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
Strongly Correlated Electrons
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
Superconductivity
Fabrication And Characterization Of High-Quality Nb/Al-AlO$_x$/Nb Cross-Type Josephson Tunnel Junctions Utilising CMP-based Planarisation Techniques
Alexander Stoll, Andreas Reifenberger, Daniel Hengstler et al. (+2 more)
Josephson tunnel junctions (JJs) are the fundamental building blocks of today's most advanced superconducting electronic components, such as
qubits and superconducting
quantum interference devices (SQUIDs). Given the ongoing demand for scalability of these devices on the wafer-scale, it is crucial to control the fabrication process as precisely as possible to ensure uniform quality and reproducibility. Today, window-type JJs are often used in the production of DC SQUIDs and while they are reliable and reproducible, they suffer from
alignment inaccuracies caused by photolithography and unavoidable parasitic capacitances, thus limiting the energy sensitivity of DC SQUIDs. These problems can be circumvented by producing JJs with cross-type geometry, which allows for smaller junction areas and eliminates parasitic capacitances. Here we discuss the fabrication of Nb/Al-AlOx/Nb-based cross-type JJs, where the trilayer is embedded in sputter-deposited SiO$_2$ to allow for planarisation of the structures and to ensure the reliable insulation of the sidewalls of the bottom electrode. Instead of lift-off processes that require a lot of time and potentially leave unwanted wings along the edges of microstructures behind that might compromise subsequent layers, we use chemical-mechanical polishing (CMP) for the removal of excess SiO$_2$. This is not only much faster, but produces smooth and uniform surfaces, which in turn effectively improves the reliability of our JJ production process resulting in a high yield of over $90\,\%$ on wafer-scale. In addition, we discuss the influence of fabrication details on the quality and electrical properties of our JJs with different junction areas down to $1\,\mathrm{\mu m} \times 1\,\mathrm{\mu m}$ distributed across the wafer and extract the junction specific quality parameters from their IV-characteristics and their Fraunhofer patterns.
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All authors Alexander Stoll, Andreas Reifenberger, Daniel Hengstler, Andreas Fleischmann, Christian Enss
Strongly Correlated Electrons
Schwinger boson perturbation theory for spin-$S$ Kitaev-Heisenberg magnets: phase diagram and dynamical response near Kitaev spin liquids
Daiki Sasamoto and Joji Nasu
We develop a Schwinger
boson perturbative framework for the
spin-$S$ Kitaev-Heisenberg model. The
spin-
liquid saddle point of the pure Kitaev model is used as the unperturbed state, and
magnetic instabilities and dynamical
spin correlations are evaluated around this saddle point. We decompose the
Hamiltonian exactly into two parts by exploiting the Klein duality intrinsic to the Kitaev-Heisenberg model. We perform the random-phase approximation by taking the part invariant under the duality transformation as the unperturbed term and treating the remaining term, which changes sign under it, as the perturbation. We determine the phase boundaries separating the
quantum spin-
liquid regimes from the adjacent magnetically ordered phases for $S=1/2$, $1$, $3/2$, and $2$. The
spin-
liquid regions shrink rapidly with increasing $S$ and become very narrow at $S=2$. We also compute the
spin dynamics of the
spin-$S$ Kitaev-Heisenberg model, focusing on $S=1$, and find that the dressed dynamical
spin structure factor retains a broad two-spinon continuum at finite energies, while the low-energy spectral weight softens at the ordering wave vectors of the adjacent
magnetic phases. Our framework thus enables thermodynamic-limit calculations of
spin dynamics near
magnetic instabilities.
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Mesoscale and Nanoscale Physics
Equivalent Circuit Representation and Thermodynamic Limitations of Non-Adiabatic Spin-Transfer Torque effect
Wataru Koshibae
We present an equivalent
circuit representation of the Thiele equation for the current-driven domain walls. We show that the non-adiabatic
spin-transfer torque (\beta-term) cannot be represented by passive elements alone (such as resistors, inductors, and capacitors) and necessarily requires active elements, corresponding to negative dissipation. Consequently, assuming that the driving current is the only power source for the texture dynamics, directly incorporating the \beta-term introduces a fundamental contradiction with thermodynamic principles. This equivalent
circuit theory indicates that the interpretation of experiments solely through the \beta-term does not fully capture the underlying physics, highlighting the need to account for effects distinct from the
spin dynamics.
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Mesoscale and Nanoscale Physics
Memory Control of Ice Growth During Non-Equilibrium Freezing of Water
Abhigyan Hazarika, Sudeep N. Punnathanam, Biman Bagchi et al. (+1 more)
Freezing of supercooled water is a classic non-
equilibrium problem, yet the influence of thermal history on crystallization remains unclear. Using molecular dynamics simulations with the TIP4P/Ice model, we investigate how the initial temperature $T_i$ shapes freezing following rapid quenching to 250 K. By monitoring the
evolution of hydrogen-bonded ring structures, we find a non-monotonic dependence of the freezing time $t_F$ on $T_i$, with the slowest crystallization occurring near 300 K. Remarkably, this means that initially hotter water can freeze faster than cooler water, a molecular-scale analogue of the Mpemba effect. A non-stationary generalized Langevin equation framework shows that two-time
memory kernels retain information about the system's thermal past, directly influencing crystallization dynamics. Structural analysis further reveals that five-membered rings act as kinetic traps, while correlations among ring types regulate the accessibility of ice-like motifs. These results uncover a molecular origin of
memory-driven freezing and establish structural
memory as a key driver of non-
equilibrium phase transitions.
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All authors Abhigyan Hazarika, Sudeep N. Punnathanam, Biman Bagchi, Prabal K. Maiti
Superconductivity
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
Strongly Correlated Electrons
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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Statistical Mechanics
Nonequilibrium stochastic thermodynamics of boundary functionals: From Zubarev's ensemble to stochastic particle separation
V. V. Ryazanov
This paper develops a generalization of Zubarev's nonequilibrium statistical operator method for the case of simultaneous inclusion of additive and nonlocal boundary functionals of trajectories. Using a unified thermodynamic approach, a three-parameter model of nonequilibrium systems is constructed, including the first-passage time, the dwell time above a given level, and the absolute extremum of the process. A correspondence is demonstrated between the maximum information
entropy method for trajectories and the Donsker-Varadan large deviation formalism. Using the Doob`s h-transform, it is demonstrated that fixing extremal functionals of history induces efficient non-Markovian transport in the system with dynamic adaptation to historical records. Criteria for the applicability of the developed apparatus in the "large time" domain and the possibilities of its use for optimizing
stochastic particle separation in periodic potentials are discussed.
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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
Strongly Correlated Electrons
Theory of Kondo hybridization wave in Kondo lattice
Yin Zhong
Recent scanning tunneling microscopy experiments have discovered emergent spatially modulated Kondo hybridization wave (KHW) order in the heavy
fermion superconductor UTe$_2$ and the artificial Kondo
lattice system 1T/1H-TaS$_2$, challenging the conventional paradigm of spatially uniform Kondo hybridization in heavy
fermion physics. Here, we develop a microscopic theory for KHW order based on the canonical square-
lattice Kondo
lattice model within the large-$N$ fermionic mean-field approximation. We systematically identify stable modulated KHW phases and establish their ground-state phase diagram. The prominent $\boldsymbol{Q}=(0,\pi)$ KHW phase yields uniaxial stripe modulation of the Kondo hybridization gap, which faithfully reproduces the spatial modulation pattern observed in UTe$_2$. Moreover, its inherent unit-
cell-doubling modulation precisely accounts for the spectroscopic features measured in 1T/1H-TaS$_2$. We further predict a characteristic in-plane conductivity anisotropy that serves as a definitive transport fingerprint to discriminate KHW states with distinct ordering wavevectors. Our work provides a microscopic foundation for the newly observed KHW order and establishes a unified theoretical framework for understanding emergent modulated hybridization phenomena in heavy
fermion materials.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Magic-free coexisting photonic and phononic moiré flat bands
Ziming Chen, Kaiyu Cui, Ning Wu et al. (+8 more)
Moiré flat bands enhance localization and interactions through suppressed group velocity, but existing approaches largely target a single physical field because distinct excitations generally require different, finely tuned magic configurations. Here we introduce a flat-band mechanism based on strong diffractive hybridization among moiré-folded bands. Period-mismatched modulations open distinct coupling channels whose hybridization renormalizes the band dispersion. An effective
Hamiltonian shows that increasing the diffractive coupling progressively suppresses the group velocity, driving the system toward a flat-band regime without field-specific magic configurations. This coupling-induced mechanism enables band flattening across distinct physical excitations. We demonstrate this mechanism in a single-layer moiré optomechanical
crystal, where photonic and phononic flat bands are simultaneously realized, and their localized modes and optomechanical interaction are experimentally observed. Beyond photonic and phononic systems, this mechanism may extend to other wave and quasiparticle platforms, providing a general route to co-localizing and coupling distinct physical fields in moiré systems.
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All authors Ziming Chen, Kaiyu Cui, Ning Wu, Shuyuan Li, Chenxuan Wang, Xue Feng, Fang Liu, Wei Zhang, Hao Sun, Yongzhuo Li, Yidong Huang
Mesoscale and Nanoscale Physics
Impurity as a probe of Berry curvature and wavefunction winding in gapped two-band models
Reda Nabil, Pascal Simon and Andrej Mesaros
We explore the possibility of using quasiparticle interference near impurities to extract non-local properties of bands. Focusing on the minimal two-band description of a system with multiple valleys, we show that the local density of states (LDOS) induced by non-
magnetic impurities can effectively probe both the Berry
curvature and the wavefunction winding, locally in each valley. We analyze gapped models based on Dirac, semi-Dirac, quadratic touching, and higher-order touching energy dispersions, in presence of a point-like potential scatterer. We find that for strong enough impurity potentials the LDOS along a contour around the impurity unambiguously shows the wavefunction winding number, in contrast to the case of gapless Dirac-like dispersions where the winding can be precluded by LDOS oscillations in the radial direction. We also establish a general connection between, on the one hand, the Berry
curvature as a function of momentum locally in a valley, and on the other hand, the wavefunction winding number and the energy dispersion parameters, making hence the local Berry
curvature directly observable from spectroscopic LDOS information.
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Mesoscale and Nanoscale Physics
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
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Non-Markovian dynamics of a qubit on the zigzag edge of photonic graphene
Enrico Di Benedetto
We present an analytical study of the dynamics of a
qubit coupled to the zigzag edge of a photonic honeycomb
lattice. Leveraging a resolvent operator approach and exact
lattice Green's functions, we map the spectrum of
qubit-
photon bound states and complex poles to uncover the long-time scaling laws of the
qubit population. Unlike a
qubit coupled to the bulk of
graphene, the presence of a zero-energy flat band connecting the Dirac points suppresses long-time branch-cut-induced tails, instead driving damped Rabi oscillations. Potential experimental platforms are briefly discussed.
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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
Superconductivity
Geometry-induced current decrowding in superconducting 3D constrictions
Igor Bogush and Oleksandr Dobrovolskiy
Current crowding is a ubiquitous limitation in nanoscale devices, where confinement and sharp features distort current flow, generating localized current-density hotspots and premature failure. In
superconductors, this effect suppresses the order parameter and promotes
vortex nucleation, reducing the critical current below the intrinsic depairing limit. Here, we demonstrate that 3D shaping of superconducting nanoarchitectures overcomes
geometric current crowding through spatial current redistribution, establishing a geometry-induced decrowding effect. Using finite-element modeling based on the time-dependent Ginzburg–Landau equation, we reveal that 3D constrictions exhibit a pronounced and tunable response to moderate in-plane
magnetic fields—a functionality absent in planar geometries. This field-controlled geometry enables critical-current modulation and unveils new
vortex-dynamics regimes, including a non-reciprocal critical current. Furthermore,
curvature and finite thickness fundamentally alter
vortex nucleation by enabling apex-mediated entry of single
vortex lines, followed by their 3D splitting into two
vortex filaments—a mechanism that does not occur in 2D
manifolds. Our findings demonstrate 3D
geometric engineering as a design paradigm for superconducting nanoarchitectures, offering control over current distribution and
vortex dynamics in devices approaching the depairing limit.
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Superconductivity · Cross-listed from quant-ph
Instantaneous-Frame Theory of Strongly Driven Parametric Gates
Kentaro Kubo, Shinichi Inoue, Jushin Tei et al. (+3 more)
Parametric two-
qubit gates using tunable couplers are a promising approach to scalable superconducting
quantum processors. However, conventional theories formulated in the idle eigenbasis break down in the large-amplitude regime required for fast gate operations. Here, we show that parametric gates are more naturally and accurately described as coherent rotations between instantaneous eigenstates rather than idle eigenstates. This approach may appear counterintuitive, since instantaneous eigenbases are usually associated with adiabatic dynamics. However, they also form a natural moving frame for driven dynamics, where the non-Abelian Berry connection governs transitions and provides a compact description of the exchange and effective $ZZ$ couplings. We show that this theory achieves quantitative agreement with exact numerical simulations across representative tunable-coupler architectures, including double-transmon, capacitively shunted double-transmon, and single-transmon couplers. The description remains accurate even in regimes where idle-frame descriptions fail, while substantially reducing the reliance on computationally demanding exact simulations. These results establish an instantaneous-frame theory of parametric gates beyond conventional idle-frame models and provide a new perspective on driven
quantum dynamics.
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All authors Kentaro Kubo, Shinichi Inoue, Jushin Tei, Yinghao Ho, Yasunobu Nakamura, Hayato Goto
Mesoscale and Nanoscale Physics
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
Superconductivity
$1/3$-Flux Bound States in Multicomponent Superconductor Exhibiting Non-Abelian Statistics of $\mathbb {Z}_3$ Parafermions
Xing-Yu Wu, Y. H. Wang, X. C. Xie et al. (+1 more)
Multicomponent
superconductors (MSCs) are predicted to host
magnetic flux quanta carrying arbitrary fractions of the superconducting flux
quantum. Recent advances have raised the expectation that $1/3$ flux quanta may emerge in MSCs with $C_3$ rotational
symmetry. Electrons bound to such fractional flux are long regarded to form anyons, yet their explicit braiding statistics remain unexplored. We propose that these $1/3$-flux bound states ($1/3$-FBSs) exhibit the intriguing non-Abelian statistics of $\mathbb{Z}_3$ parafermions. Under no-double-occupancy constraint, two successive braiding operations of $1/3$-FBSs are equivalent to a single $\mathbb Z_3$ parafermion braiding operation. The parafermion parity encoding the braiding outcome can be read out via the fermionic occupation number of the $1/3$-FBSs. Combined with a crossed-Andreev-reflection-induced Hadamard gate, one can realize the complete set of $\mathbb{Z}_3$ parafermion braiding operations.
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All authors Xing-Yu Wu, Y. H. Wang, X. C. Xie, Yijia Wu
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
Statistical Mechanics · Cross-listed from cs.IT
Physics of Information Geometry - Part I: Principle of Least Action on the Probability Simplex
C. Emre Koksal and Deniz Sargun
We develop a least-action framework for describing how a probability distribution can evolve from an
equilibrium state to a prescribed nonequilibrium state under constrained incremental changes. Taking a Gibbs distribution as the
equilibrium reference, the framework gives a direct physical meaning to the geometry of the probability simplex: distance from
equilibrium corresponds to nonequilibrium free energy, while changes between successive distributions carry an informational kinetic cost. The Pythagorean structure of relative
entropy then provides the central insight of the work. It shows that intermediate distributions chosen via sequential information projections can reduce the kinetic cost of large transitions and establishes an energy-conservation-like relation between the kinetic expenditure along a path and the free energy accumulated in reaching the target distribution. Motivated by this geometry, we construct a greedy least-action path through successive information projections, obtain a closed-form characterization of each projection through the Lambert W function, and establish a finite-step performance guarantee. We further show that state-dependent costs can be incorporated naturally by reshaping the underlying Gibbs reference, providing a thermodynamic interpretation of path penalties as modifications of the effective energy landscape. Together, these results provide a unified view of distributional
evolution through least action, information geometry, and nonequilibrium thermodynamics.
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Superconductivity
Néel-Vector Control of the Josephson Diode Effect in $\mathcal{PT}$-symmetric Antiferromagnets
Xian-Tang Xu, Xun-Jiang Luo, Mingliang Tian et al. (+1 more)
The interplay of superconductivity and magnetism gives rise to rich phenomena in Josephson junctions. In this Letter, we study Josephson junctions formed by conventional $s$-wave
superconductors and a $\PT$-symmetric collinear antiferromagnet modeled on CuMnAs. Using microscopic modeling and
symmetry analysis, we show that these junctions exhibit both the Josephson diode effect and $\varphi_{0}$-junction states. Remarkably, both effects are controlled by the Néel vector: rotating it by $90^{\circ}$ switches off both, while reversing it switches the diode polarity. To reveal the microscopic mechanism, we develop a channel-resolved scattering theory that accurately captures the anomalous phases and establishes the exact condition for the diode effect. The interplay of the channel current-phase relations yields a sizable diode efficiency, tunable by both the magnitude and direction of the exchange field. Furthermore, a Green-function reduction identifies a single renormalized $\PT$-degenerate band as the transport carrier and precisely reproduces the full current amplitudes. Our work establishes $\PT$-symmetric antiferromagnets as versatile platforms for field-free, highly tunable Josephson diodes and $\varphi_{0}$ junctions.
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All authors Xian-Tang Xu, Xun-Jiang Luo, Mingliang Tian, Ning Hao
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