Materials Science
Orbital Hall Effect in Weyl Semimetals from quantum geometric band interference
Chiara Pacella, Maximilian Ünzelmann, Ahmed Osman et al. (+4 more)
Orbital angular momentum (OAM) transport in solids, prominently manifested in the orbital
Hall effect, has emerged as a fundamental phenomenon that can decisively exceed its
spin-based counterparts. However, the microscopic mechanisms governing OAM dynamics remain only partially understood. In particular, the role of band geometry in orbital transport is still largely unresolved. Here we address this question in the TaAs family of Weyl semimetals, TaAs, TaP, NbAs, and NbP, whose well-established
topology and associated OAM textures make them an ideal platform in this context. Using ab initio density functional theory, complemented by a minimal Weyl model based on adiabatic perturbation theory, we establish — both numerically and analytically — a direct link between OAM transport, band geometry, and topological electronic structure.
Read the full abstract ▾
All authors Chiara Pacella, Maximilian Ünzelmann, Ahmed Osman, Tim Figgemeier, Friedrich Reinert, Angel Rubio, Domenico Di Sante
Statistical Mechanics · Cross-listed from quant-ph
Quantum Snapshots Reveal a Compact Conformal Boundary Mode
M. A.Rajabpour
A projective measurement of a many-body state produces a microscopic snapshot, usually viewed as random classical data. We show that partial occupation snapshots of the critical XX chain contain a universal angle with a precise conformal meaning. Dividing the ring into two measured and two unmeasured arcs, we assign geometry-dependent conformal side weights to the observed occupations and obtain a compact variable $\delta_L$. At every finite size, $\delta_L$ is fixed by the measured sites alone; the particular complete-configuration lift $X_L$ used in the proof additionally depends on unobserved particles. This angle is an exact microscopic compact coordinate whose scaling-limit law is that of the relative Dirichlet phase of the associated conformal quadrilateral—the boundary coordinate conjugate to charge in continuum post-measurement descriptions. Exact free-
fermion determinants yield all of its
Fourier moments. We prove that the lift becomes Gaussian with variance $2h(\zeta)$, where $h(\zeta)$ is the rectangle modulus, and hence $\langle e^{\ii q\delta_L}\rangle\to e^{-h(\zeta)q^2}$. Thus raw
quantum snapshots realize the heat kernel on a circle and provide an outcome-level microscopic foundation for the compact zero-mode sector of Born averages over fluctuating conformal boundary conditions.
Read the full abstract ▾
Other Condensed Matter · Cross-listed from quant-ph
Geometric-phase control of Krylov complexity in adiabatic dynamics
Han-Qi Zheng, Peng-Zhang He, Lei-Hua Liu et al. (+1 more)
We show that
geometric phases accumulated during adiabatic
evolution can be converted into observable interference in Krylov space, leading to a
geometric-phase-dependent Krylov oscillation. Adiabatic dynamics force Krylov complexity to vanish if the initial Krylov basis is an instantaneous eigenstate of the
Hamiltonian; Nevertheless, we demonstrate that the Krylov complexity will be non-vanishing if the initial Krylov basis is a superposition state rather than an eigenstate. Consequently, Krylov complexity is found to depend on the difference of dynamical phases in the Krylov space, which is deeply related to the Berry connections in the original
Hilbert space. In particular, for a single
qubit system with constant Lanczos coefficients, Krylov complexity oscillates harmonically at a frequency given by the strength of the external field and the
geometric Berry phase. Therefore, our work may provide a novel avenue to probe the
geometric phase from the Krylov complexity.
Read the full abstract ▾
All authors Han-Qi Zheng, Peng-Zhang He, Lei-Hua Liu, Hai-Qing Zhang
Statistical Mechanics · Cross-listed from hep-th
Information Spreading in Diffusion Models from Effective Field Theory
Navonil Neogi and Nabil Iqbal
We study score-matching
diffusion models with a convolutional architecture. We argue that the inductive bias of locality means that the machinery of effective field theory from physics can be usefully applied to describe the denoising dynamics. We apply this formalism first to a simple toy example which permits an analytical description, and thereafter to MNIST, and show that in both cases, the mutual information between two points grows in a manner predicted by a simple effective field theory of Brownian motion.
Read the full abstract ▾
Materials Science
Pressure-driven structural phase transition unlocks multifunctionality in KMgX (X = P, As, Sb, and Bi) compounds: A first-principles study
Chetna Saini, Neha Sadanandan, Tashi Nautiyal et al. (+3 more)
The search for materials with multifunctional properties has attracted significant
attention due to their potential applications in various energy-related devices. Pressure-induced phase transitions provide an effective strategy for accessing different structural phases of a material without altering its chemical composition, thereby enabling the tuning of its physical properties and expanding its functional applications. In this work, we investigate the previously unexplored orthorhombic (Pnma) phase of the KMgX (X = P, As, Sb, and Bi) family using first-principles calculations and identify a pressure-induced structural transition from a tetragonal to orthorhombic phase. Stability of the pressure-accessible orthorhombic structure is rigorously confirmed by equation of state analysis together with
phonon, elastic, and formation-enthalpy calculations, establishing its viability for further investigation. Optical properties calculated within the $G_0W_0$-Bethe-Salpeter equation (BSE) framework, incorporating quasiparticle corrections and excitonic effects, exhibit direct dipole-allowed transitions at the $\Gamma$ point and strong visible-light absorption with coefficients approaching $10^5~\text{cm}^{-1}$. Consequently, KMgAs and KMgSb achieve spectroscopic limited maximum efficiencies (SLME) of $27.12\%$ and $26.40\%$, respectively, at a thin-film thickness of $0.6~\mu\text{m}$. Furthermore, thermoelectric transport calculations predict (zT) values of 0.65 and 0.58 at $900~\text{K}$ for p-type and n-type KMgSb, respectively, demonstrating its potential for both legs of thermoelectric devices. These values are likely conservative, as the Slack model tends to overestimate thermal conductivity. Overall, the pressure-accessible orthorhombic phase of the KMgX family emerges as a stable multifunctional
semiconductor with coupled photovoltaic and thermoelectric energy-conversion capabilities.
Read the full abstract ▾
All authors Chetna Saini, Neha Sadanandan, Tashi Nautiyal, Hongbin Zhang, Vikrant Chaudhary, Hem C. Kandpal
Statistical Mechanics · Cross-listed from hep-lat
Entanglement spectrum ordering and flavor polarization in the two-flavor Schwinger model at vacuum angle $\theta = \pi$
Boliang Yu, Ruixin Zhou and Meisen Gao
Entanglement spectra in gauge theories can encode both
symmetry breaking and the organization of gauge sectors. In the two-
flavor Schwinger model at
vacuum angle $\theta=\pi$, we find that the joint Schmidt distribution $p_{Q_A,F_A}$, labeled by the subsystem gauge charge $Q_A$ and
flavor imbalance $F_A$, reveals a cut-dependent gauge-sector hierarchy and a mass-induced
flavor asymmetry: changing the staggered cut reorganizes the gauge-charge distribution $p_{Q_A}$, while mass imbalance breaks the $F_A\leftrightarrow-F_A$
symmetry of the conditional
flavor distribution $p_{F_A|Q_A}$. Defining the combined weight $W_F^{(q)}=p_{q,+1}+p_{q,-1}$ and conditional polarization $\mathcal P_F^{(q)}=(p_{q,+1}-p_{q,-1})/W_F^{(q)}$, we find that changing the cut reverses the weight hierarchy, $W_F^{(-1)}>W_F^{(+1)}$ at unit-
cell boundaries but $W_F^{(+1)}>W_F^{(-1)}$ at intra-
cell cuts, while mass imbalance drives $\mathcal P_F^{(q)}$ away from zero with a $q$-dependent cut response.
Symmetry resolution therefore separates gauge-sector ordering, sector weight, and
flavor polarization that are mixed in the globally ordered
entanglement spectrum.
Read the full abstract ▾
Materials Science
Efficient simulation of second-order phase transitions in quantum anharmonic materials
Andrea Baldanza and Lorenzo Monacelli
When a
crystal undergoes a second-order structural phase transition, such as in ferroelectrics, Peierls, and charge-density waves, the diverging fluctuations of the order parameter lead to the break- down of the standard
phonon quasiparticle picture. Simulating these highly anharmonic regimes is notoriously challenging, as methods such as molecular dynamics suffer from a critical slowdown near the transition point, while the harmonic approximation fails dramatically at saddle points of the energy landscape stabilized by
quantum or thermal ionic fluctuations. This work introduces a new approach, based on the variational free-energy principle, to predict critical long-range behavior and dynamical spectra in strongly anharmonic systems, even when
quantum ionic fluctuations dominate. The proposed framework builds upon the
stochastic self- consistent harmonic approximation but reduces its computational scaling with the number of atoms, N, from O(N^6) to O(N^2) and the
memory requirement from O(N^4) to O(N). We
benchmark the method on the prototypical lead-free metal-halide perovskite CsSnI3, a promising candidate for photovoltaic engineering, simulating its phase stability and Raman spectrum near the phase transition, where the breakdown of the quasiparticle picture becomes evident. We demonstrate the effectiveness of the method by computing the full free-energy Hessian and the critical temperature in a supercell with 1080 atoms. Such simulations would have required tens of thousands of years with the legacy approach; it is now feasible in a few hours on consumer hardware.
Read the full abstract ▾
Statistical Mechanics
Generalizing the multidimensional thermodynamic uncertainty relation to combinations of arbitrary counting variables
Niklas Buschmann, Udo Seifert and Alexander M. Maier
Uncertainty relations provide lower bounds for otherwise hidden quantities of a partially accessible Markov network like the mean
entropy production rate and the total dynamical activity. The thermodynamic uncertainty relation (TUR) is arguably the most prominent one and involves the precision of a fluctuating net current. One of its major generalizations is the multidimensional TUR (MTUR), which yields a tighter bound by using covariances of a set of observed net currents. We generalize this latter bound to time-dependently driven processes with arbitrary initial state and arbitrary measurement duration. Furthermore, this bound can be used with a set of fluctuating counting observables each of which can be time-antisymmetric, time-symmetric or time-asymmetric, i.e., a net current, a traffic or a flow. We can even allow for coarse-grained observations in which each counting observable could consist of multiple indiscernable observed transitions of the underlying system. Thus, we generalize the MTUR, extensions of the TUR for time-dependent processes based on one current, and an
estimator based on one flux or on one traffic in a unifying way. We illustrate this general uncertainty relation with simple examples.
Read the full abstract ▾
Soft Condensed Matter
Wave Transport in Fourier Quasicrystals Revealed by Water Waves
Angélique Campaniello, Lior Alon, Rémi Carminati et al. (+2 more)
Fourier quasicrystals are aperiodic structures whose diffraction spectrum consists not of a dense set of Bragg peaks, as in ordinary quasicrystals, but of isolated ones scattered across a discrete, nonperiodic set. This sparse reciprocal-space structure should leave wave transport largely undisturbed except at a few selected wavevectors. We put this prediction to the test using surface water waves scattering off a two-dimensional
Fourier quasicrystal. Full-field measurements reveal three distinct transport regimes as the incident wavevector increases: transparency, selective scattering, and strong scattering. By reconstructing the structure factor from the measured wavefields, we directly relate these regimes to the underlying reciprocal-space structure. Our results establish
Fourier quasicrystals as a physical platform in which wave transport can be controlled through the organization of diffraction peaks in reciprocal space.
Read the full abstract ▾
All authors Angélique Campaniello, Lior Alon, Rémi Carminati, Emmanuel Fort, Marcel Filoche
Materials Science
Dispersive-phonon-driven room-temperature Ni1+-Ni2+ polaron hopping in spin-charge coupled rutile niobate
Gourab Roy, Mohit Kumar, Sayan Ghosh et al. (+4 more)
Understanding how
lattice dynamics mediate polaron hopping is essential for designing multifunctional correlated
oxides. Here, we demonstrate room-temperature dispersive
phonon excitations and elucidate the Ni1+-Ni2+ polaron-hopping mechanism and the presence of rare
spin-charge-
phonon coupling even in a magnetically short-range-ordered state in rutile niobate, a rare room-temperature magnetodielectric system. We reveal room-temperature dispersive
phonon excitations using inelastic
neutron scattering (INS), complemented by machine-learning-based
phonon calculations, to establish the microscopic origin of the polaron-hopping mechanism. Experimental evidence of dispersive
phonon-driven polaron hopping is scarce. INS measurements show significant dispersive
phonon excitations at 21, 33, and 47 meV, implying collective
lattice dynamics that enable delocalized polaron propagation via coupled charge-
spin-
phonon interactions. Dispersive
phonons couple to charge carriers and promote correlated NiO6
lattice distortions, facilitating delocalized polaron hopping. Low-energy
magnetic excitations at 4 and 8 meV indicate the presence of local short-range
magnetic correlations or
spin-orbit-coupling-induced anisotropy in deformed NiO6 octahedra, which are thoroughly discussed. Machine-learning
phonon calculations replicate the experimentally observed
phonon excitations and demonstrate
lattice instability, which is compatible with dynamic local distortions caused by polaron production. These findings provide microscopic evidence for a coupled charge-
spin-
phonon mechanism that mediates polaron hopping in rutile
oxide systems.
Read the full abstract ▾
All authors Gourab Roy, Mohit Kumar, Sayan Ghosh, Ekta Kushwaha, Manh Duc Le, Devashibhai T. Adroja, Tathamay Basu
Mesoscale and Nanoscale Physics
Disorder signatures emerging at millikelvin temperatures in Si/SiGe field-effect stacks
Lino Visser, Alberto Mistroni, Yuji Yamamoto et al. (+9 more)
The performance and scalability of electron
spin qubits based on gate-defined
quantum-dots in undoped Si/SiGe field-effect stacks remain constrained by disorder originating from the gate stack. Its coupling to the
quantum well can be reduced by increasing the Si
quantum well depth, while electrostatic charge history, for example through interface-trap filling, can further modify the effective disorder landscape. Although such disorder is commonly benchmarked through mobility measurements using magnetotransport and
Hall bar devices, dedicated investigations at millikelvin temperatures relevant for
quantum-dot operation remain limited. Here, we use temperature-dependent magnetotransport on
Hall bar shaped field-effect transistors to investigate how mobility-based disorder signatures depend on
quantum-well depth and charge history from \(1.5~\mathrm{K}\) down to the millikelvin regime. We show that magnetotransport characterization at \(1.5~\mathrm{K}\) captures the dominant mobility improvement associated with reduced dielectric-interface coupling, but can underestimate disorder differences that emerge at millikelvin temperatures, particularly in the low-density regime. Our results therefore highlight that millikelvin magnetotransport characterization of
Hall bar devices can provide additional insight for optimizing Si/SiGe field-effect stacks, particularly in the context of gate-defined
quantum dot
spin qubits.
Read the full abstract ▾
All authors Lino Visser, Alberto Mistroni, Yuji Yamamoto, Fabian Fidorra, Oksana Fursenko, Steffen Marschmeyer, Marvin H. Zoellner, Giovanni Capellini, Dominique Bougeard, Vincent Mourik, Marco Lisker, Felix Reichmann
Materials Science
Microscopic investigation of spin dynamics in the single-chain magnet Sr4Mn2CoO9
G. Roy, S. Ghosh, M. Kumar et al. (+8 more)
One-dimensional single-chain magnets offer a unique platform for studying the interplay of
crystal-field effects, exchange interactions, and
lattice dynamics. Here, we investigate
spin excitations in Sr4Mn2CoO9 using inelastic
neutron scattering (INS) and theoretical modelling. INS reveals two low-energy
magnetic excitations at 4 and 7 meV from Mn-Co-Mn
spin chains, alongside higher-energy
crystal-electric-field (CEF) excitations from two crystallographically inequivalent Co2+ sites. Interestingly, these
spin excitations persist at room temperature, demonstrating dynamic
magnetic correlations in the absence of long-range order. Furthermore, the
crystal-field modelling, based on Stevens operator formalism, reproduces well the CEF spectra, establishing Ising-like Kramers ground-state doublets with strong uniaxial
magnetic anisotropy for both Co2+ ions. In addition, the
spin wave simulation using SpinW reproduces the
spin excitation spectrum and reveals microscopic exchange interactions in two non-interacting Mn-Co-Mn
spin chains. Finally, machine-learning
lattice-dynamics calculations confirm the
phonon spectrum and
spin-
phonon coupling. By projecting the exchange
Hamiltonian onto CEF ground-state doublets, we estimate exchange-induced splittings matching the observed excitations. Thus, our results elucidate low-energy
spin dynamics arising from combined
crystal-field anisotropy and exchange interactions, with the persistent low-energy excitation providing a microscopic pathway for thermally activated
spin relaxation. Furthermore, this work delivers a unified microscopic understanding of the interplay between
crystal-field effects,
magnetic exchange, and
lattice dynamics in Sr4Mn2CoO9, advancing insights into
spin dynamics in low-dimensional transition-metal
oxides.
Read the full abstract ▾
All authors G. Roy, S. Ghosh, M. Kumar, E. Kushwaha, J. Sannigrahi, V. Caignaert, W. Prellier, D. T. Adroja, D. Voneshen, V. Hardy, T. Basu
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Exchange-only qubit stabilized by a single-spin qubit
Irina Heinz, Mira Sharma and Joris Kattemölle
Hybrid approaches that combine different
spin qubit encodings offer promising advantages. In particular, the additional degrees of freedom available in exchange-only
qubits and their extensions enable enhanced
spin lifetimes and facilitate error detection through the use of auxiliary
spins. We show that integrating Loss-DiVincenzo with exchange-only
qubits provides a practical route to realizing these benefits while remaining compatible with
spin-shuttling architectures. We further demonstrate how the singlet-only exchange-only
qubit can be employed for error detection, and we present a fault-tolerant $\pi$-rotation about each of the three control axes of the (singlet-only) exchange-only
qubit. By enabling error detection at the lowest encoding level, our approach effectively converts charge and
nuclear noise into erasures, thereby suppressing error propagation and potentially enhancing the performance of
quantum error-correction schemes. More broadly, our work establishes a new perspective on the singlet-only exchange-only
qubit as a logical encoding, opening the door to fault-tolerant gate constructions and
spin-tailored
quantum error-correction protocols for
semiconductor-based
quantum computing.
Read the full abstract ▾
Materials Science
Probing intrinsic magnetic phases in low-dimensional nearly twin-free NiPS$_3$ single crystals
Yeochan An, Heejun Yang, Sung Jin Park et al. (+6 more)
We report the intrinsic thermal and
magnetic properties of the low-dimensional van der Waals (vdW) antiferromagnet NiPS$_3$ and explore its emergent
magnetic phases by controlling crystallographic twinning. Using nearly twin-free
crystals, we resolve intrinsic properties that are typically obscured by multidomain effects in bulk samples. Magnetization results reveal a highly anisotropic, sharp
spin-flop transition, confirming the high domain purity of our
crystals. Furthermore, high-precision thermodynamic and transport data reveal a broad fluctuation regime around the Néel temperature ($T_{\mathrm{N}}$ = 157.5 K), with a heat capacity anomaly and a concurrent suppression of thermal conductivity. Field-dependent thermal transport shows a small but distinct contribution from
spin-
lattice coupling, as evidenced by the dip at the
spin-flop transition. We develop a theoretical model to explain these properties reported in this paper, with good agreement between experiment and theory. Our work establishes a definitive baseline for bulk properties of NiPS$_3$ and demonstrates the feasibility of resolving intrinsic anisotropies by addressing crystallographic twinning in vdW magnets.
Read the full abstract ▾
All authors Yeochan An, Heejun Yang, Sung Jin Park, Giung Park, Woonghee Cho, Pyeongjae Park, Seokhwan Yun, Yoshimitsu Kohama, Je-Geun Park
Materials Science · Cross-listed from physics.chem-ph
Poly(1,4-anthraquinone) as an Organic Cathode Material: Simulation of Observable Bonding Properties to Li, Na, Mg, and Ca
Laura Femmer, Lukas Köbbing, Juliane Heitkämper et al. (+9 more)
Poly(1,4-anthraquinone) (P14AQ) has emerged as a promising cathode material, offering high capacity and good cycling stability, yet the atomic-scale mechanisms governing metal-ion binding and electrochemical behavior remain poorly understood. To address this, we investigate the binding mechanisms of Li, Na, Mg, and Ca to P14AQ using
quantum mechanical methods, particularly DFT and DFTB. A key challenge lies in the material's structural complexity: multiple conformers of P14AQ are energetically similar but kinetically isolated due to significant energy barriers. To account for this, we develop an automated method to generate all unique P14AQ conformers for a periodic
polymer chain without rotational duplicates through an orientation labeling scheme. For each conformer, we systematically place a metal atom adjacent to every oxygen site, enabling a complete exploration of binding configurations. We observe two structural motifs: a single metal-oxygen bond and coordination to two opposite oxygen atoms. While Li and Na exhibit continuous energy distributions, Mg and Ca show an energy gap between the two motifs, with a strong preference for the two-oxygen binding configuration. Galvanostatic measurements support these findings by showing lower gravimetric capacities for Ca and Mg than for Li and Na. For Na, the different numbers of metal-oxygen bonds are reflected in the two voltage plateaus observed experimentally. Overall, the combined computational and experimental results explain the higher capacity of monovalent ions in P14AQ: divalent ions cannot bind efficiently to a single oxygen site due to unfavorable energetics, and the conformational distribution of the
polymer chain prevents optimal coordination.
Read the full abstract ▾
All authors Laura Femmer, Lukas Köbbing, Juliane Heitkämper, Sibylle Riedel, Devran Cay, Florin Adler, Birgit Esser, Alexander J. C. Kuehne, Zhirong Zhao-Karger, Piotr de Silva, Juan Maria García-Lastra, Birger Horstmann
Strongly Correlated Electrons
Topological phases and quantum criticality from $SU(2)$ Chern-Simons-matter theories
Yunchao Hao, Yingcheng Li, Kangle Li et al. (+1 more)
Motivated by recent numerical studies where various $SU(2)$ Chern-Simons-matter theories emerge, we analytically study topological phases and
quantum criticality in two-dimensional systems described by such theories. First, we classify $SU(2)_k$ topological orders in all
lattice spin systems with a $p4\times SO(3)$
symmetry, where $k$ is an arbitrary nonzero integer. We find that for each odd $k$, the topological order can emerge in systems with an arbitrary Lieb-Schultz-Mattis (LSM) anomaly, and the
symmetry cannot permute anyons. If the system has a nontrivial (respectively, trivial) LSM anomaly, then there is exactly one (respectively, nine)
symmetry-enriched topological (SET) phases. On the other hand, $SU(2)_k$ topological order with any even $k$ can only emerge in systems with a trivial LSM anomaly. If $k\notin\{6, 10, 14, \cdots\}$, the
symmetry cannot permute anyons, and there are 16 SET phases. If $k\in\{6, 10, 14, \cdots\}$, there are 4 different ways how the
symmetry can permute anyons, and there are 64 SET phases. Next, we analyze the $SU(2)_k$ Chern-Simons theories coupled to $N_f$
flavors of gapless matter fields that can be either bosonic or fermionic. For both types of theories, we consider a joint large-$N_f$ and large-$k$ limit with $N_f/k$ fixed, and compute the scaling dimensions of the bilinear operators of the
bosons or
fermions to the order of $1/N_f$. These results sharpen our understanding of these emergent exotic topological phases and
quantum criticality, and provide useful guidance to explore them further.
Read the full abstract ▾
All authors Yunchao Hao, Yingcheng Li, Kangle Li, Liujun Zou
Superconductivity
Simplified Silicon Nitride Nanomembrane Circuits for van der Waals Integration
Tommaso Confalone, Vasilisa Gerega, Flavia Lo Sardo et al. (+8 more)
Two-dimensional (2D) materials and van der Waals (vdW)
heterostructures provide an exceptional platform for engineering
quantum devices, yet realizing their potential requires electrical integration without compromising the pristine properties of atomically thin
crystals through conventional nanofabrication. Transferable circuitry addresses this challenge by decoupling
circuit fabrication from device assembly, enabling electrical contacting without directly processing the active material. Here, we introduce SiN$_x$ nanomembrane (NMB)
circuits realized through a simplified top-down strategy that reduces fabrication complexity, processing steps and specialized tools required by our previous bottom-up approach. As a stringent
benchmark of material preservation, we electrically integrate a four-unit-
cell-thick, optimally doped Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$ (Bi2201) flake and observe a superconducting transition at T$_c^{inf}$~32K, close to the T$_c^{onset}$~34K measured by susceptibility in the parent
crystals. The preservation of superconductivity demonstrates electrical integration of fragile layered materials without direct exposure to conventional cleanroom procedures, providing a versatile platform for integrating increasingly complicated vdW
heterostructures, moiré materials, and hybrid
quantum architectures.
Read the full abstract ▾
All authors Tommaso Confalone, Vasilisa Gerega, Flavia Lo Sardo, Shreya Kumbhakar, Davide Massarotti, Francesco Tafuri, Shigeyuki Ishida, Hiroshi Eisaki, Kornelius Nielsch, Golam Haider, Nicola Poccia
Materials Science
Electrostatic Phenomenology Benchmarks for Machine-Learned Interatomic Potentials in Electrochemistry: Beyond the Energy-Force Metric
Barbara Sumić, Ria Vasdev, Sudheesh Kumar Ethirajan et al. (+8 more)
Accurate treatment of long-range interactions in machine learning interatomic potentials (MLIPs) is essential for electrochemical simulations. However, aggregate energy and force errors alone are insufficient to establish an MLIP's physical accuracy since they do not detect qualitative inconsistencies in the model such as the prediction of image-charge attraction, dielectric screening, or charge transfer. We introduce a
benchmark suite EPhEct (Electrostatic Phenomena for Electrochemistry) of focused test cases designed to evaluate MLIPs on electrochemically relevant physical phenomena. The tests probe for image-charge attraction at a metal electrode, the splitting between longitudinal and transverse optical
phonons as a probe of ionic and electronic screening, the dipole moment of interfacial water, and
Fermi-level pinning during ion discharge. These tests establish a qualitative diagnostic routine complementary to aggregate energy-force metrics.
Read the full abstract ▾
All authors Barbara Sumić, Ria Vasdev, Sudheesh Kumar Ethirajan, Jing Yang, Clotilde S. Cucinotta, Richard G. Hennig, Karsten Reuter, Stefan Ringe, Mira Todorova, Christoph Freysoldt, Jörg Neugebauer
Materials Science
Accurate and efficient calculation of atomic forces in solids with non-self-consistent hybrid functionals
Damian Contant and Maria Hellgren
Hybrid functionals are routinely employed self-consistently within the generalized Kohn-Sham framework. The evaluation of the nonlocal Fock exchange operator makes hybrid functional calculations computationally expensive, in particular with plane-wave basis sets. Here, we investigate the advantages of non-self-consistent hybrid functional calculations, focusing on the evaluation of atomic forces. The analytical force terms that arise due to non-self-consistency are computed using density functional perturbation theory (DFPT), as implemented within the
Quantum ESPRESSO distribution. A non-self-consistent hybrid force calculation thus consists of self-consistent DFPT calculations with a local or semi-local functional and a single evaluation of the Fock exchange operator. The overall computational cost is, thereby, reduced in general, especially for solids that require a dense Brillouin-zone sampling. Moreover, results for structural parameters are barely affected by self-consistency, and vibrational frequencies are typically agreeing within 0.5%, thus making non-self-consistent calculations an interesting alternative.
Read the full abstract ▾
Soft Condensed Matter
Contact Formation and Viscoelastic Detachment in Non-Circular Soft Adhesive Contacts
Sonu Dhiman and Debashish Das
Adhesive contact measurements on soft
polymers are commonly interpreted using Johnson-Kendall-Roberts (JKR) theory, which is formulated for circular contacts. Here, we examine contact formation and detachment in non-circular soft adhesive contacts using PDMS crossed-cylinder experiments. The crossing angle was varied from 30 to 90 degrees, producing contacts from highly elongated ellipses to nearly circular geometries while keeping the material pair fixed. During loading, the contact aspect ratio b/a rapidly approached an angle-dependent plateau, indicating approximately self-similar growth. This motivates use of the area-equivalent radius c=sqrt(a*b) and
geometric-mean
curvature radius Reff=sqrt(R1*R2). The loading branches follow a JKR-type linearization and yield a nearly angle- and preload-independent work of adhesion, W_load=24 mJ/m^2. Johnson-Greenwood elliptical-contact fits give comparable values. In contrast, unloading and pull-off are strongly history dependent. The unloading branches require a substantially larger effective separation energy, W_unload,eff, which increases with preload and decreasing crossing angle. A reduced viscoelastic model based on the same area-equivalent description captures the principal unloading response over 50-80 degrees using a single shared parameter set across angles and preloads. These results show that contact formation is governed primarily by area-equivalent scaling, whereas detachment is governed by geometry- and history-dependent dissipative separation.
Read the full abstract ▾
Other Condensed Matter · Cross-listed from physics.optics
Sharp Coherence Crossover and Multimode Phase Control in Coupled Exciton-Polariton Condensates
R. V. Cherbunin, A. D. Liubomirov, M. A. Chukeev et al. (+2 more)
We investigate the formation of mutual coherence and deterministic phase control in a multimode
exciton-polariton system realized in two optically induced traps with tunable intertrap coupling. As the coupling channel between the traps is progressively opened, the mutual first-order coherence rises sharply from nearly zero to values close to unity, revealing a threshold-like crossover from weakly correlated to highly coherent dynamics. We demonstrate deterministic multimode phase control with a short spatially localized nonresonant pulse, which allows the phase relations between selected polariton condensate modes to be set while keeping their amplitudes nearly unchanged. The induced phase transformation is read out directly from time-resolved interferograms and realized for different sets of modes in both intermediate- and high-coherence regimes. Within a reduced four-mode description, the control pulse implements an effective phase operator on the coherent multimode field with a fidelity exceeding 0.995. The same approach can be extended to larger networks of coupled traps, offering a route to optical control over phase relations in increasingly complex multimode polariton states.
Read the full abstract ▾
All authors R. V. Cherbunin, A. D. Liubomirov, M. A. Chukeev, E. S. Sedov, A. V. Kavokin
Superconductivity
Superconductivity in strongly overdoped cuprates: beyond the single-band model
Ruichao Chen, Linda Sederholm, Yannick Klein et al. (+11 more)
In order to explain the observation of an extended superconducting region in several overdoped cuprates, which contrasts the dome scenario, by means of
neutron and synchrotron x-ray powder diffraction we study the
crystal structure of YBa$_2$Cu$_3$O$_{y}$, where strong oxygen overdoping up to $y = 7.4$ is achieved under high-pressure. A bond valence sum analysis indicates that 1/5 of the extra holes created by the excess oxygen are transferred to the CuO$_2$ planes, thus increasing the hole density up to $p=0.27$ hole/Cu, where superconductivity is expected to vanish according to the dome scenario. Instead, our data confirm a previous observation [Okai, Ono and Mitsuhashi, Physica C: Superconductivity 366, 164 (2002)] that the superconducting critical temperature, $T_c$, remains constant with $y$. Our data analysis accounts for this discrepancy in terms of the much shorter bond between the apical oxygen and the planar Cu ion, which suggests that the extra holes occupy the $a_1$-
symmetry states formed by $d_{3z^2-r^2}$ orbitals, instead of the usual $b_1$-
symmetry Zhang-Rice singlet states formed by $d_{x^2-y^2}$ orbitals. Suitable spectroscopic measurements on single
crystals may support such a two-band scenario, which would require a totally different theoretical approach to explain superconductivity in cuprates.
Read the full abstract ▾
All authors Ruichao Chen, Linda Sederholm, Yannick Klein, Ludovic Delbes, Benoît Baptiste, Paraskevas Parisiades, Emmanuel Maisonhaute, Davide Delmonte, Edmondo Gilioli, Maarit Karppinen, Ronald I. Smith, David A. Keen, Yann Le Godec, Andrea Gauzzi
Materials Science · Cross-listed from cs.CL
The conditional superiority of fast silicon sampling
Nickolas Hock Yuen Lam, Ji Xuan Voo and Xiangyu Ma
Silicon sampling can produce surprisingly good population estimates at times. Does doing it fast attenuate such fidelity? In this study, we extend and assess ongoing work in silicon sampling by comparing the algorithmic fidelity of "fast" and "slow" modes of silicon sampling among a nationally representative sample of Singaporean survey respondents. We find that silicon sampling with contemporary frontier models remains a method in early development to be used only with great caution. While silicon samples are able to produce moderately faithful estimates of population means, they continue to understate opinion variance and distort the latent contextual space behind human opinions. Conditional on such limitations, we find "fast" modes of silicon sampling to be relatively superior to traditional "slow" modes of silicon sampling. Fast silicon sampling is significantly more efficient in compute resources and run-time while being monotonically superior to slower modes of sampling in algorithmic fidelity.
Read the full abstract ▾
Strongly Correlated Electrons
Grant Z. X. Yang and K. T. Law
A
magnetic impurity embedded in a metal is collectively screened by
Fermi-surface quasiparticles into a many-body
spin-singlet ground state, forming a Kondo cloud of size $\xi_{\rm K}\sim\hbar v_F/(k_B T_{\rm K})$. This kinematic picture collapses in flat bands, where $v_F=0$ and the hierarchy of dispersive energy shells is absent. Here we show that the missing organizing principle is
quantum geometry. A
magnetic impurity coupled to an isolated flat band selects a single active bath mode: a coherent superposition of flat-band Bloch states weighted by the hybridization factor $v(\mathbf{k})$, while all orthogonal flat-band modes remain dark. The resulting flat-band Kondo problem is a
quantum geometric molecule, with an algebraic Kondo scale set by the total projected hybridization strength rather than a logarithmic-renormalization scale. In real space, the
impurity-bath
spin correlation defines a
quantum geometric Kondo cloud. Its cloud-size tensor admits a gauge-invariant decomposition into a hybridization-weighted
quantum metric, a dressed Berry-connection covariance, and a positive hybridization-gradient term, yielding the lower bound $\xi_{\rm K}^2\geq \sum_{\mathbf{k}}\rho(\mathbf{k}){\rm Tr}\,g(\mathbf{k})$, where $\rho(\mathbf{k})=|v(\mathbf{k})|^2/\sum_{\mathbf{k}}|v(\mathbf{k})|^2$. Our result reveals that, in flat bands, Kondo screening is governed by the
quantum geometry and interference structure of the
impurity-selected Bloch wave packet, rather than
Fermi-surface kinematics.
Read the full abstract ▾
Strongly Correlated Electrons
Observation of in-plane anomalous Nernst effect
Tadashi Yoneda, Shinichi Nishihaya, Markus Kriener et al. (+7 more)
The Nernst effect, which enables the conversion of a heat current into a transverse voltage under
magnetic field or
spin magnetization, holds significant promise for energy harvesting and thermal management in future electronics. However, the conventional Nernst effect is fundamentally constrained by the orthogonality requirement that the applied field or spontaneous magnetization must be perpendicular to the plane defined by the temperature gradient and the induced voltage. Here we report that
symmetry-tailored ultrathin films of a prototypical
ferromagnetic oxide exhibit anomalous Nernst effect arising from intrinsic coupling to spontaneous in-plane
spin magnetization. Systematic magnetothermoelectric measurements under spherical rotations of the
magnetic field reveal that a pronounced Nernst signal, comparable in magnitude to the out-of-plane response, emerges robustly associated with out-of-plane orbital magnetization. Our findings demonstrate that the anomalous Nernst effect is no longer limited by the orthogonality condition, opening new opportunities for more flexible designs of magnetothermoelectric materials and devices.
Read the full abstract ▾
All authors Tadashi Yoneda, Shinichi Nishihaya, Markus Kriener, Haruto Kaminakamura, Ming-Chun Jiang, Naohiro Tezuka, Yoshiya Murakami, Ryotaro Arita, Hiroaki Ishizuka, Masaki Uchida
Strongly Correlated Electrons
Periodicity-driven revision of the phase diagram of the generalized Baxter-Wu model with asymmetric complex couplings
Yuting Wang, Ye Ling, Haihong Li et al. (+1 more)
The conventional self-dual lines of the generalized Baxter-Wu (GBW) model with asymmetric complex couplings are known to be $\sinh(2K)=\pm \cos(2\phi)$, where $K$ and $\phi$ are the real and imaginary parts of the coupling. We demonstrate that these lines are incomplete: the periodicity of the partition function, encoded in the cosine factor of the bundled Boltzmann weight, generates additional self-dual lines $\sinh(2K)=\pm \sin(2\phi)$. Guided by the complete set of self-dual candidates, we perform Monte Carlo simulations using brute-force reweighting (Metropolis) and the Wang-Landau methods. Simulations indicate that the self-dual lines at the partition-function minima $\phi_{\mathcal{Z}_{\min}}=(2n+1)\pi/8$ constitute a critical threshold. They are genuine critical boundaries for $|K| \ge \frac{1}{2}\operatorname{arsinh}(\cos(\pi/4)) \approx 0.32924$, while for smaller $|K|$ they are not. At $\phi_{\mathcal{Z}_{\min}}$, the sign problem is most severe and finite-size scaling corrections are largest; the local peak observed below the phase boundary in the temperature scan is thus a finite-size artifact, not a genuine new phase. We further clarify the capability and limitations of the average sign and its derivatives for detecting phase transitions. In particular, the negative peak of the average sign at $\phi_{\mathcal{Z}_{\min}}$ does not correspond to a genuine phase transition. We also evaluate the Wang-Landau method, which, despite formally circumventing the sign problem, still faces the exponential barrier.
Read the full abstract ▾
All authors Yuting Wang, Ye Ling, Haihong Li, Yuhai Liu
Materials Science · Cross-listed from quant-ph
Circuit Depth Compression via Spectral Gap Amplification in Quantum Phase Estimation
Sk Mujaffar Hossain and Satadeep Bhattacharjee
We show that
quantum phase estimation (QPE)
circuits can be significantly compressed in depth by preprocessing the input operator with a sigmoid spectral filter before estimation. For systems with small spectral gaps Delta_lambda, standard QPE requires m = ceil(log2(1/Delta_lambda)) precision
qubits and depth Theta(2^m). Applying a soft-step transformation f(lambda; tau,w) amplifies the effective gap to Delta_f > Delta_lambda (for w < 1/4), reducing the required precision to m_f = ceil(log2(1/Delta_f)) and compressing
circuit depth by 2^(alpha Delta_m), where alpha = 1 for the LMR density-
matrix exponentiation framework and alpha is in [0.11,0.42] for controlled-phase-gate
circuits. We prove that this compression is exact, bounded above by log2(1/(4w Delta_lambda)) + 1, and impossible for exactly degenerate spectra. We further show that the threshold parameter tau requires only O(w) accuracy, so classical preprocessing such as covariance diagonalisation or CASSCF avoids circularity. A net resource advantage occurs when 4w^2(2^Delta_m - 1) > Delta_lambda log(1/epsilon). Validation on LiH and BeH2 bond-stretch calculations, classical covariance
datasets, and synthetic near-degenerate cases demonstrates depth reductions of up to 27x and CX-gate reductions of up to 21x. For LiH, QPE output fidelity improves from 0.66 to 0.98 at a 1% hardware error rate. The method preserves the principal subspace to machine precision, requires no modification of QPE, and can be combined with readout-stage and state-preparation filtering. Negative-control tests establish the benefit condition: m_raw >= 2 and Delta_lambda > 0.
Read the full abstract ▾
Soft Condensed Matter
Testing the Reptation Picture: Topological Constraint from Monomer Dynamics
Xiaofei Tian, Qinhang Liu, Zhi-Chao Yan et al. (+3 more)
The reptation model postulates that entangled
polymers slide within a fractal tube. Here we employ a model-independent relation between the zero-displacement probability and the mean-square displacement that applies to time-dependent fractal structures, enabling direct measurement of the fractal dimension $d_\mathrm{f}$ of the geometry experienced by monomer motion. For two-dimensional obstacle arrays and in the slip-link model, $d_\mathrm{f}$ agrees with the reptation prediction $d_\mathrm{f}=1/\nu$ (where $\nu$ is the Flory exponent). In
polymer melts, however, we find $d_\mathrm{f} \approx 2.6$ — a value close to the fractal dimension of percolation clusters, not the reptation value $d_\mathrm{f}=2$. This contrasts sharply with the reptation picture, in which a Rouse chain slides in a fractal structure with $d_\mathrm{f}=2$, spectral dimension $d_\mathrm{s}=1$, and walk dimension $d_\mathrm{w}=4$; our results point instead to a percolation-like scenario, characterized by $d_\mathrm{f}\approx 2.6$, $d_\mathrm{s}\approx 1.3$, and $d_\mathrm{w}\approx 4$ — revealing a dynamically emergent, finite-size fractal geometry distinct from the static tube.
Read the full abstract ▾
All authors Xiaofei Tian, Qinhang Liu, Zhi-Chao Yan, Liang Gao, Tongfei Shi, Jizhong Chen
Quantum Gases
Single-impurity polarons in hard-core lattice bosons at low and intermediate fillings
Chao Zhang
We investigate a single mobile
impurity in a two-dimensional hard-core Bose–Hubbard bath at low and intermediate fillings and determine how polaronic dressing evolves with bath filling for
impurity–bath couplings ranging from weak to strong and ultimately to the two-component hard-core limit. Using large-scale, sign-problem-free worm-
algorithm quantum Monte Carlo simulations, we extract momentum-space quasiparticle properties from the
impurity Green's function and resolve the accompanying real-space bath rearrangement from an imaginary-time-averaged
impurity-centered correlator. We also vary the
impurity hopping $t_{\rm imp}$ to assess how reduced mobility modifies dressing in the strong-coupling regime. For the fillings accessible at each coupling, the
impurity remains a dressed quasiparticle whose ground-state energy, effective mass, and residue vary smoothly with filling $n_{\rm b}$. In real space, increasing $n_{\rm b}$ strengthens the short-range depletion while shifting the dominant response toward the
impurity. In the two-component hard-core limit $U_{\rm ib}/t_{\rm b}\!\to\!\infty$, the large-distance recovery of the cumulative density deformation exhibits only weak filling dependence over the range considered here, whereas short-range core indicators continue to evolve. Our results quantitatively characterize strongly dressed polarons in a correlated, compressible
lattice bath and resolve how filling and
impurity mobility modify the near-core response and spatial extent of the dressing cloud.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Thermal effect on the anomaly-induced electromechanical response in gapped graphene
A. Sedrakyan and K. Ziegler
Mechanical deformation of gapped
graphene can act on Dirac quasiparticles as an emergent gauge field. When this deformation field couples to the same current as the electromagnetic field, the parity anomaly produces a mixed electromechanical Chern-Simons response: a
phonon electric field drives a transverse electrical current, and a
phonon magnetic field binds charge. Previous zero-temperature results predict a sharp change in the response when the chemical potential crosses the band edge. We show that finite temperature replaces this sharp feature by a universal smooth crossover controlled only by the ratios of temperature, gap, and chemical potential. The response remains almost quantized in the insulating regime, is rounded over a gate window of order temperature near the band edge, and approaches the doped Berry-
curvature result with a controlled Sommerfeld correction. We apply the result to two experimentally useful drives: a traveling flexural wave, which produces a transverse second-harmonic current, and a dynamic
phonon mixed with a static ripple, which produces a fundamental-frequency signal. The same gate-temperature line shape controls both signals. This gives a direct way to separate the anomaly-induced current from ordinary electromechanical backgrounds and to extract the effective gap and electronic temperature in
graphene devices.
Read the full abstract ▾