Disordered Systems and Neural Networks
Structure of solutions to continuous constraint satisfaction problems through the statistics of wedged and inscribed spheres
Jaron Kent-Dobias
The study of random landscapes has long relied on counting stationary points: metastable states and the barriers between them. However, this method is useless for describing flat regions, common in constraint satisfaction problems. We introduce a characterization of flat regions by counting the number of spheres that can be uniquely inserted into them, either by wedging spheres of fixed radius or by inscribing spheres of variable radius. The ratio of these counts constrains the
topology of the solution space. We apply this characterization to the spherical perceptron and show the existence of at least two topological regimes.
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Strongly Correlated Electrons
Incommensurate Twisted Bilayer Graphene: emerging quasi-periodicity and stability
Ian Jauslin and Vieri Mastropietro
We consider a
lattice model of twisted
bilayer graphene (TBG) for incommensurate twist angles, focusing on the role of large-momentum-transfer Umklapp terms. These terms, which nearly connect the
Fermi points of different layers, are typically neglected in effective continuum descriptions but could, in principle, destroy the Dirac cones; they are indeed closely analogous to those appearing in
fermions within quasi-periodic potentials, where they play a crucial role. We prove that, for small but finite interlayer coupling, the semimetallic phase is stable provided the angles belong to a fractal set of large measure (which decreases with the hopping strength) characterized by a number-theoretic Diophantine condition. In particular, this set excludes the (zero measure) commensurate angles. Our method combines a Renormalization Group (RG) analysis of the imaginary-time, zero-temperature Green's functions, with number theoretic properties, and it is similar to the technique used in the Lindstedt series approach to Kolmogorov-Arnold-Moser (KAM) theory. The convergence of the resulting series allows us to rule out non-perturbative effects. The result provides a partial justification of the effective continuum description of TBG in which such large-momentum interlayer hopping processes are neglected.
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Soft Condensed Matter
Excluded volume geometry and packing fraction in binary convex hyperparticle mixtures
H.J.H. Brouwers
In this paper the excluded volume of binary similar hyperparticles with small size difference in D-dimensional Euclidean spaces R2, R3, and R4 is studied using two different statistical geometry approaches. These
geometric approaches, concerning orientation geometry and integral geometry, yield the excluded volume of particle pairs. The excluded volume of rectangles, based on orientation geometry, in Euclidean space R2 is used to derive an explicit equation for the bidisperse packing fraction, which is compatible with the expression published previously. Next, the excluded volume of pairs of convex particles in D = 2, 3 and 4, resulting from integral geometry, are presented. These excluded volumes are identical with the specific ones for circles and rectangles (D = 2) and (sphero)cylinders (D = 3), derived by orientation geometry. Furthermore, these orientation geometry-based excluded volumes contain
geometric measures: particle volume, surface area, mean
curvature and the second quermassintegral. They allow for the derivation of closed-form expressions for the random packing fraction of binary convex similar hyperparticles in Euclidean spaces R2 , R3 and R4.
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Strongly Correlated Electrons
Polarization dependency in Resonant Inelastic X-Ray Scattering
Michelangelo Tagliavini, Fabian Wenzel and Maurits W. Haverkort
Resonant Inelastic X-Ray Scattering (RIXS) is a well-established tool for probing excitations in a wide range of materials. The measured spectra strongly depend on the scattering geometry, via its influence on the polarization of the incoming and outgoing light. By employing a tensor representation of the 4-point response function that governs the RIXS intensity, we disentangle the experimental geometry from the intrinsic material properties. In dipole-dipole RIXS processes and low-
symmetry crystals, up to 81 linearly independent fundamental spectra can be measured as a function of light polarization. However, for
crystals or molecules with
symmetry, the number of independent fundamental spectra that define the RIXS tensor is significantly reduced. This work presents a systematic framework for determining the number of fundamental spectra and expressing the RIXS tensor in terms of these fundamental components. Given a specific experimental geometry, the measured spectrum can be represented as a linear combination of these fundamental spectra. To validate our approach, we performed calculations for different point group
symmetries, both with and without an applied
magnetic field. Within the same framework, we derived expressions for powder spectra in momentum-independent processes and spectra obtained using Bragg spectrometers. This formalism provides a valuable toolkit for optimizing experiment planning, data interpretation, and RIXS simulation.
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Strongly Correlated Electrons
Exotic Surface Stripe Orders in Correlated Kagome Metal CsCr3Sb5
Yunxing Li, Peigen Li, Taimin Miao et al. (+20 more)
The newly discovered kagome
superconductor CsCr3Sb5 exhibits distinct features with flat bands and unique magnetism, providing a compelling platform for exploring novel
quantum states of correlated electron systems. Emergent charge order in this material is a key for understanding unconventional superconductivity, but it remains unexplored at the atomic scale and the underlying physics is elusive. Here, we identify and unreported stripe orders on the surface which are distinct from the bulk and investigate the underlying bulk electronic properties using a combination of scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Specifically, a mixture of 2a0 * a0 and 3a0 * a0 stripe order is found on Cs-terminated surface while 4a0 * root3a0 stripe order is found on the Sb-terminated surface. The electronic spectra exhibit strongly correlated features resembling that of high temperature
superconductors, with kagome flat bands lying about 330 meV above EF, suggesting that the electron correlations arise from Coulomb interactions and Hund's coupling. Moreover, a distinct electron-
boson coupling mode is observed at approximately 100 meV. These findings provide new insights into the interplay between surface and bulk charge orders in this strongly correlated kagome system.
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All authors Yunxing Li, Peigen Li, Taimin Miao, Rui Xu, Yongqing Cai, Neng Cai, Bo Liang, Han Gao, Hanbo Xiao, Yongzhen Jiang, Jiefeng Cao, Fangyuan Zhu, Hongkun Wang, Jincheng Xie, Jingcheng Li, Zhongkai Liu, Chaoyu Chen, Yunwei Zhang, X. J. Zhou, Dingyong Zhong, Huichao Wang, Jianwei Huang, Donghui Guo
Materials Science · Cross-listed from quant-ph
Many-body post-processing of density functional calculations using the variational quantum eigensolver for Bader charge analysis
Erik Schultheis, Alexander Rehn and Gabriel Breuil
Quantum chemistry and condensed matter physics are among the most promising applications of
quantum computers. Further, estimating properties of a material is crucial to evaluate its industrial applications. To investigate charge distributions of weakly and strongly correlated systems we calculate Bader charges for various periodic systems by solving many-body
Hamiltonians using the variational
quantum eigensolver. The
Hamiltonians are computed from Kohn-Sham orbitals obtained from a prior DFT calculation. We first demonstrate the accuracy of our method on various doped MgH2 supercells. Further, we show that our approach, compared to standard DFT, significantly improves the Bader charge values for strongly correlated transition metal
oxides, where we take DFT+U results as a reference. The computational framework behind our many-body calculations, called Dopyqo, is made openly available as a software package.
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Strongly Correlated Electrons
Multi-Q spin-valley order in twisted WSe2
Arthur Bril, Nai Chao Hu and Nick Bultinck
We report on a study of the interacting phase diagram of $3.65^\circ$-twisted WSe$_2$ at moiré hole filling $\nu=1$, in which we find previously-overlooked types of magnetism. Specifically, in part of the phase diagram we obtain a
magnetic order parameter which modulates in space with four different non-zero wave vectors, corresponding to the three $M$-points and one $K$-point of the moiré Brillouin zone. These multi-Q orders, which can be coplanar or non-coplanar, are continuous deformations of the $120^\circ$
spin-valley anti-ferromagnet (AFM), where the unit
cell has expanded by a factor of four. Interestingly, we find that the multi-Q states are stabilized for experimentally relevant values of interaction strength and displacement field, and are accompanied by a softening of the
spin fluctuations near the $M$-points of the moiré
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Strongly Correlated Electrons
Exact Fractionalized Ground States in an Extended Spin-1 Kitaev Chain
Alwyn Jose Raja and R. Ganesh
Inspired by the Affleck-Kennedy-Lieb-Tasaki (AKLT) model, we present exact solutions for a
spin-1 chain with Kitaev-like couplings. We consider an expanded Kitaev model with bilinear and biquadratic terms. At an exactly solvable point, the
Hamiltonian can be reexpressed as a sum of projection operators. Unlike the AKLT model where projectors act on total
spin, we project onto components of
spin along the bond direction. This leads to exponential ground state degeneracy, expressed in terms of fractionalized
spin-$\frac{1}{2}$ objects. Each ground state can be expressed concisely as a
matrix product state. We construct a phase diagram by varying the relative strength of bilinear and biquadratic terms. The fractionalized states provide a qualitative picture for the
spin-1 Kitaev model, yielding approximate forms for the ground state and low-lying excitations.
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Statistical Mechanics · Cross-listed from quant-ph
Tunable quantum Mpemba effect in long-range interacting systems
Andrew Hallam, Matthew Yusuf, Aashish A. Clerk et al. (+2 more)
Symmetry plays a fundamental role in many-body systems, both in and out of
equilibrium. The
quantum Mpemba effect (QME) – a phenomenon where systems initially farther from
equilibrium can thermalize faster – can be understood in terms of how rapidly a
symmetry, broken by initial conditions, is dynamically restored. In this work, we study the QME in a one-dimensional
spin-1/2 XYZ model with power-law decaying interactions in the presence of a
magnetic field. In the prethermal regime generated by large field strengths, the system develops a continuous U(1)
symmetry, enabling the QME to emerge. However, due to the Hohenberg-Mermin-Wagner
theorem, the QME can only arise when interactions are sufficiently short-ranged. This leads to an interplay between the external field, interaction range, and dynamical
symmetry restoration. We systematically explore this interplay and analyze the dependence of the QME on the effective temperature set by the initial state. Our results demonstrate the tunability of the QME via long-range interactions, which can be probed in experimental platforms of trapped ions, polar molecules, and NV centers.
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All authors Andrew Hallam, Matthew Yusuf, Aashish A. Clerk, Ivar Martin, Zlatko Papić
Materials Science · Cross-listed from physics.med-ph
Scalable covalently functionalized black phosphorus hybrids for broadspectrum virucidal activity
Na Xing, Jasmin Er, Ricardo M. Vidal et al. (+14 more)
At the onset of viral outbreaks, broad-spectrum antiviral materials are crucial before specific therapeutics become available. We report scalable, biodegradable black phosphorus (BP) hybrids that provide mutation-resilient virucidal protection. BP sheets, produced via an optimized mechanochemical process, are covalently functionalized with 2-azido-4,6-dichloro- 1,3,5-triazine to form P=N bonds. Fucoidan, a sulfated polysaccharide with intrinsic antiviral activity, and hydrophobic chains are then incorporated to achieve irreversible viral deactivation. The material exhibits strong antiviral inhibition and complete virucidal activity against multiple viruses, including recent severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants. It maintains high biocompatibility, remains effective against viral mutations, and is shelf stable for at least five month. The combination of biodegradability, scalable synthesis, and synergistic antiviral and virucidal mechanisms establishes BP-conjugates as a new class of highly efficient antivirals. They offer a broad spectrum antiviral solutions that could bridge the gap between antiviral medicines and general antiseptics.
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All authors Na Xing, Jasmin Er, Ricardo M. Vidal, Sandhya Khadka, Robert Schusterbauer, Maik Rosentreter, Ranen Etouki, Rameez Ahmed, Taylor Page, Philip Nickl, Obida Bawadkji, Anja Wiesner, Joerg Radnik, Vasile-Dan Hodoroaba, Kai Ludwig, Jakob Trimpert, Ievgen S. Donskyi
Quantum Gases · Cross-listed from quant-ph
Prethermal gauge structure and surface growth in $\mathbb{Z}_2$ lattice gauge theories
Lukas Homeier, Andrea Pizzi, Hongzheng Zhao et al. (+3 more)
Universal aspects of thermalization in interacting many-body systems are challenging to derive microscopically, especially in kinetically constrained models, yet their numerical study beyond $(1+1)$D remains notoriously difficult. Here, we numerically study the mean-field dynamics of a $(2+1)$D
spin system with thousands of
spins and show that experimentally-feasible two-body Ising interactions can stabilize a prethermal $\mathbb{Z}_2$
lattice gauge structure with dynamical matter, manifested by a separation of timescales with a stable gauge-invariant plateau. Eventually, the metastable prethermal $\mathbb{Z}_2$ gauge structure breaks down via a proliferation of Gauss' law defects, similar to bubble formation in false
vacuum decay. In this regime, we discover spatio-temporal correlations described by a non-linear surface growth consistent with the $(1+1)$D Kardar-Parisi-Zhang (KPZ) universality class, revealing a previously hidden feature in the thermalization of multi-point correlators. We
benchmark our results in small systems against semi-classical discrete time Wigner approximation (DTWA) and exact diagonalization (ED), where the breakdown of DTWA signals the emergence of an extensive number of local
symmetries that strongly influence the thermalization pathway. Our model provides a testbed for
quantum simulators and is directly implementable in large-scale arrays of Rydberg atoms.
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All authors Lukas Homeier, Andrea Pizzi, Hongzheng Zhao, Jad C. Halimeh, Fabian Grusdt, Ana Maria Rey
Statistical Mechanics · Cross-listed from quant-ph
Thermodynamics of quantum processes: An operational framework for free energy and reversible athermality
Himanshu Badhani, Dhanuja G.S. and Siddhartha Das
We explore the thermodynamics of
quantum processes (
quantum channels) by axiomatically introducing the free energy for channels, defined via the
quantum relative
entropy with an absolutely thermal channel whose fixed output is in
equilibrium with a thermal reservoir. This definition finds strong support through its operational interpretations in designated
quantum information and thermodynamic tasks. We construct a resource theory of athermality for
quantum processes, where free operations are Gibbs preserving superchannels and golden units are
unitary channels with respect to absolutely thermal channel having fully degenerate output
Hamiltonian. We exactly characterize the one-shot
distillation and formation of
quantum channels using hypothesis-testing and max-relative
entropy with respect to the absolutely thermal channel. These rates converge asymptotically to the channel free energy (up to a multiplicative factor of half the inverse temperature), establishing its operational meaning and proving the asymptotic reversibility of the athermality. We show the direct relation between the resource theory of athermality and
quantum information tasks such as private randomness and purity
distillation, and thermodynamic tasks of erasure and work extraction. Our work connects the core thermodynamic concepts of free energy, energy,
entropy, and maximal extractable work of
quantum processes to their information processing capabilities.
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Strongly Correlated Electrons
Quantum critical origin of strange-metals at the end of a pseudogap phase in infinite-layer nickelates
C. Iorio-Duval, E. Beauchesne-Blanchet, F. Perreault et al. (+7 more)
The
quantum-critical origin of strange metals remains debated, particularly in cuprates where $T$-linear resistivity emerges at the end of the pseudogap phase, a regime without long-range order whose nature remains one of the largest mysteries of
quantum materials~\cite{Michon2019Thermodynamic, zhong_2022}. Superconducting infinite-layer nickelates provide a new platform to revisit this issue, given their close similarities to cuprates. Here too, $T$-linear resistivity onsets at a critical doping $x^\star$ near the middle of the superconducting dome. Establishing whether $x^\star$ is a
quantum critical point (QCP) – a zero-temperature phase transition – typically relies on the electronic specific heat $C_{\rm el}$, which follows $C_{\rm el}/T \propto \log(T)$ at a QCP, rather than the constant behaviour of a conventional metal. However, the thin-film form of infinite-layer nickelates precludes calorimetry. We therefore use the Seebeck coefficient as a low-temperature proxy for specific heat per carrier. In La$_{\rm 1-x}$Sr$_{\rm x}$NiO$_2$ at $x^\star$, the high-temperature Seebeck response is quantitatively captured by the ARPES-measured band structure, indicating well-defined quasiparticles. Below 60 kelvin, however, $S/T$ develops a logarithmic divergence, $S/T \propto \log(T)$, persisting to the lowest temperature once superconductivity is suppressed by $B=41.5$~T. This identifies $x^\star$ as a QCP terminating the underdoped phase. Finally, we find that the carrier density $n_{\rm d}$ of the Ni-$d_{\rm x^2-y^2}$ pocket drops from $1+x$ above $x^\star$ to $x$ below, mirroring the hallmark of the pseudogap phase in cuprates and iridates. These results point to a pseudogap-like underdoped regime ending at $x^\star$, from which strange-metal behaviour emerges.
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All authors C. Iorio-Duval, E. Beauchesne-Blanchet, F. Perreault, J. L. Santana González, S. Üstün Kaykusuz, W. Sun, D. Graf, Y. F. Nie, A. Gourgout, G. Grissonnanche
Quantum Gases
Kibble-Zurek Scaling and Spatial Statistics in Quenched Binary Bose Superfluids
Subhadeep Patra, Arko Roy, Seong-Ho Shinn et al. (+2 more)
The emergence of order from an initially uncorrelated state across a phase transition is a central problem in
quantum many-body physics, particularly in multicomponent systems where interactions between components lead to rich nonequilibrium dynamics. While defect formation is known to follow universal scaling laws, prior studies have focused mainly on defect density, leaving their spatial organization largely unexplored. Here we show that gradually tuning the chemical potential in a two-dimensional binary Bose gas drives condensation into either a miscible or immiscible phase. In the immiscible regime, domains form whose number, size, and boundary length obey Kibble-Zurek (KZ) scaling and evolve self-similarly. In the miscible regime,
vortices emerge with KZ scaling. In both cases, the spatial distribution of
vortices and domains is well described by a Poisson point process with KZ-determined density. These results reveal universal features of far-from-
equilibrium dynamics and provide a framework to characterize
stochastic geometry in multicomponent
quantum systems.
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All authors Subhadeep Patra, Arko Roy, Seong-Ho Shinn, Adolfo del Campo, Mithun Thudiyangal
Materials Science
Two-Dimensional Altermagnetic Iron Oxyhalides: Real Chern Topology and Valley-Spin-Lattice Coupling
Yong-Kun Wang, Si Li and Shengyuan A. Yang
Altermagnets, a novel class of collinear
magnetic materials, exhibit unique
spin-split band structures, yet topological insulating states in intrinsic altermagnetic systems are rare. Here, we identify monolayer Fe$_2X_2$O ($X$ = Cl, Br, I) as a new family of 2D altermagnetic real Chern
insulators. These materials display robust $d$-wave altermagnetic ordering, semiconducting band gaps, and nontrivial real Chern numbers per
spin channel, yielding
spin-polarized topological corner modes. They also feature
spin-polarized valleys with strong altermagnetism-valley-
spin-
lattice coupling, enabling valley-selective excitation via linear dichroism and strain-induced valley polarization. In multiferroic Fe$_2$Cl$_2$O, magnetism coexists with ferroelasticity, and an applied strain can switch the Néel vector. These findings position 2D iron oxyhalides as a promising platform for exploring altermagnetism and
magnetic topological states for spintronics and valleytronics.
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Materials Science
Impact of Oxygen Vibrations on Raman Intensity Variation in the Catalyst Fe$_2$(MoO$_4$)$_3$
Young-Joon Song and Roser Valentí
Iron molybdate (Fe$_2$(MoO$_4$)$_3$) is a widely used commercial catalyst for oxidative dehydrogenation. Recently, the possibility that bulk oxygen atoms participate in catalytic reactions has been proposed based on the experimentally observed significant reduction in Raman intensity during the catalytic process, which implies the formation of oxygen defects. In this work, we performed density functional theory (DFT) calculations to elucidate the microscopic mechanism of the experimentally observed Raman intensity variation. Our
phonon analysis reveals that oxygen-dominated vibrational modes, with a small contribution from Mo, occur near 782cm$^{-1}$– the same frequency region where the Raman intensity reduction was measured. To make the calculations computationally feasible for this large system, we introduced an effective frozen-
phonon approach to indirectly account for the effects of a very small concentration of defects on the Raman intensity. Our results suggest that oxygen vibrations are primarily responsible for the decrease in the calculated Raman intensity. Moreover, structural relaxation of Fe$_2$(MoO$_4$)$_3$ containing an oxygen vacancy indicates that oxygen
diffusion from the bulk to the surface may occur very rapidly, such that the local
symmetry remains effectively unchanged. This interpretation is in line with the absence of measurable peak shifts or broadening in the experimental Raman spectra.
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Quantum Gases · Cross-listed from quant-ph
Time-dependent Variational Principles for Hybrid Non-Unitary Dynamics: Application to Driven-Dissipative Superconductors
Pasquale Filice, Marco Schirò and Giacomo Mazza
We introduce time-dependent variational principles to study the non-
unitary dynamics of open
quantum many-body systems, including dynamics described by the full Lindblad master equation, the non-Hermitian dynamics corresponding to the no-click limit of the fully post-selected
quantum trajectories, and the dynamics described by a hybrid Lindbladian with a control parameter $\alpha$ which interpolates between the full post-selection and averaging over all
quantum trajectories. As an application we study the non-
unitary dynamics of a lossy or driven-dissipative BCS
superconductors, evolving in presence of two-body losses and two-body pumps. We show that the non-Hermitian limit acts as a singular limit of the hybrid dissipative dynamics, leading to a sharp modification of the universal approach to the driven-dissipative steady-states. By considering the dissipative dynamics with pair losses, we show that, as the non-Hermitian limit is approached, the density dynamics sharply evolves from a universal power-law to exponential decay that converges towards a quasi-steady plateau characterized by the freezing of the particle depletion due to pair losses. The reached quasi-stationary density increases as a function of the dissipation rate highlighting the emergence of a non-Hermitian Zeno effect in the lossy dynamics. For the driven-dissipative case, we show that, in the non-Hermitian limit, the system gets trapped into an effective negative temperature state, thus skipping the infinite temperature steady-state reached in the presence of finite contribution of the
quantum jumps. We rationalize these findings in terms of the conservation of the length of the pseudospins which, in the non-Hermitian limit, suppresses the effective single-particle losses and pumps acting on the non-condensed particles.
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Mesoscale and Nanoscale Physics
plasmonX: an Open-Source Code for Nanoplasmonics
Tommaso Giovannini, Pablo Grobas Illobre, Piero Lafiosca et al. (+4 more)
We present the first public release of plasmonX, a novel open-source code for simulating the plasmonic response of complex nanostructures. The code supports both fully atomistic and implicit descriptions of nanomaterials. In particular, it employs the frequency-dependent fluctuating charges ($\omega$FQ) and dipoles ($\omega$FQF$\mu$) models to describe the response properties of atomistic structures, including simple and $d$-metals,
graphene-based structures, and multi-metal nanostructures. For implicit representations, the Boundary Element Method is implemented in both the dielectric polarizable continuum model (DPCM) and integral equation formalism (IEF-PCM) variants. The distribution also includes a post-processing module that enables analysis of electric field-induced properties such as charge density and electric field patterns.
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All authors Tommaso Giovannini, Pablo Grobas Illobre, Piero Lafiosca, Luca Nicoli, Luca Bonatti, Stefano Corni, Chiara Cappelli
Superconductivity
Switchable chiral 2x2 pair density wave in pure CsV3Sb5
Wei Song, Xiao-Yu Yan, Xin Yu et al. (+9 more)
We investigate electron pairing in a super clean kagome
superconductor CsV3Sb5 with a residual resistivity ratio (RRR) of 290. By using the dilution-refrigerator-based scanning tunneling microscopy (STM) at the Synergetic Extreme Condition User Facility (SECUF), we find that the pairing gap exhibits
chiral 2x2 modulations, and their chirality can be controlled by
magnetic field training. We introduce nonmagnetic
impurities to observe the complete suppression of 2x2 pairing modulations in presence of persistent 2x2 charge order. This nonmagnetic pair-breaking effect provides phase-sensitive evidence for pair-density-wave (PDW) induced pairing modulations. Our results support switchable
chiral 2x2 PDW in this super clean kagome
superconductor.
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All authors Wei Song, Xiao-Yu Yan, Xin Yu, Desheng Wu, Deng Hu, Hailang Qin, Guowei Liu, Hanbin Deng, Chao Yan. Muwei Gao, Zhiwei Wang, Rui Wu, Jia-Xin Yin
Statistical Mechanics
Temperature and conditions for thermalization after canonical quenches
Lennart Dabelow
We consider quenches of a
quantum system that is prepared in a canonical
equilibrium state of one
Hamiltonian and then evolves unitarily in time under a different
Hamiltonian. Technically, our main result is a systematic expansion of the pre- and post-quench canonical ensembles in the quench strength. We first demonstrate how this can be used to predict the system's temperature after the quench from
equilibrium properties at the pre-quench temperature. For a thermalizing post-quench system, it furthermore allows us to calculate
equilibrium observable expectation values. Finally, in the presence of additional conserved quantities besides the
Hamiltonian, we obtain a hierarchy of necessary conditions for thermalization towards the (post-quench) canonical ensemble. At first order, these thermalization conditions have a nice
geometric interpretation in operator space with the canonical covariance as a semi-inner product: The quench operator (difference between post- and pre-quench
Hamiltonians) and the conserved quantity must be orthogonal in the orthogonal complement of the post-quench
Hamiltonian. We illustrate the results numerically for a variety of setups involving integrable and nonintegrable models.
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Materials Science
Formation of C-centers in Si-based systems by light ion irradiation
Carolina Crosta, Riccardo Nardin, Patrick Daoust et al. (+8 more)
Atomic-scale
crystal defects in Si are
quantum-light sources offering tantalizing integration with existing photonic technologies. Yet, the controlled creation of near-infrared color centers for long- haul
quantum communication and information still remains a challenge. In this work, we utilize light ions, such as H+ and He+, to gently generate
quantum emitters in a crystalline Si
matrix. Temperature-dependent photoluminescence measurements demonstrate the presence of optically-active defects, whose fluorescence matches the primary telecom window around 1550 nm. In addition, time-resolved investigations unveil long-lived excitonic states in the {\mu}s regime, thus confirming the formation of interstitial oxygen-carbon complexes, termed C-centers. Finally, we explored controlled ion irradiation strategies to seamlessly generate C-centers also in Ge-on-Si
heterostructures, which offer an advanced technological platform for the future realization of integrated
quantum photonics. This analysis, informed by practical color center synthesis and proof-of-principle experiments in epitaxial architectures, indicates intriguing prospects and profitable strategies to advance the burgeoning field of light-based
quantum technologies.
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All authors Carolina Crosta, Riccardo Nardin, Patrick Daoust, Stefano Achilli, Ian Colombo, Matteo Campostrini, Emiliano Bonera, Jacopo Pedrini, Oussama Moutanabbir, Valentino Rigato, Fabio Pezzoli
Strongly Correlated Electrons
Possible Bose-Einstein condensation of magnons in a S = 5/2 honeycomb lattice
J. Khatua, S. M. Kumawat, G. Senthil Murugan et al. (+5 more)
Quantum magnets offer a unique platform for exploring exotic
quantum phases and
quantum phase transitions through external
magnetic fields. A prominent example is the field-induced Bose–Einstein condensation (BEC) of
magnons near the saturation field. While this behavior has been observed in low-
spin systems, its realization in high-
spin, quasi-two-dimensional magnets – where multiple on-site excitations are possible – remains exceptionally rare. Here, we report thermodynamic and density functional theory results on single
crystals of the honeycomb-
lattice antiferromagnet K$_{4}$MnMo$_{4}$O$_{15}$ with $S = 5/2$. The system undergoes a field-induced transition to a fully polarized state at the critical field $\mu_{0}H_{\rm s} = 6.4$~T. Our results reveal possible thermodynamic signatures of
magnon BEC, $T_{\mathrm{N}} \sim (H_{\rm s} - H)^{2/d}$ ($d = 3$), expanding the purview of BEC-driven
quantum criticality to a high-
spin, quasi-two-dimensional antiferromagnets with negligibly small anisotropy.
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All authors J. Khatua, S. M. Kumawat, G. Senthil Murugan, C.-L. Huang, Heung-Sik Kim, K. Sritharan, R. Sankar, Kwang-Yong Choi
Statistical Mechanics
The Popkov-Schütz two-lane lattice gas: Universality for general jump rates
Herbert Spohn
We consider the asymmetric version of the Popkov-Schütz two-lane
lattice gas with general jump rates, subject to the stationary measure being of product form. This still leaves five free parameters. At density 1/2 the
eigenvalues of the flux Jacobian are degenerate. We compute the second order expansion of the average fluxes at density 1/2 and thereby identify the universality classes.
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Strongly Correlated Electrons
The anisotropic Heisenberg model close to the Ising limit: triangular lattice vs. effective models
Martin Ulaga, Jure Kokalj, Takami Tohyama et al. (+1 more)
Stimulated by recent experiments on materials representing the realization of the anisotropic Heisenberg
spin-$1/2$ model on the triangular
lattice, we explore further properties of such a model in the easy-axis regime $\alpha = J_\perp/J_z < 1$ and the plausibility of finding effective models that capture similar physics. We show that, at finite fields, the magnetization curve as well as the transverse magnetization (superfluid) order parameter $m_\perp$ of the triangular
lattice model are indeed qualitatively reproduced by anisotropic Heisenberg models on the honeycomb or the square
lattice. At the point of correspondence to the zero-field triangular
lattice model, however, the bipartite models are qualitatively different as they remain gapless even at $\alpha \ll 1$ with a small but finite $m_\perp >0 $. Conversely, we present several additional numerical studies of the full model on the triangular
lattice which support the appearance of a gap at zero field and $\alpha \ll 1$. In particular, the magnetization curve $m(h)$ as well as the
spin stiffness $\rho_s$ indicate a transition/crossover from gappless to gapped regimes at $\alpha \sim \alpha^*$ with $\alpha^* \lesssim 0.5$. We also show that deviations from the linear
spin-wave theory and the emergence of the gap can be traced back to the strong effective repulsion between
magnon excitations, showcasing similarity to strongly correlated systems.
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All authors Martin Ulaga, Jure Kokalj, Takami Tohyama, Peter Prelovšek
Soft Condensed Matter
AI-Assisted Physics-Informed Predictions of Degradation Behavior of Polymeric Anion Exchange Membranes
William Schertzer, Mohamed Al Otmi, Janani Sampath et al. (+2 more)
The global transition to hydrogen-based energy infrastructures faces significant hurdles. Chief among these are the high costs and sustainability issues associated with acid-based
proton exchange membrane fuel
cells. Anion exchange membrane (AEM) fuel
cells offer promising cost-effective alternatives, yet their widespread adoption is limited by rapid degradation in alkaline environments. Here, we develop a framework that integrates mechanistic insights with machine learning, enabling the identification of generalized degradation behavior across diverse polymeric AEM chemistries and operating conditions. Our model successfully predicts long-term hydroxide conductivity degradation (up to 10,000 hours) from minimal early-time experimental data. This capability significantly reduces experimental burdens and may expedite the design of high-performance, durable AEM materials.
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All authors William Schertzer, Mohamed Al Otmi, Janani Sampath, Ryan P. Lively, Rampi Ramprasad
Statistical Mechanics · Cross-listed from physics.soc-ph
Modeling Epidemics on Multiplex Networks: Epidemic Threshold and Basic Reproduction Number
Eric Alejandro Rozan, Mario Ignacio Simoy, Sebastian Bouzat et al. (+1 more)
Accurate epidemic
forecasting requires models that account for the layered and heterogeneous nature of real social interactions. The basic reproduction number $\mathcal R_0$, as calculated from models that assume homogeneous mixing or single-layer contact structures, has limited applicability to complex social systems. Here, we derive an expression for $\mathcal R_0$ in the context of multiplex networks, enabling the analysis of disease transmission across multiple social layers. We adapt the Degree-Based Mean-Field (DBMF) SIR model for single-layer complex networks to the multiplex setting, where each layer is characterized by its own degree distribution and infection rate. Using the Next Generation
Matrix method, we derive an analytical expression for the basic reproduction number $\mathcal R_0$. Numerical integration of the multiplex DBMF equations shows that $\mathcal R_0=1$ marks the epidemic threshold and governs the behavior of key outbreak indicators as expected. In addition to the exact expression for $\mathcal R_0$, we introduce an approximation, denoted by $\tau$, which is simpler to compute and admits a more transparent interpretation in terms of the epidemiological and topological parameters of the system.
Stochastic agent-based simulations support these findings, demonstrating a direct correspondence between $\tau$ and the average number of secondary infections generated during the early stages of an outbreak, consistent with the epidemiological interpretation of $\mathcal R_0$. This work provides a robust generalization of $\mathcal R_0$ for layered contact structures, offering a more realistic basis for epidemic
forecasting and the design of intervention strategies.
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All authors Eric Alejandro Rozan, Mario Ignacio Simoy, Sebastian Bouzat, Marcelo Nestor Kuperman
Strongly Correlated Electrons
Quantum Spin Singlet Ground State with Large Excitation Gap in the S = 3/2 quasi-1D van der Waals materials MoX3 (X = I, Br)
Jordan Teeter, Topojit Debnath, Harshil Goyal et al. (+15 more)
We report the first experimental evidence for a
quantum-disordered
spin-singlet ground state and gapped triplon excitations in quasi-one-dimensional van der Waals materials. The insulating van der Waals trihalides MoI3 and MoBr3 are analyzed in a combined thermodynamic, spectroscopic, and theoretical investigation. These materials contain structurally dimerized atomic chains of face-sharing octahedra with alternating short and long Mo-Mo separations along the chain direction. Temperature-dependent bulk
magnetic susceptibility measurements reveal a broad thermally activated response consistent with a large
spin gap. Inelastic
neutron scattering (INS) spectra provide direct evidence of a collective
spin gap at an exceptionally large energy transfer of ~ 30 meV (~ 348 K) for MoBr3. The absence of low-energy
magnetic spectral weight and the activated susceptibility are inconsistent with a conventional classical
antiferromagnetic ground state. Instead, they point to a
spin-singlet ground state with a large singlet-triplet excitation gap. To identify the microscopic origin of this gap, we perform density
matrix renormalization group (DMRG) calculations on one-dimensional
spin chains using exchange constants derived from density functional theory (DFT). The dominance of the single dimer exchange term allows the inter-dimer coupling along the chain and between chains to be treated using perturbation theory. Intrachain exchange lowers the isolated-dimer triplet energy by producing a dispersive triplon band. INS data show the triplon bandwidth to be ~ 20 meV. Interchain coupling produces negligible additional bandwidth on the order of 1 meV. The INS measurements directly establish
quantum spin-singlet and triplon physics in MoBr3 with a large singlet-triplet gap on the scale of room temperature, while the susceptibility and theoretical results indicate closely analogous behavior in MoI3.
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All authors Jordan Teeter, Topojit Debnath, Harshil Goyal, Md. Sabbir Hossen Bijoy, Maedeh Taheri, Nicholas R. Sesing, Clayton Mantz, Josemaria Garcia, Mathew B. Stone, Colin Sarkis, Do Hoon Kiem, Sohee Kwon, Mina Yoon, Fariborz Kargar, Kirill Shtengel, Tina T. Salguero, Alexander A. Balandin, Roger K. Lake
Mesoscale and Nanoscale Physics
Dissipationless transport by design in ultrathin magnetic topological insulator films
Amir Sabzalipour, Mohammad Shafiei and Milorad V. Milošević
Magnetic topological
insulators (MTIs) are among the prominent platforms for the next generation of high-speed and low-power spintronic devices. However, unlike their non-
magnetic counterparts, where the surface
spin-momentum locking prevents electrons from being scattered by non-
magnetic impurities and results in a dissipationless electronic flow,
magnetic impurities in MTIs cause dissipation by exerting
magnetic torque on the electron
spin. Decreasing this resistance is desired to reduce energy consumption and optimize performance of MTIs in envisaged applications. Here we reveal how electronic backscattering can be suppressed in a MTI thin film by external
magnetic and/or electronic stimuli, to yield an entirely dissipationless
spin-polarized charge transport. Our findings thus present an effective route to preserve
spin coherence and enhance
spin-current functionality in
magnetic topological materials, suggesting design strategies for magneto-electronic and spintronic devices with strongly reduced energy consumption.
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Strongly Correlated Electrons
The spin Hall conductivity in the hole-doped bilayer Haldane-Hubbard model with odd-parity ALM
Minghuan Zeng, Ling Qin, Shiping Feng et al. (+2 more)
Spin current generated electrically is among the core phenomena of spintronics for driving high-performance
spin device applications. Here, on the basis of systematic investigations for the hole doped single-layer Haldane-Hubbard(HH) model, we propose a new
bilayer HH model to realize the compensated odd-parity
spin splitting and the $T$-even
spin Hall conductivity where the two layers are connected by the time reversal transformation. Our results show that the vanishing layer-dependent electric potential $V_{L}$ gives rise to odd-parity ALM protected by the combined
symmetry $TM_{xy}$ with $T$ and $M_{xy}$ being the time reversal and mirror reflection perpendicular to $z$ axis, and the $T$-even
spin Hall conductivity simultaneously. In addition, though the staggered magnetization within each layer is substantially impacted by the layer-dependent electric potential, small $V_{L}$'s only bring negligible changes to the net magnetization and the
spin Hall conductivity, indicating that the alternating
spin splitting in momentum space and the
spin Hall conductivity are insusceptible to external elements. Most importantly, our work provides a general framework for the simultaneous realization of the compensated odd-parity
spin splitting in momentum space and the
spin Hall conductivity in collinear magnets, in terms of stacked multi-layer systems.
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All authors Minghuan Zeng, Ling Qin, Shiping Feng, Dong-Hui Xu, Rui Wang
Statistical Mechanics
Quantum thermodynamics of Gross-Pitaevskii qubits
Sebastian Deffner
What are the resources that can be leveraged for a thermodynamic device to exhibit genuine
quantum advantage? Typically, the answer to this question is sought in
quantum correlations. In the present work, we show that
quantum Otto engines that operate with nonlinear
qubits significantly outperform linear engines. To this end, we develop a comprehensive thermodynamic description of nonlinear
qubits starting with identifying the proper thermodynamic
equilibrium state. We then show that for ideal cycles as well as at maximum power the efficiency of the nonlinear engine is significantly higher. Interestingly, nonlinear dynamics can be thought of as an effective description of a correlated, complex
quantum many body system. Hence, our findings corroborate common wisdom, while at the same time propose a new design of more efficient
quantum engines.
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