Strongly Correlated Electrons
Evidence for Many-Body States in NiPS$_3$ Revealed by Angle-Resolved Photoelectron Spectroscopy
Miłosz Rybak, Benjamin Pestka, Biplab Bhattacharyya et al. (+11 more)
We present $\mu$-ARPES spectra of the Mott-insulating van der Waals antiferromagnet NiPS$_3$. Signatures of strong correlations – such as the onset of atomic or atomic-ligand multiplets and
spin-orbit-entangled
exciton have been observed in this material by various two-particle spectroscopies, but not previously in photoemission. Our measurements reveal a weakly dispersive feature at the valence-band edge that is absent in DFT+$U$ calculations and remains unchanged across the Néel transition. After critically examining and ruling out alternative interpretations, we show that an exact diagonalization of a NiS$_6$ cluster yields low-energy final-state configurations of mixed multiplet $d^7$ and $d^8\underline{L}$ character, whose energy differences are consistent with the observed additional feature. This implies that ARPES directly accesses local Ni-S multiplet physics in NiPS$_3$, revealing a many-body structure beyond mean-field theory. Our results confirm that NiPS$_3$ is an excellent model platform in which strong correlations, reduced dimensionality, and covalent metal-ligand bonding jointly shape both two- and single-particle spectroscopies, underscoring the need for a genuinely
quantum many-body description of two-dimensional
quantum materials.
Read the full abstract ▾
All authors Miłosz Rybak, Benjamin Pestka, Biplab Bhattacharyya, Jeff Strasdas, Adam K. Budniak, Adi Harchol, Vitaliy Feyer, Iulia Cojocariu, Daniel Baranowski, Yaron Amouyal, Efrat Lifshitz, Markus Morgenstern, Magdalena Birowska, Krzysztof Wohlfeld
Strongly Correlated Electrons
Calculating Feynman diagrams with matrix product states
Xavier Waintal
This text reviews, hopefully in a pedagogical manner, a series of work on the automatic calculations of Feynman diagrams in the context of
quantum nanoelectronics (Keldysh formalism) with an application to the Kondo effect in the out-of-
equilibrium single
impurity Anderson model. It includes a discussion of (A) how to deal with the proliferation of diagrams, (B) how to calculate them using the Tensor Cross Interpolation
algorithm instead of Monte-Carlo and (C) how to resum the obtained series. These notes correspond to a lecture given at the Autumn School on Correlated Electrons 2025 in Jullich, Germany. The book with all the lectures of the school (edited by Eva Pavarini, Erik Koch, Alexander Lichtenstein, and Dieter Vollhardt) is available in open access.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Quantum Christoffel Nonlinear Magnetization
Xiao-Bin Qiang, Xiaoxiong Liu, Hai-Zhou Lu et al. (+1 more)
The Christoffel symbol is an essential quantity in Einstein's general theory of relativity. We discover that an electric field can induce a nonlinear magnetization in
quantum materials, described by a Christoffel symbol defined in the
Hilbert space of
quantum states (
quantum Christoffel symbol). Quite different from the previous scenarios, this orbital magnetization does not need
spin-orbit coupling and inversion
symmetry breaking. Through
symmetry analysis and first-principles calculations, we identify a number of point groups and 2D material candidates (e.g., BiF$_3$, ZnI$_2$, and Ru$_4$Se$_5$) that host this
quantum Christoffel nonlinear magnetization. More importantly, this nonlinear magnetization allows the
quantum Christoffel symbol to be probed by optical techniques such as magneto-optical Kerr spectroscopy or transport measurements such as tunneling magneto-resistance. This
quantum Christoffel nonlinear magnetization gives a paradigm of how geometry dictates physics.
Read the full abstract ▾
All authors Xiao-Bin Qiang, Xiaoxiong Liu, Hai-Zhou Lu, X. C. Xie
Superconductivity
Unconventional superconductivity from lattice quantum disorder
Yu-Cheng Zhu, Jia-Xi Zeng and Xin-Zheng Li
Unconventional superconductivity presents a defining and enduring challenge in condensed matter physics. Prevailing theoretical frameworks have predominantly emphasized electronic degrees of freedom, largely neglecting the rich physics inherent in the
lattice. Although conventional
phonon theory offers an elegant description of structural phase diagrams and
lattice dynamics, its omission of
nuclear quantum many-body effects results in misleading phase diagram interpretations and, consequently, an unsound foundation for superconducting theory. Here, by incorporating
nuclear quantum many-body effects within first-principles calculations, we discover a
lattice quantum disordered phase in
superconductors H3S and La3Ni2O7. This phase occupies a triangular region in the pressure-temperature phase diagram, whose left boundary aligns precisely with Tc of the left flank of the superconducting dome. The Tcmax of this
quantum disordered phase coincides with the maximum of superconducting Tc, indicating this phase as both the origin of superconductivity on the dome's left flank and a key ingredient of its pairing mechanism. Our findings advance the understanding of high-temperature superconductivity and establish the
lattice quantum disordered phase as a unifying framework, both for predicting new
superconductors and for elucidating phenomena in a broader context of condensed matter physics.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Fluctuations of the inverted magnetic state and how to sense them
Anna-Luisa E. Römling, Artim L. Bassant and Rembert A. Duine
Magnons are the low-energy excitations of magnetically ordered materials. While the
magnetic moment of a ferromagnet aligns with an applied
magnetic field, it has been experimentally shown that the
magnetic order can be inverted by injecting
spin current into the magnet. This results in an energetically unstable but dynamically stabilized state where the
magnetic moment aligns antiparallel to an applied
magnetic field, called the inverted
magnetic state. The excitations on top of such a state have negative energy and are called antimagnons. The inverted state is subject to fluctuations, in particular, as shot noise in the
spin current, which are different from fluctuations in
equilibrium, especially at low temperatures. Here, we theoretically study the fluctuations of the inverted
magnetic state and their signatures in experimental setups. We find that the fluctuations from the injection of
spin current play a large role. In the
quantum regime, the inverted
magnetic state exhibits larger fluctuations compared to the
equilibrium position, which can be probed using a
qubit. Our results advance the understanding of the fundamental properties of antimagnons and their experimental controllability, and they pave the way for applications in spintronics and magnonics, such as
spin wave amplification and
entanglement.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Topology and energy dependence of Majorana bound states in a photonic cavity
Aksel Kobiałka, Arnob Kumar Ghosh, Rodrigo Arouca et al. (+1 more)
Light-matter interaction plays a crucial role in modifying the properties of
quantum materials. In this work, we investigate the effect of cavity induced
photon fields on a topological
superconductor hosting Majorana bound states (MBS). We model the system using a Peierls substitution of the photonic operator in the kinetic and
spin-orbit terms, and utilize an exact diagonalization of
Hamiltonian for a finite number of
photons to investigate the coupled system. We find that the MBS persist even in the presence of a cavity field and notably appear at finite and tunable energy, in contrast to a usual 1D topological
superconductor. The MBS energy is shifted by two processes: the cavity
photon energy adds a constant energy shift, while the light-matter interaction induces additional parameter dependencies, such that the MBS experience a pseudo-dispersion as a function of both light-matter interaction and
magnetic field. Additionally, we find that the MBS energy oscillations are suppressed with increasing light-matter interaction and that disorder stability is not impacted by the light-matter interaction. Combined, these offer additional tunability and stability of the MBS. As a second result, we establish a modified spectral localizer formalism as an essential tool for topological characterization of
quantum matter in a cavity. The spectral localizer allows characterization at arbitrary energies, which is needed for probing different
photon sectors. However, hybridization between different
photon sectors in the low-frequency regime limits a straightforward application of a standard spectral localizer. We fully resolve this issue by judiciously applying an energy shift to the spectral localizer. Our work thus introduces a new avenue for controlling MBS via light-matter coupling and provides a framework for exploring cavity-modified
topologies.
Read the full abstract ▾
All authors Aksel Kobiałka, Arnob Kumar Ghosh, Rodrigo Arouca, Annica M. Black-Schaffer
Disordered Systems and Neural Networks · Cross-listed from cs.LG
How to Train Your Resistive Network: Generalized Equilibrium Propagation and Analytical Learning
Jonathan Lin, Aman Desai, Frank Barrows et al. (+1 more)
Machine learning is a powerful method of extracting meaning from data; unfortunately, current digital hardware is extremely energy-intensive. There is interest in an alternative analog computing implementation that could match the performance of traditional machine learning while being significantly more energy-efficient. However, it remains unclear how to train such analog computing systems while adhering to locality constraints imposed by the physical (as opposed to digital) nature of these systems. Local learning
algorithms such as
Equilibrium Propagation and Coupled Learning have been proposed to address this issue. In this paper, we develop an
algorithm to exactly calculate gradients using a graph theoretic and analytical framework for Kirchhoff's laws. We also introduce Generalized
Equilibrium Propagation, a framework encompassing a broad class of Hebbian learning
algorithms, including Coupled Learning and
Equilibrium Propagation, and show how our
algorithm compares. We demonstrate our
algorithm using numerical simulations and show that we can train resistor networks without the need for a replica or readout over all resistors, only at the output layer. We also show that under the analytical gradient approach, it is possible to update only a subset of the resistance values without a strong degradation in performance.
Read the full abstract ▾
All authors Jonathan Lin, Aman Desai, Frank Barrows, Francesco Caravelli
Quantum Gases
Dynamic similarity of vortex shedding in a superfluid flowing past a penetrable obstacle
Junhwan Kwon and Y. Shin
We numerically investigate wake dynamics in a superfluid flowing past a penetrable obstacle. Unlike an impenetrable object, a penetrable obstacle does not fully deplete the density. We define an effective diameter $D_{\rm eff}$ from the Mach-1 contour of the time-averaged irrotational flow around the obstacle, which delineates the local supersonic region where quantized
vortices nucleate. Using this flow-defined length scale, we construct a superfluid Reynolds number $Re_{\rm s} = (v_0 - v_c) D_{\rm eff}/ (\hbar/ m)$, where $v_0$ is the flow speed, $v_c$ is the critical velocity, and m is the particle mass. We show that $Re_{\rm s}$ organizes the wake dynamics across obstacle sizes and strengths: the transition from dipole-row emission to alternating
vortex cluster shedding occurs at $Re_{\rm s}$ around 2, and both the Strouhal number and the drag coefficient collapse onto universal curves when plotted as functions of $Re_{\rm s}$. These results extend the concept of dynamic similarity in superfluid flows to penetrable obstacles and demonstrate that the dynamically relevant length scale is determined by the supersonic region rather than by the
geometric obstacle size.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Toward Polyoxometalate Nanoelectronics
Dominique Vuillaume and Anna Proust
Polyoxometalates form a large family of molecular
oxide clusters of the early transition metals with unique and tunable properties (multi-redox, thermal and chemical robustness,
magnetic). We review more than 30 years of experimental research on the electron transport properties of polyoxometalates devices, from thin films and self-assembled monolayers down to single-molecule junctions. We focus on the relationship between the polyoxometalate structures (structural type, nature of metals and heteroatoms, role of the counterions, redox states, electrode linkers and functional ligands) and the electronic structures of the polyoxometalate-based devices (energy positions of the molecular orbitals, energy offset at the interfaces). Then, we critically discuss the performances of polyoxometalates in nanoelectronics devices: capacitance and resistive switching
memories, spintronics,
quantum bits and neuromorphic devices. We conclude with a discussion about pending issues and perspectives.
Read the full abstract ▾
Materials Science · Cross-listed from physics.geo-ph
Radial gradient of superionic hydrogen in Earth's inner core
Zepeng Wu, Liangrui Wei, Chen Gao et al. (+3 more)
Hydrogen is considered a key light element in Earth's core, yet the thermodynamics of its superionic phase and its distribution in the inner core remain unclear. Here, we compute ab initio Gibbs free energies for
liquid and superionic hcp and bcc Fe-H phases and construct the superionic-
liquid phase diagram over pressure-temperature conditions relevant to the Earth's inner core. We find that phase diagrams at different inner-core pressures collapse when temperatures are scaled by the melting temperature of pure iron, indicating that solid-
liquid partitioning is controlled primarily by a reduced temperature relative to iron melting and is weakly sensitive to pressure. This scaling relation further reconciles previously reported discrepancies in partition coefficients among theoretical studies and yields good agreement with available experimental data at low pressures. By applying thermochemical constraints, our free-energy results reveal a radial hydrogen gradient within the inner core. These results demonstrate that compositional gradients of superionic hydrogen in the inner core emerge naturally from
equilibrium thermodynamics and suggest a general mechanism governing the depth-dependent distribution of light elements within Earth's inner core.
Read the full abstract ▾
All authors Zepeng Wu, Liangrui Wei, Chen Gao, Shunqing Wu, Renata M. Wentzcovitch, Yang Sun
Disordered Systems and Neural Networks
Long-range spin glass in a field at zero temperature
Maria Chiara Angelini, Saverio Palazzi, Giorgio Parisi et al. (+1 more)
We compute the critical exponents of the zero-temperature
spin glass transition in a field on a one-dimensional long-range model, a proxy for higher-dimensional systems. Our approach is based on a novel loop expansion within the Bethe $M$-layer formalism, whose adaptation to this specific case is detailed here. The resulting estimates provide crucial
benchmarks for numerical simulations that can access larger system sizes in one dimension, thus offering a key test of the theory of
spin glasses in a field.
Read the full abstract ▾
All authors Maria Chiara Angelini, Saverio Palazzi, Giorgio Parisi, Tommaso Rizzo
Materials Science
Skyrmions in 2D chiral magnets with noncollinear ground states stabilized by higher-order interactions
Mathews Benny, Moinak Ghosh, Moritz A. Goerzen et al. (+4 more)
Magnetic skyrmions are intriguing topological
spin textures that have attracted great
attention due to their potential for future spintronic devices. Skyrmions have so far been explored in different
magnetic materials, such as ferromagnets, antiferromagnets, and ferrimagnets. Here, we propose a new type of unconventional skyrmions stabilized in noncollinear magnets. Using first-principles calculations and atomistic
spin simulations, we demonstrate that a noncollinear ground state can be stabilized in Rh/Co and Pd/Co atomic
bilayers on the Re(0001) surface by four
spin exchange interactions, although Co – a material often used in applications – is a prototypical ferromagnet with strong pairwise exchange interaction. We further show that unconventional skyrmion
lattices and isolated skyrmions can emerge on this noncollinear
magnetic background. Transition-state theory calculations reveal that these metastable skyrmions are protected by large energy barriers, suggesting that they could be observed in experiments. These unconventional types of skyrmions in noncollinear magnets might open new possibilities for topological
spin transport or magnet-
superconductor hybrid systems.
Read the full abstract ▾
All authors Mathews Benny, Moinak Ghosh, Moritz A. Goerzen, Bjarne Beyer, Hendrik Schrautzer, Stefan Heinze, Souvik Paul
Superconductivity
Design of a 60.8 K superconducting hydride LiMgZr2H12 at ambient pressure via Lithium doping
Qun Wei, Xinyu Wang, Jing Luo et al. (+2 more)
High-pressure hydrogen-rich compounds have long been regarded as promising room-temperature
superconductor candidates; however, their practical applications are limited by their reliance on extreme compression. This study explores hydrogen-rich
superconductors that may be stable at ambient pressures. Inspired by recent investigations of the MgZrH2n family, the LiMgZr2H12 structure with a Pmmm
symmetry was constructed, and its thermodynamic, mechanical, and dynamical stability were evaluated using first-principles calculations. Electron-
phonon coupling (EPC) analysis suggests that LiMgZr2H12 reaches a superconducting critical temperature (Tc) of 60.8 K at ambient pressure. Compared with MgZrH6, Li doping significantly increases the contribution of hydrogen atoms to the electron density of states near the
Fermi level (EF) and enhances the EPC constant of the LiMgZr2H12 structure. LiMgZr2H12 exhibits a superconducting figure of merit of 1.56, which is significantly greater than that of MgZrH6, demonstrating its outstanding potential for practical applications. This work guides ambient-pressure design of high-Tc hydrides.
Read the full abstract ▾
All authors Qun Wei, Xinyu Wang, Jing Luo, Meiguang Zhang, Bing Wei
Materials Science
Emergent 3D Fermiology and Magnetism in an Intercalated Van der Waals System
Luigi Camerano, Emanuel A. Martínez, Victor Porée et al. (+16 more)
Intercalation of
magnetic atoms into van der Waals materials provides a versatile platform for tailoring unconventional
magnetic properties. However, its impact on electronic dimensionality and exchange mechanisms remains poorly understood. Using Fe-intercalated TaS$_2$ as a model system, we combine X-ray absorption and resonant inelastic scattering with angle-resolved photoemission and first-principles calculations to reveal that intercalation reshapes the host electronic structure. We identify a
spin-polarized intercalant-host hybridized band with pronounced out-of-plane dispersion crossing the
Fermi level, providing an itinerant channel for interlayer
magnetic exchange. This mechanism explains the breakdown of a purely atomic picture and establishes a direct link between
lattice geometry, electronic dispersion, and
magnetic order. Our findings demonstrate that intercalant-induced itinerancy enables tunable interlayer coupling in otherwise layered magnets, offering a general microscopic framework for engineering
magnetic dimensionality in a broad class of intercalated vdW materials.
Read the full abstract ▾
All authors Luigi Camerano, Emanuel A. Martínez, Victor Porée, Laura Martella, Dario Mastrippolito, Debora Pierucci, Franco D'Orazio, Polina M. Sheverdyaeva, Paolo Moras, Enrico Della Valle, Tianlun Yu, Moritz Hoesch, Craig M. Polley, Thiagarajan Balasubramanian, Alessandro Nicolaou, Luca Ottaviano, Vladimir N. Strocov, Gianni Profeta, Federico Bisti
Other Condensed Matter
Nanoscale spin-wave frequency-selective limiter for 5G technology
Kristýna Davídková, Khrystyna Levchenko, Florian Bruckner et al. (+10 more)
Power limiters are essential devices in modern
radio frequency (RF) communications systems to protect highly sensitive input channels from large incoming signals. Nowadays-used
semiconductor limiters suffer from high electronic noise and switching delays when approaching the GHz range, which is crucial for the modern generation of 5G communication technologies aiming to operate at the EU 5G high band (24.25-27.5 GHz). The proposed solution is to use ferrite-based Frequency Selective Limiters (FSLs), which maintain their efficiency at high GHz frequencies, although they have only been studied at the macroscale so far. In this study, we demonstrate a proof of concept of nanoscale FSLs. The devices are based on
spin-wave transmission affected by four-
magnon scattering phenomena in a 97-nm-thin Yttrium Iron Garnet (YIG) film.
Spin waves were excited and detected using coplanar waveguide (CPW) transducers of the smallest feature size of 250 nm. The FSLs are tested in the frequency range up to 25 GHz, and the key parameters are extracted (power threshold, power limiting level, insertion losses, bandwidth) for different
spin-wave modes and transducer lengths. An analytical theory has been formulated to describe the fundamental physical processes, and a numerical model has been developed to quantitatively describe the insertion losses and power characteristics of the FSLs. Additionally, the perspective of the
spin-wave devices is discussed, including the possibility of simultaneously integrating three devices into one: a frequency-selective limiter, an RF filter, and a delay line, allowing for more efficient use of space and energy.
Read the full abstract ▾
All authors Kristýna Davídková, Khrystyna Levchenko, Florian Bruckner, Roman Verba, Fabian Majcen, Qi Wang, Morris Lindner, Carsten Dubs, Vincent Vlaminck, Jan Klíma, Michal Urbánek, Dieter Suess, Andrii Chumak
Materials Science
Acceleration of Atomistic NEGF: Algorithms, Parallelization, and Machine Learning
Mathieu Luisier, Nicolas Vetsch, Alexander Maeder et al. (+8 more)
The Non-
equilibrium Green's function (NEGF) formalism is a particularly powerful method to simulate the
quantum transport properties of nanoscale devices such as transistors, photo-diodes, or
memory cells, in the ballistic limit of transport or in the presence of various scattering sources such as electronphonon, electron-
photon, or even electron-electron interactions. The inclusion of all these mechanisms has been first demonstrated in small systems, composed of a few atoms, before being scaled up to larger structures made of thousands of atoms. Also, the accuracy of the models has kept improving, from empirical to fully ab-initio ones, e.g., density functional theory (DFT). This paper summarizes key (algorithmic) achievements that have allowed us to bring DFT+NEGF simulations closer to the dimensions and functionality of realistic systems. The possibility of leveraging graph neural networks and machine learning to speed up ab-initio device simulations is discussed as well.
Read the full abstract ▾
All authors Mathieu Luisier, Nicolas Vetsch, Alexander Maeder, Vincent Maillou, Anders Winka, Leonard Deuschle, Chen Hao Xia, Manasa Kaniselvan, Marko Mladenovic, Jiang Cao, Alexandros Nikolaos Ziogas
Statistical Mechanics
Solving models with generalized free fermions I: Algebras and eigenstates
Kohei Fukai, Balázs Pozsgay and István Vona
We study
quantum spin chains solvable via hidden free fermionic structures. We study the
algebras behind such models, establishing connections to the mathematical literature of the so-called “graph-Clifford” or “quasi-Clifford”
algebras. We also introduce the “defining representation” for such
algebras, and show that this representation actually coincides with the terms of the
Hamiltonian in two relevant models: the XY model and the “free
fermions in disguise” model of Fendley. Afterwards we study a particular anti-symmetric combination of commuting
Hamiltonians; this is performed in a model independent way. We show that for this combination there exists a reference state, and few body eigenstates can be created by the fermionic operators. Concrete application is presented in the case of the “free
fermions in disguise” model.
Read the full abstract ▾
Materials Science
Single-Atom Adsorption on h-BN along the Periodic Table of Elements: From Pristine Surface to Vacancy-Engineered Sites
Ana S. Dobrota, Natalia V. Skorodumova and Igor A. Pašti
The adsorption of single atoms on pristine and defected hexagonal boron nitride (h-BN) was systematically investigated using density functional theory. Elements from the first three rows of the periodic table, together with selected transition and coinage metals, were examined on the pristine surface and at boron- and nitrogen-vacancy sites. On pristine h-BN, adsorption is generally weak and dominated by dispersion forces, with measurable chemisorption limited to highly electronegative atoms such as C, O, and F. The introduction of vacancies transforms h-BN into a chemically active material, increasing adsorption energies by one to two orders of magnitude. The boron vacancy strongly stabilizes metallic and electropositive species through coordination to undercoordinated nitrogen atoms, whereas the nitrogen vacancy selectively binds electronegative and covalent adsorbates. Scaling of adsorption energies with elemental cohesive energies distinguishes regimes of physisorption, chemisorption, and substitutional stabilization. These insights provide a unified description of adsorption trends across the periodic table and establish defect engineering as an effective strategy for tailoring the catalytic, sensing, and electronic properties of h-BN.
Read the full abstract ▾
Materials Science
Accelerating Complex Materials Discovery with Universal Machine-Learning Potential-Driven Structure Prediction
Yuqi An and Zhenbin Wang
Universal machine-learning interatomic potentials (uMLIPs) have become powerful tools for accelerating computational materials discovery by replacing expensive first-principles calculations in
crystal structure prediction (CSP). However, their effectiveness in identifying new, complex materials remains uncertain. Here, we systematically assess the capability of a uMLIP (i.e.,M3GNet) to accelerate CSP in quaternary
oxides. Through extensive exploration of the Sr-Li-Al-O and Ba-Y-Al-O systems, we show that uMLIP can rediscover experimentally known materials absent from its training set and identify seven new thermodynamically and dynamically stable compounds. These include a new polymorph of Sr2LiAlO4 (P3221) and a new disordered phase, Sr2Li4Al2O7 (P1_bar). Furthermore, our results show stability predictions based on the semilocal PBE functional require cross-validation with higher-level methods, such as SCAN and RPA, to ensure reliability. While uMLIPs substantially reduce the computational cost of CSP, the primary bottleneck has shifted to the efficiency of search
algorithms in navigating complex structural spaces. This work highlights both the promise and current limitations of uMLIP-driven CSP in the discovery of new materials.
Read the full abstract ▾
Soft Condensed Matter · Cross-listed from physics.flu-dyn
How Spontaneous Electrowetting and Surface Charge affect Drop Motion
Chirag Hinduja, Benjamin Leibauer, Rishi Chaurasia et al. (+5 more)
Water drops sliding on hydrophobic surfaces spontaneously separate charges at their rear. It is unclear how this charge separation affects the contact angles of a sliding drop. We slide grounded and insulated drops on hydrophobic surfaces at low capillary numbers (\leq 10^{-4}). We find that drop charge leads to spontaneous electrowetting, which decreases the contact angles. Additionally, the deposited charges lead to a surface charge effect and decrease the contact angle. Both phenomena compensate each other at the receding contact line, resulting in an insignificant change in the receding contact angle of a sliding drop.
Read the full abstract ▾
All authors Chirag Hinduja, Benjamin Leibauer, Rishi Chaurasia, Nikolaus Knorr, Aaron D. Ratschow, Shalini Singh, Hans-Jürgen Butt, Rüdiger Berger
Strongly Correlated Electrons
Thermal conductivity in noncollinear magnets
Margherita Parodi and Sergey Artyukhin
Magnetic memory and logic devices, including prospective ones based on skyrmions, inevitably produce heat. Thus, controlling heat flow is essential for their performance. Here we study how non-collinear
spin arrangement affects the
magnon contribution to thermal conductivity. As a paradigm system, we consider the most basic non-collinear magnet with a
spin spiral ground state.
Spin noncollinearity leads to anharmonic terms, resulting in
magnon fusion and decay processes. These processes determine the
magnon lifetime, which can be used to estimate thermal conductivity in a single-mode approximation. However, by solving the full Boltzmann equation numerically, we find a much higher thermal conductivity. This signifies that heat is carried not by individual
magnons but by their linear combinations – relaxons. The thermal conductivity is found to increase with the diminishing spiral pitch, consistent with recent experiments. The results provide the blueprint for calculating
magnetic thermal transport in non-collinear magnets.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Direct nanoscale mapping of band alignment in single-layer semiconducting lateral heterojunctions
Chakradhar Sahoo, Suman Kumar Chakraborty, A. Kousika et al. (+15 more)
Atomic-scale control over band
alignment in single-layer lateral
heterostructures (LHSs) of dissimilar transition metal dichalcogenides (TMDCs) is critical for nextgeneration electronic, optoelectronic, and
quantum technologies. However, direct experimental access to interfacial electronic states with nanometer precision remains a significant challenge. Here, we employ angle-resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) to directly map the epitaxial
alignment and valence band
evolution across MoSe2-WSe2 LHSs. By combining nanoARPES with spatially resolved photoluminescence, we correlate the
evolution of the valence band maximum and
exciton features across both atomically sharp and compositionally graded diffusive interfaces. We identified type-II band
alignments governed by both material composition and interstitial-induced modifications of band offsets, in close agreement with density functional theory calculations. These results reveal fundamental mechanisms of electronic structure modulation at 1D TMDC heterointerfaces and provide a robust platform for tailored band engineering in van der Waals materials.
Read the full abstract ▾
All authors Chakradhar Sahoo, Suman Kumar Chakraborty, A. Kousika, Alfred J. H. Jones, Manas Sharma, Thomas S. Nielsen, Zhihao Jiang, Ihsan A. Kolasseri, Subhadip Das, Matthew D. Watson, Cephise Cacho, Kenji Watanabe, Takashi Taniguchi, Yong P. Chen, Tony F. Heinz, Ananth Govind Rajan, Prasana K. Sahoo, Søren Ulstrup
Materials Science · Cross-listed from cs.LG
Information-Theoretic Multi-Model Fusion for Target-Oriented Adaptive Sampling in Materials Design
Yixuan Zhang, Zhiyuan Li, Weijia He et al. (+4 more)
Target-oriented discovery under limited evaluation budgets requires making reliable progress in high-dimensional, heterogeneous design spaces where each new measurement is costly, whether experimental or high-fidelity simulation. We present an information-theoretic framework for target-oriented adaptive sampling that reframes optimization as trajectory discovery: instead of approximating the full response surface, the method maintains and refines a low-
entropy information state that concentrates search on target-relevant directions. The approach couples data, model beliefs, and physics/structure priors through dimension-aware information budgeting, adaptive bootstrapped
distillation over a heterogeneous surrogate reservoir, and structure-aware candidate
manifold analysis with Kalman-inspired multi-model fusion to balance consensus-driven exploitation and disagreement-driven exploration. Evaluated under a single unified protocol without
dataset-specific tuning, the framework improves sample efficiency and reliability across 14 single- and multi-objective materials design tasks spanning candidate pools from $600$ to $4 \times 10^6$ and feature dimensions from $10$ to $10^3$, typically reaching top-performing regions within 100 evaluations. Complementary 20-dimensional synthetic
benchmarks (Ackley, Rastrigin, Schwefel) further demonstrate robustness to rugged and
multimodal landscapes.
Read the full abstract ▾
All authors Yixuan Zhang, Zhiyuan Li, Weijia He, Mian Dai, Chen Shen, Teng Long, Hongbin Zhang
Mesoscale and Nanoscale Physics
Robust Interlayer Exciton Interplay in Twisted van der Waals Heterotrilayer on a Broadband Bragg Reflector up to Room Temperature
Bhabani Sankar Sahoo, Shachi Machchhar, Avijit Barua et al. (+6 more)
We report robust room temperature interlayer
excitons in transition metal dichalcogenide
heterostructures engineered via precise stacking orientation and twist-angle control. We integrate 2H-stacked MoSe$_{2}$/$^{1}$WSe$_{2}$/$^{2}$WSe$_{2}$ heterotrilayer onto a chirped distributed Bragg reflector that acts as a backside mirror. This way, we fabricate a platform that hosts distinct heterotrilayer, heterobilayer, and homobilayer regions with enhanced excitonic features at elevated temperatures. Although the heterobilayer supports temperature-tunable singlet and triplet interlayer
excitons, it exhibits low emission yield at 4 K. In comparison, the heterotrilayer shows remarkable excitonic properties, including pronounced band modulation, intervalley interlayer
exciton transitions, and a tenfold photoluminescence enhancement along with a sevenfold increase in
exciton decay time at cryogenic temperatures compared to the heterobilayer system. Temperature-dependent studies reveal intriguing interlayer
exciton dynamics in the heterotrilayer, including the emergence of valley-polarized interlayer
excitons, and the ability to maintain optical stability up to room temperature. Our results establish a clear strategy for engineering excitonic states across multilayer van der Waals
heterostructures from 4 K to room temperature, providing a versatile platform for excitonic optoelectronics,
quantum photonics, and tunable long-lived interlayer
exciton states in scalable TMD
heterostructures.
Read the full abstract ▾
All authors Bhabani Sankar Sahoo, Shachi Machchhar, Avijit Barua, Martin Podhorský, Seth Ariel Tongay, Takashi Taniguchi, Kenji Watanabe, Chirag Chandrakant Palekar, Stephan Reitzenstein
Strongly Correlated Electrons · Cross-listed from quant-ph
Comprehensive Numerical Studies of Barren Plateau and Overparametrization in Variational Quantum Algorithm
Himuro Hashimoto, Akio Nakabayashi, Lento Nagano et al. (+4 more)
The variational
quantum algorithm (VQA) with a parametrized
quantum circuit is widely applicable to near-term
quantum computing, but its fundamental issues that limit optimization performance have been reported in the literature. For example, VQA optimization often suffers from vanishing gradients called barren plateau (BP) and the presence of local minima in the landscape of the cost function. Numerical studies have shown that the trap in local minima is significantly reduced when the
circuit is overparametrized (OP), where the number of parameters exceeds a certain threshold. Theoretical understanding of the BP and OP phenomena has advanced over the past years, however, comprehensive studies of both effects in the same setting are not fully covered in the literature. In this paper, we perform a comprehensive numerical study in VQA, quantitatively evaluating the impacts of BP and OP and their interplay on the optimization of a variational
quantum circuit, using concrete implementations of one-dimensional transverse and longitudinal field
quantum Ising model. The numerical results are compared with the theoretical diagnostics of BP and OP phenomena. The framework presented in this paper will provide a guiding principle for designing VQA
algorithms and ansatzes with theoretical support for behaviors of parameter optimization in practical settings.
Read the full abstract ▾
All authors Himuro Hashimoto, Akio Nakabayashi, Lento Nagano, Yutaro Iiyama, Ryu Sawada, Junichi Tanaka, Koji Terashi
Strongly Correlated Electrons
Single crystal growth and properties of Au- and Ge-substituted EuPd$_2$Si$_2$
Michelle Ocker, Robert Möller, Marius Peters et al. (+7 more)
We report on the single
crystal growth of Eu(Pd$_{1-x}$Au$_x$)$_2$Si$_2$, $0< x\leq 0.2$, from a levitating Eu-rich melt using the Czochralski method. Our structural analysis of the samples confirms the ThCr$_2$Si$_2$-type structure as well as an increase of the room temperature $a$ and $c$
lattice parameters with increasing $x$. Chemical analysis reveals that, depending on the Au concentration, only about 25-35% of the amount of Au available in the initial melt is incorporated into the
crystal structure, resulting in a decreasing substitution level for increasing $x$. Through Au substitution, chemical pressure is applied and large changes in valence crossover temperatures are already observed for low substitution levels $x$. In contrast to previous studies, we do not find any signs of a first-order transition in samples with $x_{\rm nom}=0.1$ or AFM order for higher $x$. Furthermore, we observe the formation of quarternary side phases for a higher amount of Au in the melt. In addition, cubic-mm-sized single
crystals of EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$ with $x_{\rm nom}=0.2$ were grown. The analysis of the X-ray fluorescence revealed that the
crystals exhibit a slight variation in the Ge content. Such tiny compositional changes can cause changes in the sample properties concerning variations of the crossover temperature or changes of the type of the transition from crossover to
magnetic order. Furthermore, we report on a new orthorhombic phase EuPd$_{1.42}$Si$_{1.27}$Ge$_{0.31}$ that orders antiferromagnetically below $17\,\rm K$.
Read the full abstract ▾
All authors Michelle Ocker, Robert Möller, Marius Peters, Franziska Walther, Vivien Kirschall, Dominik C. Hezel, Michael Merz, Christo Guguschev, Cornelius Krellner, Kristin Kliemt
Other Condensed Matter · Cross-listed from physics.optics
Generalized Time-Varying Drude Model for Dispersive and Lossy Modulations
Antonio Ganfornina-Andrades, J. Enrique Vázquez-Lozano, Iñigo Liberal et al. (+1 more)
We develop a generalization of the time-varying Drude model, treating carrier density, effective mass, and collision rate as explicit functions of time. We derive expressions for polarization, susceptibility, displacement, and permittivity in different domains. Our analysis reveals that non-adiabatic modulations and time-dependent losses induce rich and distinct behaviors, leading to temporal blurring, selective gating and suppression, and low-frequency spectral reshaping. Besides underpinning and upgrading the current framework on photonics of time-varying media, this model may be useful in the design and fitting theoretical models with experimental realizations.
Read the full abstract ▾
All authors Antonio Ganfornina-Andrades, J. Enrique Vázquez-Lozano, Iñigo Liberal, S. A. R. Horsley
Statistical Mechanics · Cross-listed from quant-ph
Liouvillian Gap in Dissipative Haar-Doped Clifford Circuits
Ha Eum Kim, Andrew D. Kim and Jong Yeon Lee
Quantum chaos is commonly assessed through probe-dependent signatures that need not coincide. Recently, a dissipative signature was proposed for chaotic Floquet systems, where infinitesimal bulk dissipation induces a non-zero constant intrinsic relaxation rate quantified by the Liouvillian gap. This raises a question: what minimal departure from Clifford dynamics is required to generate such intrinsic relaxation? To address this, we study a Floquet two-
qubit Clifford
circuit doped with Haar-random single-
qubit gates and subject to local dissipation of strength $\gamma$. We find a structure-dependent crossover. The undoped iSWAP-class
circuit exhibits a weak-dissipation singularity, with a gap that grows with $N$ for any $\gamma>0$. Haar doping preserves this undoped-like growth for any subextensive doping pattern. At finite doping density, there exist patterns that yield an $\mathcal{O}(1)$ gap for any fixed $\gamma$ as $N\to\infty$, yet remain singular as $\gamma\to0^+$. Because our bounds depend only on the spatial doping pattern, they remain valid even when the Haar rotations are independently redrawn each Floquet period. Overall, our findings provide a
circuit-level perspective on intrinsic relaxation, and thus irreversibility, in open many-body systems.
Read the full abstract ▾
Quantum Gases
Tuning interactions between static-field-shielded polar molecules with microwaves
Christopher J. Ho, Joy Dutta, Bijit Mukherjee et al. (+2 more)
The ability to tune interparticle interactions is one of the main advantages of using ultracold
quantum gases for
quantum simulation of many-body physics. Current experiments with ultracold polar molecules employ shielding with microwave or static electric fields to prevent destructive collisional losses. The interaction potential of microwave-shielded molecules can be tuned by using microwaves of two different polarisations, while for static-field-shielded molecules the tunability of interactions is more limited and depends on the particular species. In this work, we propose a general method to tune the interactions between static-field-shielded molecules by applying a microwave field. We carry out coupled-channel scattering calculations in a field-dressed basis set to determine loss rate coefficients and scattering lengths. We find that both the s-wave scattering length and the dipole length can be widely tuned by changing the parameters of the microwave field, while maintaining strong suppression of lossy collisions.
Read the full abstract ▾
All authors Christopher J. Ho, Joy Dutta, Bijit Mukherjee, Jeremy M. Hutson, Michael R. Tarbutt
Materials Science · Cross-listed from physics.optics
Single acquisition reconstruction of nonlinear susceptibility and Raman tensors at the diffraction limit
Volodymyr Multian, Luigi Bonacina and Jérémie Teyssier
Raman spectroscopy and Second Harmonic Generation (SHG) are complementary, non-destructive techniques that provide rich and distinct insights into the structural and electronic properties of materials. Raman spectroscopy offers detailed information on vibrational modes, phase transitions, temperature, and local stress, while SHG is highly sensitive to
symmetry and orientation, particularly in non-centrosymmetric structures. In this work, in addition to combining both techniques, we propose a novel approach to determine the nonlinear optical tensor, leveraging the spatial and ultra-fast temporal offset of a Bessel-Gaussian
laser beam at the microscope's focal point.
Read the full abstract ▾