Strongly Correlated Electrons · Cross-listed from hep-th
Why Cooper pairs live in AdS2: a spectral analysis of the Yukawa-SYK model
Veronika Carolin Stangier and Jörg Schmalian
We establish the spectral foundation of the
geometric formulation of Cooper pairing in the Yukawa–Sachdev–Ye–Kitaev model. Starting from the large-$N$ bilocal effective action, we derive the Gaussian fluctuation kernel in the even-frequency
spin-singlet Cooper channel. Following the construction of Maldacena and Stanford, we determine the kernel
eigenvalue $k\left(h\right)$ analytically for arbitrary conformal weight $h$ and resolve the pairing fluctuations into the continuous and discrete sectors of the associated de-Sitter space
Laplacian. We show that the superconducting instability and the universal low-energy fluctuations near it reside entirely in the continuous scattering sector, while the discrete modes remain non-critical. Expanding the kernel about the lowest continuum mode yields a Klein–Gordon action on ${\rm dS}_2$, restricted to the continuous spectral subspace. This is precisely the subspace on which the inverse Radon transform to ${\rm AdS}_2$ is well defined. The projected bilocal Cooper-pair field can therefore be mapped onto a scalar matter field propagating in ${\rm AdS}_2$, without requiring any further spectral restriction on the bulk theory. Our results provide the missing microscopic justification for the projection implicit in earlier holographic formulations and clarify how a local bulk field emerges from the bilocal pairing theory.
Read the full abstract ▾
Superconductivity
Exact pair density wave in topological moire flat bands and universal superfluid stiffness
Zhengzhi Wu, Ming-rui Li and Hong Yao
Pair-density waves (PDWs) are unconventional superconducting states beyond the BCS paradigm, but identifying them unambiguously in microscopic
lattice models is generally challenging due to various competing orders. In particular, an exact realization of PDW in interacting models with topological bands remains elusive. Here we construct an interacting model on a twisted bilayer checkerboard
lattice (TBCB) featuring topological flat bands, and rigorously show that an exact PDW ground state can be induced by
quantum geometric nesting (QGN), owing to its momentum-space nonsymmorphic
symmetry. We further prove that the superfluid stiffness of any nondegenerate QGN
superconductor (including the PDW studied here and uniform
superconductor) obeys the universal relation $D_s=2N_{\rm flat}\nu(1-\nu)m_{\rm pair}^{-1}$, where $N_{\rm flat}$, $\nu$, and $m_{\rm pair}$ are the number of flat bands, flat band filling, and the two-particle effective mass, respectively. Our results reveal a rich interplay among PDW order,
quantum geometry, and band
topology.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from quant-ph
Least Variable Quantum Counting Processes
Bita Olamaei, Florian Meier, Costantino Budroni et al. (+2 more)
Counting processes provide a fundamental description of
stochastic events ranging from
photon detection to clock ticks. A central question is how accurately such events can be timed when only finite
memory resources are available. Here, we investigate this problem within a general framework of finite-dimensional classical and
quantum counting processes. We derive a rigorous finite-
memory variance bound obeyed by every classical $d$-state counting process, which is tight and saturated by a discrete Erlang-type ladder process. Through numerical optimization, we identify
quantum counting processes that violate this classical bound, achieving smaller first-tick fluctuations than any classical process with the same
memory size and mean tick time. For the
qubit case, we further derive an analytical large-mean bound within a single-Kraus no-tick family, showing that the
quantum advantage persists asymptotically within this class. The optimized
quantum processes exhibit coherent conditioned dynamics and approach a continuous-time
quantum-jump description as the mean increases. Our results establish a finite-
memory quantum advantage in temporal precision and connect discrete-time counting processes with continuous-time
quantum timekeeping.
Read the full abstract ▾
All authors Bita Olamaei, Florian Meier, Costantino Budroni, Pharnam Bakhshinezhad, Giuseppe Vitagliano
Materials Science
When chemical potential continuity fails: kinetic interface models for hydrogen isotope transport
Remi Delaporte-Mathurin and James Dark
Macroscopic hydrogen transport codes model material interfaces with local thermodynamic
equilibrium (LTE), imposing continuity of chemical potential as a per-species constraint. Three assumptions hide in that condition: fast interfacial equilibration, a single exchange pathway between the two sides, and a carrier species known in advance on each side. The literature scrutinises the first, but the other two are the more consequential failures, and neither survives at a metal/molten-salt interface. We replace the constraint with reversible reaction channels at the interface that obey mass action, with detailed balance fixing each ratio of rate constants from the thermodynamic data that already parameterise LTE, and we implement the framework in festim. LTE is recovered as the fast-kinetics limit of a single channel, in both its Sieverts/Sieverts and its Sieverts/Henry form, so the framework generalises LTE and does not compete with it. A Damköhler number delimits validity within a channel, a branching ratio between channels. In a representative nickel/FLiBe system, hydrogen partitions kinetically between molecular and fluoride carriers. The apparent interfacial law then drifts between Sieverts and Henry with loading and salt redox state, and an LTE condition underestimates the steady permeating flux. The measured pressure exponent is set by the branching ratio, not by any fixed property of the salt; a redox sweep at fixed temperature should continuously shift it between 0.5 and 1. With two isotopes, two metal-side species feed five salt-side carriers, and a per-species LTE condition is ill-posed.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Multicomponent Magnetic Domain Walls in Rhombohedral Graphene
Mainak Das, Nemin Wei and Chunli Huang
Spatial textures of
magnetic order, such as domain walls and skyrmions, are fundamental objects in magnetism. In rhombohedral multilayer
graphene,
magnetic order involves
spin and valley degrees of freedom, opening the possibility of qualitatively new spatial textures. Here, we explore this possibility through a microscopic study of a one-dimensional domain wall in the valley-imbalanced quarter-metal phase of rhombohedral
graphene. We uncover two different classes of domain walls. One resembles a conventional
magnetic domain wall, locally rotating between the two bulk states, whereas the other is intrinsically multicomponent and explores states that are not occupied in either bulk domain. Which texture is realized is controlled by the competition between intervalley Hund's coupling and
spin-orbit coupling, and we identify experimental signatures to distinguish them. For a superconducting junction formed across the wall, we further show that the superconducting phase difference couples directly to the intervalley-coherent phase of the texture, allowing precession of this internal phase to generate a voltage. This mechanism provides an explanation for the resistive domain walls recently observed in chiral
superconductors [arXiv2605.13303] and predicts accompanying magnetization oscillations that could be detected using GHz-frequency AC probes. Our theory establish a microscopic connection between multicomponent
magnetic textures, their internal dynamics, and superconducting transport.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Viscochiral Transport: Chiral Selection of Hydrodynamic Vortices by Berry Curvature
Archisman Panigrahi and Khachatur Nazaryan
We predict a new viscochiral regime of electronic transport in which spatially varying Hall viscosity selects vortical flow patterns. Although uniform Hall viscosity cannot alter incompressible bulk flow, its spatial gradient redistributes vorticity, amplifying
vortices in one chamber while suppressing the
vortex in the other. We further determine the underlying mechanism to be generic to recirculating flows and insensitive to the details of the device geometry. The paper maps the resulting phase diagram and shows that the regime is experimentally accessible in valley-polarized bilayer
graphene.
Read the full abstract ▾
Quantum Gases
Exact quantum geometry from sublattice symmetry: Closed-form solution of the quarter-flux Harper-Hofstadter model
Isaac Tesfaye and André Eckardt
Quantum geometry has emerged as a guiding principle across atomic and condensed-matter physics, shaping the topological responses of Bloch bands and the stability of the correlated phases they host. Sublattice
symmetry, though common among bipartite
lattice models, has not yet been exploited to obtain closed-form
quantum geometry in multiband systems. For this purpose, we derive a general expression for the QGT of sublattice-symmetric systems in terms of contributions from the individual sublattice sectors, and show that this
symmetry renders the Bloch
Hamiltonian of a paradigmatic four-band model, the quarter-flux Harper-Hofstadter model, anti-block-diagonal, analytically yielding the spectrum, eigenstates, and full
quantum geometric tensor (QGT), including the Berry
curvature and
quantum metric, for all four bands. The model, describing charged particles on a two-dimensional square
lattice subjected to a uniform
magnetic field, has recently been realized experimentally with ultracold atoms,
photons, and superconducting
circuits. Finally, we evaluate fractional-Chern-
insulator stability criteria analytically and quantify the lowest band of the quarter-flux Harper-Hofstadter model to be a nearly ideal Chern band. Our approach opens a route for studying also the
quantum geometry of other sublattice-symmetric multiband systems.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from quant-ph
Yang-Lee Criticality as a Dissipative Dynamical Phase Transition: Quantum Simulation of non-Hermitian Physics without Post-selection
Stephen W. Yan
We show that the $d+0$-dimensional Yang-Lee theory describing classical Ising
spins in an imaginary
magnetic field can be realized, without post-selection, within a $(d-1)+1$ open
quantum system whose dynamics consist of local
unitaries and engineered dissipation. Competition between the coherent
unitary and dissipative dynamics drives a transition wherein the time-dependence of a particular class of linear observables changes from damped oscillatory "underdamped" to purely exponential "overdamped" decay. Our construction relies on an extensive number of weak-
symmetries of the Lindbladian fixed by the choice of observable but is otherwise exact. Consequently, we show that the dynamics are described by the non-Hermitian generator of the Yang-Lee transfer
matrix, leading to an effective Yang-Lee theory defined on the spacetime history of the open system. By locally modifying the dynamics, we directly measure
spin correlation functions of the Yang-Lee theory as well as a related "Loschmidt Echo" correlator which we detail. We explicitly show that the required dissipation channels can be obtained through local $2$-
qubit gates and discuss potential realization on near-term
quantum simulator devices. Finally, we generalize our construction to embed arbitrary non-Hermitian
Hamiltonians within an open
quantum system under Lindbladian time-
evolution without post-selection, drawing connections between unconditional open
quantum dynamics, exceptional point physics, and non-
unitary statistical mechanics.
Read the full abstract ▾
Materials Science · Cross-listed from cs.AI
SwarmWorld: Stigmergic technological evolution in societies of language-model agents
Subhadeep Pal, Fiona Y. Wang and Markus J. Buehler
Collective intelligence can emerge when individuals coordinate through a shared environment, allowing local actions to accumulate into durable social organization.
Language-model
agents offer a new substrate for this process, yet most multi-
agent systems rely on direct conversation, predefined roles, or centralized workflows. It remains unclear whether decentralized
agents can build functional technologies and outperform independent search. Here, initially homogeneous LLM
agents in SwarmWorld self-organize without assigned roles or recipes into evolving technological societies.
Agents explore a spatial environment, process resources, test materials, construct persistent artifacts, and write executable controllers evaluated by a deterministic simulator under unseen disturbances after the
agents are removed. SwarmWorld splits cognition from consequence:
agents propose architectures and controllers within fixed action and material schemas, while the simulated world determines function. Shared societies develop broader, more resilient technological portfolios than a strong best-of-N isolated-search baseline, although isolated search remains competitive for the strongest artifact.
Agents differentiate into exploration, construction, maintenance, and coordination behaviors, transitioning as the world matures. Technologies accumulate through collaborative construction, executable inheritance, and persistent
agent-artifact networks, with most reuse beginning through physical observation rather than communication. Explicit cultural mechanisms amplify collaboration and organization, but functional benefits depend on outcome and timescale. Physical stigmergy alone supports capable societies, while interaction drives persistent technological ecologies rather than universally superior individual inventions.
Read the full abstract ▾
Strongly Correlated Electrons
Parity Anomaly as Modular Commutator with Massless Dirac Fermion
Meng Zeng
The modular commutator $J(A,B,C) = i\langle[K_{AB},K_{BC}]\rangle$ extracts the chiral central charge $c_-$ from a single bulk wavefunction of a gapped 2d state, where $3J/\pi=c_-$. Inspired by the recent developments in the field of gapless
symmetry-protected topological phases, we ask: what does the modular commutator measure, if it is well-defined at all, when the 2d bulk becomes gapless? Several interesting new insights can already be obtained using the simple Haldane honeycomb model. For the critical point hosting an isolated Dirac node we find that $J$ remains sharp: it converges to a half-quantized value, with corrections that decay as a power law in the subsystem size rather than exponentially, mirroring the power-law correlations in gapless systems. We prove the half-quantization using an emergent reflection
symmetry of the massless Dirac cone, and show that the half-quantized contribution comes from the other gapped cone (the massive partner of the massless one). This massive partner can be interpreted as the physical incarnation of the Pauli-Villars regulator, which is the origin of the parity-breaking level-$\frac{1}{2}$ Chern-Simons term (with half-quantized Hall conductance) and the parity anomaly. When protected chiral edge modes coexist with a bulk Dirac node we obtain $3J/\pi = c_-+\frac{1}{2}$. The half-quantization is also shown to be robust against tripartition deformation, tuning Dirac velocity and Dirac cone anisotropy. We further investigate other types of gaplessness—quadratic nodes (in contrast to linear Dirac) and the case with Fermi surface—and show that the robust half-quantization of $J$ is lost in such non-Dirac cases. These results generalize the modular commutator beyond gapped phases, and at the same time provide an information-theoretic measurement of the parity anomaly.
Read the full abstract ▾
Strongly Correlated Electrons
Incommensurate spin fluctuations in one-dimensional Kondo metal CeCo2Ga8
Yixuan Huang, P. Murgatroyd, Yi Wu et al. (+15 more)
We present an experimental and numerical study of the
spin fluctuations in 1D Kondo metal CeCo$_2$Ga$_8$. Using inelastic
neutron spectroscopy, we measure highly one-dimensional magnetism with low-energy incommensurate short-ranged
magnetic fluctuations. ARPES similarly shows a highly one-dimensional electronic band structure, confirming the one-dimensional nature of the system. We use density
matrix renormalization group (DMRG) simulations of the 1D Kondo
lattice model to interpret the measured spectrum, which successfully reproduce the
neutron scattering features. We are thus able to place CeCo$_2$Ga$_8$ within the emergent incommensurate phase of the 1D Kondo
lattice phase diagram, and demonstrate that the Kondo
lattice simulated non-perturbatively is an accurate microscopic model for heavy
fermion physics. This shows CeCo$_2$Ga$_8$ to be one-dimensional despite its complexities, and reveals a coexistence of low-energy Kondo and
magnetic features in its inelastic spectrum.
Read the full abstract ▾
All authors Yixuan Huang, P. Murgatroyd, Yi Wu, M. Cook, P. F. S. Rosa, E. D. Bauer, Asish K. Kundu, A. Rajapitamahuni, E. Vescovo, S. Zhang, V. Anil, P. Piyawongwatthana, N. Murai, M. Kofu, K. M. Shen, F. Ronning, Jian-Xin Zhu, A. Scheie
Materials Science · Cross-listed from physics.geo-ph
Lab earthquakes confirm the theory of frictional slip pulses
Alina Shafir, Tom Gabrieli, Yuval Tal et al. (+1 more)
Large natural earthquakes are typically mediated by frictional pulse-like rupture, which features a finite slipping zone. Recently, a comprehensive two-dimensional theory of frictional slip pulses has been developed. It predicts that pulses are categorically unstable rupture modes, whose
evolution is intrinsically slow. Unsteady pulses satisfy an equation of motion expressed in terms of discrete observables, which is inherently related to their steady-state counterparts. The theory also predicts a transition from decaying to slowly growing pulses. Here, we perform extensive lab earthquake experiments to test the theory. The experiments confirm the theoretical predictions for pulse-like lab earthquakes over a range of prestress levels, rupture nucleation conditions and small-scale fault roughness amplitudes. Specifically, the predicted time-dependent dynamics are tested in a plane defined by the evolving pulse size and peak slip rate, along with measurements of the dimensionless growth rate of pulses, demonstrating their intrinsically slow unsteady nature. The predicted transition between decaying and growing pulses is also experimentally demonstrated. These results constitute major progress in understanding a dominant earthquake rupture mode.
Read the full abstract ▾
All authors Alina Shafir, Tom Gabrieli, Yuval Tal, Eran Bouchbinder
Mesoscale and Nanoscale Physics
Depth Control of Room-Temperature Quantum Emitters in Gallium Nitride
Alexandros Bampis, Johann Stachurski, Anna Schwab et al. (+3 more)
Bright
quantum emitters are key components for
quantum communication systems. Radiative point defects in gallium nitride (GaN) are promising candidates for room-temperature single-
photon emission, operating from the visible to the telecom O-band. Despite their potential, their integration into photonic structures has remained limited in the literature, with experimental
photon extraction efficiencies far below simulated predictions. To identify the origin of this limitation, we investigate visible and near-infrared
quantum emitters in GaN epilayers grown on $c$-plane sapphire substrates exhibiting narrow linewidths ($\sim$4 nm), high
photon count rates ($ > $2 MHz), and strong antibunching, reaching $g^{(2)}(0)$ values as low as 0.06 at room temperature. We find that these emitters are located near the GaN/substrate interface, explaining their limited coupling to optical modes. Building on this observation, we show that the insertion of a thin low-temperature GaN interlayer enables the formation of
quantum emitters at arbitrary depths with sub-60 nm accuracy, independent of the substrate. The intentionally introduced emitters retain optical properties comparable to naturally occurring ones, including narrow linewidths ($\sim$6 nm), saturation count rates exceeding 1.5 MHz, high Debye-Waller factors (0.69-0.98), and strong antibunching. The resulting epilayer fully coalesces within less than 250 nm ensuring compatibility with GaN-based cavity fabrication and enabling emitter placement within intrinsic regions of p-i-n diode architectures. These results mark a decisive step toward efficient emitter-cavity coupling, enabling the realization of cavity-enhanced
quantum emission in GaN.
Read the full abstract ▾
All authors Alexandros Bampis, Johann Stachurski, Anna Schwab, Jean-François Carlin, Raphaël Butté, Nicolas Grandjean
Statistical Mechanics
Topology of Fluctuation Bands in Chiral Active Crystals
Raphaël Maire
While band
topology is usually associated with the deterministic dynamics of a system, we show that it can instead reside in its fluctuations. Using a reciprocal
lattice driven by nonequilibrium chiral active noise, we find that the displacement spectrum—which quantifies displacement fluctuations—admits bands with nonzero Chern numbers despite a Chern-trivial deterministic mechanics. A two-band valley theory captures the emergence of this
topology through a Dirac mass inversion, a Haldane-type mechanism, or a quadratic band touching, depending on the relevant transition. Through the bulk–boundary correspondence, we find boundary-localized fluctuation modes that are distinct from the usual propagating mechanical edge states.
Read the full abstract ▾
Materials Science · Cross-listed from physics.plasm-ph
Experimental Characterization of Additively Manufactured Metallic Alloys for Electric Propulsion Applications
J. Chamberlain and A. Shashurin
This work explores the sputtering of additively manufactured (AM) materials for use in gridded ion source applications. The first part of the paper uses 316L stainless steel as an example to demonstrate that additively manufactured material does not exhibit adverse sputtering behavior, such as higher sputter yield, compared with conventionally manufactured material. To this end, three additively manufactured 316L stainless steel samples were exposed to the beam of a KDC-40 electrostatic gridded ion source at three distinct energy levels of 400, 600, and 800 eV on each side of the sample for a duration of one hour. The samples were masked to create a distinct boundary between treated and untreated regions, identifiable using profilometry, and were biased to -18V for testing. Samples were then examined using a Bruker optical profilometer and further processed using the open-source software Gwyddion to evaluate the sputtering yield. The sputter yield varied in the range 0.2-2 atoms/ion for 400-800 eV ions and increased with ion energy. The measured sputtering yield was fairly consistent with predictions from analytical models developed in prior literature, while exhibiting some variations potentially due to added effects of increased temperature and oxide layers. The second part of the paper demonstrates feasibility of using an additively manufactured tungsten-rhenium grids in existing KDC-40 electrostatic gridded ion source.
Read the full abstract ▾
Superconductivity
Electrical manipulation of oxygen stoichiometry in multiterminal YBa$_2$Cu$_3$O$_{7-\delta}$ junctions
Daniel Stoffels, Caio C. Quaglio-Gomes, Nicolas Lejeune et al. (+7 more)
Local manipulation of oxygen stoichiometry offers a route to control the electronic properties of complex oxides, yet the selective modification of individual current-carrying branches through oxygen redistribution remains unexplored in multiterminal high-temperature superconducting junctions. In a YBa$_2$Cu$_3$O$_{7-\delta}$ Y-shaped three-terminal device, we demonstrate the possibility to electrically control oxygen vacancy migration on a hand-picked terminal while largely preserving the other two. Oxygen-depleted propagating fronts are directly visualized by the resulting change in optical reflectivity and they are linked to the
evolution of the electrical response. The process is highly directional and determined by the polarity of the applied current, allowing for the creation of either a converging or a diverging propagating front from the central node of the Y-shaped device. The associated changes in resistance exhibit relaxation on a timescale of minutes, driven by the vacancy concentration gradient. Effects of oxygen migration are also mapped by Kelvin Probe Force Microscopy and Scanning
Laser Microscopy, which probe work-function changes and spatially resolved variations in the superconducting transition, respectively. Notably, the Tc contrast revealed by the latter provides a quantitative handle on the underlying oxygen content, enabling direct visualization of oxygen redistribution. Finite-element modeling and nanoprobe X-ray diffraction qualitatively reproduce the observed vacancy redistribution. These results establish a post-fabrication route to locally tune properties of superconducting multiterminal devices such as nanocryotrons, yTron, and tunable weak links.
Read the full abstract ▾
All authors Daniel Stoffels, Caio C. Quaglio-Gomes, Nicolas Lejeune, Emile Fourneau, Pedro Schio, Huidong Li, Lourdes Fabrega, Anna Palau, Maycon Motta, Alejandro V. Silhanek
Soft Condensed Matter · Cross-listed from physics.flu-dyn
A Scalable OpenLB LAMMPS Framework for Fully Resolved Simulations of Hindered Settling of Arbitrary Non-Spherical Particles
Varghese Babu, Adrian Kummerländer, Mathias J. Krause et al. (+2 more)
Hindered settling of non spherical particles remains significantly less understood than spherical particles due to the computational challenges in resolving the complex contact mechanics and hydrodynamic interactions. In this paper, we present a scaleable fluid structure interaction (FSI) framework coupling the open-source LBM software in OpenLB with the Discrete Element Method (DEM) implemented in LAMMPS to simulate arbitrary shaped rigid bodies in a fluid. Particle contacts are captured using a multi-sphere "clump" representation in DEM, while particle geometries are resolved on the fluid grid via voxelization. We validate our model against single and multi-particle
benchmarks, and proceed to study the hindered setttling of cubes in systems containing upto 100,000 cubes. Our simulations show distinct differences between the settling of cubes and sphere, as cubes form pronounced coordination shells without face-parallel contact, in contrast to the contact-dominated clustering observed in spheres. Our results find that correlation length in velocity fluctuations scale with system size even for the largest system studied. These findings highlight the role of particle morphology in suspension dynamics and demonstrate a robust framework for simulating large-scale geotechnical and particulate flows.
Read the full abstract ▾
All authors Varghese Babu, Adrian Kummerländer, Mathias J. Krause, Santosh Ansumali, Dilip Gersappe
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Immittance formulas for exact blackbox quantization and divergence-free effective models in circuit QED
Philippe Gigon, Peter Rabl and Adrian Parra-Rodriguez
Building on the first-order
circuit quantization method [arXiv:2304.12252, arXiv:2401.09120], we provide simple formulas to construct exact
Hamiltonians for Josephson-junction-based superconducting qudits capacitively, inductively, or galvanically coupled to passive linear environments. These environments may be multiport, multimode, discrete or continuous, reciprocal or nonreciprocal, and are characterized directly by their impedance or admittance
matrices. In the weak-coupling regime, we further derive divergence-free dispersive
Hamiltonians for mode-resolved environments and transition-resolved weak-coupling master equations for dissipative continua. Mode structure, frequency renormalizations, environment-mediated interactions, decay rates, and directional cross couplings then follow from the same causal immittance response, while spurious Lamb-shift divergences arising from uncontrolled approximations in previous treatments are made explicit and avoided. We apply the theory to a set of illustrative
circuits comprising a discrete resonator filter, finite-band metamaterial environments, nonreciprocal waveguide-QED systems, and superconducting giant atoms, for which analytical response
matrices can be obtained, although the method is particularly well suited to numerical responses from electromagnetic solvers or experimental characterization. We thereby extend the black-box quantization framework to multiport, dissipative, and nonreciprocal settings, establishing a simple and scalable route toward optimized and automated electromagnetic design of large-scale superconducting
quantum hardware.
Read the full abstract ▾
Materials Science
Electron spin resonance driven photogalvanic effect in graphene-based structures
C. Bray, I. Yahniuk, L. E. Golub et al. (+13 more)
We report an electron-
spin-resonance-driven linear photogalvanic effect (LPGE) in unbiased monolayer
graphene and WSe_2/
graphene heterostructures. Under linearly polarized 45–75 GHz radiation, the photovoltage exhibits pronounced resonant features in both Faraday and Voigt geometries. Multiple resonances associated with the electron
spin resonance in
graphene are observed for both out-of-plane and in-plane
magnetic-field orientations. Their
magnetic-field positions vary linearly with frequency, their amplitudes reverse sign across the charge-neutrality point, and the resonant contribution has the opposite sign to the nonresonant Drude photogalvanic background. We develop a microscopic theory in which radiation-induced momentum
alignment followed by skew scattering generates both contributions. Their opposite signs originate from the orthogonal momentum
alignments produced by indirect Drude absorption and direct
spin-resonant transitions. The theory describes well the main features of the observed resonant photocurrent and provides a microscopic description of ESR-induced LPGE in two-dimensional systems. These results establish the photogalvanic response as a probe of ESR in unbiased micron-scale
graphene-based devices.
Read the full abstract ▾
All authors C. Bray, I. Yahniuk, L. E. Golub, M. Marocko, C. Consejo, B. Benhamou-Bui, Ziyang Gan, A. George, A. Turchanin, P. Sadovyi, K. Watanabe, T. Taniguchi, J. Eroms, J. Fabian, F. Teppe, S. D. Ganichev
Materials Science
Oxidation-resilient structural modifications in Nickel-functionalized 3D-graphene for hydrogen storage applications
Filippo Fincato, Ylea Vlamidis, Markus Leitgeb et al. (+6 more)
Porous materials represent a versatile solution for several applications. Indeed, the recent development of a new material, named 3D-
Graphene, which combines the exceptional characteristics of
graphene with a three-dimensional structure, opens perspectives for applications where a high surface-to-volume ratio is beneficial. In this study, we explore the functionalization of 3D-
Graphene with nickel (Ni)-nanoparticles as a strategy to enhance hydrogen storage capabilities, and we assess the influence of the NPs on hydrogen uptake and oxidation resilience. The morphology and structural properties of pristine and Ni-functionalized samples were characterized using Scanning Electron Microscopy. Additionally, X-ray Photoelectron Spectroscopy was employed to analyze the surface chemical composition of the functionalized samples. Samples have been hydrogenated supplying molecular or atomic hydrogen, and hydrogen storage performance was assessed through Thermal Desorption Spectroscopy. Afterwards, oxidation effects were systematically studied by exposing the samples to atmospheric oxygen, followed by further hydrogenation experiments. Our results indicate that Ni functionalization influences both hydrogen adsorption and oxidation behavior, with potential implications for improving the stability of the material, especially for hydrogen storage applications.
Read the full abstract ▾
All authors Filippo Fincato, Ylea Vlamidis, Markus Leitgeb, Georg Pfusterschmied, Ulrich Schmid, Valentina Zannier, Silvia Rubini, Stefan Heun, Stefano Veronesi
Strongly Correlated Electrons
Rare-earth oxysulfides RE$_2$O$_2$S as model mixed-anion frustrated magnets
Austin M. Ferrenti, Ksenia Khoroshun, Mohamed Oudah et al. (+3 more)
The study of low-dimensional and anisotropic magnetism is a promising avenue for the discovery of novel
quantum phenomena. Mixed-anion materials, defined by the coordination of metal cations by two or more distinct anionic species, provide an intrinsically anisotropic platform for the tuning of structural,
magnetic, and electronic properties. In this work, we report the synthesis and characterization of a family of rare-earth oxysulfide (RE$_2$O$_2$S) antiferromagnets (AFM) possessing a triangular-bilayer slab
lattice geometry. Long-range AFM order is observed for the majority of compositions, with several (RE = Ce, Pr, Nd, Sm) having been previously unreported. Although assumed to form stoichiometrically, pair distribution function (PDF) analysis provides evidence for significant, synthesis-dependent interslab structural disorder as RE$_2$O$_{2+x}$S$_{1-x}$, resulting in significant variability in the bulk
magnetic response of the Nd member. This work highlights the tunability of frustrated
magnetic ground states in rare-earth-based mixed-anion materials, and the importance of thorough structural characterization in the discovery of new mixed-anion magnets.
Read the full abstract ▾
All authors Austin M. Ferrenti, Ksenia Khoroshun, Mohamed Oudah, Graham King, Jonathan Gaudet, Alannah M. Hallas
Superconductivity
Symmetry Origins of the Field-Free Superconducting Diode Effect in the Kagome Superconductor CsV$_3$Sb$_5$
Xin-Jie Liu, Shengbiao Sun, Ke-Fan Song et al. (+14 more)
Field-free superconducting diode effects require both inversion-
symmetry breaking and an internal time-reversal-
symmetry (TRS) breaking field, making them sensitive probes of hidden order in
superconductors. In centrosymmetric kagome AV$_3$Sb$_5$, the inversion
symmetry generally should generally preclude the observation of the superconducting diode effect. Furthermore, though TRS breaking has been reported in the superconducting regime of CsV$_3$Sb$_5$, whether it is generated by superconductivity or inherited from charge-density-wave (CDW) order remains unresolved. Here we show that pristine CsV$_3$Sb$_5$ devices exhibit no intrinsic field-free superconducting diode effect, whereas surface oxidation or asymmetric etching activates a large nonreciprocal supercurrent. Moreover, the response is
stochastic, with sweep-dependent polarity and magnitude, indicating metastable TRS-breaking domain configurations. Small out-of-plane
magnetic fields stabilize the superconducting diode response, consistent with field selection of such domains. Finally, when long-range CDW order is suppressed by Ti doping, the SDE disappears. Our results establish the
symmetry requirements for the field-free SDE in CsV$_3$Sb$_5$, reveal its
stochastic domain-controlled character, and link superconducting-state TRS breaking to CDW-related order.
Read the full abstract ▾
All authors Xin-Jie Liu, Shengbiao Sun, Ke-Fan Song, Jia-Peng Peng, Xilin Feng, Lang Xiao, Tong Liu, Qilin Han, Ya-Qing Bie, Ning Kang, Xiaosong Wu, Yanfei Wu, Shouguo Wang, Kam Tuen Law, Shuo Wang, Dapeng Yu, Ben-Chuan Lin
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
The Gain-Engineered Transmon
Ian Yang, Francesco Adinolfi, Alessandro Bruno et al. (+3 more)
The interaction between a
qubit and its environment can be engineered such that one error channel dominates over all others, resulting in noise bias. This property enables error correction codes to focus on the dominant error type, thereby significantly reducing the number of physical systems required for fault-tolerant
quantum computation. However, engineering noise bias typically introduces complexity at the physical system level, which decreases its usefulness by limiting scalability. Here, we introduce and experimentally realize a noise-biased
qubit in a standard transmon-readout resonator
circuit, one of the most common superconducting architectures, by only adding a single microwave tone. We encode the
qubit in the transmon $|\mathrm{g}\rangle$- and $|\mathrm{f}\rangle$-states, and engineer a frequency-selective gain channel that counteracts single-
photon loss errors between the computational states. We demonstrate an order-of-magnitude enhancement in relaxation time compared to the $|\mathrm{g}\rangle-|\mathrm{e}\rangle$ encoding, conceding only a factor-of-two decrease in the echo-coherence time. Furthermore, we show that this
qubit is compatible with fast, high-fidelity operations. Our results open a path towards using this system as a simple building-block for hardware-efficient
quantum error detection and correction schemes.
Read the full abstract ▾
All authors Ian Yang, Francesco Adinolfi, Alessandro Bruno, Venus Hasanuzzaman Kamrul, Daniel Z. Haxell, Alexander Grimm
Materials Science
Bayesian Optimization for Self-Driving Materials Laboratories: From Algorithms to Physics-Informed Workflows
Yuki K. Wakabayashi and Takuma Otsuka
Self-driving laboratories (SDLs) are transforming materials research by closing the loop among synthesis, characterization, data analysis and experimental decision making.
Bayesian optimization (BO) is a decision engine for these loops because it can select experiments from scarce and noisy data while balancing exploitation and exploration. Yet real materials campaigns often depart from the standard black-box setting, involving failed or missing experiments, noise and drift, mixed variables, constraints, multiple objectives, variable cost and fidelity, transfer from historical data, batch or asynchronous operation, and prior physics knowledge. This review presents BO for materials SDLs through the lens of these practical challenges. We summarize Gaussian-process-based BO and the formulation of materials goals as quantitative objectives, then discuss major choices in surrogate modelling and acquisition. Particular emphasis is placed on physics-informed
Bayesian optimization (PIBO), in which domain knowledge enters through representations, priors, kernels, acquisition functions, and constraints. We survey achievements enabled by BO and related active-learning approaches across
semiconductors, catalysis, chemical reactions, batteries,
alloys, functional materials and
quantum materials, highlighting advances beyond parameter optimization, including new materials and synthesis routes, improved functional performance, and reusable scientific knowledge. We conclude by outlining open problems for BO-driven materials SDLs, including nonstationarity,
multimodal observations, adaptive problem formulation, and scientific
reasoning by humans, large
language models and research
agents. Addressing these challenges may advance SDLs beyond efficient optimization toward interpretable and knowledge-generating experimentation.
Read the full abstract ▾
Materials Science
Watching a GaN Transistor Switch: Real-Time Nanoscale Strain and Heat Dynamics
C. Corley-Wiciak, N. T. Sammler, B. Butej et al. (+16 more)
Digital and energy technologies depend on microelectromechanical and power electronic components whose performance is critically impacted by rapid, cyclic deformations. Real-time information on their operation has remained inaccessible due to the need for nanosecond and nanometer resolution in fully integrated devices. We break this limitation by imaging the complete switching cycle of an industrial GaN high electron mobility transistor through stroboscopic dark field X ray microscopy at a fourth-generation synchrotron, resolving electromechanical and thermal micro strain fields across the entire device and correlating them with time dependent voltage characteristics. Coupled simulations benchmarked against the measurements reproduce electric field
evolution and transient thermal hotspots. This combined approach provides direct insight into device physics and informs design strategies for next generation energy and information processing technologies.
Read the full abstract ▾
All authors C. Corley-Wiciak, N. T. Sammler, B. Butej, M. Petersmann, A.A. Corley-Wiciak, L. Neumann, Juan M. Carrillo-Larrea, P. Schmiedeke, M. Strätgen, P. A. Douissard, S. J. Leake, P. Boesecke, M. Sievers, P. Imrich, M. Nelhiebel, M. Glavanovics, D. Pogany, M. Reisinger, T.U. Schulli
Other Condensed Matter
Landau Theory for Commensurate Charge-Density Waves Coupled to Uniform Lattice Deformation
Keiji Nakatsugawa, Toshiyuki Fujii and Satoshi Tanda
We formulate a minimal Landau theory for a charge-density wave (CDW) whose commensurability is defined with respect to a deformed
lattice. The motivation is provided by recent observations on an isolated single NbS$_3$ chain, which exhibits a commensurate CDW state accompanied by a $6\%$ shrinkage of the
lattice constant. A uniform stretch $a_0\to a_0(1+\varepsilon)$ changes the reciprocal
lattice wave number to $G(\varepsilon)=G_0/(1+\varepsilon)$, so that an $N$-fold commensurate CDW has the wave number $Q_\mathrm{C}(\varepsilon)=G(\varepsilon)/N$, whereas the wave number $Q_\mathrm{IC}$ favored by the incommensurate instability remains fixed. We propose an amplitude-strain free energy for both $N=3$ and $N=4$, in which the CDW induces a finite uniform strain by relieving the mismatch between $Q_\mathrm{C}(\varepsilon)$ and $Q_\mathrm{IC}$. The mismatch is shared between the CDW and the
lattice in a proportion set by their stiffness ratio; since the CDW stiffness grows with the CDW amplitude, the
lattice takes up an increasing share of the mismatch as the CDW develops. Our results suggest a reexamination of lock-in theories and of strain-tuning experiments on density-wave systems.
Read the full abstract ▾
Superconductivity
Fluxtube Bouquets and Type-1.5 Clustering in Superfluid Neutron Star Cores
Adarsh Karekkat, Gabriele Montefusco and Marco Antonelli
We study mesoscopic configurations of a
neutron superfluid coupled to a
proton superconductor in the outer core of a
neutron star. The condensates are described by a two-component Ginzburg-Landau free energy with local couplings, neglecting genuine phase-gradient entrainment. In two spatial dimensions, we minimize the free energy using quasi-periodic boundary conditions and constrained phase-imprinting calculations to study
vortex-fluxtube and fluxtube-fluxtube interactions. We find that, for locally attractive couplings in the free energy,
vortex-fluxtube overlap is energetically favoured and several pre-existing
proton fluxtubes can bind around a
neutron vortex, forming finite
vortex-centred aggregates that we call fluxtube bouquets. These bouquet configurations may become so dense that a
vortex can effectively accommodate several quanta of
magnetic flux. We also confirm the possible presence of a type-1.5-like regime and find that it survives in the zero-entrainment regime considered here. In this type-1.5 regime, the fluxtube-fluxtube interaction is repulsive at short distances and attractive at intermediate distances, leading to self-assembled clusters while the individual fluxtubes remain topologically distinct. Possible implications for dissipative coupling and transport in
neutron stars are discussed.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Size and Impurity Effects on Scattering of Valley Hall Modes in Gate-Defined Bilayer Graphene Superlattices
Marcus N. Kanestrøm, Antonio L. R. Manesco and D. O. Oriekhov
In the present paper we perform a tight-binding simulation of gate-defined islands in Bernal bilayer
graphene (BLG). The inversion of the gap sign on the boundaries of the islands creates topologically-protected valley Hall modes. We focus on the specific questions of whether the valley Hall modes around such islands could serve as a host for
quantum walks or simulate weakly coupled systems, and how their tunneling is affected by in-gap impurities. In addition, we discuss the effect of misalignment of top and bottom gate patterns on the tunneling properties between islands. Our main results show that resonant tunneling via an impurity enhances overlap between superlattice islands, while misalignment does not break topological protection over a wide parameter regime. In addition, we study the two-island geometry and show that it is possible to leverage suppressed scattering to place islands more densely on a single sample.
Read the full abstract ▾
Strongly Correlated Electrons · Cross-listed from quant-ph
Eleonora Lamma, Tim Bauer, Marcello Dalmonte et al. (+1 more)
Quantum spin liquids (QSLs) are long-range entangled phases of matter and a natural setting for exploring how
quantum correlations generate
quantum complexity. Motivated by the emergence of magic, or nonstabilizerness, as a diagnostic of many-body complexity beyond
entanglement, we study magic of QSLs by computing the stabilizer Rényi
entropy (SRE) of the Kitaev honeycomb model. We derive a correspondence between Pauli strings and products of itinerant Majorana operators in the model's free-
fermion description; this enables the sampling of SRE using an optimized
algorithm for Gaussian states in systems with thousands of
spins. Our results show that magic is largest in the gapless phase, where subleading volume-law corrections indicate nonlocal contributions, while in the gapped phases, SRE decreases in quantitative agreement with a perturbative expansion that we develop in the anisotropic limit. At the topological phase transition, SRE exhibits universal scaling dictated by critical exponents.
Read the full abstract ▾
All authors Eleonora Lamma, Tim Bauer, Marcello Dalmonte, Mario Collura
Statistical Mechanics
Current fluctuations in a gas of active Ornstein-Uhlenbeck particles
Sandeep Jangid, Aman Kumbhakar, Juliane U. Klamser et al. (+1 more)
We investigate the statistics of the time-integrated current in an infinite one-dimensional gas of independent active Ornstein–Uhlenbeck particles, as a model system for studying an active generalisation of the corresponding passive (diffusive) phenomenology. Unlike the latter, where current fluctuations exhibit universal sub-diffusive scaling, active systems display diffusive, super-diffusive, and sub-diffusive regimes over different time scales. We fully characterise the distribution of current in terms of large-deviation asymptotics, showing that all of these scaling regimes are described by a single scaled cumulant generating function. Moreover, the statistics retain a dependence on the initial condition even at large times, revealing a persistent
memory of the initial state. We further obtain the joint large-deviation statistics of currents measured at two distinct times, characterising temporal correlations. Our analytical predictions are verified using rare-event importance sampling, which resolves probabilities as small as $10^{-1000}$.
Read the full abstract ▾
All authors Sandeep Jangid, Aman Kumbhakar, Juliane U. Klamser, Tridib Sadhu