We use scanning superconducting quantum interference device (SQUID) microscopy to image individual vortices in superconducting strips fabricated from NbTiN thin films. By repeatedly field cooling strips of different widths in applied magnetic fields, we extract the threshold field at which the first vortex enters a strip, as well as the number and spatial configuration of vortices beyond this threshold. We model vortex behavior with and without considering the effect of pinning by numerically minimizing the Gibbs free energy of vortices in the strips. Our measurements provide an experimental benchmark for understanding the flux-trapping properties of NbTiN thin films, directly relevant to NbTiN-based superconducting circuits and devices.

As an unconventional superconducting system capable of reaching 60 K under ambient pressure, the ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ thin-film superconductor has recently become a focal point in the field of superconductivity, calling for further theoretical exploration of its possible pairing mechanisms. In this work, we employ the fluctuation exchange (FLEX) approximation to systematically analyze the superconducting properties of a previously proposed two-site, two-orbital model for the ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ thin film in the weakly correlated regime, with particular emphasis on its dependence on hole doping. Through a more detailed examination of the Fermi-surface topology, we find that when a $\delta$ pocket composed of the $d_{z^2}$ antibonding orbital emerges near the $\mathrm{\Gamma }$ point, its nesting with the $\gamma$ pocket, together with the nesting between the $\alpha$ and $\beta$ pockets, leads to a mutual enhancement of $s\pm$-wave pairing at the corresponding wave vector. Furthermore, we propose that this nesting-driven enhancement of spin-fluctuation-induced pairing may provide a viable mechanism for enhancing superconductivity.

Kitaev chains realized in quantum dots coupled via superconducting segments provide a controllable platform for engineering Majorana zero modes (MZMs). In these systems, subgap states in the hybrid region mediate the effective coupling between quantum dots and determine the emergence of sweet spots where MZMs are strongly localized. However, existing minimal treatments often oversimplify the mesoscopic hybrid region. We perform a full microscopic treatment of this hybrid segment, capturing the quasiparticle continuum and spin-split Andreev bound states (ABSs), and show that it fundamentally alters the minimal picture. We derive analytical expressions for the renormalized couplings and sweet-spot conditions, establishing a direct link between microscopic chain parameters and Majorana optimization and identifying experimentally relevant regimes for improved device performance. Critically, we find that parity crossings of the ABS, marking the onset of an odd-parity spin-polarized regime in the segment, identify the optimal operating windows where MZMs are simultaneously well localized with a large gap to excited states.

We establish a correspondence between the fault tolerance of local stabilizer codes experiencing measurement and physical errors and the mixed-state phases of decohered resource states in one higher dimension. Drawing from recent developments in mixed-state phases of matter, this motivates a diagnostic of fault tolerance, which we refer to as the spacetime Markov length. This is a length scale determined by the decay of the (classical) conditional mutual information of repeated syndrome measurement outcomes in spacetime. The diagnostic is independent of the decoder, and its divergence signals the intrinsic breakdown of fault tolerance. As a byproduct, we find that decoherence may be useful for exposing transitions from higher-form symmetry-protected topological phases driven by both incoherent and coherent perturbations.

$\mathrm{C}{\mathrm{o}}_2\mathrm{MnGa}$, a magnetic Weyl semimetal exhibiting significant anomalous Hall conductivity (AHC) and anomalous Hall angle (AHA) over a wide temperature range, provides an excellent platform for tuning and revealing the rules of the intrinsic and extrinsic contributions to electronic transverse transports. In the dual-component magnetic Weyl semimetal $\mathrm{C}{\mathrm{o}}_2\mathrm{MnGa}$, we modulate the intrinsic and extrinsic components of AHC through doping strategies. In the case of $\mathrm{C}{\mathrm{o}}_{1.8}\mathrm{F}{\mathrm{e}}_{0.2}\mathrm{MnGa}$, AHC is entirely contributed by intrinsic mechanisms without extrinsic contribution over the temperature range from 2 to 300 K. Conversely, for all concentrations of Ni doping, the AHC arises from dual-component contributions. Our analysis also uncovers a hyperbolic relationship between the AHA and longitudinal conductivity (${\sigma }_{\mathrm{xx}}$), with a distinct minimum value, suggesting that large AHA can be achieved in both clean and disordered regimes. Additionally, we present a schematic diagram illustrating the evolution of the extrinsic contribution to AHC and propose tuning strategies for optimizing AHC by incorporating extrinsic components and adjusting the Fermi level. Our work provides essential physical insights into the evolution of intrinsic and extrinsic components of electronic transport, facilitating the exploration of applications for magnetic Weyl semimetals.

Magnetic switching in antiferromagnets relies on Néel spin-orbit torque (NSOT), which originates from an electric-field-induced staggered spin polarization of itinerant electrons. In collinear antiferromagnets, such a response requires the spin susceptibility to be odd under combined space-time inversion symmetry ($\mathcal{PT}$), and is conventionally attributed to symmetric scattering processes. Here, we identify an additional $\mathcal{PT}$-odd spin polarization in the linear response regime, generated by the interplay between antisymmetric higher-order scattering processes and the impurity-induced correction to the spin expectation value. Its compact weak-disorder form is controlled by band geometry, or the anomalous spin polarizability (ASP) of Bloch electrons, which converts an otherwise $\mathcal{PT}$-even susceptibility into a staggered spin polarization. Using a minimal model of tetragonal $\mathrm{CuMnAs}$, we show that the resulting anomalous skew-scattering contribution can be comparable to, and for sufficiently strong impurity effects in the present model can exceed, the conventional symmetric scattering (Drude) contribution. Our results identify a new band-geometry-assisted disorder mechanism for NSOT and clarify a route by which impurity scattering can enhance electrical control of antiferromagnets.

The emerging altermagnetism, featured by robust time-reversal symmetry breaking, antiparallel magnetic order, and alternating spin-splitting band structures, enables phenomena and functionalities that are inaccessible in conventional collinear ferromagnets and antiferromagnets. In this study, we employ first-principles calculations and a tight-binding model to investigate the potential of altermagnetism in quasi-one-dimensional nanotubes derived from altermagnetic monolayer ${\mathrm{V}}_2{\mathrm{Se}}_2\mathrm{O}$. Our findings demonstrate that rolling an altermagnetic monolayer into a nanotube generates a diverse array of chirality-dependent magnetic properties. Notably, $(n,0)$ nanotubes exhibit pronounced alternating spin-splitting band structures, whereas such a spin-splitting phenomenon is entirely absent in $(n,n)$ nanotubes. Furthermore, we analyze the effects of curvature on the energetic stability, spin-splitting, and band edges of the ${\mathrm{V}}_2{\mathrm{Se}}_2\mathrm{O}$ nanotubes. These results expand the understanding of altermagnetism and present avenues for the customization of properties and functionalities in low-dimensional altermagnetic materials.

Recent advances in numerical analytic continuation with physics-motivated constraints now allow spectral functions with sharp features, such as peaks and edges, to be extracted from imaginary-time correlation functions computed by quantum Monte Carlo (QMC) simulations. Here, we test these approaches on various one-dimensional $S=1/2$ spin systems with a single ejected fermion, i.e., extracting the single-hole momentum ($k$) and energy ($\omega$)-dependent spectral function $A(k,\omega )$. We compute the distance ($r$)- and imaginary time ($\tau$)-dependent Green's function $G(r,\tau )$ via Angelucci's canonical transformation [Phys. Rev. B 51, 11580 (1995)] of the fermionic Hamiltonian, implementing it for stochastic series expansion QMC simulations. Our calculations of $A(k,\omega )$ focus on the different characteristics of systems with spin-charge separation and those in which a spin polaron forms instead because of effectively attractive interactions between the spin and the charge. Spin-charge separation is well established in the conventional $t\text{−}J$ chain, which we confirm here as a demonstration of the method. Turning on a multispin interaction $Q$ that eventually drives the system into a spontaneously dimerized (valence-bond solid, VBS) state, we can observe the features of spin-charge separation until the VBS transition takes place. While generally good agreement is found with the conventional analytical spin-charge separation ansatz, we point out the formation of a gap between two holon bands that in the ansatz are degenerate (crossing each other versus the momentum) at $k=0$ and $k=\pi$. Inside the VBS phase, effectively attractive interactions may lead to the binding of the spinon and holon, for which we find evidence at large $Q/J$. In the statically dimerized $t\text{−}J$ chain (i.e., with alternating strengths of the model parameters), we find equally spaced spin-polaron bands corresponding to increasingly large bound states with two internal spin-polaron modes—even and odd with respect to parton permutation. Our results overall demonstrate the power of modern analytic continuation tools in combination with large-scale quantum Monte Carlo simulations.

The theoretical investigation of electronic properties of the cylindrical quantum dot made of gapped monolayer graphene and subject to an external magnetic field is presented. The single electron bound states are obtained within the continuum model of the graphene, including substrate interaction potential. The effective two-dimensional Dirac equation has been solved analytically in a consistent manner for bulk and edge states, using infinite mass boundary conditions imposed at armchair edges of the dot. The band structure of the system in the function of magnetic flux has been observed and bulk–band gap and edge–band gap dependence on the model parameters have been analyzed. In addition, pseudospin-resolved electron densities, the local densities of states, as well as the persistent currents have been calculated in the function of magnetic flux. It has been demonstrated that edge modes are promising candidates for defining the nonlocal quantum bit with a basis state distributed close to opposite edges, by which coherent superposition can be tuned by magnetic flux.

Several studies propose two-dimensional (2D) materials as candidates for spintronic and valleytronic devices. The capability to access two well-defined spin-valley polarization states is the main factor for a good spin-valleytronic device. Each 2D material possesses certain characteristics that can improve the spin-valley polarization. Here, we study the spin and valley transport properties in single ferromagnetic $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ junctions. The transmission probabilities are calculated with the transfer matrix method. The Landauer-Büttiker formalism is used to compute the conductance. We take into account an external electric field to modulate the band gap of the $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ monolayer. Also, the proximity effect originating from the ferromagnetic layer interaction with the $1T^{\prime }\text{−}{\mathrm{MoS}}_2$ monolayer is considered. The combination of both the external electric field and the proximity effect gives rise to two well-defined positive and negative spin-valley polarization states. These findings indicate that the proposed system can be suitable for spintronic and valleytronic devices.

In relation to recent experimental data [Y. Manassen et al., J. Magn. Reson. 374, 107863 (2025)], we develop a theory framework for demonstrating the feasibility of detecting sharp Nuclear Magnetic Resonance (NMR) oscillations in a real-time ESR data. The procedure is to follow real-time oscillations of the ESR signal measured at a selected frequency of a hyperfine transition. We study a variety of systems such as a single radical molecule with one or two hyperfine coupled nuclei or two molecules that coexist as either radicals or nonradicals, facilitated by charge transfer. We develop a master equation for describing these scenarios and find parameters for which a sharp NMR line can be observed. We show that in all cases an off-diagonal term in the hyperfine tensor is essential for the observation.

Inferring properties of microscopic disorder potential from macroscopic transport measurements is a formidable challenging inverse problem in the low-dimensional nanostructures, particularly when the disorder is dynamic and experimentally uncontrolled. In this work, we investigate the inverse problem using the conventional quantum point contact (QPC) devices, modeling the impurity (its concentration can be expressed as $n$) induced disorder potential as an ensemble of randomly distributed two-dimensional circular Gaussian barriers, characterized by amplitude $A$ and spatial width $\delta$. By averaging the conductance over a large number of disorder configurations and comparing it with target data via a misfit function, we search for optimal parameter combinations that best reproduce the transport response. Our results reveal that at low impurity concentrations, the inversion uniquely identifies the correct $(n,$ $\delta )$ pair. However, at high concentrations, multiple distinct combinations yield nearly identical average conductance, indicating that the optimal solution is not a single point but a finite-width region in $(n,$ $\delta )$ parameter space. To resolve this degeneracy, we employ two complementary approaches: statistical analysis of the spatial dispersion of disorder potentials using a centroid-based standard deviation, and angular-resolved analysis of the partial local density of states after coordinate transformation to polar coordinates. The methods show that while both parameters influence transport, $\delta$ plays a dominant role in shaping the location, morphology, and extent of the optimal solution region. The significance of this study lies in revealing that the inverse problem for disordered mesoscopic systems inherently admits a continuum of equivalent solutions, highlighting the need for statistical and scattering-path analyses to distinguish microscopic configurations that are otherwise indistinguishable from conductance alone, together with providing critical insight for interpreting experimental transport data and guiding the design of quantum devices with reliable performance.

Broken inversion symmetry at the surfaces of centrosymmetric collinear antiferromagnets lifts the combined inversion and time-reversal symmetry ($PT$) and can enable nonrelativistic $d$-wave spin splitting, termed surface altermagnetism. Combining symmetry analysis with first-principles calculations, we show that inversion breaking alone is necessary but not sufficient for this effect. Instead, surface altermagnetism emerges only when no degeneracy-protecting symmetry survives at the surface that exchanges the two antiferromagnetically coupled sublattices. We demonstrate this mechanism for the $G$-type antiferromagnets ${\mathrm{V}}_3\mathrm{Al}$ and ${\mathrm{BaMn}}_2{\mathrm{Sb}}_2$, and contrast it with MnPt, where the translation–time-reversal symmetry ($tT$) survives at the surface and preserves spin degeneracy despite broken inversion symmetry. We further show that the mechanism applies across multiple classes of centrosymmetric antiferromagnets and remains robust against spin-orbit coupling, although relativistic spin mixing in heavier-element compounds may reduce the observable spin polarization. These results establish a symmetry-based route toward realizing robust nonrelativistic momentum-dependent spin polarization at antiferromagnetic surfaces and interfaces.

The Hall effect under in-plane magnetic field has emerged as a sensitive probe of quantum geometric properties in solids. In trigonal systems, the in-plane anomalous Hall effect (AHE) originates from unconventional off-diagonal coupling between the magnetic field and the Hall vector on the principal plane. Here, we investigate this coupling in trigonal antiferromagnet ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$ thin films by systematically tracking the (001) plane across distinct magnetic phases. Around zero field, anomalous Hall resistivity as well as out-of-plane Weyl points splitting shows pronounced magnetocubic dependence, persisting not only in the paramagnetic phase but also in the antiferromagnetic phase. Above the magnetic ordering temperature, the off-diagonal octupolar tensor component decays anomalously with an approximate inverse-cubic dependence on temperature. In contrast, in the forced ferromagnetic phase, AHE is governed by dominantly magnetolinear dependence, continuing to increase up to very high fields. These findings establish multipolar nature of off-diagonal couplings underlying in-plane AHE, broadening the scope of Hall physics beyond conventional paradigms.

We study elementary semiconductors and insulators that are symmetric under spatial inversion: silicon, diamond, germanium, and black phosphorene. These materials are ideal candidates for realizing obstructed atomic insulators, which differ from trivial atomic insulators by a quantized spatial shift of their electronic Wannier centers with respect to the atomic lattice. We use symmetry indicator invariants that allow the prediction of nontrivial responses to crystal dislocations with an integer Burgers vector in these materials, and generally, in all inversion-symmetric obstructed atomic insulators. Unlike weak topological insulators where the response only depends on the Burgers vector, the dislocation response of three-dimensional (3D) inversion-symmetric obstructed atomic insulators can also be affected by the line vector of the dislocation. In such insulators, we find that edge dislocations generically exhibit a nontrivial response, while in all 3D obstructed atomic insulators, screw dislocations always display a trivial response. With the aid of numerical simulations of realistic tight-binding models, we confirm the presence of midgap polarization bands localized along dislocations in silicon, diamond, and germanium.

A phonon dynamics framework for atomistic simulation is proposed for studying large-scale system with accuracy comparable to first-principles methods. In this framework, atomic dynamics are reformulated in terms of phonon degrees of freedom, where the localized phonon modes are derived from the phonon dispersion using the lattice Wannier function scheme. The phonon-coupling potential function is expressed analytically through symmetry-invariant terms, forming an effective Hamiltonian whose parameters are determined via an active-learning strategy based on first-principles calculations. We present a comprehensive workflow for constructing phonon dynamics potentials and demonstrate its general applicability to both perovskite ${\text{BaTiO}}_3$ and nonperovskite ${\text{NbOCl}}_2$ examples. This framework enables physically interpretable simulation for diverse materials with speedup of approximately two orders of magnitude compared with the conventional molecular dynamics simulations using first-principles-based potentials.

We investigate how silicon vacancies modify the elastic response and mechanical stability of cubic $3C$-SiC. Our approach employs path-integral molecular dynamics simulations, including the classical-nuclei limit, based on an efficient tight-binding Hamiltonian, whose accuracy is validated against density-functional-theory calculations. This framework enables a quantitative assessment of nuclear quantum effects arising from zero-point motion. Across a broad range of temperatures and hydrostatic pressures, spanning both tensile and compressive regimes, silicon vacancies are found to substantially renormalize the elastic constants $C_{11}$, $C_{12}$, and $C_{44}$, as well as the bulk modulus, relative to the defect-free crystal. Inclusion of nuclear quantum motion produces an additional softening of these elastic properties, particularly at low temperatures, demonstrating that quantum fluctuations make a measurable contribution to the mechanical response of defective SiC. Vacancies also affect the mechanical stability domain of $3C$-SiC, lowering the maximum sustainable tensile pressure by approximately 4 GPa for a defect concentration of 0.016 per lattice site. These results reveal an interplay between point defects and quantum lattice fluctuations in determining the elastic behavior of SiC, providing microscopic insight relevant for both extreme-environment structural applications and defect-based quantum technologies.