Superconductivity
Nonrelativistic-Ising superconductivity in p-wave magnets
Maxim Khodas, Libor Šmejkal and I. I. Mazin
We discuss a possibility of superconductivity in the p-wave magnets. These are recently discovered materials that have zero net magnetization by
symmetry and finite non-relativistic
spin splitting of electron bands, like in altermagnets. Similarly, the
spin polarizations is collinear in the momentum space. Yet, as opposed to altermagnets, the magnetization is noncollinear in the real space, and the
spin splitting obeys time-reversal
symmetry in the momentum space. As a result, if such material harbors superconductivity (due to
phonons, or any other mechanism), the only supported superconducting
symmetry is Ising superconductivity, an exotic
symmetry where any Cooper pair is a 50:50 mix of singlet and triplet. This unusual behavior is also in stark contrast to regular antiferromagnet, which can support Cooper pairs of any parity, and altermagnets, which can only support nonunitary triplet pairs. The presence of large triplet component and enhanced resilience against pair breaking is inherent to the p-wave magnets and as such is unconventional as it does not materialize in conventional
spin-orbit coupling induced Ising
superconductors.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from physics.soc-ph
Nonequilibrium phase transitions in a racism-spreading model with interaction-driven dynamics
Nuno Crokidakis and Lucas Sigaud
Racism remains a persistent societal issue, increasingly amplified by the structure and dynamics of online social networks. In this work, we propose a three-state compartmental model to study the spreading and suppression of racist content, drawing from epidemic-like dynamics and interaction-driven transitions. We analyze the model on fully-connected (homogeneous mixing) networks using a set of coupled differential equations, and on Barabási-Albert (BA) scale-free and Watts-Strogatz (WS) small-world networks through
agent-based simulations. The system exhibits three distinct stationary regimes: two racism-free absorbing states and one active phase with persistent racist content. We identify and characterize the phase transitions between these regimes, discuss the role of network
topology, and highlight the emergence of absorbing states. Our findings illustrate how statistical physics tools can help uncover the macroscopic consequences of microscopic social interactions in digital environments.
Read the full abstract ▾
Materials Science
Atomic imaging of 2D transition metal dihalides
Wendong Wang, Gareth R.M Tainton, Nick Clark et al. (+14 more)
Transition metal di-iodides such as FeI2, NiI2 and CoI2 are an emerging class of 2D magnets exhibiting rich and diverse
magnetic behaviour, but their study at the monolayer limit has been severely hindered by fabrication challenges due to their air-sensitivity. Here, we introduce a
polymer-free method for clean, rapid, and high-yield assembly of hermetically encapsulated suspended samples of air-sensitive monolayers. Applying it to di-iodides enables atomic resolution characterisation of thin samples - down to the monolayer limit - for the first time. Our imaging, combined with complementary first-principles calculations, reveals an unusually small energy barrier between alternate stable stacking polytypes in few-layer films, enabling extrinsic control of the stacking phase. We also observe stable isolated iodine vacancies that do not aggregate to form extended structures, and identify and verify the stability of the various edge configurations of thin samples. These results establish the unique structural characteristics of these materials in the thin limit, and more broadly demonstrate the utility of our transfer platform for creating atomically clean suspended vdW
heterostructures.
Read the full abstract ▾
All authors Wendong Wang, Gareth R.M Tainton, Nick Clark, James G. McHugh, Xue Li, Sam Sullivan-Allsop, David G. Hopkinson, Oldrich Cicvarek, Francisco Selles, Rui Zhang, Joshua D. Swindell, Alex Summerfield, David J. Lewis, Vladimir I Falko, Zdenek Sofer, Sarah J. Haigh, Roman Gorbachev
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Covariant formulation of the Berry connection in non-Hermitian systems
Ievgen I. Arkhipov
Non-Hermitian systems exhibit spectral and topological phenomena absent in Hermitian physics; however, their
geometric characterization remains subtle due to the intrinsic ambiguity of biorthogonal eigenspaces. Since left and right eigenvectors are not related by Hermitian conjugation, the associated Berry connection is generally nonunique, leading to complex
geometric phases and ambiguously defined holonomies. Here we formulate a covariant
geometric framework for non-Hermitian
quantum systems based on the metric structure of the underlying
Hilbert space. We show that, in the
quantum regime with continuous state
evolution, the conventional Berry connection and the associated Berry holonomy over closed parameter-space loops can be consistently defined only in the pseudo-Hermitian limit, where the spectrum is real. For generic non-Hermitian
Hamiltonians with complex spectra, the relevant
geometric object is instead the Aharonov–Anandan holonomy associated with cyclic
evolution in projective
Hilbert space. Within the pseudo-Hermitian regime, we construct a unique Hermitian Berry connection that is covariant under arbitrary ${\rm GL}(N,\mathbb C)$ frame transformations and reduces to the standard Berry connection in the Hermitian limit. The resulting formalism separates the intrinsic geometry of the
Hamiltonian eigenspace from contributions arising from the parameter dependence of the
Hilbert-space metric, revealing that the conventional biorthogonal formulation generally mixes these distinct
geometric effects. Consequently,
geometric phases, synthetic gauge fields, and topological characteristics commonly attributed to non-Hermitian eigenspace geometry may, in part, originate from the underlying metric structure. Our framework therefore provides a consistent
geometric foundation for Berry phases, non-Abelian holonomies, and topological invariants in non-Hermitian
quantum systems.
Read the full abstract ▾
Materials Science
Comparative Analysis of Plasticity-based GND Density Estimation Methods in Crystal Plasticity Finite Element Models
Michael Pilipchuk, Chaitali Patil and Veera Sundararaghavan
In
crystal plasticity finite element (CPFE) simulations, accurately quantifying geometrically necessary dislocations (GNDs) is critical for capturing strain gradients in polycrystals. We compare different methods for quantifying GNDs, all of which originate from the Nye tensor, which is computed as the curl of the plastic deformation gradient. The projection technique directly decomposes the Nye tensor onto individual screw and edge dislocation components to compute GNDs. This approach requires converting a nine-component Nye tensor into densities for a larger number of dislocation systems, a fundamentally underdetermined (non-unique) process, which is resolved using $L2$ minimization. In contrast, when employing CPFE analysis, one could directly compute dislocation densities on each slip system using shear gradients. Projection and slip gradient methods are compared with respect to their prediction of GNDs with changing grain size, strain, and grain neighborhoods, including multigrain junctions. Although these techniques match analytical GND densities for single slip, single
crystal deformation, and are consistent with anticipated overall GND trends, we find that the GND densities from projection techniques are significantly lower than those predicted from CPFE-based slip gradients in polycrystals. A suggested improvement of only using the active dislocation systems in the projection technique almost entirely resolved this mismatch.
Read the full abstract ▾
Disordered Systems and Neural Networks
Observation of Erratic Non-Hermitian Skin Localization and Transport
Jia-Xin Zhong, Jee Woo Kim, Stefano Longhi et al. (+1 more)
Localization is a pervasive phenomenon across physics, shaping transport from electrons in solids to light and sound in engineered media. In traditional settings, disorder strongly impedes transport, resulting in dynamical localization or, at best, sub-ballistic or diffusive dynamics. A distinct and previously unobserved regime, erratic non-Hermitian skin localization (ENHSL), can arise in globally reciprocal non-Hermitian
lattices with disorder. It features macroscopic, disorder-dependent localization at irregular bulk positions with subexponential decay, linked to
stochastic interfaces governed by the universal order statistics of random walks. We realize this regime experimentally in an acoustic
lattice implementing a disordered Hatano-Nelson chain with imaginary gauge fields. Using Green's-function-based spectroscopy together with time-resolved measurements on the same platform, we reconstruct the full complex spectrum and eigenstates, and directly observe wave-packet dynamics. Remarkably, we observe ballistic transport despite strong spectral localization. We develop a transport theory that connects the dominant propagation site to the maximal random-walk excursion within an expanding light cone and predicts a universal Levy-arcsine statistics, in quantitative agreement with experiment. Our results decouple eigenstate localization from transport and establish ENHSL as a new paradigm for wave dynamics.
Read the full abstract ▾
All authors Jia-Xin Zhong, Jee Woo Kim, Stefano Longhi, Yun Jing
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Quantum Light Detection with Enhanced Photonic Neural Network
Stanisław Świerczewski, Dogyun Ko, Amir Rahmani et al. (+7 more)
Advances in
quantum technologies are accelerating the demand for optical
quantum state sensors that combine high precision, versatility, and scalability within a unified hardware platform.
Quantum reservoir computing offers a powerful route toward this goal by exploiting the nonlinear dynamics of
quantum systems to process and interpret
quantum information efficiently. Photonic neural networks are particularly well suited for such implementations, owing to their intrinsic sensitivity to
photon-encoded
quantum information. However, the practical realisation of photonic
quantum reservoirs remains constrained by the inherently weak optical nonlinearities of available materials and the technological challenges of fabricating densely coupled
quantum networks. To address these limitations, we introduce a hybrid
quantum-classical detection protocol that integrates the advantages of
quantum reservoirs with the adaptive learning capabilities of analogue neural networks. This synergistic architecture substantially enhances information-extraction accuracy and robustness, enabling low-cost performance improvements of
quantum light sensors. Based on the proposed approach, we achieved significant improvements in
quantum state classification,
tomography, and feature regression, even for reservoirs with a relatively small nonlinearity-to-losses ratio $U/\gamma \approx 0.02$ in a network of only five nodes. By reducing reliance on material nonlinearity and reservoir size, the proposed approach facilitates the practical deployment of high-fidelity photonic
quantum sensors on existing integrated platforms, paving the way toward chip-scale
quantum processors and photonic sensing technologies.
Read the full abstract ▾
All authors Stanisław Świerczewski, Dogyun Ko, Amir Rahmani, Juan Camilo López Carreño, Wouter Verstraelen, Piotr Deuar, Barbara Piętka, Timothy C. H. Liew, Michał Matuszewski, Andrzej Opala
Statistical Mechanics · Cross-listed from quant-ph
Approximate Decoherence, Recoherence and Records in Isolated Quantum Systems
Philipp Strasberg, Joseph Schindler, Jiaozi Wang et al. (+1 more)
Using the framework of decoherent histories, we study which past events leave detectable records in isolated
quantum systems under the realistic assumption that decoherence is approximate and not perfect. In the first part we establish – asymptotically for a large class of (pseudo-)random histories – that the number of reliable records can be much smaller than the number of possible events, depending on the degree of decoherence. In the second part we reveal a clear decoherence structure for long histories based on a numerically exact solution of a random
matrix model that, as we argue, captures generic aspects of decoherence. We observe recoherence between histories with a small Hamming distance, for localized histories admitting a high purity Petz recovery state, and for maverick histories that are statistical outliers with respect to Born's rule. From the perspective of the Many Worlds Interpretation, the first part – which views the self-location problem as a coherent version of
quantum state discrimination – reveals a "branch selection problem", and the second part sheds light on the emergence of Born's rule and the theory confirmation problem.
Read the full abstract ▾
All authors Philipp Strasberg, Joseph Schindler, Jiaozi Wang, Andreas Winter
Materials Science · Cross-listed from physics.chem-ph
Locally Scaled Self-Interaction Corrected Energy Functionals with Complex Optimal Orbitals
Jukka John, Hlynur Gu{\dh}mundsson, I{\dh}unn Björg Arnaldsdóttir et al. (+2 more)
We present a fully variational locally scaled self-interaction corrected (SIC) energy functional using complex optimal orbitals. This represents an important milestone for fully variational SIC energy functionals, which have been shown to improve the prediction of the properties of atomic, molecular and solid state systems in general, in both ground and excited states. However, it depends on the system and property of the system whether it is beneficial to scale the SIC correction by a factor of one-half, which makes the application of SIC inconsistent. In the limit of a single electron the SIC exactly cancels the self interaction error, but overcorrects the error in regions of high density where there is large overlap between occupied orbitals. The newly implemented local scaling function, $z(\mathbf{r})$, which is based on an iso-orbital indicator derived from considering the kinetic energy density in the iso-electron and many electron case, and takes into account that the orbitals are complex, naturally scales the SIC correction from $0\leq z(\mathbf{r}) \leq 1$ in regions of high and low (isolated orbital) electron density. The locally scaled and fully variational SIC framework is general and applicable to atomic, molecular and solid-state systems.
Read the full abstract ▾
All authors Jukka John, Hlynur Gu{\dh}mundsson, I{\dh}unn Björg Arnaldsdóttir, Hannes Jónsson, Elvar Örn Jónsson
Materials Science
Revealing the (111) surface electronic structure of epitaxially grown Na$_2$KSb photocathode
N.Yu. Solovova, V.A. Golyashov, S.V. Eremeev et al. (+5 more)
A recent study has established the Na$_2$KSb(Cs) photocathode as a highly efficient emitter of
spin-polarized electrons. However, the electronic structure of alkali antimonides remains poorly understood. In this work, we report the first crystalline epitaxial growth of Na$_2$KSb films, achieved via chemical vapor deposition (CVD) on a
graphene-coated SiC(0001) substrate. The high crystalline quality of these films enabled a direct investigation of the material's electronic structure using angle-resolved photoemission spectroscopy (ARPES). By comparing the experimental results with density functional theory (DFT) calculations, we have identified dispersive surface states originating from different terminations of the Na$_2$KSb(111) surface. Furthermore, we demonstrate that the crystalline order of the film is preserved following its activation via the deposition of Cs and Sb. This finding opens a pathway for investigating the electronic structure of multialkali Na$_2$KSb(Cs) photocathodes and for rationally improving their properties.
Read the full abstract ▾
All authors N.Yu. Solovova, V.A. Golyashov, S.V. Eremeev, S.Yu. Priobrazhenskii, S.P. Lebedev, A.A. Lebedev, V.S. Rusetsky, O.E. Tereshchenko
Strongly Correlated Electrons · Cross-listed from quant-ph
Efficient Application of Tensor Network Operators to Tensor Network States Through Successive Deterministic Compression
Richard M. Milbradt, Shuo Sun, Christian B. Mendl et al. (+2 more)
We introduce an
algorithm to apply tree tensor network operators to tree tensor network states followed by compression. Especially when applying a
matrix product operator to
matrix product states, this serves as a key subroutine in tensor network
algorithms. We name the method successive deterministic compression (SDC). We compare SDC to existing operator application and compression
algorithms in
benchmarks involving random tensor network operators and states, as well as
circuit simulation with standard entangling gates. We find that successive deterministic compression is consistently among the best-performing techniques when the tensor network state (after the operator application) is not highly compressible. Our results also highlight the flexibility of general tree tensor network structures for simulating
circuits with long-range
entanglement.
Read the full abstract ▾
All authors Richard M. Milbradt, Shuo Sun, Christian B. Mendl, Johnnie Gray, Garnet K.-L. Chan
Statistical Mechanics
Pietro F. Dias, Fabio M. Zimmer, Nikolaos G. Fytas et al. (+1 more)
We investigate the frustrated $J_1$-$J_2$-$J_3$ Ising model on the honeycomb
lattice, featuring first- and second-neighbor
ferromagnetic couplings ($J_1>0$ and $J_2>0$) and third-neighbor
antiferromagnetic interactions ($J_3<0$). Using the cluster mean-field method, we analyze the phase transitions in the regime $1/2 < J_2/J_1 \le 1$, where
ferromagnetic and
antiferromagnetic phases compete. Our results reveal that near the strongly frustrated limit $J_3/J_1 = -1$, the system exhibits order-by-disorder state selection, tricritical and bicritical behavior, critical endpoints, and two successive phase transitions. The
ferromagnetic-paramagnetic transition remains second order across the entire interaction range, whereas the
antiferromagnetic-paramagnetic boundary shows a richer behavior, including both first- and second-order transitions as well as tricriticality. Increasing the second-neighbor coupling $J_2/J_1$ narrows the range of $J_3/J_1$ where first-order
antiferromagnetic-paramagnetic transitions occur; beyond a certain threshold, only second-order order-disorder transitions persist. Consequently, the tricritical point shifts toward $J_3/J_1 \approx -1$ as $J_2/J_1$ increases, culminating in a bicritical point where the
antiferromagnetic,
ferromagnetic, and paramagnetic phases meet.
Read the full abstract ▾
All authors Pietro F. Dias, Fabio M. Zimmer, Nikolaos G. Fytas, Mateus Schmidt
Mesoscale and Nanoscale Physics
Fundamental Relations as the Leading Order in Nonlinear Thermoelectric Responses with Time-Reversal Symmetry
Ying-Fei Zhang, Zhi-Fan Zhang, Hua Jiang et al. (+2 more)
In recent years, nonlinear transport phenomena have garnered significant interest in both theoretical explorations and experiments. In this work, we utilize the semi-classical wave packet theory to calculate disorder-induced second-order transport coefficients: second-order electrical ($\sigma$), thermoelectric ($\alpha$), and thermal ($\kappa$) coefficients, capturing the interplay between side-jump and skew-scattering contributions in systems with time-reversal
symmetry. Using a topological
insulator model, we quantitatively characterize the
Fermi-level dependence of these second-order transport coefficients by explicitly including Coulomb
impurity potentials. Furthermore, we elucidate the relationships between these coefficients, establishing the second-order Mott relation and the Wiedemann-Franz law induced by disorder. This study develops a comprehensive theoretical framework elucidating the nonlinear thermoelectric transport mechanisms in
quantum material systems.
Read the full abstract ▾
All authors Ying-Fei Zhang, Zhi-Fan Zhang, Hua Jiang, Zhen-Gang Zhu, Gang Su
Mesoscale and Nanoscale Physics
Microscopic theory of an atomic spin diode
William J. Huddie and Rembert A. Duine
We present a microscopic theory of an atomic
spin diode. Our proposed system consists of two
magnetic adatoms deposited on the surface of a two-dimensional electron gas with Rashba
spin-orbit coupling. A local s-d type coupling between the local
spins and the
spins of the electrons induces a non-local Ruderman-Kittel-Kazuya-Yoshida type interaction and a Dzyalonshinskii-Moriya interaction, in addition to dissipative interactions, between the
spins. We derive the effective action for the
spins using the Keldysh formalism. From the effective action, we also derive equations of motion for the
spins which are shown to be of Landau-Lifshitz-Gilbert (LLG) type, and give expressions for the effective field and Gilbert damping which appear in this equation. From our microscopic theory, we find that for an in-plane
magnetic field perpendicular to the vector connecting the two atoms, the magnitude of the field and the distance between the atoms can always be tuned to engender perfectly diodic coupling. Our findings may pave the way to experimental realisation of atomic
spin diodes.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Ruishi Qi, Qize Li, Haleem Kim et al. (+9 more)
Strong Coulomb interactions can drive electrons to crystallize into a Wigner
lattice. Achieving the bosonic analogue - a
crystal of
excitons - has remained elusive due to their short lifetimes and weaker interactions. Here, we report the observation of a thermodynamically stable
exciton crystal in an excitonic
insulator coupled to a moiré potential. Using an electron-hole
bilayer composed of a monolayer MoSe2 and a WS2/WSe2 moiré superlattice, we construct a tunable extended Bose-Hubbard model with electrical control over
exciton and charge doping in thermal
equilibrium. Optical spectroscopy reveals spontaneous crystallization of long-lived
excitons at one
exciton filling per three moiré sites, evidenced by strong Umklapp scattering peaks in the optical spectrum.
Exciton transport measurements further show a pronounced
exciton resistance peak at the same filling, consistent with suppressed
exciton hopping in a crystalline phase. When doped away from net charge neutrality, this moiré electron-hole
bilayer can host new correlated insulating phases where dipolar excitonic
insulators form on top of the background of a hole Mott
insulator or generalized Wigner
crystals in the moiré superlattice. These findings establish moiré excitonic
insulators as a versatile platform for realizing correlated crystalline phases of
bosons and
fermions.
Read the full abstract ▾
All authors Ruishi Qi, Qize Li, Haleem Kim, Jiahui Nie, Zuocheng Zhang, Ruichen Xia, Zhiyuan Cui, Jianghan Xiao, Takashi Taniguchi, Kenji Watanabe, Michael F. Crommie, Feng Wang
Statistical Mechanics
Effects of Dynamic Disorder on Diffusion in Rugged Energy Landscapes
Biman Bagchi
Established theoretical studies of
diffusion in rugged (or rough) potential surfaces have largely focused on quenched energy landscapes. Here we study
diffusion on a rugged energy landscape in the presence of dynamic disorder, a situation relevant to a wide range of disordered systems, including glasses, disordered solids, and biomolecular transport. For static (quenched) Gaussian disorder, Zwanzig derived a compact mean field expression for the
diffusion constant, showing that increasing ruggedness leads to a sharp reduction of diffusive transport. Subsequent work demonstrated that in one-dimensional discrete
lattices diffusion is further suppressed by rare but long-lived multi-site traps that lie beyond the mean-field description. In many physical systems, however, the local energy landscape is not frozen but fluctuates in time, there by modifying trap lifetimes and transport properties. In this work we develop a minimal, analytically tractable theory of
diffusion on rugged energy landscapes with dynamic disorder by allowing site or barrier energies to fluctuate as dichotomic (telegraph) processes with given amplitude and flipping rate. Using a Kehr type formulation appropriate for discrete hopping processes, we derive an analytic expression for the
diffusion constant in terms of mean waiting times. We show that dynamic disorder induces a continuous crossover from quasi-quenched, trap-dominated transport to an annealed, motional narrowing regime as the fluctuation rate increases. Explicit numerical calculations confirm this crossover, interpolating between rare-event-dominated
diffusion and Zwanzig mean-field regime.
Read the full abstract ▾
Superconductivity · Cross-listed from quant-ph
Flux-tunable transmon incorporating a van der Waals superconductor via an Al/AlO$_x$/4Hb-TaS$_2$ Josephson junction
Eliya Blumenthal, Ilay Mangel, Amit Kanigel et al. (+1 more)
Incorporating van der Waals (vdW)
superconductors into Josephson elements extends
circuit-QED beyond conventional Al/AlO$_x$/Al tunnel junctions and enables microwave probes of unconventional condensates and subgap excitations. In this work, we realize a flux-tunable transmon whose nonlinear inductive element is an Al/AlO$_x$/4Hb-TaS$_2$ Josephson junction. The tunnel barrier is formed by sequential deposition and full in-situ oxidation of ultrathin Al layers on an exfoliated 4Hb-TaS$_2$ flake, followed by deposition of a top Al electrode, yielding a robust, repeatable hybrid junction process compatible with standard transmon fabrication.
Embedding the device in a three-dimensional copper cavity, we observe a SQUID-like flux-dependent spectrum that is quantitatively reproduced by a standard dressed transmon–cavity
Hamiltonian, from which we extract parameters in the transmon regime. Across measured devices we obtain sub-microsecond energy relaxation ($T_1$ from $0.08$ to $0.69~\mu$s), while Ramsey measurements indicate dephasing faster than our $16$ ns time resolution. We also find a pronounced discrepancy between the Josephson energy inferred from spectroscopy and that expected from the Ambegaokar–Baratoff relation using room-temperature junction resistances, pointing to nontrivial junction physics in the hybrid Al/AlO$_x$/4Hb-TaS$_2$ system. Although we do not resolve material-specific subgap modes in the present geometry, this work establishes a practical route to integrating 4Hb-TaS$_2$ into coherent
quantum circuits and provides a baseline for future edge-sensitive designs aimed at enhancing coupling to boundary and subgap degrees of freedom in vdW
superconductors.
Read the full abstract ▾
All authors Eliya Blumenthal, Ilay Mangel, Amit Kanigel, Shay Hacohen-Gourgy
Statistical Mechanics
Learning the Intrinsic Dimensionality of Fermi-Pasta-Ulam-Tsingou Trajectories: A Nonlinear Approach using a Deep Autoencoder Model
Gionni Marchetti
We address the intrinsic dimensionality (ID) of high-dimensional trajectories, comprising $n_s = 4\,000\,000$ data points, of the
Fermi-Pasta-Ulam-Tsingou (FPUT) $\beta$ model with $N = 32$ oscillators. To this end, a deep autoencoder (DAE) is used to infer the ID in the weakly nonlinear regime where energy recurrences are observed ($\beta \lesssim 1$). We find that the trajectories lie on a nonlinear Riemannian
manifold of dimension $m^{\ast} = 2$ embedded in a $64$-dimensional phase space. By contrast, principal component analysis (PCA) together with the Participation Ratio (PR) method provides only a reasonable upper bound on the ID for each value of $\beta$. Our DAE further reveals that the ID increases to $m^{\ast} = 3$ at $\beta = 1.1$, coinciding with a
symmetry-breaking (SB) phenomenon characteristic of the $\beta$ model, in which additional energy modes with even wave numbers $k = 2, 4$ become excited. Notably, the SB phenomenon cannot be detected by the linear approach provided by PCA.
Read the full abstract ▾
Materials Science
Lanthanide-Dependent Clustering in Yb$^{3+}$/Ln$^{3+}$ Co-Doped CaF$_2$ Nanocrystals: Correlating Spectroscopic Signatures with DFT Insights
Sangeetha Balabhadra, Haoming Xu, Jiajia Cai et al. (+3 more)
The formation of heterogeneous lanthanide-ion clusters in CaF$_2$ was investigated experimentally and computationally. CaF$_2$ nanoparticles co-doped with 20~mol% Yb$^{3+}$ and 2~mol% Ln$^{3+}$ (Ln$^{3+}$ = Ce$^{3+}$, Pr$^{3+}$, Nd$^{3+}$, Sm$^{3+}$, Eu$^{3+}$, Gd$^{3+}$, Ho$^{3+}$, Er$^{3+}$, and Tm$^{3+}$) were synthesized via a hydrothermal method. The structural and morphological properties were characterized using powder X-ray diffraction, dynamic light scattering, and transmission electron microscopy techniques. High-resolution
Fourier transform infra-red spectroscopy revealed the presence of Yb$^{3+}$ isolated cubic centers and various cluster sites. The relative concentration of the clusters varied with the choice of the co-doping ion. Calculations based on density functional theory were used to estimate the formation energies and local coordination structures of different clusters. The calculations indicate that the neutral $C_{4v}$ aggregations containing Ln$^{3+}$ tend to decrease across the lanthanide series, while the negatively charged derivatives of hexameric clusters are relatively constant. This variation matches the experimental results. This study advances understanding of the clustering mechanisms in lanthanide-doped CaF$_2$ nanoparticles and has implications for luminescence optimization in advanced nanomaterials.
Read the full abstract ▾
All authors Sangeetha Balabhadra, Haoming Xu, Jiajia Cai, Chang-Kui Duan, Michael F. Reid, Jon-Paul R. Wells
Materials Science
All-electrical switching of spin texture in a strain-tunable 2D Janus ferroelectric altermagnet
Tao Yao, Quan Shen, Wenhu Liao et al. (+2 more)
Altermagnetism (AM), a collinear
magnetic phase with momentum-dependent
spin splitting, is a promising candidate for strong magnetoelectric coupling. However, realizing direct and tunable coupling between ferroelectricity (FE) and AM within a single two-dimensional (2D) material remains an outstanding challenge. Here, based on first-principles calculations, we identify the distorted phase of monolayer Janus VOClBr as an intrinsic 2D FE-AM. This phase demonstrates robust magnetoelectric coupling, as evidenced by a complete reversal of momentum-space
spin polarization upon FE switching, and further supported by
spin texture analysis and the magneto-optical Kerr effect. Notably, the FE properties are highly strain-tunable: biaxial compression strain of -4% reduces the FE polarization switching barrier by approximately 87%, whereas a tensile strain of +3% induces a phase transition to an antiferromagnet. Leveraging the lock-in between the electrically controlled
spin texture and the magneto-optical Kerr effect signal, we propose a non-volatile, polymorphic spintronic
memory device featuring all-electrical writing and optical readout. This work establishes 2D FE-AMs as a versatile platform for coupled ferroic orders and paves the way for voltage-controlled, multifunctional
spin-logic devices.
Read the full abstract ▾
All authors Tao Yao, Quan Shen, Wenhu Liao, Jianing Tan, Jiansheng Dong
Mesoscale and Nanoscale Physics
Dual-Switch Control of a Layer-Locked Anomalous Valley Hall Effect in a Sliding Ferroelectric Antiferromagnet
Quan Shen, Wenhu Liao, Degao Xu et al. (+2 more)
The integration of ferroelectric (FE) and
antiferromagnetic (AFM) orders in twodimensional (2D) materials provides a promising avenue for the nonvolatile control of coupled
spin and valley degrees of freedom, a capability central to advancing spinvalleytronics. However, realizing a single material system where these
quantum states can be independently and reversibly manipulated by distinct stimuli, a prerequisite for multifunctional devices, has remained elusive. Here, we demonstrate a dual-switch mechanism in
bilayer VS2, a room-temperature FE-AFM system, that enables electrical and
magnetic control of a layer-locked anomalous valley
Hall effect (AVHE). First-principles calculations reveal that interlayer sliding breaks spatial inversion
symmetry, inducing a switchable out-of-plane FE polarization that coexists with interlayer AFM. The
spin-orbit coupled valley polarization can be reversibly switched either by FE polarization reversal or by a
magnetic-field-induced
spin-flip transition, confirming the existence of electrically and magnetically addressable valley states. The Berry
curvature exhibits both valley-contrasting and layer-locked characteristics, which underpin a switchable
Hall response. Notably, electric and
magnetic switching are functionally equivalent in modulating valley, layer, and
spin indices, revealing strong magnetoelectric coupling. This work establishes a multidegree-of-freedom operational paradigm in 2D multiferroics and opens a viable design pathway toward multi-state
memory and
spin-valleytronic logic devices.
Read the full abstract ▾
All authors Quan Shen, Wenhu Liao, Degao Xu, Jiansheng Dong, Jianing Tan
Materials Science
Discrete Dislocation Dynamics Modeling of Nanotwinned Materials: Orientation Effects in a Multilayer Twinned Structure of Copper
DeAn Wei, Michael Zaiser, Jing Tang et al. (+1 more)
The impact of twin boundaries (TBs) on the microstructure
evolution and plastic deformation mechanisms of face-centered cubic (FCC) metals has been extensively studied since the discovery that nanotwinned materials exhibit a favorable combination of high strength and ductility. In this work, a dislocation-twin boundary interaction model for copper is incorporated into a three-dimensional discrete dislocation dynamics (DDD) framework. This approach is applied to systematically investigate the orientation effects on the deformation of nanotwinned copper, utilizing a multilayer twinned structure (MTS) with a twin thickness of 160 nm. The simulation results show that the stress-strain response of MTSs under uniaxial loading depends significant on the orientation of the loading axis. Dislocations inclined to TBs are confined to slip in single- or multi-layer twin lamellae; when the loading axis is oriented perpendicular or parallel to TBs, such whereas when loading axis inclined to TBs, the dislocations with glide plane parallel to TBs are easily activated (mainly twinning dislocations) and the TBs do not hinder the dislocations and behave in soft modes. If the hard mode dominates the deformation mechanism, microstructures with single-layer confined slip lead to significant hardening behavior, while microstructures with multilayer confined slip maintain stable plastic flow and do not lead to hardening. Finally, through the introduction of critical resolved shear stresses (CRSSs) specific to various deformation modes and the adaptation of Schmid's law, we have effectively projected the additional anisotropic characteristics induced by TBs in MTSs.
Read the full abstract ▾
All authors DeAn Wei, Michael Zaiser, Jing Tang, Xu Zhang
Materials Science
Near-field effects on cathodoluminescence outcoupling in perovskite thin films
Robin Schot, Imme Schuringa, Álvaro Rodríguez Echarri et al. (+7 more)
Halide perovskite
semiconductors are a promising material for high-efficiency
solar cells. Their optical properties can vary within and between crystallographic grains. We present spatially-resolved cathodoluminescence (CL) spectroscopy at 2 keV and 5 keV on polycrystalline CsPbBr3 perovskite films to study these variations at the nanoscale. The CL maps show a strongly reduced intensity near the polycrystalline grain boundaries. We perform numerical simulations of the far-field emission of the electron beam-generated optical near fields using the surface profiles from AFM as input. We find that near grain boundaries the light outcoupling is strongly reduced due to enhanced internal reflection and light trapping at the curved surfaces. Lateral variations in CL intensity inside grains are due to Fabry-Perot-like resonances in the film, with the substrate acting as a back reflector. Our results show that near-field coupling and interference effects can dominate nanoscale luminescence maps of halide perovskite films. The results are broadly relevant for the analysis of cathodoluminescence and photoluminescence of corrugated thin films.
Read the full abstract ▾
All authors Robin Schot, Imme Schuringa, Álvaro Rodríguez Echarri, Lars Sonneveld, Tom Veeken, Yang Lu, Samuel D. Stranks, Albert Polman, Bruno Ehrler, Saskia Fiedler
Mesoscale and Nanoscale Physics
Nonlinear waves: a review Vector $0\pi$ pulse and the generalized perturbative reduction method
G. T. Adamashvili
In this review, a more general theory of self-induced transparency (SIT) in comparison with the theory of McCall and Hahn is considered. Using the recently developed generalized perturbative reduction method (GPRM) the SIT equations are reduced to vector (coupled) nonlinear Schrodinger equations for auxiliary functions. This approach demonstrates that, unlike McCall and Hahn SIT theory in which single-component scalar breather can propagate independently, in the more general theory of SIT the second derivatives with respect to the spatial coordinate and time of the wave equation play a significant role and describe the interaction of two scalar SIT breathers forming a coupled pair. This is a vector 0\pi pulse of SIT - a two-component vector breather oscillating with the sum and difference of frequencies and wave numbers. The profile, parameters and properties of this pulse differ significantly from the characteristics of the McCall and Hahn pulses. Using GPRM it is shown that besides the scalar
soliton and the scalar breather, the vector $0\pi$ pulse is also a universal nonlinear wave, arising in virtually all areas of physics where nonlinear phenomena are described by nonlinear equations containing second-order and higher-order derivatives. A number of such nonlinear equations are presented. Among them almost all well known nonlinear equations, as well as the general fourth-order nonlinear partial differential equation and the sixth-order generalized Boussinesq-type equations.
Read the full abstract ▾
Quantum Gases
Analytical solution of the Schrödinger equation with $1/r^3$ and attractive $1/r^2$ potentials: Universal three-body parameter of mixed-dimensional Efimov states
Yuki Ohishi, Kazuki Oi and Shimpei Endo
We study the Schrödinger equation with $1/r^3$ and attractive $1/r^2$ potentials. Using the
quantum defect theory, we obtain analytical solutions for both repulsive and attractive $1/r^3$ interactions. The obtained discrete-scale-invariant energies and wave functions, validated by excellent agreement with numerical results, provide a natural framework for describing the universality of Efimov states in mixed dimension. Specifically, we consider a three-body system consisting of two heavy particles with large dipole moments confined to a quasi-one-dimensional geometry and resonantly interacting with an unconfined light particle. With the Born-Oppenheimer approximation, this system is effectively reduced to the Schrödinger equation with $1/r^3$ and $1/r^2$ potentials, and manifests the Efimov effect. Our analytical solution suggests that, for repulsive dipole interactions, the three-body parameter of the mixed-dimensional Efimov states is universally set by the dipolar length scale, whereas for attractive interactions it explicitly depends on the short-range phase. We also investigate the effects of finite transverse confinement and find that our analytical results are useful for describing the Efimov states composed of two polar molecules and a light atom.
Read the full abstract ▾
Superconductivity
Bosonic phases across the superconductor-insulator transition in infinite-layer samarium nickelate
Menghan Liao, Heng Wang, Mingwei Yang et al. (+14 more)
Superconductivity arises from the global phase coherence of Cooper pairs. Modulation of phase coherence leads to
quantum phase transitions, serving as an important tool for studying unconventional superconductivity. Here, we demonstrate bosonic phases across the
superconductor-
insulator transition in infinite-layer nickelate superconducting films by the control of spatially periodic network patterns. Magnetoresistance oscillations with a periodicity of h/2e provide direct evidence of 2e Cooper pairing in nickelates. The phase transition is predominantly driven by enhanced superconducting fluctuations, and Cooper pairs are involved in charge transport across the transition. Notably, we observe two types of anomalous metallic phases, emerging respectively at finite
magnetic fields and down to zero
magnetic field. They can be characterized by bosonic excitations, suggesting the dynamic roles of
vortices in the ground states. Our work establishes nickelates as a key platform for investigating the rich landscape of bosonic phases controlled via the phase coherence of Cooper pairs.
Read the full abstract ▾
All authors Menghan Liao, Heng Wang, Mingwei Yang, Chuanwu Cao, Jiayin Tang, Wenjing Xu, Xianfeng Wu, Guangdi Zhou, Haoliang Huang, Kaiwei Chen, Yuying Zhu, Peng Deng, Jianhao Chen, Zhuoyu Chen, Danfeng Li, Kai Chang, Qi-Kun Xue
Materials Science
Si-Ga2O3/p-GaN epitaxial heterostructure based self-powered and visible-blind UV photodetectors with fast and electrically tuneable response time
Ajoy Biswas, Amandeep Kaur, Bhabani Prasad Sahu et al. (+5 more)
n-Ga2O3/p-GaN heterojunction based photodetector devices are fabricated on Si-doped (-201) \beta-Ga2O3 epitaxial layers grown by pulsed
laser deposition (PLD) technique on p-type c-GaN/sapphire templates. These devices demonstrate the ability to act as highly efficient self-powered visible blind UV-photodetectors with fast response time. It has been found that the optimum performance of the detector in terms of its responsivity, detectivity and response time could be achieved by adjusting the Si doping level and the thickness of the Ga2O3 layer. Our best performing device showing the peak responsivity and detectivity of 56.8 mA/W and 3*10^12 Jones, respectively, is achieved for 660 nm thick Ga2O3 layer with Si-concentration of 8*10^18 cm^-3. Moreover, as low as a few nW of optical signal can be sensed by the detector. The response time of the detector is found to be only a few tens of nanoseconds, which highlights their potential for application in ultrafast detection of UV light. These devices also exhibit a slower component of photoresponse with a timescale of a few tens of milliseconds. Interestingly, the time-scale of the slower response can be prolongated by several orders of magnitude through enhancing the applied reverse bias. Such an electrical tuneability of the response time is highly desirable for neuromorphic device applications.
Read the full abstract ▾
All authors Ajoy Biswas, Amandeep Kaur, Bhabani Prasad Sahu, Sushantika Saha, Umakanta Patra, Rupa Jeena, Pradeep Sarin, Subhabrata Dhar
Strongly Correlated Electrons
Hongqin Xiao, Geng Li, Yuxuan He et al. (+8 more)
Wigner-Mott insulating states represent a paradigmatic manifestation of strong electronic correlations, in which long-range Coulomb interactions drive spontaneous charge ordering and enable Mott localization at fractional electronic fillings. Such states have been theoretically proposed to arise from the cooperative interplay between onsite and inter-site Coulomb interactions. However, experimental realizations of the simultaneous microscopic observation of interaction-driven charge order and genuine Mott localization, which are the defining hallmarks of a Wigner-Mott
insulator, have remained elusive. Here we report the observation of a Wigner-Mott insulating state in 6R-TaS$_2$ using scanning tunneling microscopy. By locally injecting electrons into the depleted 1T layer, we induce distinct
Star-of-David charge-ordered superstructures and realize a cascade of insulating phases. In particular, a $\sqrt{3}\times \sqrt{3}$ charge-ordered superstructure at one-third filling hosts a robust Mott gap despite fractional filling. The spontaneous relaxation from excited states back to the ground state demonstrates that this Wigner-Mott phase is stabilized by the cooperative effects of onsite and inter-site Coulomb interactions. Our results provide direct microscopic evidence for a Wigner-Mott mechanism and establish 6R-TaS$_2$ as a platform for the controlled realization and investigation of Wigner-Mott insulating states.
Read the full abstract ▾
All authors Hongqin Xiao, Geng Li, Yuxuan He, Ke Zhu, Yuhan Ye, Yumeng Li, Lijing Huang, Pucen Xiong, Haitao Yang, Ziqiang Wang, Hong-Jun Gao
Superconductivity
Paramagnetically driven superconducting re-entrance in Eu-doped infinite layer nickelates
Lucia Varbaro, Lukas Korosec, Chih-Ying Hsu et al. (+11 more)
The breakthrough discovery of superconductivity in infinite-layer nickelates, and subsequently in several superconducting nickelates with more complex layered structures, capped a search spanning more than two decades and opened an entirely new field of research. Significant efforts aim to increase the critical temperature, to determine the electronic structure of the system, the underlying pairing mechanism, and the similarities between this system and cuprates - Ni1+ in infinite-layer nickelates being isoelectronic to Cu2+ in high-Tc cuprates. Here, we explore the unique role of
magnetic rare earth ions in superconducting Eu-doped NdNiO2. We show that the field-induced re-entrant superconductivity which we evidence in this compound is the result of a delicate balance between the competing effects of the Eu2+ and Nd3+ ions. Our analyses of the extraordinary
Hall effect and modeling of the superconducting critical fields demonstrate that the influence of these ions on magneto-transport is only felt when they are polarized by a
magnetic field.
Read the full abstract ▾
All authors Lucia Varbaro, Lukas Korosec, Chih-Ying Hsu, Duncan T.L. Alexander, Pau Torruella, Clémentine Thibault, Benjamin A. Piot, David Le Boeuf, Javier Herrero Martin, Weibin Li, Evgenios Stylianidis, Marta Gibert, Marc Gabay, Jean-Marc Triscone
Soft Condensed Matter
Multiple charge carrier species as a possible cause for triboelectric cycles
Juan Carlos Sobarzo and Scott Waitukaitis
The tendency of materials to order in triboelectric series has prompted suggestions that contact electrification might have a single, unified underlying description. However, the possibility of triboelectric cycles, i.e. series that loop back onto themselves, is seemingly at odds with such a coherent description. In this work, we propose that if multiple charge carrying species are at play, both triboelectric series and cycles are possible. We show how series arise naturally if only a single charge carrier species is involved and if the driving mechanism is approach toward thermodynamic
equilibrium, and simultaneously, that cycles are forbidden under such conditions. Suspecting multiple carriers might relax the situation, we affirm this is the case by explicit construction of a cycle involving two carriers, and then extend this to show how more complex cycles emerge. Our work highlights the importance of series/cycles towards determining the underlying mechanism(s) and carrier(s) in contact electrification.
Read the full abstract ▾