Quantum Gases · Cross-listed from quant-ph
Many-body gravitating quantum systems with Bose-Einstein condensates and dipolar analogue
Youssef Trifa, Dario Cafasso, Marco Fattori et al. (+1 more)
Quantum probes of
gravity in the Newtonian regime, based on mass-energy equivalence in clocks or spatial superpositions in interferometers, share a common description in terms of an effective
qubit-
qubit coupling. Here we extend this framework to atomic ensembles, regarded as interacting collective qudits. The many-body enhancement boosts the signal-to-noise and increases the effective interaction rate, facilitating the observation of gravitationally-induced
entanglement and decoherence, certified by metrological witnesses based on local and collective
spin squeezing. We further identify trapped bimodal Bose-Einstein condensates with long-range interactions, including dipolar couplings, as a programmable analogue platform for simulating gravitating
quantum dynamics at accessible time and energy scales. Extending the protocol to a sensor network broadens the
entanglement-detection window.
Read the full abstract ▾
All authors Youssef Trifa, Dario Cafasso, Marco Fattori, Luca Pezzè
Strongly Correlated Electrons
Magnetic order and excitations in Ce$_3$TiBi$_5$ and Ce$_3$ZrBi$_5$
Pyeongjae Park, Qianli Ma, Wei Tian et al. (+7 more)
The R3MBi5 rare-earth intermetallics (R = rare earth, M = Ti, Zr, Sc) provide a versatile platform to explore how Kondo hybridization, RKKY exchange,
magnetic frustration, and broken inversion
symmetry may cooperate to generate unusual
magnetic behavior. We present a comprehensive
neutron scattering investigation of the
magnetic structure,
crystal electric field (CEF), and low-energy excitations in the locally noncentrosymmetric Kondo-
lattice compounds Ce3TiBi5 and Ce3ZrBi5. Powder and single-
crystal neutron diffraction reveals incommensurate cycloidal
antiferromagnetic order in Ce3TiBi5 with propagation vector k = (0, 0, 0.388) and a reduced ordered moment of m = 0.53(3)$\mu_{B}$. Ce3ZrBi5 exhibits a qualitatively similar
magnetic diffraction profile, with k $\simeq$ (0, 0, 0.37). Inelastic
neutron scattering measurements resolve two clear, well-separated CEF excitations in both compounds with nearly the same profile, confirming a well-isolated Kramers doublet ground state. At low energies, a broad, quasi-elastic
magnetic response is observed at T $\simeq$ TN, whose momentum-dependence is inconsistent with that expected from conventional collective excitations of localized moments. This discrepancy, along with a Kondo temperature estimate TK ~ 3–5 K – comparable to TN – indicates sizable Kondo hybridization, which accounts for the moment reduction and the spiral
magnetic order that appears to involve the
magnetic hard direction. Our results place these compounds in a regime where local inversion
symmetry breaking, anisotropic CEF effects, and competing Kondo and RKKY interactions collectively give rise to unconventional
magnetic order.
Read the full abstract ▾
All authors Pyeongjae Park, Qianli Ma, Wei Tian, Stuart Calder, Matthias Frontzek, G. Sala, D. Mandrus, Shirin Mozaffari, Andrew D. Christianson, Matthew B. Stone
Mesoscale and Nanoscale Physics
Electromechanical Switching and Momentum-Selective Transport in Geometry-Defined Blue Phosphorus Homojunctions
Zewen Wu, Min Zhou, Yanxia Xing et al. (+1 more)
Developing intrinsic homojunctions without chemical heterogeneity remains a key challenge in future two - dimensional devices. Here, we report a geometry - defined metal–
semiconductor–metal homojunction in
bilayer blue phosphorus (BlueP) created by a localized bubble corrugation, without chemical doping or foreign - material interfaces. First - principles calculations show that enlarging the interlayer separation in the metallic A\(_1\)B\(_1\) - stacked BlueP
bilayer opens a band gap, enabling a semiconducting barrier embedded between metallic segments. First - principles
quantum - transport simulations reveal a crossover from ballistic to tunneling transport upon bubble formation. In the tunneling regime, transmission decreases exponentially with bubble width while remaining weakly sensitive to bubble height and bulging direction. The junction acts as an orientation - dependent \(k\) - space filter, producing transport anisotropy and momentum selectivity. Orbital - resolved scattering analysis shows that intralayer - bonding channels persist under deformation whereas interlayer - hybridized channels are quenched, and that \sigma - type bonding yields higher conductance than \pi - type bonding. These insights motivate two electromechanical device concepts: a mechanically switchable
memory element with ON/OFF ratios up to 30 and a nanoscale sliding rheostat with reproducible exponential resistance tuning for Å - scale displacement sensing.
Read the full abstract ▾
All authors Zewen Wu, Min Zhou, Yanxia Xing, Xianghua Kong
Mesoscale and Nanoscale Physics
Extrinsic Spin Splitter Currents in Altermagnets
Sanjay Sarkar, Sayan Sarkar and Amit Agarwal
Altermagnets exhibit momentum-dependent
spin splitting despite having zero net magnetization. This enables a
spin-splitter effect in which an external electric field generates transverse
spin currents by separating oppositely polarized carriers. Here, we develop a unified semiclassical theory of linear extrinsic
spin-splitter currents, incorporating
impurity-induced side-jump and skew-scattering contributions, and apply it to the $d$-wave altermagnet \ch{FeSb2}. We demonstrate that asymmetric
impurity scattering provides a dominant channel for
spin-splitter currents. Remarkably, the resulting extrinsic
spin conductivity is time-reversal even, in contrast to previously studied
spin-splitter responses arising from symmetric scattering.
Read the full abstract ▾
Materials Science
Accounting for the length-scale dependence of thermal diffusivity in 3C-SiC measured with transient thermal gratings
Keshav Vasudeva, Samuel Huberman, Angus P.C. Wylie et al. (+7 more)
Pump-probe optical methods like transient grating spectroscopy (TGS) enable rapid, nondestructive thermoelastic property measurements. But, in
phonon-dominated ceramics, they can underpredict bulk thermal diffusivity when long mean free path (MFP)
phonons do not equilibrate over experimental length scales. We combine in situ TGS with Si4+ ion irradiation of CVD 3C-SiC (300 and 550C, 0.5-1 dpa) and density functional theory informed Boltzmann transport equation solutions to understand the origins of this offset. We show how the discrepancy between
laser flash analysis (LFA) and TGS-measured thermal diffusivity varies with grain-boundary density, temperature, and defect concentration. We introduce a dimensionless suppression factor that accounts for this discrepancy and demonstrate its utility by using it to show an agreement between the thermal defect resistance of
neutron irradiated 3C-SiC (measured using LFA) and ion irradiated 3C-SiC (measured using TGS). This theory-informed experimental framework enables quantitative, in situ tracking of ion irradiation damage induced thermal transport degradation in ceramics.
Read the full abstract ▾
All authors Keshav Vasudeva, Samuel Huberman, Angus P.C. Wylie, Maxwell Rae, Joey Demiane, Jamal A. Haibeh, Elena Botica-Artalejo, Kevin B. Woller, Michael P. Short, Sara E. Ferry
Superconductivity
Threefold error in the reported zero-field cooled magnetic moment of single crystal $La_2SmNi_2O_7$
Aleksandr V. Korolev and Evgeny F. Talantsev
For a relatively long time, the observation of the DC diamagnetic state in highly compressed nickelate
superconductors [1],[2] has been a challenging experimental problem. And recently Li et al.[3] reported on the measurements of the DC diamagnetism in zero-field-cooled (ZFC) and field-cooled (FC) pressurized single
crystal $La_2SmNi_2O_7$. From the analysis of experimental data, Li et al.[3] reported that the superconducting phase fraction in their $La_2SmNi_2O_7$ sample measured in the ZFC mode is 62.1%, and the superconducting phase fraction in the FC mode is 14.4%. It should be clarified that we regard the measurements of the DC diamagnetic state [3] in $La_2SmNi_2O_7$ (and more recently in $Pr_4Ni_3O_{10}$ [4]) as outstanding experimental results confirming bulk superconductivity in pressurized nickelates. However, we should note that Li et al.[3] made a threefold error in their calculations of the superconducting phase fraction in $La_2SmNi_2O_7$. We believe that correcting this and other errors in Ref.[3] will benefit the physics community.
Read the full abstract ▾
Quantum Gases · Cross-listed from quant-ph
Polarization-selective quantum cooperative response in dual-species atom arrays
Huan Wang, Shangguo Zhu, Yun Long et al. (+4 more)
Atom arrays have emerged as a powerful platform for
quantum light-matter interfaces, yet single-species arrays are constrained by in-plane
symmetry, restricting polarization control. Here we investigate the cooperative optical response of dual-species subwavelength atom arrays, in which intrinsic polarizability difference breaks in-plane
symmetry. By engineering the
lattice constants and detunings, the arrays exhibit polarization-dependent subradiant modes, enabling complete reflection of a specific polarization component. Leveraging this mechanism, we assemble array units as functional pixels and demonstrate a scalable polarization-selective
quantum light modulator. Our work establishes a dynamically reconfigurable atomic-photonic platform for versatile subwavelength
quantum optical elements.
Read the full abstract ▾
All authors Huan Wang, Shangguo Zhu, Yun Long, Fei Zhang, Yinghui Guo, Mingbo Pu, Xiangang Luo
Materials Science
Efficient training of generative models from multireference simulations and its application to the design of Dy complexes with large magnetic anisotropy
Zahra Khatibi, Lorenzo A. Mariano, Lion Frangoulis et al. (+1 more)
Generative machine learning models can potentially provide direct access to novel and relevant portions of the full chemical space, overcoming the cost of systematic sampling. However, the training of these models generally requires a large amount of data, often precluding the use of expensive high-level ab initio simulations for this task. The generation of coordination compounds of Dy with large
magnetic anisotropy represents a topical example, where multireference simulations of large molecules are necessary to perform reliable predictions. Here, we show that a semi-supervised chemically-inspired training-by-proxy of generative variational autoencoders can reduce the cost associated with building a training set from multireference simulations by two orders of magnitude. We illustrate the power of this approach by generating 100s of new organic ligands for Dy(III) pentagonal bipyramidal complexes exhibiting record values of
magnetic anisotropy, while starting from
datasets as small as 1k multireference calculations. This work thus paves the way to the computational generation of molecules as complex coordination compounds with target electronic and
magnetic properties.
Read the full abstract ▾
All authors Zahra Khatibi, Lorenzo A. Mariano, Lion Frangoulis, Alessandro Lunghi
Statistical Mechanics · Cross-listed from quant-ph
Quantum diffusion for a quantum particle with a correlated Gaussian noise
Yun Jeong Kang, Sung Kyu Seo and Kyungsik Kim
We investigate the diffusive behavior of a
quantum particle driven by a correlated Gaussian noise. We derive the analytical solution of the joint probability density function and obtain explicit expressions for the mean square momentum and the mean square displacement.
Statistical Mechanics
Mesoscopic fluctuation theory of particle systems driven by Poisson noise: study of the $q$-TASEP
Alexandre Krajenbrink and Pierre Le Doussal
We pursue our study of integrable weak noise theories of directed
polymer and interacting particle
stochastic models in the 1D KPZ universality class. Here we focus on the $q$-TASEP in either continuous or discrete time. Each particle on $\mathbb{Z}$ jumps independently by $+1$ with a rate (or probability) depending on the gap to the next particle on its right. We consider initial conditions (either step or random) which are empty of particles on $\mathbb{Z}^+$, and focus on the dynamics of the $N$ rightmost particles. In the limit $q \to 1$ and at large time (and large gaps) we identify a new intermediate "mesoscopic" (i.e. finite $N$) regime which corresponds to weak noise. In that regime Poisson noise remains important. We obtain the large deviations of the position of a given particle by two methods. The first derives asymptotics of $q$-TASEP Fredholm determinant formula. The second maps the weak noise limit to a system of semi-discrete or fully discrete, non linear differential equations. These are obtained as saddle point classical equations of a dynamical field theory, and their solutions represent the optimal configurations in the large deviation regime. We show the classical integrability of these two systems, and exhibit their explicit Lax pair. In the case of the continuous time $q$-TASEP it provides the first instance of classical integrability arising in a
stochastic system, with signatures of the Poisson noise persisting in the weak noise limit. For this model, we solve the scattering problem associated to its Lax pair and fully characterize the large deviations associated to the weak noise theory. Finally, we supplement this work with an Appendix on the first cumulant method to obtain the large deviations of several
lattice polymer models (Strict Weak, Log Gamma, Beta).
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Dimensional and doping stability of Peierls charge density waves in arrays of coupled one-dimensional chains
Aitor Garcia-Ruiz, Che-Pin Hsu, Ming-Hao Liu et al. (+1 more)
The Peierls instability, the spontaneous dimerization of a one-dimensional metallic chain at half filling, is a paradigmatic mechanism for charge-density-wave (CDW) formation. Here we test its robustness under finite doping and interchain hybridization in finite-thickness arrays of identical chains. We find that the stacking geometry plays a decisive role in stabilizing CDW order away from half filling. In particular, parallel-coupled chains exhibit a bistable regime where the normal and dimerized states coexist as local minima of the total energy, while skew-coupled chains display reentrant CDW order upon doping. Our results demonstrate that even minimal models of coupled atomic chains host rich phase diagrams controlled by doping,
lattice rigidity, and interchain coupling geometry.
Read the full abstract ▾
All authors Aitor Garcia-Ruiz, Che-Pin Hsu, Ming-Hao Liu, Marcin Mucha-Kruczynski
Disordered Systems and Neural Networks · Cross-listed from q-bio.NC
Collective Dynamics in Spiking Neural Networks Beyond Dale's Principle
Ross Ah-Weng and Hardik Rajpal
Dale's Principle has historically guided neuroscience research as a valuable rule of thumb, namely that all synapses on each
neuron release the same set of neurotransmitters. Most existing Spiking
Neuron Network models share this dichotomous assumption that
neurons are either excitatory or inhibitory; however, recent experimental evidence points towards co-release mechanisms that violate this assumption. Here, we introduce a minimal model of "Bilingual"
neurons violating Dale's principle that can exert both excitatory and inhibitory effects. We identify parameter regimes in which this architecture exhibits transitions between synchronous and asynchronous dynamics that differ quantitatively from those observed in a matched monolingual control architecture. We report distinct information-processing signatures both at the level of
neurons and higher-order interactions between them near the phase transitions. These results suggest that the population of
neurons violating Dales principle may provide an alternative mechanism for regulating large-scale oscillatory activity in neural
circuits.
Read the full abstract ▾
Strongly Correlated Electrons
Extended Ashkin-Teller transition in two coupled frustrated Haldane chains
Bowy M. La Rivière and Natalia Chepiga
We report an extremely rich ground state phase diagram of two
spin-1 Haldane chains frustrated with a three-site exchange and coupled by the
antiferromagnetic Heisenberg interaction on a zig-zag ladder. A particular feature of the phase diagram is the extended
quantum phase transition in the Ashkin-Teller universality class that separates the plaquette phase, which spontaneously breaks translation
symmetry, and the uniform disordered phase. The former is connected to the Haldane phase, stabilized by large inter-chain coupling, via the topological Gaussian transition. Upon decreasing the inter-chain interactions, this intermediate disorder phase vanishes, giving place to a dimerized phase separated from the plaquette phase on one side via a non-
magnetic Ising transition and from the Haldane phase on the other side by a topological weak first-order transition. Finally, in the limit of two decoupled chains, we recover a
quantum critical point that corresponds to two copies of the Wess-Zumino-Witten $\mathrm{SU(2)}_2$ criticality with a total central charge $c=3$.
Read the full abstract ▾
Soft Condensed Matter
Persistence-Driven Void Formation in Dense Active-Passive Mixtures
Giulia Janzen, Liesbeth M. C. Janssen, Nuno A. M. Araújo et al. (+2 more)
It is well established that dilute active dopants can melt an arrested amorphous solid by enhancing cage breaking and accelerating structural relaxation. Yet it remains unclear whether increasing persistence simply amplifies this effective melting or instead reorganizes the fluidization mechanism itself. Here we show that, in a minimal active-passive mixture, increasing persistence drives a crossover from homogeneous fluidization to a localized mechanical instability, demonstrating that sustained active forcing restructures relaxation in space rather than merely strengthening it. Persistent dopants accumulate stress and nucleate voids as their mechanically perturbed regions overlap. In this regime, rearrangements localize at void boundaries, and active and passive particles exhibit comparable mobility, producing dynamics reminiscent of crowd mosh pits. Persistence therefore reorganizes fluidization through stress accumulation and confinement, revealing a distinct nonequilibrium localization mechanism in disordered solids.
Read the full abstract ▾
All authors Giulia Janzen, Liesbeth M. C. Janssen, Nuno A. M. Araújo, Rastko Sknepnek, D. A. Matoz-Fernandez
Strongly Correlated Electrons · Cross-listed from hep-lat
Symmetric Mass Generation via Multicriticality in a 3D Lattice Gross-Neveu Model
Sandip Maiti, Debasish Banerjee, Shailesh Chandrasekharan et al. (+1 more)
We investigate a three-dimensional
lattice model of two
flavors of massless staggered
fermions coupled through two independent four-
fermion interactions, $U_I$ and $U_B$. Using large-scale
fermion-bag Monte Carlo simulations, we map out the phase diagram in the $(U_I, U_B)$ parameter space and identify three distinct phases: a massless
fermion phase, a
symmetry-broken massive phase, and a symmetric massive phase. When one of the interactions is absent ($U_B=0$), the system undergoes a single continuous transition directly connecting the massless and symmetric massive phases, a feature previously associated with unconventional
fermion mass generation. We find that turning on a nonzero $U_B$ separates this direct transition into two successive transitions with an intermediate
symmetry-broken phase. The transition from the massless to the broken phase belongs to the Gross-Neveu universality class, while the transition from the broken to the symmetric massive phase falls into the three-dimensional XY universality class. Our results indicate that the special point at vanishing coupling, where the direct transition occurs, plays the role of a multicritical point organizing the surrounding phase structure. These findings provide a unified
lattice perspective on conventional and unconventional mechanisms of
fermion mass generation within a single model.
Read the full abstract ▾
All authors Sandip Maiti, Debasish Banerjee, Shailesh Chandrasekharan, Marina K. Marinkovic
Soft Condensed Matter
Rheological properties and shear-induced structures of ferroelectric nematic liquid crystals
Ashish Chandra Das, Sathyanarayana Paladugu and Oleg D. Lavrentovich
Recently discovered ferroelectric nematic (NF)
liquid crystals are fluids with a polar orientational order. The electric polarization vector can be aligned by an electric field and by surface anchoring. Here, we explore how the polarization field and effective viscosity of the NF materials are affected by shear flows. We explore three NF materials, abbreviated RM734, DIO, and a room-temperature FNLC919, all of which exhibit a paraelectric nematic (N) and the NF phase. All materials show an increase of the viscosity upon cooling, with an Arrhenius behavior. In DIO and FNLC919, the antiferroelectric SmZA phase shows a strong dependence of the effective viscosity on the shear rate: this viscosity is lower than the viscosity of the N and NF phases at high shear rates but is much higher when the shear rate is low. The behavior is associated with the layered structure of the SmZA phase. All mesophases exhibit shear-thinning behavior at low shear rates and a nearly Newtonian behavior at higher shear rates. In terms of
alignment, we observe three regimes in the N and NF phases: flow-
alignment at low shear rates, log-rolling regime with the director and polarization along the vorticity axis at high shear rates, and polydomain structures at intermediate rates. In the flow-aligning regime, the NF polarization does not tilt away from the shear direction, which is in sharp contrast to the flow-induced tilt of the N director. The effect is attributed to the avoidance of splay deformations and associated space charge in the flowing NF. The temperature and shear rate dependencies of the viscosity and the uncovered shear-induced structural effects of NF advance our understanding of these materials and potentially facilitate their applications.
Read the full abstract ▾
Materials Science
Engineering in-plane anisotropy in 2D materials via surface-bound ligands
Tomoaki Sakurada, Woo Seok Lee, Yeongsu Cho et al. (+12 more)
2D materials exhibiting in-plane anisotropy enable novel functionality in electronic, optoelectronic, and photonic devices, yet their availability is generally limited to naturally-occurring low-
symmetry van der Waals compounds. Here, we demonstrate an approach to structural engineering in a family of blue-emitting 2D silver phenylchalcogenide
semiconductors based on steric interactions among surface-bound organic molecular ligands. By strategically halogenating specific sites of phenyl ligands, we demonstrate dramatic changes to the inorganic AgSe plane in mithrene (silver phenylselenolate, AgSePh). Density functional theory revealed pronounced in-plane electronic anisotropy for direct-gap fluorinated derivatives, while a chlorinated variant exhibited a direct-to-indirect bandgap transition. Furthermore, some fluorinated variants displayed strongly polarized absorption and luminescence, accompanied by a 10x enhancement in photoluminescence
quantum yield. This work establishes a versatile approach for tailoring optoelectronic properties in hybrid
semiconductors that is difficult or impossible to achieve in all-inorganic materials alone, offering new opportunities in advanced material design.
Read the full abstract ▾
All authors Tomoaki Sakurada, Woo Seok Lee, Yeongsu Cho, Rattapon Khamlue, Petcharaphorn Chatsiri, Nicholas Samulewicz, Tejas Deshpande, Annlin Su, Peter Müller, Tadashi Kawamoto, Shun Omagari, Martin Vacha, Watcharaphol Paritmongkol, Heather J. Kulik, William A. Tisdale
Materials Science
Landau level spectroscopy in current solid state physics
Ana Akrap and Milan Orlita
Landau level spectroscopy plays an important role in modern condensed-matter physics. In this technique, electrons in a solid are subjected to quantizing
magnetic fields and probed experimentally, often through optical methods. Direct and detailed insights into the electronic properties of crystalline materials are obtained, particularly the properties related to their band structure. Landau level spectroscopy enables the precise extraction of key parameters such as effective mass, carrier density, mobility, and band gap, and serves as a powerful tool for studying interactions between electrons and other quasiparticles in solids. Over its more than seventy-year history, Landau level spectroscopy has been applied mainly to
semiconductors and semimetals. Today, its scope also includes
graphene-based systems, surface and bulk states in topological materials, and other emergent systems with a narrow or vanishing band gap. In this work, we review the fundamentals of Landau level spectroscopy and illustrate them with selected examples from the literature.
Read the full abstract ▾
Quantum Gases
A Maxwell Fish-Eye Lens in a Bose-Einstein Condensate
Jelte Duchêne, Elinor Kath, Floriane Arrouas et al. (+7 more)
We experimentally realize an analogue of the optical Maxwell fish-eye lens (MFEL) using phononic excitations in a Bose-Einstein condensate (BEC). A MFEL is characterized by a radially symmetric, spatially varying refractive index with the remarkable property that rays emitted from any point within the lens are perfectly focused at their antipodal points. While the implementation of such gradient-index lenses is challenging in conventional optical systems, BECs offer a highly tunable platform in which the spatially varying speed of sound of collective excitations –
phonons, the acoustic analogues of
photons – can be engineered and their dynamics observed in real time. Time-resolved measurements of
phonon wavefronts reveal focusing behavior that shows good agreement with analytical theory and numerical simulations. This work provides both a
geometric and physical framework for engineering effective refractive indices using ultracold atoms, and simulating wave propagation on effective spherical geometries.
Read the full abstract ▾
All authors Jelte Duchêne, Elinor Kath, Floriane Arrouas, Hanyi Jang, Helmut Strobel, Markus K. Oberthaler, Jay Mehta, Liam M. Farrell, Wyatt Kirkby, Duncan H.J. O'Dell
Statistical Mechanics
Thermodynamic uncertainty relation under continuous measurement and feedback with quantum-classical-transfer entropy
Kaito Tojo, Takahiro Sagawa and Ken Funo
We derive a thermodynamic uncertainty relation (TUR) under
quantum continuous measurement and feedback control. By incorporating the
quantum-classical-transfer
entropy, which quantifies the information gained by continuous measurement, we show that the precision of currents is constrained by information-thermodynamic costs such as the
entropy production and information gain. Our result shows that information gain has the potential to enhance the precision of currents beyond the bounds set by the conventional TUR. We illustrate the bound with a driven two-level system under continuous measurement and feedback, demonstrating that feedback achieves higher precision of currents while suppressing the
entropy production.
Read the full abstract ▾
Soft Condensed Matter
Depth-dependent interplay of dynamical heterogeneity and chain dynamics at the surface of glass-forming polymers
Bao T. Ma and David S. Simmons
Polymer thin films exhibit pronounced interfacial mobility gradients that modify chain relaxation, yet how these gradients govern chain-scale dynamics across depth remains incompletely understood. Using molecular dynamics simulations of freestanding glass-forming
polymer films, we resolve how depth-dependent variations in segmental relaxation shape chain dynamics across a wide range of displacement scales. Near the free surface, accelerated segmental mobility suppresses Rouse-regime scaling exponents to values as low as gamma = 0.4, reflecting transient localization induced by interfacial mobility gradients rather than topological
entanglement. In contrast, the film interior exhibits enhanced Rouse scaling exponents consistent with predictions of the Heterogeneous Rouse Model (HRM), indicating that bulk dynamic heterogeneity compresses the Rouse regime. Mapping the minimum scaling exponent gamma_min across depth reveals a linear gradient that separates the bulk-like enhancement regime from the surface-induced suppression regime of chain dynamical scaling. Together, these results demonstrate that bulk and interfacial dynamic heterogeneity modify chain relaxation in opposite ways and establish Rouse scaling as a sensitive, spatially resolved probe of glassy dynamical heterogeneity and interfacial dynamical gradients in
polymers.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Coupling-energy driven pumping through quantum dots: Role of coherences
Lukas Litzba, Gernot Schaller, Jürgen König et al. (+1 more)
We study the impact of off-resonant tunneling and coherences on the electron pumping through
quantum dots. Thereby, we focus on two electron-pump setups where lowest-order tunneling processes are suppressed and the pump is exclusively driven by modulations of the coupling energy. The first setup is driven by switching on and off the couplings between the
quantum dot and the leads, while the second setup employs measurements of the dot occupation. We derive exact solutions for arbitrarily strong tunnel couplings in the absence of Coulomb interaction, identify parameter regimes with optimal pumping currents or optimal energy efficiency, and discuss similarities between both pumping mechanisms.
Read the full abstract ▾
All authors Lukas Litzba, Gernot Schaller, Jürgen König, Nikodem Szpak
Materials Science
Machine Learning for Electron-phonon Interactions From Finite Difference
Zun Wang, Wenhui Duan and Zuzhang Lin
First-principles investigations of electron-
phonon interactions (EPIs) play a crucial role in understanding a wide range of phenomena in physics and materials science. Among various approaches, the finite difference method offers a direct route to capture higher-order EPIs and is compatible with diverse electronic structure solvers. However, its considerable computational cost limits its broader application. To overcome this bottleneck, we present a machine learning electron-
phonon interaction (MLEPI) pipeline that predicts force constants and electronic
Hamiltonians for modeling EPIs from finite difference calculations, improving efficiency by orders of magnitude without compromising accuracy. The performance of MLEPI is validated by studying the temperature dependence of the electronic band properties in
bilayer graphene, where both first- and second order EPIs are treated on an equal footing. Using a heterogeneous edge network, the pipeline integrates both interlayer and intralayer interactions, making it particularly suitable for studying multilayer materials. With its inherent adaptability and ease of transfer to other applications, our methodology provides a robust tool with a very favorable accuracy/efficiency balance for investigating EPIs in large-scale material systems.
Read the full abstract ▾
Quantum Gases
Finite-time thermal refrigerator in interacting Bose-Einstein Condensates
Joaquín I. Ganly, Julián Amette Estrada, Franco Mayo et al. (+2 more)
We study a finite-time thermodynamic refrigeration cycle realized numerically in three-dimensional, weakly interacting Bose-Einstein condensates (BECs). The setup consists of three spatially separated condensates – system, piston, and reservoir – coupled through time-dependent potential barriers that implement compression, expansion, and contact strokes. Finite-temperature initial states are generated with the
Stochastic Ginzburg-Landau equation, and the subsequent dynamics are evolved using the truncated Gross-Pitaevskii equation. To measure temperatures we use a momentum-space thermometry method that provides estimates for each condensate. We find that despite mass transfer and sound excitations, the protocol achieves successful cooling during consecutive cycles: the first cycle lowers its temperature by ~20%, and a second cycle yields additional, though reduced, cooling, reaching a final ~27% cooling from the initial state. Our results show that interacting BECs can sustain finite-time
quantum thermal cycles under realistic conditions, and provide a platform for exploring different refrigeration schemes, optimized control protocols, and shortcuts to adiabaticity.
Read the full abstract ▾
All authors Joaquín I. Ganly, Julián Amette Estrada, Franco Mayo, Augusto J. Roncaglia, Pablo D. Mininni
Strongly Correlated Electrons
$Z_3$ confined and deconfined Coulomb liquids in $S_{\rm eff} = 3/2$ pyrochlore magnets
Jay Pandey, Souvik Kundu and Kedar Damle
We identify an interesting regime in the physics of pyrochlore magnets in which
spin-orbit and
crystal field effects lead to two low-lying
magnetic doublets that can be modeled as an effective
spin $S=3/2$ degree of freedom that sees a dominant easy-axis
antiferromagnetic exchange $J>0$ favoring the local $[111]$ axes, which competes with a comparably strong single-ion anisotropy $\Delta = J+\mu/2$ (with $|\mu| \ll J$) favoring the perpendicular planes. For a precise analysis, we study the $T/J \rightarrow 0$ limit in which $w \equiv \exp(-\mu/T)$ is the control variable. In this limit, we find two topologically distinct zero-field Coulomb phases separated by a first-order $Z_3$ confinement transition at $w_c \approx 2.02$. Both Coulomb phases admit a description in terms of the fluctuations of a coarse-grained divergence-free polarization field. However, the flux of this polarization field is restricted to integer multiples of $3$, and only charges that are multiples of 3 are deconfined in one of these phases, while all integer fluxes are allowed and all integer charges are deconfined in the other phase. Experimental systems with small negative $\mu$ (i.e., $-J \ll \mu < 0$) are therefore predicted to exhibit signatures of this topological transition when cooled below $T_c \approx 1.42|\mu|$.
Read the full abstract ▾
Disordered Systems and Neural Networks
Dynamics of neural scaling laws in random feature regression with powerlaw-distributed kernel eigenvalues
Jakob Kramp, Javed Lindner and Moritz Helias
Training large neural networks exposes neural scaling laws for the generalization error, which points to a universal behavior across network architectures of learning in high dimensions. It was also shown that this effect persists in the limit of highly overparametrized networks as well as the Neural network Gaussian process limit. We here develop a principled understanding of the typical behavior of generalization in Neural Network Gaussian process regression dynamics. We derive a dynamical mean-field theory that captures the typical case learning dynamics: This allows us to unify multiple existing regimes of learning studied in the current literature, namely
Bayesian inference on Gaussian processes, gradient flow with or without weight-decay, and
stochastic Langevin training dynamics. Employing tools from statistical physics, the unified framework we derive in either of these cases yields an effective description of the high-dimensional microscopic behavior of networks dynamics in terms of lower dimensional order parameters. We show that collective training dynamics may be separated into the dynamics of N independent eigenmodes, those
evolution equations are only coupled through collective response functions and a common statistics of an effective, independent noise. Our approach allows us to quantitatively explain the dynamics of the generalization error by linking spectral and dynamical properties of learning on data with power law spectra, including phenomena such as neural scaling laws and the effect of early stopping.
Read the full abstract ▾
Materials Science
Tracking the Lithiation State of Li$_x$Si from Machine-Learned XPS Binding Energies
Michael Alejandro Hernandez Bertran, Davide Tisi, Federico Grasselli et al. (+3 more)
X-ray Photoelectron Spectroscopy (XPS) is a powerful technique to probe chemical states and interfacial processes in battery materials, but a quantitative interpretation is often hindered by the complex, heterogeneous microstructures that form during operation and dominate electrochemical cycling. Silicon based anodes represent a paradigmatic example in Li batteries, as (de)lithiation proceeds through the formation of strongly disordered Li$_x$Si phases and
crystal-amorphous transformations that are hard to characterize. Here, we introduce a computational framework that combines machine-learning (ML) prediction of core-level binding energies to large-scale atomistic simulations – Grand Canonical Monte Carlo (GCMC) complemented with molecular dynamics (MD), driven by a ML potential – for a systematic sampling of lithiation states and local atomic environments. This approach yields stoichiometry maps that match the characteristic experimental trends observed in operando and ex situ XPS measurements, including the distinctive Si $2p$ spectroscopic signatures associated with the
crystal-to-amorphous disordering driving early delithiation.
Read the full abstract ▾
All authors Michael Alejandro Hernandez Bertran, Davide Tisi, Federico Grasselli, Michele Ceriotti, Elisa Molinari, Deborah Prezzi
Quantum Gases
Equal-spin and opposite-spin density-density correlations in the BCS-BEC crossover: Gauge Symmetry, Pauli Exclusion Principle, Wick's Theorem and Experiments
Nikolai Kaschewski, Axel Pelster and Carlos A. R. Sá de Melo
We develop a general theory of
spin-dependent density-density correlations, that is valid for any temperature, interactions, dimensions and mass or population status of
Fermi gases with two internal states. We use gauge invariance and the Pauli principle to establish constraints on the
spin-dependent density-density correlations that are consistent with the fluctuation-dissipation and Wick's
theorem. As an example, we study the
spin-dependent density-density correlations from the BCS to the Bose regime in two dimensions at zero temperature, inspired by experiments in 6Li. We show that two-particle irreducible contributions involving collective excitations, many-particle scattering and vertex corrections, are essential to describe experiments. In particular they turn out to be responsible for the emergence of an experimentally observed minimum in the opposite-
spin density-density correlations.
Read the full abstract ▾
Materials Science
Highly Efficient Second/Third Harmonic Generation in van der Waals Layered Material AgScP2S6 with Anisotropic Polarization and Temperature Dependence
Mohamed Yaseen Noor, Ryan Siebenaller, Wenhao Liu et al. (+12 more)
Single-
crystal X-ray diffraction and nonlinear optical measurements, especially second- and third-harmonic generation (SHG/THG) are comprehensively investigated for the van der Waals layered material AgScP2S6 with a non-centrosymmetric P31c (159) space group. Linear optical constants are extracted using spectroscopic ellipsometry and applied in fitting the harmonic generation behavior. Polarization-resolved SHG and THG measurements exhibit pronounced anisotropy, with emission patterns well-described by theoretical models derived from the khi(2) and khi(3) tensor elements. The material demonstrates exceptionally high nonlinear susceptibilities, with khi(2) ~ 10^(-8) m/V and khi(3) ~ 10^(-17) m^2/V^2 which is a few orders of magnitude greater than comparable 2D materials reported in the literature. Temperature-dependent SHG and THG measurements from 300 K to 25 K reveal exponential decay in harmonic signal intensities, attributed to reduced carrier mobility, with no evidence of structural phase transitions, consistent with results from single
crystal diffraction and heat capacity measurements. Polarization-resolved SHG and THG measurements also reveal distinct orientation and ellipticity trends, highlighting the anisotropic nonlinear tensor contributions and contrasting polarization selection rules in the material. These results establish AgScP2S6 as a high-performance, thermally stable, and highly anisotropic nonlinear candidate material suitable for compact photonic applications such as ultrafast optical modulators, polarization-sensitive detectors, and wavelength-tunable light sources.
Read the full abstract ▾
All authors Mohamed Yaseen Noor, Ryan Siebenaller, Wenhao Liu, Zixin Zhai, Conrad Kuz, Simin Zhang, Mousumi Upadhyay Kahaly, Gergely Nagy, Aamir Mushtaq, Rahul Rao, Emmanuel Rowe, Benjamin S. Conner, Bing Lv, Michael A. Susner, Enam Chowdhury
Strongly Correlated Electrons
Quantum magnetic phase transitions in a Kugel-Khomskii model including spin-orbit coupling
D. E. Chizhov, P. A. Igoshev and V. Yu. Irkhin
Using the formalism of pseudospin and isospin operators the
Hamiltonian of an effective Kugel-Khomskii model with
spin-orbit coupling is derived with an exact account of the $t_{2g}$ multiplet splitting by the
crystal field. An analytical solution is obtained for an arbitrary relation between the Hubbard repulsion and
crystal field splitting, i.e., interpolating the cases of Mott-Hubbard and charge-transfer
insulators. A description of orbital orders is given in terms of octupole moments. The ground-state phase diagram is constructed in the parameter space spanned by
spin-orbit coupling, Hund's exchange, and Hubbard interaction. We investigate a
quantum phase transition between a state exhibiting hidden
magnetic and orbital long-range order and a
ferromagnetic state with a reduced
magnetic moment accompanied by antiferroorbital order. It is shown that the cooperative effect of Hund's and
spin-orbit interactions gives rise to an easy-plane-type anisotropy.
Read the full abstract ▾