Strongly Correlated Electrons
Sign-Resolved Statistics and the Origin of Bias in Quantum Monte Carlo
Ryan Larson, Rubem Mondaini and Richard T. Scalettar
Quantum simulations are a powerful tool for exploring strongly correlated many-body phenomena. Yet, their reach is limited by the
fermion sign problem, which causes configuration weights to become negative, compromising statistical sampling. In auxiliary-field
Quantum Monte Carlo calculations of the doped Hubbard model, neglecting the sign ${\cal S}$ of the weight leads to qualitatively wrong results – most notably, an apparent suppression rather than enhancement of $d$-wave pairing at low temperature. Here we approach the problem from a different perspective: instead of identifying negative-weight paths, we examine the statistics of measured observables in a sign-resolved manner. By analyzing histograms of key quantities (kinetic energy,
antiferromagnetic structure factor, and pair susceptibilities) for configurations with ${\cal S}=\pm1$, we derive an exact relation linking the bias from ignoring the sign to the difference between sign-resolved means, $\Delta\mu$, and the average sign, $\langle {\cal S}\rangle$. Our framework provides a precise diagnostic of the origin of measurement bias in
Quantum Monte Carlo and clarifies why observables such as the $d$-wave susceptibility are especially sensitive to the sign problem.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Configurable antiferromagnetic domains and lateral exchange bias in atomically thin CrPS4
Yu-Xuan Wang, Thomas K. M. Graham, Ricardo Rama-Eiroa et al. (+12 more)
Interfacial exchange coupling between antiferromagnets (AFMs) and ferromagnets (FMs) crucially makes it possible to shift the FM hysteresis, known as exchange bias, and to switch AFM states. Two-dimensional magnets unlock opportunities to combine AFM and FM materials; however, the buried AFM-FM interfaces obtained by stacking remains challenging to understand. Here we demonstrate interfacial control via intralayer exchange coupling in the layered AFM CrPS$_4$, where connected even and odd layers realize pristine lateral interfaces between AFM-like and FM-like regions. We distinguish antiphase even-layer states by scanning nitrogen-vacancy centre (NV) magnetometry due to a weak surface magnetization. This surface magnetization enables control over the even-layer state, with different regions switching at distinct fields due to their own lateral couplings. We toggle three AFM domains adjacent to a FM-like region and demonstrate a tunable multilevel exchange bias. Our nanoscale visualization unveils the microscopic origins of exchange bias and advances single two-dimensional
crystals for hybrid AFM-FM technologies.
Read the full abstract ▾
All authors Yu-Xuan Wang, Thomas K. M. Graham, Ricardo Rama-Eiroa, Md Ariful Islam, Mohammad H. Badarneh, Rafael Nunes Gontijo, Ganesh Prasad Tiwari, Tibendra Adhikari, Xin-Yue Zhang, Kenji Watanabe, Takashi Taniguchi, Claire Besson, Elton J. G. Santos, Zhong Lin, Brian B. Zhou
Mesoscale and Nanoscale Physics
High-order two-component fractional quantum Hall states around filling factor $\nu = 1$
E. Bell, K. W. Baldwin, L. N. Pfeiffer et al. (+2 more)
Two-component fractional
quantum Hall (2C-FQH) states in electron
bilayers have been known for decades, yet their experimental realization remained limited to low-order fractions. Here we report on several families of high-order 2C-FQH states that emerge when an in-plane
magnetic field drives a controlled monolayer-to-
bilayer transition in an ultra-high-mobility GaAs
quantum well. These families of states proliferate symmetrically toward the filling factor $\nu = 1$, from both $\nu = 2/3$ and $\nu = 4/3$, thereby respecting particle-hole
symmetry. Surprisingly, many unbalanced states (with unequal layer fillings) are more robust than their parent balanced states, defying the expected hierarchy of Jain sequences. Our findings substantially expand the known landscape of 2C-FQH states, highlighting the unexpected richness of the
bilayer quantum Hall regime and opening new routes for probing the interplay of
symmetry,
topology, and interactions in
quantum Hall systems.
Read the full abstract ▾
All authors E. Bell, K. W. Baldwin, L. N. Pfeiffer, K. W. West, M. A. Zudov
Materials Science
Machine Learning Pipeline for Denoising Low Signal-To-Noise Ratio and Out-of-Distribution Transmission Electron Microscopy Datasets
Brian Lee, Meng Li, Judith C Yang et al. (+2 more)
High-resolution transmission electron microscopy (HRTEM) is crucial for observing material's structural and morphological
evolution at Angstrom scales, but the electron beam can alter these processes. Devices such as CMOS-based direct-electron detectors operating in electron-counting mode can be utilized to substantially reduce the electron dosage. However, the resulting images often lead to low signal-to-noise ratio, which requires frame integration that sacrifices temporal resolution. Several machine learning (ML) models have been recently developed to successfully denoise HRTEM images. Yet, these models are often computationally expensive and their inference speeds on GPUs are outpaced by the imaging speed of advanced detectors, precluding in situ analysis. Furthermore, the performance of these denoising models on
datasets with imaging conditions that deviate from the training
datasets have not been evaluated. To mitigate these gaps, we propose a new self-supervised ML denoising pipeline specifically designed for time-series HRTEM images. This pipeline integrates a blind-spot convolution neural network with pre-processing and post-processing steps including drift correction and low-pass filtering. Results demonstrate that our model outperforms various other ML and non-ML denoising methods in noise reduction and contrast enhancement, leading to improved visual clarity of atomic features. Additionally, the model is drastically faster than U-Net-based ML models and demonstrates excellent out-of-distribution generalization. The model's computational inference speed is in the order of milliseconds per image, rendering it suitable for application in in-situ HRTEM experiments.
Read the full abstract ▾
All authors Brian Lee, Meng Li, Judith C Yang, Dmitri N Zakharov, Xiaohui Qu
Materials Science
Quantum theory of nonlinear phononics
Francesco Libbi and Boris Kozinsky
The recent capability to use THz pulses to control the
nuclear quantum degrees of freedom in
crystals has opened promising avenues for the advanced manipulation of material properties. While numerical approaches exist for studying the time
evolution of the
quantum nuclear density
matrix, an interpretable analytical framework to explicitly analyze the influence of
quantum fluctuations on
nuclear dynamics remains lacking. In this work, we present an analytical
quantum theory of nonlinear phononics. This framework is a basis for deriving models of realistic materials, allowing for exact solutions of the
nuclear time
evolution with full consideration of
quantum fluctuations. This is accomplished by treating for all possible third- and fourth-order
phonon couplings and expressing forces as analytic functions of such fluctuations. We provide an analytic proof that, in general, a strong pulse displacing a
phonon mode from
equilibrium induces the quenching, or squeezing, of its
quantum lattice fluctuations. This finding, which establishes a systematization of the mechanism observed in Ref. 1, introduces a new paradigm in nonlinear phononics, harnessing this cooling effect to drive
symmetry breaking in
quantum paraelectric materials.
Read the full abstract ▾
Disordered Systems and Neural Networks
Testing the Localization Landscape Theory on the Bethe Lattice
Lorenzo Tonetti, Leticia F. Cugliandolo and Marco Tarzia
The Localization Landscape Theory (LLT) provides a classical picture of Anderson localization by introducing an effective confining potential whose percolation is proposed to coincide with the mobility edge. Although this proposal shows remarkable numerical agreement in three dimensions, its fundamental validity remains unsettled. Here we test the LLT analytically on the Bethe
lattice, where both the Anderson localization transition and the LLT percolation problem are exactly solvable. We find that the two transitions do not coincide, and their critical behaviors differ markedly. In particular, LLT percolation displays standard mean-field percolation criticality that is fundamentally distinct from the peculiar critical behavior of the Anderson transition on the Bethe
lattice. Our results provide an exact
benchmark showing that, while geometrically intuitive, the LLT does not capture the true
quantum critical properties of localization.
Read the full abstract ▾
Materials Science
The Loss Landscape of Powder X-Ray Diffraction-Based Structure Optimization Is Too Rough for Gradient Descent
Nofit Segal, Akshay Subramanian, Mingda Li et al. (+2 more)
Solving
crystal structures from powder X-ray diffraction (XRD) is a central challenge in materials characterization. In this work, we study the powder XRD-to-structure mapping using gradient descent optimization, with the goal of recovering the correct structure from moderately distorted initial states based solely on XRD similarity. We show that commonly used XRD similarity metrics result in a highly non-convex landscape, complicating direct optimization. Constraining the optimization to the ground-truth
crystal family significantly improves recovery, yielding higher match rates and increased mutual information and correlation scores between structural similarity and XRD similarity. Nevertheless, the landscape may remain non-convex along certain
symmetry axes. These findings suggest that
symmetry-aware inductive biases could play a meaningful role in helping learning models navigate the inverse mapping from diffraction to structure.
Read the full abstract ▾
All authors Nofit Segal, Akshay Subramanian, Mingda Li, Benjamin Kurt Miller, Rafael Gomez-Bombarelli
Materials Science
Anisotropic Phonon Dynamics and Directional Transport in Actinide van der Waals Semiconductor USe$_3$
Aljoscha Söll, Valentino Jadrisko, Sourav Dey et al. (+13 more)
Direction-dependent charge transport and optical responses are characteristic of van der Waals (vdW) materials with strong in-plane anisotropy. While transition-metal trichalcogenides (TMTCs) exemplify this behavior, heavier analogs remain largely unexplored. In this study we examine USe$_3$ as an anisotropic vdW material and a heavier analog of the well-studied TMTCs. We reveal strong in-plane anisotropy using polarization-resolved Raman spectroscopy, investigate strain-induced shifts of
phonon modes, and quantify direction-dependent charge-carrier mobility through transport measurements on field-effect devices. First-principles calculations based on density-functional theory corroborate our findings, providing a theoretical basis for our experimental observations. Casting USe$_3$ as an actinide analog of a TMTC establishes a platform for exploring low-dimensional
semiconductors that combine strong in-plane anisotropy with f-electron physics.
Read the full abstract ▾
All authors Aljoscha Söll, Valentino Jadrisko, Sourav Dey, Nassima Benchtaber, Kalyan Sarkar, Borna Radatovic, Jan Luxa, Fedor Lipilin, Kseniia Mosina, Vojtech Kundrat, Jakub Zalesak, Jana Vejpravova, Martin Zacek, Christoph Gadermaier, José J. Baldoví, Zdeněk Sofer
Statistical Mechanics · Cross-listed from physics.comp-ph
Predicting parameters of a model cuprate superconductor using machine learning
V. A. Ulitko, D. N. Yasinskaya, S. A. Bezzubin et al. (+2 more)
The computational complexity of calculating phase diagrams for multi-parameter models significantly limits the ability to select parameters that correspond to experimental data. This work presents a machine learning method for solving the inverse problem -
forecasting the parameters of a model
Hamiltonian for a cuprate
superconductor based on its phase diagram. A comparative study of three deep learning architectures was conducted: VGG, ResNet, and U-Net. The latter was adapted for regression tasks and demonstrated the best performance. Training the U-Net model was performed on an extensive
dataset of phase diagrams calculated within the mean-field approximation, followed by validation on data obtained using a semi-classical heat bath
algorithm for Monte Carlo simulations. It is shown that the model accurately predicts all considered
Hamiltonian parameters, and areas of low prediction accuracy correspond to regions of parametric insensitivity in the phase diagrams. This allows for the extraction of physically interpretable patterns and validation of the significance of parameters for the system. The results confirm the promising potential of applying machine learning to analyze complex physical models in condensed matter physics.
Read the full abstract ▾
All authors V. A. Ulitko, D. N. Yasinskaya, S. A. Bezzubin, A. A. Koshelev, Y. D. Panov
Materials Science
Construction of minimal integrity basis for anisotropic hyperelasticity via structural tensors
Brain M. Riemer, Jörg Brummund, Karl A. Kalina et al. (+3 more)
We present minimal integrity bases for all common anisotropies in hyperelasticity via the structural tensor concept, which can be used to formulate any algebraic invariant function in the elements of the respective bases. Hence, the provided minimal integrity bases are of great interest for formulating a concise but general anisotropic material model. Our work covers results for the 11 types of anisotropy that arise from the classical 7
crystal systems, as well as findings for 4 additional non-
crystal anisotropies derived from the cylindrical, spherical, and icosahedral
symmetry systems. By using well-known results from literature about structural tensors, isotropic invariants, and isotropic extension, functional bases are directly determined. A simple analytical-numerical approach is employed to identify
polynomial relations between the invariants of these functional bases, thereby enabling the construction of functional bases of reduced cardinality. After that, we show that the determined reduced functional bases are also minimal integrity bases by identifying
polynomial relations to known integrity bases from literature. Furthermore, fundamental concepts from invariant theory, including the Hironaka decomposition of invariant rings and the closely related
Hilbert series, are employed to further validate the results. Alongside the presented findings, this article also aims to provide an introductory overview of the complex field of modeling anisotropic materials, especially for researchers with an engineering background.
Read the full abstract ▾
All authors Brain M. Riemer, Jörg Brummund, Karl A. Kalina, Abel H. G. Milor, Franz Dammaß, Markus Kästner
Materials Science
Non-radiative energy transfer between boron vacancies in hexagonal boron nitride and other 2D materials
Jules Fraunié, Mikhail M. Glazov, Sébastien Roux et al. (+13 more)
Boron vacancies ($V_B^-$) in hexagonal boron nitride (hBN) have emerged as a promising platform for two-dimensional
quantum sensors capable of operating at atomic-scale proximity. However, the mechanisms responsible for photoluminescence quenching in thin hBN sensing layers when placed in contact with absorptive materials remain largely unexplored. In this Letter, we investigate non-radiative Förster resonance energy transfer (FRET) between $V_B^-$ centers and either monolayer
graphene or 2D
semiconductors. Strikingly, we find that the FRET rate is negligible for hBN sensing layers thicker than 3 nm, highlighting the potential of $V_B^-$ centers for integration into ultra-thin
quantum sensors within van der Waals
heterostructures. Furthermore, we experimentally extract the intrinsic radiative decay rate of $V_B^-$ defects.
Read the full abstract ▾
All authors Jules Fraunié, Mikhail M. Glazov, Sébastien Roux, Abraao Cefas Torres-Dias, Cora Crunteanu-Stanescu, Tom Fournier, Maryam S. Dehaghani, Tristan Clua-Provost, Delphine Lagarde, Laurent Lombez, Xavier Marie, Benjamin Lassagne, Thomas Poirier, James H. Edgar, Vincent Jacques, Cedric Robert
Statistical Mechanics
Collective dynamics of trail-interacting particles
Paul Pineau, Samuel Bell, Raphaël Voituriez et al. (+1 more)
Trail interactions occur when past particle trajectories bias future motion, rendering the system out of thermodynamic
equilibrium. While such systems are abundant in nature, their understanding is limited to the single-particle level or phenomenological mean-field theories. Here, we introduce a minimal model of many trail-interacting particles, which extends this paradigm to the fluctuating collective level in arbitrary dimension. Particles diffuse while depositing long-lasting repelling/attracting trails that act as a shared
memory field, coupling their dynamics across time and space. Using
stochastic density functional theory, we derive fluctuating hydrodynamic equations and analyze analytically and numerically the resulting behaviors. We show that
memory, coupled with fluctuations, fundamentally reshapes collective dynamics; In the repulsive case, the particle density displays superdiffusive spreading for $d=1$ and diffusive spreading for $d\geq2$, characterized by transient clustering and ballistic motion; In the attractive case, the system condensates in finite time into frozen, localized states. Our results establish general principles for trail-interacting systems and reveal how persistent fields generate novel instabilities and drive self-organization.
Read the full abstract ▾
All authors Paul Pineau, Samuel Bell, Raphaël Voituriez, Ram M. Adar
Materials Science
Influence of a generative parameter on the mechanical performance of topological interlocking assemblies of a hexagonal block
Lukas Schnelle, Meike Weiß, Reymond Akpanya et al. (+2 more)
A topological interlocking assembly is an arrangement of blocks, where all blocks are kinematically constrained by their neighboring blocks and a fixed frame. This concept has been known for a long time, attracting recent interest due to its advantageous mechanical properties, such as reusability, redundancy and limited crack propagation. New mathematical methods enable the generation of vast numbers of new topologically interlocking blocks. A natural next question is the quantification of the mechanical performance of these new blocks. We conduct a numerical study of topological interlocking assemblies whose blocks are constructed based on the hexagonal grid. By varying a design parameter used in the generation of these blocks, we study its influence on the structural performance of the entire assembly. The results improve our understanding of the link between the block parameters and the mechanical performance. This enhances the ability to custom design blocks for certain mechanical requirements of the topological interlocking assemblies.
Read the full abstract ▾
All authors Lukas Schnelle, Meike Weiß, Reymond Akpanya, Kai-Uwe Schröder, Alice C. Niemeyer
Statistical Mechanics · Cross-listed from quant-ph
Thermodynamics of an Open Two-Level $\mathcal{PT-}$Symmetric Quantum System
Baibhab Bose, Devvrat Tiwari and Subhashish Banerjee
For a subclass of a general $\mathcal{PT}-$symmetric
Hamiltonian obeying anti-commutation relation with its conjugate, a Hermitian basis is found that spans the bi-orthonormal energy eigenvectors. Using the modified projectors constructed from these eigenvectors, the generalized density
matrix of the $\mathcal{PT}-$symmetric
evolution is calculated, and subsequently, ergotropy for a closed system is obtained. The $\mathcal{PT}-$symmetric system, in an open system scenario, is studied to understand ergotropy under different regimes of non-Hermiticity of the
Hamiltonian. The consistency of the three laws of thermodynamics for the $\mathcal{PT}-$symmetric system in an open system scenario is also analyzed.
Read the full abstract ▾
Disordered Systems and Neural Networks
A microscopic theory of Anderson localization of electrons in random lattices
Václav Janiš
The existence of Anderson localization, characterized by vanishing
diffusion due to strong disorder, has been demonstrated in numerous ways. A systematic approach based on the Anderson
quantum model of the
Fermi gas in random
lattices that can describe both diffusive and localized regimes has not yet been fully established. We build on a recent publication \cite{Janis:2025ab} and present a microscopic theory of disordered electrons that covers both the metallic phase with extended Bloch waves and the localized phase, where a propagating particle forms a
quantum bound state with the hole left behind at the origin. The general theory provides a framework for constructing controlled approximations to one- and two-particle Green functions that satisfy the necessary conservation laws and causality requirements across the full range of disorder strength. It is used explicitly to derive a local, mean-field-like approximation for the two-particle irreducible vertices, enabling quantitative analysis of the solution's dynamic properties in both metallic and localized phases, including critical behavior at the mobility edge. A new instability line for the dynamical electron-hole correlation function of the metallic phase is introduced.
Read the full abstract ▾
Superconductivity
P. García-Campos, V.O. Dolocan, M.-K. Arfaoui et al. (+3 more)
Superconductivity is characterized by vanishing electrical resistance and
magnetic flux expulsion. For conventional type II
superconductors, the
magnetic flux expulsion is incomplete in an applied
magnetic field above a critical value and
magnetic flux penetrates the bulk of the
superconductor in discrete quantized
magnetic flux tubes (
vortices), each carrying a single
quantum of flux (h/2e). Investigating the unconventional
superconductor UPt$_{3}$ with a scanning superconducting
quantum interference device (SQUID) microscope, we observed mobile half-
quantum vortices together with one
quantum vortices. Cooling the material under a higher
magnetic field revealed the presence of lines of
magnetic contrast resembling domain walls. These observations agree with theoretical predictions for
chiral superconductivity with a two dimensional complex order-parameter with sheets of half-
quantum vortices separating domains of opposite order-parameter chirality.
Read the full abstract ▾
All authors P. García-Campos, V.O. Dolocan, M.-K. Arfaoui, D. Aoki, A. D. Huxley, K. Hasselbach
Soft Condensed Matter
Speciation and hydration forces in sodium carbonate/bicarbonate aqueous solutions nanoconfined between mica sheets
Daria Turculet, Shurui Miao, Kieran Agg et al. (+1 more)
The
equilibrium between hydrated and hydrolysed forms of CO2 in water is central to a multitude of processes in geology, oceanography and biology. Chemistry of the carbonate system is well understood in bulk solution, however processes such as mineral weathering and biomineralisation frequently occur in nano-confined spaces where carbonate chemistry is less explored. For confined systems, the speciation
equilibria are expected to tilt due to surface reactivity, electric fields and reduced configurational
entropy. In this discussion paper we provide measurements of interaction force between negatively charged aluminosilicate (mica) sheets across aqueous carbonate/bicarbonate solutions confined to nanoscale films in
equilibrium with a reservoir of the solution. By fitting the measurements to a Poisson-Boltzmann equation modified to account for charge regulation at the bounding walls, we discuss features of the bicarbonate speciation in confinement. We find that (i) the presence of bicarbonate in the bulk reservoir causes a repulsive excess pressure in the slit compared to pH-neutral salt solutions at the same concentration, arising from a higher (negative) effective charge on the mica surfaces; (ii) the electrostatic screening length is lower for solutions of Na2CO3 compared to NaHCO3 at the same bulk concentration, due to a shift in the speciation
equilibria with pH and in accordance with Debye-Hückel theory; (iii) hydration forces are observed at distances below 2 nm with features of size 0.1 nm and 0.3 nm; this was reproducible across the various bicarbonate electrolytes studied, and contrasts with hydration forces of uniform step size measured in pH-neutral electrolytes.
Read the full abstract ▾
All authors Daria Turculet, Shurui Miao, Kieran Agg, Susan Perkin
Strongly Correlated Electrons · Cross-listed from quant-ph
A Quantum Algorithm with Polylogarithmic Depth per Trotter Step for the Extended Hubbard Model
Yu Wang, Martina Nibbi, Maxine Luo et al. (+4 more)
The extended Hubbard model on a two-dimensional
lattice captures key physical phenomena, but its simulation remains challenging because long-range interactions give rise to a large number of interaction terms. Here we present Q2FMM, an efficient
quantum algorithm for simulating this model within the Trotter product formula. Inspired by the fast multipole method, Q2FMM replaces site-site interactions with interactions between hierarchical coarse-grained boxes across multiple length scales. In addition, the multipole expansions of boxes are reused for their parent boxes, further enhancing the efficiency. To enable this hierarchical reuse coherently, we design a reversible
quantum circuit that removes garbage information through uncomputing. The resulting
circuit depth for a single Trotter step scales polylogarithmically with system size.
Read the full abstract ▾
All authors Yu Wang, Martina Nibbi, Maxine Luo, Isabel Nha Minh Le, Yanbin Chen, J. Ignacio Cirac, Christian B. Mendl
Materials Science
Resolving Structural Transitions in Lanthanide High-Entropy Oxides
Billy E. Yang, Saeed S. I. Almishal, Sai Venkata Gayathri Ayyagari et al. (+6 more)
We report a temperature-composition phase diagram for the chemically disordered and CeO2-LA2O3 high
entropy oxides (HEOs), where LA denotes equimolar Y, La, Sm, and Pr, delineating stability regions for bixbyite, disordered fluorite, and intermediate vacancy-ordered fluorite phases. The diagram is constructed from a characterization package applied to bulk ceramics including X-ray diffraction (XRD), transmission electron microscopy (TEM) electron diffraction, Raman spectroscopy, energy-dispersive spectroscopy, X-ray absorption near-edge structure spectroscopy, and ultraviolet-visible spectroscopy, to quantify
crystal structure at multiple length-scales, local coordination environments, and electronic structures across the formulation space. This comprehensive measurement suite is critical to identify boundaries between the closely related phases. For example, Raman scattering reveals local structural and defect environments unique to bixbyite local order that persist to ~50% Ce under
equilibrium synthesis conditions but are invisible to XRD and TEM. We also report a companion thin film study to demonstrate that quenched kinetic energy from a physical deposition process can metastabilize the high
symmetry, and thus high
entropy, fluorite phase with only 20% Ce. This is noteworthy because electroneutrality constraints demand an exceptionally vacated oxygen sublattice; we estimate 16.7%, approaching that of delta-Bi2O3. Together, our
equilibrium ceramics and far-from-
equilibrium thin films show that when synthesis is coupled with rigorously chosen, multi-length-scale characterization, now one can identify the phase stability thermodynamic drivers and simultaneously derive practical guidelines for experimentally realizing targeted phases and structures - and thereby deliberately engineer properties in CeO2-LA2O3 HEOs, whose broad defect chemistries demand such an approach.
Read the full abstract ▾
All authors Billy E. Yang, Saeed S. I. Almishal, Sai Venkata Gayathri Ayyagari, Mary Kathleen Caucci, Gerald Bejger, Christina M. Rost, Nasim Alem, Susan B. Sinnott, Jon-Paul Maria
Mesoscale and Nanoscale Physics
Laser-induced modulation of conductance in graphene with magnetic barriers
Rachid El Aitouni, Miloud Mekkaoui, Pablo Díaz et al. (+2 more)
We study how electrons move across a
graphene sheet when it encounters two
magnetic barriers with a region in between that is continuously driven by
laser light. Rather than acting as a static obstacle, this illuminated middle section becomes a Floquet cavity that opens new transport channels through controlled
photon absorption and emission. By combining Floquet theory with the transfer
matrix method, we track electron transmission through both the main energy band and the emerging
photon-assisted sidebands. We find that the
laser does more than modify the potential–it reshapes how electrons interact between the
magnetic barriers, enabling a switch from ordinary transmission to transport dominated by
photon exchange. Because the
magnetic field and the optical drive are applied to separate sections of the device, the system supports interference between cyclotron-filtered motion and discrete
photon-pumping channels, producing Fano resonances and angle-dependent transmission zeros that cannot appear in double
magnetic or double
laser barrier systems alone. Under well-defined conditions, the distance between the
magnetic barriers controls the coupling between Floquet channels, allowing highly tunable resonances and even perfect transmission, despite strong
magnetic confinement. We also observe that low-energy carriers are efficiently blocked by the
magnetic regions, while conductance steadily rises with energy until it reaches a clear saturation plateau. This hybrid design provides a versatile way to steer
graphene electrons by balancing optical pumping and
magnetic momentum filtering.
Read the full abstract ▾
All authors Rachid El Aitouni, Miloud Mekkaoui, Pablo Díaz, David Laroze, Ahmed Jellal
Statistical Mechanics
Classification of diffusion processes in dimension $d$ via the Carleman approach with applications to models involving additive, multiplicative or square-root noises
Cecile Monthus
The Carleman approach is well-known in the field of deterministic classical dynamics as a method to replace a finite number $d$ of non-linear differential equations by an infinite-dimensional linear system. Here this approach is applied to a system of $d$
stochastic differential equations for $[x_1(t),..,x_d(t)]$ when the forces and the
diffusion-
matrix elements are
polynomials, in order to write the linear system governing the dynamics of the averaged values ${\mathbb E} ( x_1^{n_1}(t) x_2^{n_2}(t) ... x_d^{n_d}(t) )$ labelled by the $d$ integers $(n_1,..,n_d)$. The natural decomposition of the Carleman
matrix into blocks associated to the global degree $n=n_1+n_2+..+n_d$ is useful to identify the models that have the simplest spectral decompositions in the bi-orthogonal basis of right and left eigenvectors. This analysis is then applied to models with a single noise per coordinate, that can be either additive or multiplicative or square-root, or with two types of noises per coordinate, with many examples in dimensions $d=1,2$. In $d=1$, the Carleman
matrix governing the dynamics of the moments ${\mathbb E} ( x^{n}(t) )$ is diagonal for the
Geometric Brownian motion, while it is lower-triangular for the family of Pearson
diffusions containing the Ornstein-Uhlenbeck and the Square-Root processes, as well as the Kesten, the Fisher-Snedecor and the Student processes that converge towards steady states with power-law-tails. In dimension $d=2$, the Carleman
matrix governing the dynamics of the correlations ${\mathbb E} ( x_1^{n_1}(t) x_2^{n_2}(t) )$ has a natural decomposition into blocks associated to the global degree $n=n_1+n_2$, and we discuss the simplest models where the Carleman
matrix is either block-diagonal or block-lower-triangular or block-upper-triangular.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Modelling the Impact of Device Imperfections on Electron Shuttling in SiMOS devices
Jack J. Turner, Christian W. Binder, Guido Burkard et al. (+1 more)
Extensive theoretical and experimental work has established high-fidelity electron shuttling in Si/SiGe systems, whereas demonstrations in Si/SiO2, also known as silicon metal-
oxide-
semiconductor (SiMOS), devices remain at an early stage. To help address this, we perform full 3D simulations of conveyor-belt charge shuttling in a realistic SiMOS device, building on earlier 2D modelling. We solve the Poisson and time-dependent Schrodinger equations for varying shuttling speeds and gate voltages, focusing on potential pitfalls of typical SiMOS devices such as
oxide-interface roughness, gate fabrication imperfections, and charge defects along the transport path. The simulations reveal that for low clavier-gate voltages, the additional
oxide screening in multi-layer gate architectures causes conveyor-belt shuttling to collapse to the bucket-brigade mode, inducing considerable orbital excitation in the process. Increasing the confinement restores conveyor-belt operation, which we find to be robust against interface roughness, gate misalignment, and charge defects buried in the
oxide. However, our results indicate that defects located at the Si/SiO2-interface can induce considerable orbital excitation. For lower conveyor gate biases, positive defects in the transport channel can even capture passing electrons. Hence we identify key challenges and find operating regimes for reliable charge transport in SiMOS architectures.
Read the full abstract ▾
All authors Jack J. Turner, Christian W. Binder, Guido Burkard, Andrew J. Fisher
Statistical Mechanics · Cross-listed from quant-ph
Density of states of quantum systems from free probability theory: a brief overview
Keun-Young Kim and Kuntal Pal
We provide a brief overview of approaches for calculating the density of states of
quantum systems and random
matrix Hamiltonians using the tools of free probability theory. For a given
Hamiltonian of a
quantum system or a generic random
matrix Hamiltonian, which can be written as a sum of two non-commutating operators, one can obtain an expression for the density of states of the
Hamiltonian from the known density of states of the two component operators by assuming that these operators are mutually free and by using the free additive convolution. In many examples of interacting
quantum systems and random
matrix models, this procedure is known to provide a reasonably accurate approximation to the exact numerical density of states. We review some of the examples that are known in the literature where this procedure works very well, and also discuss some of the limitations of this method in situations where the free probability approximation fails to provide a sufficiently accurate description of the exact density of states. Subsequently, we describe a perturbation scheme that can be developed from the subordination formulas for the Cauchy transform of the density of states and use it to obtain approximate analytical expressions for the density of states in various models, such as the Rosenzweig-Porter random
matrix ensemble and the Anderson model with on-site disorder.
Read the full abstract ▾
Superconductivity
Super-hard and superconducting boron clathrates in the prediction of U-B compounds
Juefei Wu, Dexi Shao, Junjie Wang et al. (+6 more)
The binary metal borides provide a promising platform for searching unique materials with superconductivity and super-hardness under high pressure, owing to the distinctive bonding characters of boron. In this work, combined the first-principles calculations and
crystal structure predictions, we predicted 4 exotic stoichiometries and 8 unique U-B compounds under high pressure. The predicted compounds have layered or caged structure units and 4 of them host high hardness under ambient pressure. By removal of the U atoms, we predicted three meta-stable boron clathrates at ambient pressure. Remarkably, the Vickers hardness of the predicted C2/m-B6 is estimated to be 49-53 GPa, and the C2/m-B12 is superconducting with the Tc value of 16.12 K. Our calculations enrich the phase diagram of binary metal borides and boron allotropes, providing insights for the future theoretical and experimental studies on unique materials.
Read the full abstract ▾
All authors Juefei Wu, Dexi Shao, Junjie Wang, Yu Han, Bangshuai Zhu, Cuiying Pei, Qi Wang, Jian Sun, Yanpeng Qi
Mesoscale and Nanoscale Physics
Quantum-Geometric Fingerprints of Altermagnetic Order in Planar Magnetotransport
Zhichun Ouyang, Wei-Jing Dai, Zi-Ting Sun et al. (+2 more)
Identifying altermagnetic order through transport requires signatures that are sensitive to
magnetic symmetry but do not rely on a net magnetization. Here we show that planar magnetotransport provides such
quantum-
geometric fingerprints. In two-dimensional altermagnets with $C_n\mathcal{T}$
magnetic symmetry, an in-plane Zeeman field explicitly breaks the mirror and emergent $C_{2z}$
symmetries that otherwise suppress intrinsic
Hall and second-order transport responses. The resulting
magnetic field susceptibilities of the Berry
curvature and
quantum metric produce linear planar
Hall, nonlinear planar
Hall, and nonreciprocal longitudinal responses. Crucially, the leading
magnetic field powers and angular periodicities of these responses are fixed by the underlying altermagnetic order. For $d$-, $g$-, and $i$-wave altermagnets, we find distinct fingerprint patterns associated with
quantum geometric susceptibilities. Our results establish planar magnetotransport as a
symmetry selective probe of both band
quantum geometry and altermagnetic order.
Read the full abstract ▾
All authors Zhichun Ouyang, Wei-Jing Dai, Zi-Ting Sun, Jin-Xin Hu, K. T. Law
Superconductivity
Highly Anisotropic Charge Dynamics and Spectral Weight Redistribution in the Trilayer Nickelate La$_{4}$Ni$_{3}$O$_{10}$
Zhe Liu, Jie Li, Deyuan Hu et al. (+10 more)
We study the $ab$-plane and $c$-axis charge dynamics of La$_{4}$Ni$_{3}$O$_{10}$ using optical spectroscopy. While a pronounced Drude profile, i.e. metallic response, is observed in the $ab$-plane optical conductivity $\sigma_{1}^{ab}(\omega)$, the $c$-axis optical spectra $\sigma_{1}^{c}(\omega)$ exhibit semiconducting behavior. The zero-frequency extrapolation of the optical conductivity $\sigma_{1}(\omega \rightarrow 0) \equiv 1/\rho_{\text{dc}}$ gives a resistivity anisotropy of $\rho_{c}/\rho_{ab} \simeq 366$ at 300~K for La$_{4}$Ni$_{3}$O$_{10}$, which is much larger than the values in iron-based
superconductors but comparable to those in high-$T_{c}$ cuprates. The interband response is also highly anisotropic, showing salient orbital selectivity for light polarized in the $ab$ plane and along the $c$ axis. The interband-transition peaks in both $\sigma_{1}^{ab}(\omega)$ and $\sigma_{1}^{c}(\omega)$ are located at lower energies compared to density-functional-theory predictions, signifying considerable electronic correlations. By investigating the spectral weight transfer, we find that in the pristine phase, Coulomb correlations have a marked impact on the charge dynamics of \LNO, whereas in the density-wave state, a gap opens with the Ni-$d_{z^{2}}$ orbital being involved.
Read the full abstract ▾
All authors Zhe Liu, Jie Li, Deyuan Hu, Bingke Ji, Haoran Zhang, Jiahao Hao, Yaomin Dai, Qing Li, Mengjun Ou, Bing Xu, Yi Lu, Meng Wang, Hai-Hu Wen
Disordered Systems and Neural Networks
Remembrance of Tasks Past in Tunable Physical Networks
Purba Chatterjee, Marcelo Guzman and Andrea J. Liu
Sequential learning in physical networks is hindered by catastrophic forgetting, where training a new task erases solutions to earlier ones. We show that we can significantly enhance
memory of previous tasks by introducing a hard threshold in the learning rule, allowing only edges with sufficiently large training signals to be altered. Thresholding confines tuning to the spatial vicinity of inputs and outputs for each task, effectively partitioning the network into weakly overlapping functional regions. Using simulations of tunable resistor networks, we demonstrate that this strategy enables robust
memory of multiple sequential tasks while reducing the number of edges and the overall tuning cost. Our results hint at constrained training as a simple, local, and scalable mechanism to overcome catastrophic forgetting in tunable matter.
Read the full abstract ▾
Superconductivity
Proximity-induced superconductivity in magnetic topological insulator films
Daniele Di Miceli, Eduárd Zsurka, Kristof Moors et al. (+2 more)
Inducing superconducting correlations in
magnetic topological
insulators (MTIs) is emerging as a promising route toward the realization of topological superconductivity and Majorana modes. Here, we develop an analytical model for the proximity effect induced by an ordinary s-wave
superconductor (SC) placed on top of a MTI thin film with finite thickness. Using a perturbative approach with respect to the electron tunneling between MTI and SC, we derive the leading-order correction to the anomalous Green's function and evaluate the position-dependent induced pairing as a function of all the system parameters. This framework allows us to resolve the spatial,
spin, and momentum structure of the induced superconducting order parameter. In particular, we derive an explicit expression for the decay length of the pairing amplitude at the $k_x=k_y=0$ point, and show that increasing magnetization enhances the
spin-polarized triplet components and the p-wave contributions of the anomalous Green's function. These findings highlight the interplay between
topology, magnetism, and superconductivity in MTI films, providing analytical insight into the emergence of unconventional pairing
symmetries relevant for the realization of Majorana modes in finite geometries.
Read the full abstract ▾
All authors Daniele Di Miceli, Eduárd Zsurka, Kristof Moors, Llorenç Serra, Thomas L. Schmidt
Materials Science
Interfacial Control of Orbital Occupancy and Spin State in LaCoO$_3$
Ellen M. Kiens, Nicolas Gauquelin, Arno Annys et al. (+11 more)
Transition metal
oxides exhibit a wide range of tunable electronic properties arising from the complex interplay of charge,
spin, and
lattice degrees of freedom, governed by their $d$ orbital configurations, making them particularly interesting for
oxide electronics and (electro)catalysis. Perovskite
oxide heterointerfaces offer a promising route to engineer these orbital states. In this work, we tune the Co $3d$ orbital occupancy in LaCoO$_3$ from a partial $d^7$ to a partial $d^5$ state through interfacial engineering with LaTiO$_3$, LaMnO$_3$, LaAlO$_3$ and LaNiO$_3$. Using X-ray absorption spectroscopy combined with charge transfer multiplet calculations, we identify differences in the Co valence and
spin state for the series of
oxide heterostructures. LaTiO$_3$ and LaMnO$_3$ interfaces result in interfacial charge transfer towards LaCoO$_3$, resulting in a partial $d^7$ orbital occupancy, while a LaNiO$_3$ interface results in a partial Co $d^5$ occupancy. Strikingly, a LaAlO$_3$ spacer layer between LaNiO$_3$ and LaCoO$_3$ results in a Co $d^6$ low
spin state. These results indicate that the Co
spin state, like the valence state, is governed by the interfacial environment. High-resolution scanning transmission electron microscopy imaging reveals a clear connection between strain and
spin configuration, emphasizing the importance of structural control at
oxide interfaces. Overall, this work demonstrates that interfacial engineering simultaneously governs orbital occupancy and
spin state in correlated
oxides, advancing
spin-engineering strategies in correlated
oxides and offering new insights for the rational design of functional
oxide heterostructures.
Read the full abstract ▾
All authors Ellen M. Kiens, Nicolas Gauquelin, Arno Annys, Emma van der Minne, Iris C.G. van den Bosch, Matthijs A. van Spronsen, Zezhong Zhang, Annick de Backer, Sandra van Aert, Jo Verbeeck, Gertjan Koster, Bastian Mei, Frank M.F. de Groot, Christoph Baeumer
Materials Science
Poly- and single-crystalline diamond nitrogen-induced TLS losses estimation with superconducting lumped elements micro-resonators
Francesco Mazzocchi, Martin Neidig, Hideaki Yamada et al. (+3 more)
Research on diamond has intensified due to its exceptional thermal, optical, and mechanical properties, making it a key material in
quantum technologies and high-power applications. Diamonds with engineered nitrogen-vacancy (NV) centers represent a very sensitive platform for
quantum sensing, while high-optical quality diamond windows represent a fundamental safety component inside Electron Cyclotron Resonance Heating (ECRH) systems in
nuclear fusion reactors. A major challenge is the development of ultra-low-loss, high-optical-quality single-
crystal diamond substrates to meet growing demands for
quantum coherence and power handling. Traditionally, dielectric losses ($\tan \delta$) in diamonds are evaluated using Fabry-Perot microwave resonators, in which the resonance quality factors Q of the cavity with and without the sample are compared. These devices are limited to resolutions around 10$^{-5}$ by the need to keep the resonator dimensions within a reasonable range. In contrast, superconducting thin-film micro-strip resonators, with Q factors exceeding 10$^6$, are stated to provide higher sensitivity for assessing ultra-low-loss materials. This study examines four diamond samples grown through different processes, analyzing their dielectric losses at extreme low temperatures (sub-Kelvin) within the Two-Level System (TLS) framework. Complementary Raman spectroscopy measurements allowed us not only to associate higher nitrogen content with increased losses, but also to investigate how the different growth process influence the way these defects are incorporated in the
crystal lattice.
Read the full abstract ▾
All authors Francesco Mazzocchi, Martin Neidig, Hideaki Yamada, Sebastian Kempf, Dirk Strauss, Theo Scherer