. A. Bobkov, I. A. Shvets, I. V. Bobkova et al. (+3 more)
The
superconductor/ferromagnet/
superconductor (S/F/S) Josephson junctions (JJs) with an anomalous ground state phase shift $\varphi_0 \neq 0,\pi$ ($\varphi_0$-S/F/S JJs) enable the implementation of the zero-field Josephson diode effect with the possibility to control the diode efficiency and polarity. It is just as important that in this case $\varphi_0$ provides a coupling between the superconducting phase and the magnetization of the interlayer. Such $\varphi_0$-S/F/S JJs can be used for superconducting
memory and logic
circuit applications. Here we present the results of theoretical calculation of the current-phase relationship (CPR), exhibiting the Josephson diode effect and $\varphi_0\neq 0,\pi$, for a JJ through a specific
magnetic material. As the interlayer of the JJ we consider an ultra-thin film of intermetallic lanthanide ($Ln$)-based compound $\mathrm{GdIr_2Si_2}$. Using the density functional theory (DFT) methods, we study the electronic structure and
magnetic properties of the film. Then the effective tight-binding
Hamiltonian (TBH), demonstrating high quantitative consistency with the electronic properties obtained from DFT calculations, is constructed. The TBH is used to calculate CPR in the framework of the Bogolubov-de Gennes approach. The CPRs demonstrate a pronounced $\varphi_0$ of the order of unity and a pronounced Josephson diode effect with the diode efficiency $ \lesssim 0.3$. Moreover, the efficiency can be controlled via rotation of in-plane magnetization in the interlayer. The prospects for utilizing alternative
magnetic $Ln$-based materials of the $LnT_2X_2$ family ($T$ is a transition metal and $X$ is a $p$-element from groups III-V) for the implementation in $\varphi_0$-S/F/S JJs are also discussed.
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All authors G. A. Bobkov, I. A. Shvets, I. V. Bobkova, A. M. Bobkov, S. V. Eremeev, E. V. Chulkov
Strongly Correlated Electrons
Clustering-Enhanced Time- and Angle-Resolved Photoemission Study of LaTe$_3$: Absence of a Photoinduced Secondary CDW in the Electronic Structure
Gesa-R. Siemann, Davide Curcio, Anders S. Mortensen et al. (+9 more)
Optical control offers a compelling route for tailoring material properties on an ultrafast time scale. Ordered states such as charge density waves (CDWs) can be transiently melted by an ultrafast light excitation. This is also the case for the rare-earth tritelluride LaTe$_3$, a prototypical CDW compound. For this material it has recently been reported that the suppression of the primary CDW allows the transient formation of a second CDW, whose wave vector is orthogonal to the primary one. This creates the intriguing scenario where light enables switching between two distinct ordered phases of the material. While the second CDW has so far been observed by structural techniques, it remains an open question how the interplay of the two CDW phases is reflected in the material's electronic structure. We investigate this via time- and angle-resolved photoemission measurements of LaTe$_3$. The complex
Fermi contour is probed using a FeSuMa analyzer, which records the photoemission intensity of the entire
Fermi contour at once. The dynamics revealed by the FeSuMa analyzer are complemented by measurements using a conventional hemispherical electron analyzer. We combine conventional data analysis with $k$-means clustering, an unsupervised machine learning technique, demonstrating its strong potential for disentangling large
datasets. While we do not find any features that cannot be explained by the melting and re-establishment of the primary CDW, distinct dynamics and coherent oscillations are observed in the different branches of the
Fermi contour.
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All authors Gesa-R. Siemann, Davide Curcio, Anders S. Mortensen, Charlotte E. Sanders, Yu Zhang, Jennifer Rigden, Paulina Majchrzak, Deepnarayan Biswas, Emma Springate, Ratnadwip Singha, Leslie M. Schoop, Philip Hofmann
Materials Science
Al$_{1-x}$Hf$_{x}$N Thin Films with Enhanced Piezoelectric Responses for GHz Surface Acoustic Wave Devices
Laura I. Wagner, Verena Streibel, Esperanza Luna et al. (+12 more)
Ternary compounds obtained by alloying wurtzite AlN with transition metals have emerged as promising materials with significantly enhanced piezoelectric characteristics relative to binary AlN. The increased electromechanical coupling in these compounds boosts the performance of high-frequency acoustic devices. So far, progress has largely focused on Al$_{1-x}$Sc$_x$N, which is costly and poorly compatible with complementary metal-
oxide-
semiconductor (CMOS) technologies. Here, we investigate aluminum hafnium nitride (Al$_{1-x}$Hf$_{x}$N) as a scalable and potentially CMOS-compatible alternative to Al$_{1-x}$Sc$_x$N. Using reactive co-sputtering on both Si and sapphire substrates, we demonstrate wurtzite Al$_{1-x}$Hf$_{x}$N thin films ($x \leq 0.17$) with strong $c$-axis texture and nearly isotropic
lattice expansion upon Hf incorporation. X-ray absorption spectroscopy indicates cross-gap hybridization between N 2$p$ and Hf 5$d$ states, which can enhance the Born effective charge and, thereby, the piezoelectric response. Correspondingly, we observe a multifold enhancement in the piezoelectric coefficient, $d_{33}$, relative to AlN, despite increasing structural disorder in Al$_{1-x}$Hf$_{x}$N. Building on this finding, we demonstrate Al$_{1-x}$Hf$_{x}$N GHz surface acoustic wave (SAW) resonators that exhibit enhanced performance, as well as efficient excitation of bulk acoustic waves with low propagation losses. These results establish Al$_{1-x}$Hf$_{x}$N as a promising platform for next-generation high-frequency electromechanical devices, with prospects for further piezoelectric enhancements through improved epitaxy.
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All authors Laura I. Wagner, Verena Streibel, Esperanza Luna, Katarina S. Flashar, Valentin Walbrunn, Walid Anders, Nicole Volkmer, Doreen Steffen, Katrin Morgenroth, Frans Munnik, Tsedenia A. Zewdie, Saswati Santra, Jutta Schwarzkopf, Ian D. Sharp, Mingyun Yuan
Strongly Correlated Electrons
Web of Non-invertible Dualities for (2+1) Dimensional Models with Subsystem Symmetries
Avijit Maity, Vikram Tripathi and Andriy H. Nevidomskyy
We extend non-invertible duality concepts from one-dimensional systems to two spatial dimensions by constructing a web of non-invertible dualities for
lattice models with subsystem
symmetries. For the $\mathbb{Z}_2 \times \mathbb{Z}_2$ subsystem
symmetry on the square
lattice, we build two complementary dualities: a map that sends spontaneous subsystem
symmetry-broken (SSSB) phases to the trivial phase (the analogue of the Kramers-Wannier (KW) duality in 1+1D), and a generalized subsystem Kennedy-Tasaki (KT) transformation that maps SSSB phases to subsystem
symmetry-protected topological (SSPT) phases while leaving the trivial phase invariant. These dualities are boundary-sensitive. On open
lattices, both subsystem KW and KT transformations act as
unitary, invertible operators. In particular, the KT map not only matches the bulk
Hamiltonians of the dual phases but also carries the spontaneous ground-state degeneracy of the SSSB phase onto the protected boundary degeneracy of the SSPT phase. On closed
manifolds, however, both maps become intrinsically non-
unitary and non-invertible when restricted to the original
Hilbert space. We demonstrate this non-invertibility via ground-state degeneracy matching (in two copies of the Xu-Moore/Ising-plaquette model), analysis of
symmetry-twist sectors mapping, and the fusion
algebra of the duality operator. Enlarging the
Hilbert space to include twisted sectors allows the subsystem KW map to be formulated as a projective
unitary preserving
quantum transition probabilities, consistent with generalized Wigner-
theorem-based constructions. We also show that the KT map faithfully transmits the algebraic content of bulk and edge invariants diagnosing strong SSPT order: although strictly local SSPT repair operators map to highly nonlocal objects in the dual SSSB phase, the essential commutation
algebra and the bulk-edge correspondence remain intact.
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Superconductivity
Superconducting spintronics with electron symmetry filtering and interfacial spin-orbit coupling
Pablo Tuero, César González-Ruano, Igor Žutić et al. (+3 more)
Over the recent years, crossroads of magnetism and superconductivity led to the emerging field of superconducting spintronics. A cornerstone of this venture is the generation of equal-
spin triplet Cooper pairs in
superconductor-ferromagnet hybrids, enabling long-range
spin-polarized supercurrents and
magnetic control over superconducting
quantum states for the development of energy-efficient cryogenic devices. Until now, nearly all superconducting spintronic devices have relied on direct interfaces between
superconductors and ferromagnets, since it was believed that an insulating barrier would decouple
spin and charge transport. This assumption, however, appears to be invalid when a thin
spin- and orbit-filtering barrier couples epitaxial ferromagnet and the
superconductor.
Symmetry filtering plays a crucial role in enhancing
giant tunneling magnetoresistance (TMR) by selectively allowing specific electronic states to tunnel through the barrier. Such a mechanism is key for high-performance spintronic devices like
magnetic random access
memories,
magnetic sensors or
spin-light emitting diodes. This manuscript provides a comprehensive review of superconducting spintronics driven by electron
symmetry filtering and interfacial SOC. It emphasizes the critical role of a crystalline MgO barrier in selectively transmitting specific electronic states between V(100) and Fe(100). The manuscript also highlights how interfacial SOC enables
symmetry mixing, allowing for the interaction between
ferromagnetic and superconducting orderings though MgO(100). This mutual interaction, mediated by interfacial SOC, facilitates the conversion of
spin-singlet to
spin-triplet Cooper pairs. The work provides key insights into designing SOC based
superconductor-ferromagnet hybrid structures for advanced superconducting spintronic functionalities.
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All authors Pablo Tuero, César González-Ruano, Igor Žutić, Yuan Lu, Coriolan Tiusan, Farkhad G. Aliev
Statistical Mechanics
Conservation laws and slow dynamics determine the universality class of interfaces in active matter
Raphaël Maire, Andrea Plati, Frank Smallenburg et al. (+1 more)
While
equilibrium interfaces display universal large-scale statistics, interfaces in phase-separated active and driven systems are predicted to belong to distinct non-
equilibrium universality classes. Yet, such behavior has proven difficult to observe, with most systems exhibiting
equilibrium-like fluctuations despite their strongly non-
equilibrium microscopic dynamics. We introduce a hard-disk model driven by active collisions, conceived as an effective 2D description of a vibrofluidized granular system that, contrary to self-propelled models, displays clear non-
equilibrium interfacial scaling. We observe for the first time, the $|\boldsymbol q|$KPZ and wet-$|\boldsymbol q|$KPZ universality classes while revealing a new, previously overlooked universality class arising in systems with slow solid-like or glassy dynamics. Conservation laws and slow dynamics select these distinct classes.
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All authors Raphaël Maire, Andrea Plati, Frank Smallenburg, Giuseppe Foffi
Superconductivity
Giant Domain Walls and Intrinsic Heterogeneity in 214 Cuprate Superconductors
Evie Ladbrook, Mark S. Senn and Jon Wright
Structural phase transitions generate complex microstructures that often govern material functionality, yet directly resolving their three-dimensional organisation in bulk samples remains challenging. Here we employ scanning three-dimensional X-ray diffraction to resolve the bulk microstructure of La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_{4}$, a prototypical 1/8-doped cuprate in which structural and electronic heterogeneity is well established. We reveal remarkably broad tetragonal-like domain wall regions within the nominally orthorhombic
crystal structure, and, upon cooling to 100 K, a fine microstructure of orthorhombic-like stripes embedded within the tetragonal
matrix that has significant consequences for interpreting the interplay between structural and electronic heterogeneity in this class of materials. More broadly, this work establishes 3DXRD as a powerful approach for resolving bulk microstructures and understanding their role in emergent functionality.
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Materials Science
Device-Scale Atomistic Simulations of Heat Transport in Advanced Field-Effect Transistors
Ke Xu, Gang Wang, Ting Liang et al. (+8 more)
Self-heating in next-generation, high-power-density field-effect transistor limits performance and complicates fabrication. Here, we introduce NEP-FET, a machine-learned framework for device-scale heat transport simulations of field-effect transistors. Built upon the neuroevolution potential, the model extends a subset of the OMat24
dataset through an active-learning workflow to generate a chemically diverse, interface-rich reference set. Coupled with the FETMOD structure generator module, NEP-FET can simulate realistic field-effect transistor geometries at sub-micrometer scales containing millions of atoms, and delivers atomistic predictions of temperature fields, per-atom heat flux, and thermal stress in device structures with high fidelity. This framework enables rapid estimation of device-level metrics, including heat-flux density and effective thermal conductivity. Our results reveal pronounced differences in temperature distribution between fin-type and gate-all-around transistor architectures. The framework closes a key gap in multiscale device modeling by combining near-
quantum-mechanical accuracy with device-scale throughput, providing a systematic route to explore heat transport and thermo-mechanical coupling in advanced transistors.
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All authors Ke Xu, Gang Wang, Ting Liang, Yang Xiao, Dongliang Ding, Haichang Guo, Xiang Gao, Lei Tong, Xi Wan, Gang Zhang, Jianbin Xu
Soft Condensed Matter
Structure factor realizability reveals the glass-dynamics onset temperature
Bowen Duan and Ge Zhang
When
liquids are cooled rapidly, they bypass crystallization and instead enter a supercooled state and then a glass state. Previous studies have shown that the static structure factors of high-temperature
liquids, supercooled
liquids, and glasses exhibit only subtle differences, leading to the conclusion that the glass transition cannot be predicted solely from structure factor changes. Our research challenges this limitation. Specifically, we studied the difficulty of generating configurations corresponding to target structure factors using
stochastic gradient descent optimizations. While such optimizations easily converge when targeting the structure factors of higher temperature
liquids, the difficulty significantly increases for lower temperature
liquids and glasses. By quantifying this difficulty through the mean squared error achieved, we found a kink at the onset temperature of glass dynamics. Our results suggest that the onset of glass dynamics can be explained by a topological change in the realizability landscape of the structure factor, even though the structure factor itself only changes smoothly. Our results are currently based on computer simulations using original and modified Dzugutov interactions, and future work will determine whether our theory is applicable to other glass-forming systems.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.acc-ph
Strong Energy Dependent Transition Radiation in a Photonic Crystal
V.Gareyan and Zh.Gevorkian
Radiation of a charged particle crossing an alternating stack of slabs in the optical region is considered. Both disordered and periodic stacks are investigated. It is shown that for special type of alternating disordered and periodic stacks the radiation problem can be solved exactly for backward and forward Brewster observation angles. Strong $N^2$ dependence of radiation intensity on slab number is re-established in special case of the disordered stack. This leads to strong directivity either on forward or on backward Brewster angles depending on the type of stack randomness. In certain type of periodic photonic
crystal, a strong energy dependence $E^4$ for relativistic particles of the radiation intensity, observed at Brewster's angle is found. Further increment of particle energy leads to saturation. The band structure of the corresponding photonic
crystal (PhC) has a behavior, analogous to the Dirac cones in
graphene. We suggest this special type $1D$ photonic
crystal for application as a detector of relativistic particles.
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Materials Science
Observation of cooperative strong coupling between optical phonon and crystal-field excitations in a pseudo Jahn-Teller system
Fangliang Wu, Xiaoxuan Ma, Zhongwei Zhang et al. (+6 more)
Cooperative interactions between localized electronic excitations and
crystal lattice are central to the emergence of complex structural phases in materials. However, the scaling relations governing these collective behaviors remain largely unexplored. Here, using magneto-Raman spectroscopy, we report the direct observation of the strongly coupled optical
phonon and non-degenerate
crystal-field excitations (CFEs) in ErFeO3. By independently tuning the effective population of Jahn-Teller-active erbium ions through temperature and chemical dilution with Jahn-Teller-inactive yttrium ions, we identify the coupling strength varies linearly with the square root of electronic excitations population. Notably, Y-doping reveals the hybridization gap reduces significantly faster than predicted by density scaling alone, indicating
phonon coherence is essential for establishing this cooperative interaction. Our findings highlight the role of optical
phonons in mediating short-range interactions that drive cooperative Jahn-Teller effect, evidencing the pathway for tailoring electronic and vibrational properties of Jahn-Teller materials through population control.
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All authors Fangliang Wu, Xiaoxuan Ma, Zhongwei Zhang, Motoaki Bamba, Haowen Wu, Jian Sun, Yuan Wan, Shixun Cao, Qi Zhang
Soft Condensed Matter
Emergence of oscillatory states of self-propelled colloids under optical confinement
Farshad Darabi and Juan Ruben Gomez-Solano
We investigate experimentally the single-particle motion in water of silica colloidal beads half-coated with carbon under the action of a converging
laser beam. The beads are self-propelled in this medium by means of self-thermophoresis resulting from local heating as a result of light absorption by their carbon cap. Within a certain
laser power range, we find that these particles exhibit a quasi-two-dimensional active motion near a solid surface with
stochastic rotational reversals when propelling themselves away from the region of maximum intensity, which leads to a stable trapping with oscillatory-like behavior inside the illuminated region. The orientation autocorrelation function of this type of confined active motion displays damped oscillations whose characteristic frequency increases with increasing propulsion speed, thus resulting in four regimes of translational motion depending on the observation time scale: thermal
diffusion, ballistic motion, oscillatory behavior, and confinement. Our experimental findings are well described by a minimal phenomenological model that includes the nonlinear effect of a torque that reorients the particle toward the center of the optical confinement, which in combination with rotational
diffusion gives rise to the observed orientational changes that allow their oscillatory trapping inside the light field. We also show that a similar active trapping mechanism emerges in the case of Janus colloidal rods, even though the periodicity is hindered by their three-dimensional rotation in the
laser beam.
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Materials Science
Detecting Linear Dichroism with Atomic Resolution
Roger Guzman, Ján Rusz, Ang Li et al. (+3 more)
X-ray linear dichroism has been pivotal for probing electronic anisotropies, but its inherent limited spatial resolution precludes atomic-scale investigations of orbital polarization. Here we introduce a versatile electron linear dichroism methodology in scanning transmission electron microscopy that overcomes these constraints. By exploiting momentum-transfer-dependent electron energy-loss spectroscopy with an atomic-sized probe, we directly visualize orbital occupation at individual atomic columns in real space. Using strained La0.7Sr0.3MnO3 thin films as a model system, we resolve the Mn-3d eg orbital polarization with sub-angstrom precision. We show that compressive strain stabilizes 3z2-r2 occupation while tensile strain favors x2-y2. These results validate our approach against established X-ray measurements while achieving the ultimate single atomic-column sensitivity. We further demonstrate two optimized signal extraction protocols that adapt to experimental constraints without compromising sensitivity. This generalizable platform opens unprecedented opportunities to study
symmetry-breaking phenomena at individual defects, interfaces, and in
quantum materials where atomic-scale electronic anisotropy governs emergent functionality.
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All authors Roger Guzman, Ján Rusz, Ang Li, Juan Carlos Idrobo, Wu Zhou, Jaume Gazquez
Mesoscale and Nanoscale Physics
Impedance-matched High-Overtone Thickness-Shear Bulk Acoustic Resonators with Scalable Mode Volume
Zi-Dong Zhang, Zhen-Hui Qin, Yi-Han He et al. (+5 more)
High overtone bulk acoustic resonators are essential components in microwave signal processing and emerging
quantum technologies; however, conventional designs suffer from limited impedance matching, spurious mode interference, and restricted scalability. Here we introduce a laterally excited high overtone thickness shear bulk acoustic resonator, abbreviated as X HTBAR, that overcomes these limitations through a fully planar excitation scheme. The X HTBAR employs a 3 micron thick 128 degree Y cut LiNbO3 piezoelectric film on a 500 micron high resistivity silicon substrate, enabling efficient excitation of thickness shear modes through lateral electrodes without the need for bottom electrodes and confining the acoustic field between the top electrodes. This configuration removes parasitic loss channels, increases energy transfer efficiency to greater than ninety nine percent, and provides a stable free spectral range of about 5.75 MHz with very small fluctuations. Experimental measurements show comb like
phonon spectra spanning 0.1 to 1.8 GHz, high quality factors in the range of ten to the power of three to ten to the power of five, frequency quality products larger than ten to the power of thirteen at room temperature, and a low temperature coefficient of frequency. In addition, a gridded electrode design together with the intrinsic properties of 128 degree Y cut LiNbO3, including insensitivity to electrode spacing and a large electromechanical coupling coefficient, suppresses spurious modes and allows tunable mode volumes from 0.008 to 0.064 cubic millimeters. These combined features give X HTBAR devices excellent integration compatibility and strong immunity to electrode related perturbations, making them promising multimode
phonon sources for large scale
quantum interconnects and microwave photonic integrated
circuits.
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All authors Zi-Dong Zhang, Zhen-Hui Qin, Yi-Han He, Yun-Fei Cheng, Hao Yan, Si-Yuan Yu, Ming-Hui Lu, Yan-Feng Chen