Materials Science
Study on Thickness and Temperature Dependence of Thermoelectric Properties in SnS Nanofilms
Liqi Chen, Ziyang Wang, Donghao Li et al. (+5 more)
SnS as an environmentally friendly, cost-effective, and earth-abundant narrow-bandgap
semiconductor material, has demonstrated significant application potential in the field of medium-temperature thermoelectric conversion. However, the thermoelectric performance of its bulk counterpart is inherently constrained by intrinsic point defects (e.g., vacancies) and the material's specific band structure. Low-dimensional engineering has emerged as a pivotal strategy for overcoming these limitations and enhancing thermoelectric performance. In this work, we systematically investigate the thermoelectric properties of SnS nanofilms with distinct thicknesses (82 nm, 199 nm, 616 nm, and 813 nm) across a temperature range of 300-600 K. Measurements were conducted using time-domain thermoreflectance (TDTR) and a dedicated thin-film thermoelectric parameter test system (ZEM-3). Our results confirm that low-dimensionalization effectively boosts the thermoelectric performance of SnS, with the thermoelectric figure of merit (ZT) displaying a pronounced dependence on both film thickness and temperature. All four SnS thin films exhibit thermoelectric performance that is markedly superior to that of bulk SnS. This enhancement is primarily attributed to the
quantum confinement effect, energy filtering effect, and intensified
phonon scattering, all of which are induced by the low-dimensional structural characteristics. This work provides not only experimental evidence and theoretical insights for the performance optimization of SnS nanofilms but also establishes a foundational framework for the development of high-efficiency, eco-friendly medium-temperature thermoelectric materials, thereby holding significant scientific value and practical implications.
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All authors Liqi Chen, Ziyang Wang, Donghao Li, Jingye Wang, Ning Zhao, Jun Zhou, Jie Zhu, Dawei Tang
Materials Science
Pressure Dependence of Ferromagnetism in Uranium Hydride UH$_3$ up to 20 GPa Revealed by NV Centers Magnetometry
Valentin Schmidt, Loïc Toraille, Florent Occelli et al. (+2 more)
The origin of ferromagnetism in the stable $\beta$-UH$_3$ phase is still debated. With a high Curie temperature and a short uranium-uranium interatomic distance, $\beta$-UH$_3$ is placed outside the known systematics of uranium compounds. Pressure provides a powerful means of tuning magnetism toward its suppression, thereby offering valuable insights into its underlying mechanisms, yet the high-pressure behavior of $\beta$-UH$_3$ has remained largely unexplored. Here, we combine in the Diamond Anvil
Cell (DAC) the development of pure $\beta$-UH$_3$ synthesis and widefield nitrogen-vacancy (NV) center magnetometry to measure the pressure dependence of the Curie temperature in $\beta$-UH$_3$ up to about 20~GPa. We present two data analysis methods, vector
magnetic field reconstruction and statistical analysis of the optically detected
magnetic resonance (ODMR) response, which enable us to directly image the
magnetic dipole of $\beta$-UH$_3$ during isobaric warming. We observe a linear decrease in the Curie temperature with pressure, yielding a slope of $\text{d}T_C/\text{d}P=-3.86\,(8)$~K/GPa. Ferromagnetism in $\beta$-UH$_3$ is predicted to reach 0~K at approximately 44~GPa, where a
quantum critical point may emerge.
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All authors Valentin Schmidt, Loïc Toraille, Florent Occelli, Jean-François Roch, Paul Loubeyre
Materials Science · Cross-listed from cond-mat.soft
Effective particle size governs structure and dynamics in rough hard-particle fluids
Nanqing Xiao, Zhen Zhang, Walter Kob et al. (+1 more)
We numerically investigate how particle surface roughness affects the static and dynamic properties of a hard-particle fluid across a wide range of densities, rho. These simulations of a simple model of granular systems reveal that, although the amplitude and coverage of surface corrugation significantly influence the rho-dependence of system properties, the qualitative behavior of this dependence remains unchanged. These findings can be described quantitatively by introducing an effective particle size, which enables a direct mapping of the rough particle systems to equivalent hard-disk systems. Analytical calculations provide an explicit form of this mapping, and allow us to predict the static and dynamic properties of rough particles using standard
liquid-state theories for hard disks.
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All authors Nanqing Xiao, Zhen Zhang, Walter Kob, Yujie Wang
Materials Science · Cross-listed from cond-mat.str-el
$g$-wave altermagnetic order parameter in hematite
Tianren Wang, Yuehong Li, Yu Feng et al. (+11 more)
Altermagnets combine the vanishing net magnetization of antiferromagnets with momentum-dependent
spin splitting.
Magnon band splitting provides a direct probe of altermagnetic order and may enable chirality-selective
magnon transport, yet the momentum-space
symmetry of this splitting has not been determined quantitatively. Here we use inelastic
neutron scattering to map the momentum dependence of altermagnetic
magnon splitting in hematite ($\alpha$-Fe$_2$O$_3$). The splitting vanishes along nodal directions and reaches maxima off the nodes, revealing the $g$-wave
symmetry of the altermagnetic order parameter. These results agree with linear
spin-wave theory calculations based on the altermagnetic model, which further identify the nondegenerate branches as
magnons of opposite chirality and trace the splitting to
symmetry-inequivalent long-range exchange interactions. Our results provide the first quantitative determination of the momentum-space
symmetry of altermagnetic chiral
magnons. These findings, together with hematite's high
magnetic ordering temperature and low
magnon damping, establish it as a promising platform for low-dissipation,
symmetry-selective magnonic applications.
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All authors Tianren Wang, Yuehong Li, Yu Feng, Andong Liu, Yuetong Wu, Qian Zhao, Yujie Yan, Wei Luo, Xin Tong, Yi Lu, Yao Shen, Stefano Agrestini, Jaewon Choi, Qisi Wang
Materials Science · Cross-listed from cond-mat.mes-hall
Wafer-Level 1/f Noise Characterization of Scaled P-Type Nanosheets and Comparison with Planar HKMG Transistors
Ruben Asanovski, Anabela Veloso, Ben Kaczer et al. (+2 more)
We present a comprehensive wafer-level 1/f noise study of scaled Gate-All-Around (GAA) p-type nanosheet transistors and
benchmark them against large-area planar High- ąppa} Metal Gate (HKMG) devices to assess the impact of device architecture on reliability. By statistically analyzing noise data from 188 nanosheets, we extract the effective trap density in the dielectric and compare it to that of planar transistors with identical gate stack, comparable processing thermal budgets, and no specific reliability anneals. The effective trap density extracted from 1/f noise is comparable in planar and nanosheet architectures. This indicates that transitioning to GAA nanosheets does not increase noise, which remains governed by gate stack quality.
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All authors Ruben Asanovski, Anabela Veloso, Ben Kaczer, Naoto Horiguchi, Jacopo Franco
Materials Science
Pulse-Burst Excitation Reveals Time-Dose Reciprocity Breakdown in Mixed-Halide Perovskites
Alexandr Marunchenko, Shivam Singh, Daniel Lizotte et al. (+3 more)
Time-dose reciprocity, commonly associated with the Bunsen-Roscoe law, states that the response of a photosensitive system depends only on the total exposure dose, regardless of how that energy is delivered over time. Light-sensitive processes in mixed-halide perovskites, such as photoinduced halide segregation, often exhibit threshold-like behavior that may violate this principle and enable material-state control by
photon timing. We test this using pulse-burst excitation, which introduces an additional temporal control dimension beyond conventional parameters such as pulse fluence, repetition rate, and average power. By redistributing the same
photon dose over microsecond-to-millisecond timescales, we create distinct nonequilibrium excitation conditions and show that mixed-halide perovskites can evolve into different metastable states, revealing a breakdown of time-dose reciprocity in the combined processes of halide segregation and remixing. This additional temporal degree of freedom not only enables control of the material state but also provides a new experimental framework for disentangling the competing processes underlying photoinduced halide redistribution. Our findings establish
photon timing as a control parameter for perovskite photochemistry and open additional opportunities for optical
memory and neuromorphic photonic applications.
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All authors Alexandr Marunchenko, Shivam Singh, Daniel Lizotte, Bhaskar De, Yana Vaynzof, Ivan G. Scheblykin
Materials Science
Polymorph Engineering of the Layered Rare-Earth Magnet GdAlGe
Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov et al. (+7 more)
The recent advances in research on layered magnets have established them as invaluable materials for spintronic applications and precursors to 2D magnets. The problem is that the number of such materials available for experimentation is still low. To tackle the problem, one may employ phase engineering; in particular, the interplay between the phase stability and dimensionality provides great opportunities for design of layered magnets. Here, this interrelation is harnessed to produce epitaxial films of an overlooked layered polymorph of GdAlGe. The compound is formed by alternating triangular Gd and honeycomb AlGe
lattices. It is stable in ultrathin films, up to 5 monolayers. In thicker films, an additional unwanted phase emerges. The structural quality of the ultrathin films is witnessed by electron and X-ray diffraction as well as electron microscopy. Magnetization measurements detect an anisotropic ferromagnetic state. The GdAlGe magnetism is corroborated by a study of electron transport revealing the anomalous Hall effect and negative magnetoresistance. The material is naturally integrated with Ge, a technological
semiconductor, which should facilitate applications. The present study can serve as a blueprint for design of layered magnets via polymorph engineering.
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All authors Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov, Oleg E. Parfenov, Alexey N. Mihalyuk, Ivan A. Yakovlev, Igor A. Karateev, Oleg A. Kondratev, Andrey M. Tokmachev, Vyacheslav G. Storchak
Materials Science
The Hidden Cost of Alloying: Disorder-Driven Transport Collapse in TMDs
Michele Pisarra, Clara Rebanal, Enrique Arévalo Rodríguez et al. (+19 more)
Alloying in two dimensional
semiconductors is widely used to tune bandgaps, yet its implications for charge and energy transport remain poorly understood. Here, we investigate MoS2xSe2(1-x)
alloys as a model system to study the interplay between composition, thickness, and disorder. Optical transitions and valence band dispersions evolve continuously with both stoichiometry and number of layers, with negligible bandgap bowing and a composition dependent attenuation of thickness driven renormalization. In contrast, time resolved spatial mapping of photoexcited carriers reveals a pronounced and asymmetric collapse of carrier diffusivity at intermediate compositions, which cannot be accounted for by changes in effective mass or band
alignment, and instead emerges from strong real space fluctuations in the local energetic landscape generated by random chalcogen substitution. Microscopic simulations reproduce the experimental trends and show that the character of disorder depends critically on the direction of alloying, producing either scattering barriers or deep trapping sites. Together, these results demonstrate that transport in TMD
alloys is governed by disorder physics, overlooked by conventional optical and photoemission probes at
equilibrium. Our findings establish transport as a stringent metric of electronic quality and high-light intrinsic limitations in the usage of TMD
alloys for layered
semiconductor devices.
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All authors Michele Pisarra, Clara Rebanal, Enrique Arévalo Rodríguez, Marc Meléndez, Elena Blundo, Giacomo Amadore, Jonathan J. Finley, Fabián Calleja, Marc G. Cuxart, Jesús Álvarez, Ma-ría José Capitán, Fernando J. Urbanos, Julia García Pérez, Ramón Bernardo Gavito, Daniel Granados, Ji Dai, Massimo Tallarida, Antonello Sindona, Fernando Martín, Ferry Prins, Iolanda Di Bernardo, Amadeo L. Vázquez de Parga
Materials Science · Cross-listed from cond-mat.str-el
Magnetic phases of Kondo lattice materials Ce$_5$RhGe$_2$ and Ce$_5$IrGe$_2$
Jiawen Zhang, Yanan Zhang, Mingyi Wang et al. (+5 more)
Single
crystals of Ce$_5$RhGe$_2$ and Ce$_5$IrGe$_2$ have been systematically investigated by electrical resistivity, specific heat, and magnetization measurements. Together with Ce$_5$CoGe$_2$, all three compounds crystallize in the orthorhombic Pnma structure, with the
lattice parameters increasing monotonically from Co to Rh to Ir, consistent with the effect of negative chemical pressure. Magnetization measurements along the three principal crystallographic axes identify the a axis as the easy magnetization direction throughout the series. Ce$_5$RhGe$_2$ exhibits ferromagnetic ordering with a Curie temperature of approximately 11.5 K and shows
magnetic behavior closely resembling that of Ce$_5$CoGe$_2$. In contrast, Ce$_5$IrGe$_2$ undergoes two successive
magnetic transitions at $T_{\rm M1}=12.7$ K and $T_{\rm M2}=11.8$ K, and there are multiple metamagnetic transitions under
magnetic fields, giving rise to magnetization plateaus at fractions of the saturation magnetization $M_{\rm s}$ of approximately $M_{\rm s}/5$ and $M_{\rm s}/3$. The low-field metamagnetic transition along the easy axis shifts to lower field with decreasing temperature, and eventually a pronounced hysteresis loop is observed about zero-field, establishing that Ce$_5$IrGe$_2$ exhibits a ferrimagnetic ground state at the lowest measured temperatures.
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All authors Jiawen Zhang, Yanan Zhang, Mingyi Wang, Ye Chen, Yu Liu, Yongjun Zhang, Michael Smidman, Huiqiu Yuan
Materials Science · Cross-listed from cond-mat.supr-con
Thomas-Fermi screening of electrostatic fields in a type-I superconductor
Nikhil Seeja Sivakumar, Tyler James, Frederick Carlisle et al. (+2 more)
The empirical London equations make distinct predictions for a
superconductor's longitudinal and transverse electrodynamic response. Conventionally, this framework attributes the Meissner effect to the transverse component, with the longitudinal response predicted to remain unchanged on entering the superconducting state, i.e. a static electric field is screened over the Thomas-Fermi length ($\lambda_{\mathrm{TF}} \sim 1$~Å), just as in the nonsupercondcuting metal. J.~E.~Hirsch~[Phys.~ Rev.~B~69,~214515~(2004)] has developed an alternative formalism, which predicts that the longitudinal screening length should instead be governed by the London penetration depth as the system is cooled below the superconducting transition temperature ($T_{\mathrm{c}}$). Here we use a combination of qPlus atomic force microscopy and scanning tunneling microscopy/spectroscopy of single-
crystal Pb(111) at $\sim$~340~mK~ \mbox{($T/T_{\mathrm{c}}\sim0.05$)} in an attempt to detect any modifications in electrostatic screening of the longitudinal tip field upon entering the superconducting phase. We quench superconductivity using a
magnetic field of 200 mT normal to the Pb(111) surface. By measuring force-distance curves and local field-emission resonance spectra at the same sample position in the presence and absence of the
magnetic field, we constrain the change in screening between the normal and superconducting state to less than $\sim 1 \%$. This is between two to three orders of magnitude smaller than that predicted by Hirsch's theory, and entirely consistent with unmodified Thomas-Fermi screening across the superconducting transition.
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All authors Nikhil Seeja Sivakumar, Tyler James, Frederick Carlisle, Philip Moriarty, Brian Kiraly
Materials Science · Cross-listed from cond-mat.str-el
High-resolution angle-resolved photoemission spectroscopy with tunable magnetic field
Jairo Obando-Guevara, Huu-Thong Le, Emiliano Corcino Aracena et al. (+7 more)
The control and perturbation of
quantum phenomena with
magnetic fields is an indispensable tool in materials research. Recently, in-situ field tuning was implemented into angle-resolved photoemission spectroscopy (magneto-ARPES), which provides direct momentum and energy-resolved information of the field-dependent electronic structure. However, aberrations of the electron trajectories were shown to be substantial, leading to significant spectral distortions and broadening even in small fields. Here we show that the electronic structure can be recovered from magneto-ARPES spectra with high accuracy while maintaining high momentum resolution even when strong trajectory aberrations are present. We studied Bi$_2$Se$_3$ in a dipole field of a coil using a
laser-based ARPES system. The electronic structure was reconstructed in post-processing using detailed electron trajectory simulations. We identify two-dimensional (2D) momentum mapping, a micron beam spot size, and precise numerical field simulations as critical technical requirements for high-resolution magneto-ARPES. We show how circular dichroism can provide additional information about the coupling of the
magnetic field to the
spin. The experimental achievements and the scaling laws from our simulations provide a road map towards magneto-ARPES in larger fields.
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All authors Jairo Obando-Guevara, Huu-Thong Le, Emiliano Corcino Aracena, Sayan Singha, Kyungchan Lee, Yingdong Guan, Zhiqiang Mao, Dezhe Jin, Chaoxing Liu, Heike Pfau
Materials Science
Phonon-Programmable Hidden Unconventional Magnetism in Two-Dimensional Spin-Degenerate Antiferromagnets
Xiaonong Shen, Cheng Tang and Wei Ren
Spin-degenerate antiferromagnets can host hidden unconventional magnetism in their
lattice degrees of freedom. We show that coherent
phonons activate this magnetism by removing the
spin-layer operations that enforce
equilibrium band degeneracy without changing the collinear Néel order. The frequency and polarization of a pump electric field select a resonant \(\Gamma\)-point optical
phonon and, within a doublet, its coordinate direction. This choice fixes the residual
spin-layer
symmetry. In monolayer MnPSe$_3$, an \(A_{2u}\) mode produces \(i\)-wave splitting odd in the mass-weighted
phonon coordinate $Q$, reversing sign under $Q\to-Q$, whereas two orthogonal directions of the same doubly degenerate \(E_u\) doublet produce \(d\)- and \(s\)-wave splitting at a common resonance. Rotating the in-plane pump field \(\bm E_\parallel\) therefore programs both the
spin-splitting texture and the thermoelectric
spin current, continuously tuning the response between transverse pure-
spin and longitudinal
spin-polarized currents. A complete classification of two-dimensional collinear
spin layer groups identifies the \(\Gamma\)-point coordinates that remove the degeneracy-enforcing operations and activate such unconventional magnetism.
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Materials Science
Thermal response of an in-situ STEM MEMS chip under rapid pulse heating
Phillip Dumitraschkewitz and Thomas Kremmer
In-situ rapid solidification studies demand measurements of thermal histories with high temporal resolution. We present a simple, effective setup to quantify the cooling response of an uncoated commercial Protochips Fusion MEMS chip in an in-situ scanning transmission electron microscopy (STEM) context. We drive user-defined temperature programs via an arbitrary waveform generator (AWG), while recording the voltage drops across a series shunt to reconstruct chip resistance and temperature at sub-millisecond resolution. We confirm the response times inferred from the current; however, the temperature obtained from the physically linked resistance, $T(R)$, evolves more slowly. Analysis of the maximum cooling step reveals an exponential-like relaxation with time constant $\tau=1.80$ ms, consistent with reported thermal lag constants for fast scanning calorimetry. From the time to reach $95\%$ of the temperature difference $\Delta T$, we measure an average cooling rate of $\approx 7.9\times 10^{4}$ K/s. Robustness checks include repeated $R(T)$ measurements (revealing a modest downward drift approaching an asymptote), a 10 k$\Omega$ test load, and characterization of small off-duty arbitrary waveform generator leakage/offsets. These findings define practical bounds on achievable thermal-path rates when planning in-situ electron microscopy experiments with this chip platform.
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Materials Science
Laser Shock Peening in Hydrogen Environments: Coupled Stress Transport Trapping Mechanisms and Application Gaps
Elzbieta Gadalinska, Jan Kaufman, Jan Smaus et al. (+1 more)
Hydrogen embrittlement limits the deployment of high-strength steels and advanced
alloys in hydrogen infrastructure.
Laser shock peening (LSP) is increasingly considered as a mitigation route because it combines deep compressive residual stresses with near-surface microstructural modification. This review critically assesses LSP not as an isolated strengthening treatment, but as a surface layer design strategy governed by coupled stress, hydrogen transport and trapping mechanisms. Evidence from steels, nickel based
alloys and additively manufactured materials shows that compressive residual stresses may suppress stress assisted hydrogen transport and delay crack initiation, while LSP-induced nanostructuring, dislocations, twins and interfaces can either redistribute hydrogen beneficially or promote localized plasticity and damage. Reported trends are frequently confounded by hydrogen charging mode, surface roughness, contamination, residual stress depth profiling and limited structure performance correlations. Two design critical gaps are identified: the lack of quantitative links between post-LSP stress/defect architectures and hydrogen assisted fatigue crack growth, and the near absence of impact toughness data after LSP under hydrogen exposure. The review proposes mechanism informed qualification routes combining residual stress mapping, hydrogen characterization, service representative mechanical testing and modelling.
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All authors Elzbieta Gadalinska, Jan Kaufman, Jan Smaus, Jan Brajer
Materials Science · Cross-listed from cond-mat.mes-hall
From London to Morse via Binnig, Quate, and Gerber
Sofia Alonso Perez, Matthew O. Blunt, Frederick Carlisle et al. (+30 more)
In their landmark paper introducing the atomic force microscope [Phys. Rev. Lett. 56, 930 (1986)], Binnig, Quate, and Gerber presciently anticipated that the technique would ultimately be capable of probing interactions running the gamut from weak van der Waals interactions to strong covalent bonding. They also highlighted that the tip-sample forces central to AFM are present, and often highly influential, in scanning tunnelling microscopy; indeed, this realisation directly inspired the invention of the force microscope. In this perspective for the Forty Years of AFM special issue, we review selected aspects of two decades of work from our group at the University of Nottingham that span the force range highlighted by BQG and are united by a common, central theme: the probe as active participant rather than passive observer. Our selection of results also covers length- and correlation-scales from the microscopic right down to the single chemical bond limit, tracking a spectrum of interactions from van der Waals/Hamaker forces, through hydrogen bonding, to covalent bonds and, finally, atom-by-atom assembly of metal clusters via vertical tip-sample transfer. Echoing BQG's own observations on the prevalence of probe-sample forces in STM, we also discuss recent evidence that tip-induced heterogeneity underpins first-passage dynamics in molecular
diffusion and highlight the challenges in acquiring non-invasive measurements of
diffusion barriers for adsorbed molecules that are readily perturbed by the probe. We close with a perspective on machine learning's growing role in automating tip-driven atomic and molecular manipulation.
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All authors Sofia Alonso Perez, Matthew O. Blunt, Frederick Carlisle, Neil R. Champness, Janette L. Dunn, Matthew Edmondson, Rowan Evers, Connor Fields, Subhashis Gangopadhyay, James Hayton, Samuel P. Jarvis, Filipe Junqueira, Lev Kantorovich, Brian Kiraly, Natalio Krasnogor, Ioannis Lekkas, Morten Møller, Philip Moriarty, Chris Pakes, Emmanuelle Pauliac-Vaujour, Oliver Phillips, Adrian Radocea, Philipp Rahe, Mohammad Abdur Rashid, Hongqian Sang, Alex Saywell, Nikhil Seeja Sivakumar, Peter Sharp, Andrew Stannard, Julian Stirling, Adam Sweetman, Simon Taylor, Richard A.J. Woolley
Materials Science · Cross-listed from cs.LG
MLIP Detective: Active Failure Mode Discovery Beyond Benchmark Scores for Machine-Learning Interatomic Potentials
Ryuhei Okuno, Nontawat Charoenphakdee, Kaoru Hisama et al. (+1 more)
Universal machine-learning interatomic potentials (u-MLIPs) aim to generalize across diverse configurations.
Benchmarks enable reproducible evaluation but may not expose failures outside their predefined scope. Here, we show that physics-informed search can complement
benchmark-based evaluation by uncovering hidden failure modes. We introduce MLIP Detective, an agentic framework for active failure mode discovery. Starting from
benchmark evidence, MLIP Detective generates falsifiable, physics-informed failure hypotheses, screens them with inexpensive simulations, and escalates only the most suspicious cases to human experts together with proposed verification protocols. Without issue-specific prompting, MLIP Detective identified and characterized a systematic anomaly in MACE-MPA-0: the model predicted some relaxed adsorbate-surface systems involving O- or F-containing adsorbates to be higher in energy than their corresponding separated fragments. Using cross-model comparisons, MLIP Detective further inferred a likely training-data origin for the anomaly, consistent with recent reports.
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All authors Ryuhei Okuno, Nontawat Charoenphakdee, Kaoru Hisama, Yuta Tsuboi
Materials Science
A thermally grown SiO2 diffusion barrier enabling high-temperature investigation of Ag-Au-Pd-Pt thin films
Elaheh Akbarnejad, Aleksander Kostka, Advika Chesetti et al. (+6 more)
Combinatorial processing platforms (CPPs), integrating Si microtip arrays with combinatorial thin film synthesis and atom probe
tomography (APT), enable near-atomic-scale characterization of compositionally complex solid solutions (CCSSs) under diverse processing and reaction conditions, including oxidation, thermal phase stability and electrocatalytic reactions. Their application at elevated temperatures, however, can be limited when CCSS constituents such as Pd and Pt react with the Si support to form silicides. Although thermally grown SiO2 has proven effective as a
diffusion barrier between pure Pt and Si, its performance for multicomponent CCSS thin films is unclear. Here, using Ag-Au-Pd-Pt as a model system, we compare a 25 nm thermally grown SiO2 barrier with native Si oxide during annealing using APT and transmission electron microscopy. Native Si oxide prevents detectable interfacial reactions up to 300{\deg}C, but at 400{\deg}C Pd and Pt react with Si, causing silicide formation and substantial redistribution of the film constituents. At 600{\deg}C, extensive substrate reactions disrupt the CCSS film and produce a pronounced needle-shaped silicide morphology. In contrast, thermally grown SiO2 suppresses CCSS thin film-substrate reactions up to 600{\deg}C and retains the CCSS composition. The thermally grown SiO2 thus extends the applicable temperature range of Si-based CPPs to at least 600{\deg}C for near-atomic-scale characterization of CCSS thin films.
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All authors Elaheh Akbarnejad, Aleksander Kostka, Advika Chesetti, Alan Savan, Georg Fritz, Kamen Kozhuharov, Matthias Karl Klein, Yujiao Li, Alfred Ludwig
Materials Science
Davydov Splitting Without a Davydov Pair and Highly Mobile Singlet Excitons in Perylene Red Microcrystals
Chris Rehhagen, Tolibjon Abdurakhmonov, Magnus Frank et al. (+2 more)
We investigate the excitonic properties of perylene red microcrystals, whose unit
cell contain eight molecules, using both experimental and theoretical methods. Only two of the nominal eight Davydov transitions are experimentally observed, with an apparent splitting of 610 cm$^{-1}$ that is reasonably reproduced by a Frenkel-Holstein
exciton model parametrized from density functional theory. A
symmetry-based analysis of the eigenstates reveals that the two observed transitions do not belong to the same Davydov pair, so the splitting does not directly report on the Coulomb coupling within the unit
cell. The complex mixture of local excitations produces a J-like band for the dominant transitions, favouring
exciton transfer through increased spectral overlap. Consistent with this picture, time-correlated single-
photon counting of the emission and ultrafast transient absorption spectroscopy show that the dynamics is dominated by highly mobile singlet Frenkel
excitons. The
exciton mobility extracted from experiment agrees very well with that obtained from Kinetic Monte Carlo simulations, supporting a picture of incoherent hopping transport.
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All authors Chris Rehhagen, Tolibjon Abdurakhmonov, Magnus Frank, Oliver Kühn, Stefan Lochbrunner
Materials Science · Cross-listed from cond-mat.mes-hall
The First Magic Angle Beyond the Chiral Limit in Twisted Bilayer Graphene
Leonardo A. Navarro-Labastida, Pierre A. Pantaleon, Francisco Guinea et al. (+1 more)
We develop a squared-
Hamiltonian description of twisted bilayer
graphene beyond the chiral limit to explain why the first magic angle remains robust under
lattice relaxation, while higher-order magic angles are strongly destabilized. Starting from the non-chiral Bistritzer–MacDonald model with finite same-sublattice tunneling, we show that
lattice relaxation reshapes the effective confinement landscape rather than acting as a simple perturbation of the chiral theory. A central result is that the realistic relaxation-renormalized tunneling ratio lies close to a special confinement point where the oscillatory part of the symmetric confinement potential nearly cancels. This places realistic twisted bilayer
graphene near a nearly uniform confinement regime. At the same time, finite same-sublattice tunneling activates an additional inter-sublattice current-like channel that competes with the chiral orbital channel. The first magic angle survives because these confinement and current-like contributions remain balanced, whereas higher-order magic angles lose this balance through stronger remote-band hybridization and enhanced real-space localization around AA regions. Our results provide a single-particle mechanism for the breakdown of the chiral magic-angle hierarchy and clarify why the experimentally relevant first magic angle remains the most stable remnant of the chiral flat-band structure.
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All authors Leonardo A. Navarro-Labastida, Pierre A. Pantaleon, Francisco Guinea, Gerardo G. Naumis
Materials Science
EBSDmagus: Managing Multi-Stage Dynamical Electron Backscatter Diffraction Simulations
Ulrich Kerzel, Lukas Berners and Sanddra Korte-Kerzel
Dynamical electron backscatter diffraction (EBSD) simulations increasingly support systematic studies of how material and experimental parameters affect diffraction patterns. Investigations that combine composition and
crystal structure, including changes in atomic order, with accelerating voltage, temperature, and many orientations or detector conditions can require large sets of related calculations. Several packages provide dynamical EBSD simulation; we use the open-source, scriptable EMsoft programs because they are well suited to large studies on high-performance computing systems. An EMsoft investigation nevertheless spans separate configuration, structure, scattering, and orientation files and several dependent calculation stages. As variations multiply, manual preparation becomes difficult to check, interruptions obscure which results remain usable, and the origin of individual patterns becomes laborious to reconstruct. With EBSDmagus, researchers define fixed and varying parameters once. The software prepares the required EMsoft calculations, reuses compatible intermediate results, and checks that the generated files represent the requested investigation before execution. After execution, it checks the expected outputs and, following an interruption, resumes only unresolved calculations while preserving completed work. A portable run record links each output to its inputs and calculation history, providing the provenance needed when the results are deposited as findable, accessible, interoperable, and reusable (FAIR) data. We assess this approach using a completed representative calculation, a larger study prepared and checked before submission, two observed cluster interruptions, and a controlled job cancellation. During recovery, EBSDmagus retained completed calculations and resubmitted only incomplete work.
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Materials Science
Band Structure Modulation of ZrO2 Nanoparticles for Control of CO Adsorption Properties: A Combined Density Functional Theory - Density Functional Tight Binding Study
Kexin Chen, William Dawson, Aulia Sukma Hutama et al. (+4 more)
We present a combined density functional theory (DFT) and density functional tight binding (DFTB) study of zirconia (ZrO2) nanoparticles of experimentally relevant sizes of several nanometers and their interactions with the CO molecule. A hybrid DFTB - Force Field (DFTB-FF) framework is developed, whereby band structure calculations rely on an existing Slater-Koster framework, while the accuracy of structural optimization and adsorption properties is controlled by the introduction of classical long-range interatomic potentials into DFTB instead of the traditional repulsive potentials. Additionally, coordination-dependent Zr-C potentials are introduced to account for the distinct local chemical environments of bulk-like facet sites and under-coordinated tip and edge sites, thereby improving the description of CO adsorption. This hybrid DFTB-FF approach substantially improves the robustness of geometry optimization and provides a practical strategy for extending the applicability of DFTB to complex oxide nanostructures. The calculations reveal that termination stoichiometry can be used to engineer intrinsic, p-type, or n-type electronic structures and thereby tune the adsorption activity of zirconia nanoparticles. While stoichiometric nanoparticles do not activate the C-O bond, low-coordinated sites in Zr-rich (n-type) nanoparticles exhibit chemisorption accompanied by charge donation into a CO antibonding LUMO-derived orbital, resulting in C-O bond activation. These results demonstrate that stoichiometry-controlled electronic structure and under-coordinated surface sites introduced by nanostructuring play a key role in governing the adsorption strength and reactivity of zirconia nanoparticles.
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All authors Kexin Chen, William Dawson, Aulia Sukma Hutama, Takahito Nakajima, Keisuke Kameda, Manabu Ihara, Sergei Manzhos
Materials Science
Flexoelectric Polarization in Wrinkled Janus Transition-Metal Dichalcogenide Monolayers
Stefan Velja, Surender Kumar, Domenico Corona et al. (+1 more)
Strain-gradient engineering via out-of-plane wrinkling offers a powerful route to tune electronic and electromechanical properties in two-dimensional (2D) materials. Here, we systematically investigate the electronic and flexoelectric response of wrinkled Janus MoSSe/MoSeS monolayers using density functional theory (DFT) calculations coupled with continuum elastica modeling. Exploring varying wrinkle sizes and compressive strain levels ($5\%-20\%$), we show that the global out-of-plane polarization follows a linear behavior when parameterized by the projected aspect ratio of the nanowrinkles. On this basis, we develop a physically grounded
geometric model incorporating an effective 2D flexoelectric coefficient, which accurately predicts DFT polarizations without requiring higher-order nonlinear parameters. Atom- and orbital-resolved charge density analyses reveal the microscopic origin of this behavior: while the central Mo $4d$-orbital
manifold acts as a robust, linear flexoelectric core, local
curvature drives continuous, chemically asymmetric charge transfer between the S $3p$ and Se $4p$ sublayer
manifolds. Our findings establish clear
geometric design rules for harnessing Janus-based flexoelectricity for flexible nanoelectronics and optoelectronics.
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All authors Stefan Velja, Surender Kumar, Domenico Corona, Caterina Cocchi
Materials Science
Light-facilitated ferroelectric switching in wurtzite crystals
Ricardo Jiménez-Sánchez, Fernando Salazar, Miguel Cruz-Irisson et al. (+2 more)
Wurtzite ferroelectrics combine large remanent polarization with full CMOS compatibility, positioning them as a leading platform for next-generation non-volatile
memory. Their practical deployment, however, is hindered by an intrinsically large coercive field, rooted in the high energy barrier separating the polar wurtzite phase from the nonpolar hexagonal phase that mediates polarization switching. Here, using first-principles calculations, we propose an alternative, field-free strategy for lowering this barrier: above-bandgap electronic photoexcitation. Taking LaN as a representative wurtzite ferroelectric, we show that light induced carriers dramatically reduce the energy difference between the hexagonal intermediate phase and the wurtzite ground state, sharply reducing the energy barrier to ferroelectric switching. This effect originates from a photoinduced partial metallization of the polar phase, which screens the dipole-dipole interactions that stabilize ferroelectric order and thereby favors the competing nonpolar structure. The robustness of this mechanism is further confirmed for the rocksalt polymorph. Our results establish light as a powerful, non-invasive route to controlling ferroelectric switching in wurtzites, opening a path toward faster, lower-voltage, and more energy-efficient non-volatile
memory technologies.
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All authors Ricardo Jiménez-Sánchez, Fernando Salazar, Miguel Cruz-Irisson, Riccardo Rurali, Claudio Cazorla
Materials Science · Cross-listed from cond-mat.str-el
Hong-Hao Song and Gang v. Chen
We show that zero-energy gapless Weyl-line
phonons of the Kane-Lubensky's type can arise in the three-dimensional Maxwell
lattice frustrated Mott
insulators through the magnetopological mechanics. In a pyrochlore antiferromagnet with the
spin-
lattice coupling, a
magnetic field selects the
spin state whose
lattice distortion generates a $P4_3 32$ topological
lattice. More crucially, the
spin-
lattice coupling and the
spin configuration cause the bending of the neighbouring bonds, and converts the system into the topological Maxwell
lattice. Remarkably, the resulting system is found to host the bulk zero-frequency Weyl-line
phonons protected topologically, and these gapless
phonons are not Goldstone modes. Unlike the conventional ${C_{\rm ph}\sim T^3}$ for the Goldstone
phonons, these one-dimensional zero-mode
manifolds yield a characteristic low-temperature
phonon specific heat ${C_{\rm ph}\sim T^2}$. Our results could find applications in the Cr-based spinel systems, and moreover, we establish a low-energy platform where an extensive number of topological zero-frequency
phonons can strongly couple to other degrees of freedom, opening a route to exotic
phonon-mediated phenomena.
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Materials Science
Pressure Evolution of Atomic Volume Systematics in Transition Metals
Masaaki Geshi and Yuichi Akahama
We investigated the
evolution of the well-known parabolic dependence of atomic volume on atomic number in transition metals under extreme compression at pressures up to 400 GPa using density functional theory calculations. Our results reveal that the ambient-pressure parabolic trend transforms into a characteristic cubic-like behavior at high pressures. This
evolution is attributed to the higher compressibility of bcc transition metals associated with comparatively large increases in the total energy. The present findings are discussed in relation to previous experimental observations and first-principles calculations.
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Materials Science · Cross-listed from cond-mat.str-el
Observation of multipartite spin entanglement in a cuprate chain
S. F. R. TenHuisen, Z. Shen, V. Bhartiya et al. (+17 more)
Quantum materials are believed to host highly entangled states of matter, but probing and quantifying such
entanglement has long remained experimentally elusive. Here, we use resonant inelastic X-ray scattering (RIXS) as a probe of multipartite
spin entanglement. By projecting the RIXS cross section onto the appropriate
spin excitation channel, we show that the
Quantum Fisher Information can be extracted directly from the measured
spin fluctuation spectrum. We detect at least 7-partite
spin entanglement in the model one-dimensional cuprate Sr$_2$CuO$_3$, revealing one of the largest
entanglement depths yet reported in a solid. The observed
entanglement depth agrees with Hubbard-model expectations and persists to elevated temperatures. Our results establish RIXS as an experimental probe of many-body
spin entanglement and provide a platform for extensions to charge and orbital sectors and nonequilibrium settings.
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All authors S. F. R. TenHuisen, Z. Shen, V. Bhartiya, V. Menon, P. Sharma, H. Padma, Z. Guan, W. He, M. K. Lajer, J. Li, D. Banerjee, J. Pelliciari, I. A. Zaliznyak, G. D. Gu, M. D. Lukin, S. Johnston, M. P. M. Dean, V. Bisogni, Y. Wang, M. Mitrano
Materials Science
Atomistic modeling of molecular beam epitaxy growth of SrTiO3 and Sr2TiO4 thin films
Guangfu Luo and Dane Morgan
Molecular beam epitaxy (MBE) is renowned for its potential for atomic layer control, but unexpected growth mechanisms can potentially compromise this level of precision. In this study, we employ first-principles calculations to investigate the atomistic processes governing the MBE growth of perovskite SrTiO3 and Ruddlesden-Popper Sr2TiO4 films on a SrTiO3 substrate. We systematically explore the potential molecular species in the gas phase and their reactions and
diffusion dynamics on the film surfaces and layer edges. Our analyses uncover three mechanisms of importance for understanding this type of growth. First, oxygen vacancies can be dynamically induced during surface
diffusion on defect-free substrate and noticeably accelerate the
diffusion processes. Second, while the SrO layer is expected to grow in a single-layer growth mode, the presence of potential TiSr defects may promote the formation of SrO islands. Lastly, adsorbed Ti atoms and TiO2 molecules on the SrO bilayer can insert into SrO bilayers, resulting in an unexpected growth sequence. These findings may have broader implications for the MBE growth of metal oxide films and provide guidance for achieving improved control over their growth processes.
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Materials Science · Cross-listed from cs.LG
Learning Metamaterial Eigenmodes with Wavelet-Encoded Fourier Neural Operators
Han Zhang, Alexander Ogren, Cynthia Rudin et al. (+2 more)
Machine learning surrogates based on neural operators have shown broad applicability in solving forward PDE problems. However,
eigenvalue problems, in which an eigenparameter and one of several valid eigenmodes must be simultaneously solved, remain difficult because standard operator learning formulations assume a unique input-output map. This work demonstrates that
Fourier Neural Operators (FNOs), combined with wavelet-based encodings of PDE inputs, can learn and predict multiple eigenmodes of the elastic wave equation, corresponding to deformation modes of acoustic waves propagating through arbitrary metamaterial geometries. We provide a mechanistic explanation and experimental evidence for why wavelet encodings are well matched to the dual spatial-spectral structure of the FNO, enabling deterministic mode selection on both continuous-valued and binary-valued geometries within a single model, and for why prediction accuracy varies with
geometric discontinuities. For metamaterial design, the resulting surrogate accelerates the simulation stage of the design cycle by three orders of magnitude relative to finite element analysis on a consumer-grade CPU, while preserving high fidelity. These results also carry broader implications for designing input encodings in other multi-mode PDE solvers based on spectral neural operators.
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All authors Han Zhang, Alexander Ogren, Cynthia Rudin, Johann Guilleminot, L. Catherine Brinson
Materials Science · Cross-listed from cond-mat.mes-hall
Electronic Orbital Angular Momentum Driven by Finite-Momentum Phonons: Beyond Chiral and Axial Phonons
Yongho Park, Jeonghun Sohn, Sejoong Kim et al. (+1 more)
We show that finite-momentum
phonons generate electronic orbital angular momentum (OAM) even without
phonon axiality or chirality, with the response controlled by the
phonon wave vector $q$ and frequency $\omega$. We develop a general gauge-field theory in which a
unitary transformation absorbs the
phonon displacement into emergent vector and scalar potentials acting on the electrons, providing a perturbative classification of the OAM response in $q$ and $\omega$. We derive $q$- and $\omega$-scaling laws for AC and DC responses. Notably, AC OAM arises even for linearly polarized
phonons, with its magnitude and sign tunable by $q$. Its generation is governed by the matching between the
phonon geometry and the electronic orbital texture rather than solely by the
phonon angular momentum. The connection of the DC response to the electronic Berry
curvature further supports that
phonon angular momentum is not the only degree of freedom governing electronic OAM generation. Time-dependent tight-binding simulations under acoustic-
phonon driving independently confirm the core predictions. Our results extend
phonon-driven OAM beyond chiral and axial
phonons and establish a wave-vector-tunable route to orbitronics, accessible with surface acoustic waves.
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All authors Yongho Park, Jeonghun Sohn, Sejoong Kim, Kyoung-Whan Kim
Materials Science · Cross-listed from cond-mat.str-el
Selective coupling of high-order phonons in La2-xSrxCuO4
Ke-Jun Xu, Paulina Majchrzak, Nathan Giles-Donovan et al. (+14 more)
In
crystals and molecules with strong coupling between the charge carriers and atomic vibrations, high order harmonics of the vibrational excitations can be observed with intensity following the Franck-Condon envelope. Here, we uncover a new regime of electron-
phonon coupling in La2-xSrxCuO4 using resonant inelastic X-ray scattering. In the undoped compound, we find sharp peaks at approximately 85$\pm$5 meV, 180$\pm$7 meV, and 330$\pm$5 meV with no observable dispersion, and an absence of appreciable intensity from other modes observed in Raman spectroscopy in this energy range. The 180 meV and 330 meV excitations have energies approximately consistent with two-
phonon and four-
phonon in-plane Cu-O bond stretching mode, suggesting that the resonantly excited valence electrons strongly couple to this mode. These excitations exhibit significant doping dependence, eventually becoming unresolvable at 10% hole doping, where the low energy charge excitations are dominated by dispersive plasmons. The observation of selective coupling to even-ordered
phonons and stark contrast with the Raman spectra indicate anomalous electron-
phonon coupling beyond the Franck-Condon picture. One intriguing possibility is the existence of locally paired quasiparticles in insulating cuprates.
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All authors Ke-Jun Xu, Paulina Majchrzak, Nathan Giles-Donovan, Sangheon Kim, Jaewon Choi, Jun Okamoto, Ganesha Channagowdra, Hsiao-Yu Huang, Di-Jing Huang, Seiki Komiya, Takao Sasagawa, Shuichi Wakimoto, Wei-Sheng Lee, Zhi-Xun Shen, Thomas P. Devereaux, Dung-Hai Lee, Robert J. Birgeneau