We present a study of the low-temperature, high-field magnetotransport behavior of epitaxially grown ${\mathrm{CrO}}_2$ thin films on (100) ${\mathrm{TiO}}_2$ substrates. Electron transport measurements confirm high sample quality, with a residual resistivity ratio as large as 45. A logarithmic fit of the low-temperature regime yields a $T^{4.5}$ power law, indicative of the elusive double-magnon scattering in half-metallic ferromagnets. Angle-dependent anisotropic magnetoresistance (AMR) measurements reveal a large projected density of states along [001] with a maximum AMR value of 2.4%. Pronounced, axis-dependent Shubnikov–de Haas (SdH) oscillations are observed in the longitudinal magnetoresistance (MR), with discrete Landau levels mapped at various tilt angles of the magnetic field. Their angular dependence follows a $1/cos\theta$ relation pointing to a highly anisotropic Fermi surface, and amplitude scaling adheres closely to the thermodynamic Lifshitz-Kosevich formalism. The out-of-plane MR reaches 6.58%, the largest reported for ${\mathrm{CrO}}_2$ thin films. Notably, this study presents an observation of SdH oscillations in a half-metallic oxide with near-perfect spin polarization, a significant advancement in the field of spintronics.

An ab initio scheme based on the Kubo-Greenwood linear response theory of exchange torque correlation is presented to calculate intrinsic Gilbert damping parameters in magnets of reduced dimensions. The method implemented into the real-space Korringa-Kohn-Rostoker (RS-KKR) Greens' function framework enables to obtain diagonal elements of the atomic-site-dependent on-site and nonlocal Gilbert damping tensor. Going from the three-dimensional bulk and surfaces of iron and cobalt ferromagnets addressed in our previous work [B. Nagyfalusi et al., Phys. Rev. B 109, 094417 (2024)], in the present paper monolayers of Fe and Co on (001)- and (111)-oriented Cu, Ag, and Au substrates are studied, and particularly the substrate-dependent trends are compared. Furthermore, the Gilbert damping parameters are calculated for Fe and Co adatoms and dimers on (001)-oriented substrates. It is investigated how the damping parameter of single adatoms depends on their vertical position. This dependence is quantified in relation to the adatoms' density of states at the Fermi energy showing a nonmonotonic behavior. By rotating the spin moment of the adatoms and collinear magnetic dimers, an anisotropic behavior of the damping is revealed. Finally, a significant, three to ten times increase of the on-site Gilbert damping is found in antiferromagnetic dimers in comparison to the ferromagnetic ones, while the intersite damping is even more enhanced.

We propose a method to evaluate the Gibbs free energy from constant-volume first-principles phonon calculations. The volume integral of the pressure is performed by determining the volume and the bulk modulus in equilibrium at finite temperatures, where the pressure and its volume derivative are evaluated utilizing first-principles calculations of the Grüneisen parameter without varying the volume. We validate our method for fcc Al by comparing it with the conventional quasiharmonic approximation. Furthermore, we integrate our method with self-consistent phonon theory and apply it to calculations for bcc Ti, hcp Ti, and tetragonal ${\mathrm{ZrO}}_2$. We demonstrate the accuracy and computational efficiency of our method by comparing results with those obtained from directly volume-varied self-consistent phonon calculations. In all cases, our method accurately evaluates the free energy change caused by thermal expansion using only constant-volume phonon calculations.

The extreme sensitivity of non-Hermitian Hamiltonians exhibiting the non-Hermitian skin effect (NHSE) has been extensively studied in recent years with well-established theoretical explanations. However, this sensitivity is often overlooked in numerical simulations, leading to unreliable results. In this work, we reexamine Hatano-Nelson and symplectic Hatano-Nelson models studied in previous work [K. Kawabata et al., Phys. Rev. X 13, 021007 (2023)], and compare their results with our high-precision calculations. We systematically investigate inaccuracies in physical results arising from numerical instability during diagonalization and non-Hermitian Hamiltonian evolution. We find that these instabilities arise from a large condition number that scales exponentially with system size due to the NHSE, signaling strong non-normality. Strikingly, a reliable spectrum alone is shown to be insufficient for accurate non-Hermitian evolution, while the reliability of wave functions plays a more critical role. Our findings underscore the necessity of evaluating the condition number to ensure the validity of numerical studies on systems with NHSE, implying that some prior numerical findings in this area may require careful reexamination.

We investigate the effect of Mn substitution on the electronic, magnetic, and electrical transport properties of ${\mathrm{Fe}}_2{\mathrm{Ti}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$. Spin-polarized density of states calculations using density functional theory indicate a half-metallic ground state in Mn-rich compositions. Localized magnetic moments at Mn sites interact through the conduction electron cloud. Electrical resistivity and magnetotransport measurements show dominant Kondo-like scattering at low temperatures alongside a distinctive linear negative temperature coefficient of resistance at higher temperatures. These findings are further supported by specific heat measurements. Isothermal magnetization as a function of the applied magnetic field identifies the magnetic ground state of ${\mathrm{Fe}}_2{\mathrm{Ti}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$ compositions as a ferromagnet with a wandering axis that aligns with the direction of the applied field. Temperature-dependent magnetization measurements highlight features indicative of weak anisotropy in the system, while the x-ray diffraction analysis reveals a highly ordered cubic structure with reduced antisite disorder. Investigation of the local crystal structure using x-ray absorption fine structure spectroscopy shows that the random anisotropy arises from local lattice distortions around Mn atoms. These findings shed light on the emergence of a spin-polarized band structure and a unique magnetic ground state in Mn-substituted ${\mathrm{Fe}}_2{\mathrm{Ti}}_{1-x}{\mathrm{Mn}}_x\mathrm{Sn}$, offering insights into spintronic materials.

Two-dimensional Chern insulators, characterized by broken time-reversal symmetry and chiral edge states, are a promising platform to engineer exotic light-matter interactions. While most previous studies focused on bulk optical properties in extended media, investigations uncovering the unique photonic features of finite topological structures have been rare. In this work, we consider the optical response in nanoflakes of the prototypical Haldane model, which describes graphene-like systems where time reversal and sublattice symmetry breaking drive a topological phase. A simple argument elucidating the interplay between these fundamental properties and the optical spin angular momentum (SAM) of external light singles out these nanoflakes as prime candidates for SAM-sensitive optics. Building on these insights, we conduct a linear response analysis which reveals highly selective optical behavior, manifesting in strongly enhanced preferential absorption. Our results bridge topological materials and photonics, highlighting a direct link between topological properties and characteristics of electromagnetic radiation.

The measurement of quasiparticle scattering patterns on material surfaces using scanning tunneling microscopy is now an established technique for accessing the momentum-resolved electronic band structure of solids. However, since these quasiparticle interference (QPI) patterns reflect spatial variations related to differences in the band momenta rather than the momenta themselves, their interpretation often relies on comparisons with simple geometrical models such as the joint density of states (JDOS) or with the convolution of Green's functions. In this paper, we highlight nonintuitive differences between Green's function and JDOS results. To understand the origin of these discrepancies, we analyze the convolution of Green's functions using the Feynman parametrization technique and introduce a framework that we call the intermediate band analysis. This approach allows us to derive simple selection rules for interband QPI based on electron group velocities. Connecting the intermediate band analysis with the experiment, we consider experimental Bogoliubov QPI patterns measured for ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$, which were recently used to demonstrate a highly anisotropic superconducting gap, indicating superconductivity mediated by nematic fluctuations [Nag et al., Nat. Phys. 21, 89 (2025)]. The calculated Green's functions convolutions reproduce the particle-hole asymmetry in the intensity of QPI patterns across the Fermi level observed in experiments. Finally, we demonstrate the utility of intermediate band analysis in tracing the origin of this asymmetry to a coherence factor effect of the superconducting state.

We investigate Riemannian quantum-geometric structures in semiclassical transport features of two-dimensional multigap topological phases. In particular, we study nonlinear Hall-like bulk electric current responses and, accordingly, semiclassical equations of motion induced by the presence of a topological Euler invariant. We provide analytic understanding of these quantities by phrasing them in terms of momentum-space geodesics and geodesic deviation equations and further corroborate these insights with numerical solutions. Within this framework, we moreover uncover anomalous bulk dynamics associated with the second- and third-order nonlinear Hall conductivities induced by a patch Euler invariant. As a main finding, our results show how one can reconstruct the Euler invariant by coupling to electric fields at nonlinear order and from the gradients of the electric fields. Furthermore, we comment on the possibility of deducing the nontrivial non-Abelian Euler class invariant specifically in second-order nonlinear ballistic conductance measurements within a triple-contact setup, which was recently proposed to probe the Euler characteristics of more general Fermi surfaces. Generally, our results provide a route for deducing the topology in real materials that exhibit the Euler invariant by analyzing bulk electrical currents.

Two mixed-state geometric phases, known as the Uhlmann phase and interferometric geometric phase (IGP), of spin coherent states (CSSs) and spin squeezed states (SSSs) are analyzed. Exact solutions and numerical results of selected examples are presented. For the $j=3/2$ CSS, the Uhlmann phase exhibits finite-temperature topological phase transitions characterized by abrupt jumps. The IGP for the same state similarly shows discontinuous jumps as the temperature varies. In the case of the $j=1$ one-axis SSS, both the Uhlmann phase and IGP display discrete finite-temperature jumps. By contrast, the $j=1$ two-axis SSS shows no such transitions because the Uhlmann phase and IGP both vary smoothly with temperature. We also briefly discuss potential realizations and simulations related to these phenomena in spin systems.

Systematic investigations of rare-earth ($R$)-based intermetallic materials are a leading strategy to reveal the underlying mechanisms governing a range of physical phenomena, such as the formation of a Kondo lattice and competing electronic and magnetic anisotropies. In this work, the magnetic, thermal, and transport properties of $R{\mathrm{Co}}_2{\mathrm{Al}}_8 (R=\mathrm{La},\mathrm{Ce},\mathrm{Pr},\mathrm{Nd}, \mathrm{and} \mathrm{Sm})$ single crystals are presented. ${\mathrm{LaCo}}_2{\mathrm{Al}}_8$ is characterized as a Pauli paramagnet, and transport measurements, with the current along and perpendicular to the orthorhombic $c$-axis (${\rho }_c$ and ${\rho }_{ab}$, respectively), reveal a clear electronic anisotropy, with ${\rho }_{ab}\approx (4$–$7){\rho }_c$ at $300\mathrm{K}$. We show that ${\mathrm{CeCo}}_2{\mathrm{Al}}_8$ is a Kondo lattice for which the Kondo coherence temperature $T_{\text{K}}^{*}$, deduced from broad maximums in ${\rho }_c$ and ${\rho }_{ab}$ at $\approx 68$ and 46 K, respectively, is also anisotropic. This finding is related to a possible underlying anisotropy of the Kondo coupling in ${\mathrm{CeCo}}_2{\mathrm{Al}}_8$. The Pr- and Nd-based materials present strong easy-axis anisotropy ($c$-axis) and antiferromagnetic (AFM) orders below $T=4.84$ and $8.1\mathrm{K}$, respectively. Metamagnetic transitions from this AFM to a spin-polarized paramagnetic phase state are investigated by isothermal magnetization measurements. The Sm-based compound is also an easy-axis AFM with a transition at $T=21.6\mathrm{K}$.

Guided by the multiparticle Mie theory, we address the scattering of a Dirac electron from a one-dimensional array of electrostatically defined core-shell quantum dots in graphene. We show that the gate-controlled grating offers exciting opportunities for Dirac electron steering: The undesired grating diffraction orders can be suppressed via the interference of partial waves scattered by quantum dots. By applying appropriate voltages to the core and shell regions, almost perfect transmission, almost perfect reflection, large-angle negative refraction, and large-angle negative reflection of Dirac electrons are achievable. Indeed, deflection angles as large as ${114}^{\circ }$ are realizable.

While the exponential decay of tunneling probability with barrier thickness is well-known, the accompanying oscillations with thickness have been comparatively less explored. Using a tight-binding model, we investigate an $\mathit{AB}$-stacked bilayer graphene region acting as an energy barrier between two monolayer graphene leads under a vertical electric field. We discuss the case where the energy gap induced by the vertical electric field is comparable to the interlayer transfer integral. In the up (down) junction, the left and right monolayer leads are connected to different layers (a common layer) of the central bilayer, while the remaining, unconnected layers form armchair-type open edges. We reveal a characteristic relation between the tunneling probability and the wave function structure. Among the valley-resolved transmission probabilities, only the valley-reversed transmission in the up junction exhibits even symmetry with respect to energy $E$. This result is counterintuitive. The interlayer wave function ratio $\beta$ is asymmetric in $E$, i.e., $\beta (-E)\ne \beta \left(E\right)$, and electrons cannot bypass the interlayer path in the up junction, whereas they can in the down junction. We attribute this unexpected symmetry to a self-cancellation effect of $\beta$, which arises from chiral and rotational symmetry operations combined with the conservation of probability. Our results demonstrate that the energy dependence of conductance in double junction structures serves as evidence of this effect.

Typically, metallic systems localized under strong disorder exhibit a transition to delocalization as the kinetic terms increase. In this Letter, we reveal the opposite effect—increasing kinetic terms leads to an unexpected reduction of mobility, enhancing localization of the system, and even leading to reentrant delocalization transitions. Specifically, we add a nearest-neighbor hopping with amplitude $\kappa$ to the Rosenzweig-Porter (RP) model with fractal on-site disorder and surprisingly see that, as $\kappa$ grows, the system initially tends to localization from the fractal phase, but then reenters the ergodic phase. We build an analytical framework to explain this re-entrant behavior, supported by exact diagonalization results. The interplay between the spatially local $\kappa$ term, insensitive to fractal disorder, and the energy-local RP coupling, sensitive to fine-level spacing structures, drives the observed reentrant behavior. This mechanism offers a distinct pathway to reentrant localization phenomena in many-body quantum systems.

Nanomagnetism concerns the engineering of magnetic interactions in heterostructures that consist of layers of magnetic and nonmagnetic materials. Mostly, these interactions are dominated by the minimization of energy. Here, we propose an effective magnetic interlayer coupling that is dominated by the maximization of entropy. As an example, we consider the system that mediates the effective interactions to be square spin ice, in which case we find purely entropic interactions that are long-ranged. We argue that in the thermodynamic limit the entropic interlayer coupling gives rise to entropic torques on the magnetization direction. For small systems, the physical properties are well characterized by the mutual information between the two magnets that are coupled. Because entropic interactions typically become stronger for higher temperatures, our findings may benefit the development of nanomagnetic devices that require thermal stability.

Topological qubits based on non-Abelian Majorana bound states (MBSs) are protected by parity which is challenged by quasiparticle poisoning (QPP). In this work, we show how QPP affects transport through a pair of coupled MBSs weakly connected to two current leads, using an open system approach and full counting statistics. We find that the correct low-energy physics requires one to include next to leading order tunneling events in the coupling to the leads. In particular, our results show that QPP causes super-Poissonian local shot noise with a Fano factor that diverges with decreasing bias voltage, while the current and the nonlocal (cross) noise are only little affected. We explain that these features are a direct consequence of the nature of MBSs being their own antiparticle making noise measurements a viable tool to search for MBSs in the presence of QPP.

We propose an all-electrical setup to generate valley polarization in graphene. A finite graphene sheet is connected to two normal-metal electrodes, each with two terminals along its zigzag edges, while the armchair edges remain free. When a bias is applied to one terminal and the others are grounded, valley polarization emerges due to transverse momentum matching between the graphene and the metal electrodes. Significant valley polarization is achieved when the Fermi wave vector in the metal exceeds half the separation between the $K$ and $K^{\prime }$ valleys in graphene. We analyze how conductance and valley polarization depend on geometric and electronic parameters. While increasing the width enhances both conductance and polarization, increasing the length introduces Fabry-Pérot oscillations and suppresses valley polarization due to enhanced intervalley mixing. We also examine the effects of disorder: On-site disorder in graphene increases conductance near the Dirac point but reduces valley polarization. Finally, we study the impact of imperfect armchair edges and interface roughness, finding that moderate deviations from ideal conditions still yield substantial valley polarization. Our results demonstrate a viable route to electrically controlling valley degrees of freedom in graphene-based devices.