Odd-parity superconductivity is a fundamentally interesting but rare state of matter with a potential for applications in topological quantum computing. Crystals with staggered locally noncentrosymmetric structures have been proposed as platforms where a magnetic field can induce a transition between even- and odd-parity superconducting (SC) states. The strongly correlated superconductor ${\mathrm{CeRh}}_2{\mathrm{As}}_2$, with the critical temperature $T_{\mathrm{c}}\approx 0.4\mathrm{K}$, is likely the first example material showing such a phase transition, which occurs at the magnetic field ${\mu }_0{H}^{*}=4\mathrm{T}$ applied along the crystallographic $c$ axis. ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ also undergoes a phase transition of an unknown origin at $T_0=0.5\mathrm{K}$. By subjecting ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ to hydrostatic pressure and mapping the resultant changes to the SC phase diagrams we investigated how the lattice compression and changes to the electronic correlations affect the stability and relative balance of the two SC states. The abnormally high in-plane upper critical field becomes even higher close to a quantum critical point of the $T_{\text{0}}$ order. Remarkably, the SC phase-switching field $H^{*}$ is drastically reduced under pressure, dropping to 0.3 T at 2.7 GPa. This result signals an apparent strengthening of the local noncentrosymmetricity and forecasts a possible stabilization of the putative odd-parity state down to zero field, hitherto not considered by theoretical models.

Discovering mixed state quantum orders is an ongoing issue. Recently, it has been recognized that there are (at least) two kinds of symmetries in the mixed state: strong and weak symmetries. Under symmetry-respective decoherence, spontaneous strong-to-weak symmetry breaking (SSSB) can occur. This paper provides a scheme to describe SSSB and other decoherence phenomena in the mixed state by employing the stabilizer formalism and the efficient numerical algorithm of Clifford circuits. We present two systematic numerical studies. In a two-dimensional circuit with a stochastic Ising type decoherence, an SSSB phase transition is clearly observed and its criticality is elucidated by the numerical methods. In particular, we calculate Rényi-2 correlations and estimate critical exponents of the SSSB transition. For the second system, we introduce an idea of subgroup SSSB. As an example, we study a system with symmetry-protected-topological order provided by both one-form and zero-form symmetries, and observe how the system evolves under decoherence. After displaying numerical results, we show that viewpoint of percolation is quite useful to understand the SSSB transition, which is applicable for a wide range of decohered states. Finally, we comment on SSSB of one-form-symmetry exemplifying toric code.

Optical rectification of intense, circularly polarized light penetrating a material generates a static magnetization through the inverse Faraday effect and, therefore, a magnetic field aligned with the light's direction of propagation. Recent ultrafast experiments have unveiled a substantial, orders-of-magnitude gap between the observed effective field and theoretical predictions. In this study, we show that the discrepancy arises due to a missing factor on the order of ${\alpha }^{-2}\approx 2\times {10}^4$, where α is the fine-structure constant. We demonstrate that alongside Maxwellian magnetization, circular polarization creates large non-Maxwellian fields that disrupt time reversal symmetry, effectively mimicking authentic magnetic fields within the material while eluding detection externally. These unconventional fields, reaching effective magnitudes as high as 100 T, lead to phenomena akin to Faraday rotation and robustly interact with magnons in magnetically ordered materials.

Magnon band structures in altermagnets are characterized by an energy splitting of modes with opposite chirality, even in the absence of applied external fields and relativistic effects, because of an anisotropy in the Heisenberg exchange interactions. We perform quantitative atomistic spin dynamics simulations based on ab initio electronic structure calculations on rutile ${\mathrm{RuO}}_2$, a prototypical “d-wave” altermagnet, to study magnon currents generated by thermal gradients. We report substantial spin Seebeck and spin Nernst effects, i.e., longitudinal or transverse spin currents, depending on the propagation direction of the magnons with respect to the crystal, together with a finite spin accumulation associated with nonlinearities in the temperature profile. Our findings are consistent with the altermagnetic spin-group symmetry, as well as predictions from linear spin-wave theory and semiclassical Boltzmann transport theory.

Here we study ${\mathrm{YbI}}_3$, a quasi-two-dimensional layered material with Yb atoms arranged on an ideal honeycomb network of edge-sharing ${\mathrm{YbI}}_6$ octahedra, analogous to the low-temperature phase of $\alpha \text{−}{\mathrm{RuCl}}_3$. High-quality single crystals of ${\mathrm{YbI}}_3$ are grown from Yb and ${\mathrm{I}}_2$ as starting precursors, using the vapor transport technique. The as-grown crystals are characterized by single-crystal x-ray diffraction, Raman spectroscopy, magnetization, and heat capacity probes. The crystal-field split ground state of ${\mathrm{Yb}}^{3+}$ in ${\mathrm{YbI}}_3$ is a well-isolated Kramers doublet with an effective moment $J_{\mathrm{eff}}=1/2$. On cooling, the low-temperature heat capacity of ${\mathrm{YbI}}_3$ reveals a broad peak at $T_1=0.95\mathrm{K}$ due to short-range ordering of the Yb moments followed by a sharp peak at $T_2=T_N=0.6\mathrm{K}$ due to long-range ordering. The magnetic behavior is found to be weakly anisotropic with ${\chi }^{\parallel }>{\chi }^{\perp }$, where ${\chi }^{\parallel }$ and ${\chi }^{\perp }$ refers to the in-plane $(H\parallel ab)$ and out-of-plane $(H\perp ab)$ susceptibilities. The 2 K isothermal magnetization saturates at $\approx 1.5{\mu }_B/{\mathrm{Yb}}^{3+}$ (in-plane) and $\approx 1{\mu }_B/{\mathrm{Yb}}^{3+}$ (out-of-plane), suggesting the anisotropy to be easy-plane type. The low-temperature heat capacity, well below $T_N$, is found to vary as $T^{\alpha }$ with $\alpha \approx 2.5$, indicating a possible unconventional magnetic ground state for ${\mathrm{YbI}}_3$.

In spatially inverted systems, the complex entanglement of Dzyaloshinskii-Moriya interaction (DMI) and other magnetic anisotropies, mediated by spin-orbit coupling (SOC), influences the emergence and dynamics of the chiral spin textures such as skyrmion. The competing and unified effect of these anisotropies––which is expected to amplify the skyrmionics response in the quantum transport phenomena––is not yet known. Here, we investigate this template and engineer the topological Hall effect (THE) arising from chiral spin texture in a range of $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3/\mathrm{CaIr}{\mathrm{O}}_3$ superlattices. The strength of SOC and interfacial DMI are controlled via the architectural design and charge transfer across the interface. All the superlattices display anomalous Hall effect, accompanied by the hump like feature. In ${\left(L_3{I}_y\right)}_4$ ($y=4$, 6, and 8) superlattices, the humplike feature that is deemed as the THE is intrinsic in nature and stems from the chiral spin texture. For the intermediate strength of SOC, unique eightfold anisotropic magnetoresistance oscillations manifest owing to the modulation of the magnetic easy axis in the presence of competing anisotropies. For this superlattice, THE shows remarkable enhancement of the order such that it takes complete precedence over anomalous contribution. The thicker superlattice with higher fraction of charge transfer augments ferromagnetic interactions, and the artificial THE appears as a consequence of a dual-channel anomalous Hall effect. This manipulation of the THE is intricately connected to the concurrent presence of magnetic anisotropies, altering the dynamics of chiral spin texture. These findings expand the understanding of the corroborative contributions of competing anisotropies and yield a comprehensive control of chiral properties––a dimension for the utility in next-generation spintronics technologies.

Utilizing the electron orbital degree of freedom in heterostructures is attracting increasing attention due to the possibility of achieving much larger conversion rates between charge and orbital angular momentum flow compared to the intrinsic electron spin. Here, we consider orbital angular momentum currents in a tight-binding multiorbital lattice model and derive their continuity equation. From it, we observe that the current is not conserved and apply similar considerations to the recently discovered altermagnets. We find nonzero orbital torque terms, elucidate their physical mechanism, and show numerically that they contribute to dampening the orbital angular momentum current flowing in multiorbital heterostructures. Moreover, we compute the orbital RKKY interaction and find it exhibits similar characteristics as the orbital angular momentum current mediating it, thus serving as a direct experimental probe of such currents.

Bogoliubov Fermi surfaces (BFSs) of superconducting states arise from point or line nodes by breaking time-reversal symmetry. Because line and point nodes often accompany topologically protected zero-energy surface Andreev bound states (SABSs) and thereby lead to a characteristic zero-bias conductance peak (ZBCP) in tunneling spectroscopy, we investigate how these properties change when the line and point nodes deform into BFSs. In this paper, we consider spin-quintet $J_{\mathrm{pair}}=2$ pairing states of spin-$\frac{3}{2}$ electrons with BFSs and calculate the surface density of states and the charge conductance. Comparing the obtained results with the cases of spin-singlet $d$-wave pairing states having the same symmetry, we find that the ZBCP associated with point and/or line nodes is blunted or split in accordance with the appearance of the BFSs. On the other hand, when the spin-singlet $d$-wave state has point nodes but does not have SABS on the surface, we obtain a nonzero small electron conductivity at zero bias through the zero-energy states on the BFSs.

The electronic structure of $\mathrm{S}{\mathrm{c}}_{1-x}{\mathrm{V}}_x{\mathrm{N}}_y$ epitaxial films with different alloying concentrations of V are investigated with respect to effects on thermoelectric properties. Band structure calculations on $\mathrm{S}{\mathrm{c}}_{0.75}{\mathrm{V}}_{0.25}\mathrm{N}$ indicate that V $3d$ states lie in the band gap of the parent ScN compound in the vicinity of the Fermi level. Thus, theoretically, the presence of light (dispersive) bands at the Γ point with band multiplicity is expected to lead to lower electrical resistivity, while flat (heavy) bands at $X-W-K$ symmetry points are associated with higher Seebeck coefficients than that of ScN. Hence, to probe the thermoelectric properties experimentally, epitaxial $\mathrm{S}{\mathrm{c}}_{1-x}{\mathrm{V}}_x{\mathrm{N}}_y$ thin film samples were deposited on MgO(001) substrates. All the samples showed N substoichiometry and pseudocubic crystal structure. The N-vacancy-induced states were visible in the Sc $2p$ x-ray absorption spectroscopy spectra. The reference ScN and $\mathrm{S}{\mathrm{c}}_{1-x}{\mathrm{V}}_x{\mathrm{N}}_y$ samples up to $x=0.12$ were $n$ type, exhibiting carrier concentration of ${10}^{21} \mathrm{c}{\mathrm{m}}^{-3}$, typical for degenerate semiconductors. For the highest V alloying of $x=0.15$, holes became the majority charge carriers, as indicated by the positive Seebeck coefficient. The underlying electronic structure and bonding mechanisms in $\mathrm{S}{\mathrm{c}}_{1-x}{\mathrm{V}}_x{\mathrm{N}}_y$ influence the electrical resistivity, Seebeck coefficient, and Hall effect. Thus, this paper contributes to the fundamental understanding to correlate defects and thermoelectric properties to the electronic structure in the Sc-N system with V alloying.

We investigate the electronic and magnetic properties of graphene channels (2–4 nm wide) embedded within fluorographene, focusing on two distinct interfaces: the fully fluorinated $\alpha$ interface and the half-fluorinated $\beta$ interface. Density functional theory (DFT) calculations reveal that $\alpha \alpha$ systems exhibit semiconducting behavior with antiferromagnetic ordering, closely resembling pristine zigzag graphene nanoribbons. In contrast, $\alpha \beta$ systems display ferromagnetism and a width-dependent semiconductor-to-metal transition. To enable the study of larger systems, we develop and validate effective Hubbard models for both $\alpha \alpha$ and $\alpha \beta$ channels. Building upon DFT results and a Wannier function analysis, these models accurately reproduce the electronic structure and magnetic ordering observed in DFT calculations. Crucially, our $\alpha \beta$ model successfully captures the semiconductor-to-metal transition. Application of this model to larger systems reveals the persistence of a ferromagnetic state with spin polarization localized at the $\alpha$ edge. Our results demonstrate the potential of fluorination for targeted property engineering and provide a basis for exploring graphene-fluorographene systems in device applications ranging from microelectronics to spintronics.

The dipole polarizability of nanorings threaded by an Aharonov-Bohm (AB) magnetic flux displays an intriguing sensitivity to flux values. Thus, for certain characteristic values, neighboring angular momentum eigenstates become degenerate causing the polarizability to diverge. In nonrelativistic settings, such characteristic values correspond to half-integer multiples of the flux quantum ${\mathrm{\Phi }}_0=h/e$. This picture is severely modified in the Dirac model of two-dimensional materials with two distinct valleys. Thus, degeneracy occurs at valley-specific flux values and may shift as far as $\pm 0.2{\mathrm{\Phi }}_0$ in the massless limit representing graphene. Based on an analytic solution of the Dirac equation perturbed by both AB flux and electric fields, we derive an exact expression for the dipole polarizability. Relativistic effects on split divergencies are studied numerically for various geometries and mass terms. Finally, the Dirac equation results are verified by comparison to atomistic models of hexagonal and circular graphene nanorings.

We theoretically investigate the engineering of two-dimensional second-order topological insulators with corner states by coupling two first-order topological insulators. We find that the interlayer coupling between two topological insulators with opposite topological invariants results in the formation of edge state gaps, which are essential for the emergence of the corner states. Using the effective Hamiltonian framework, we elucidate that the formation of topological corner states requires either the preservation of symmetry in the crystal system or effective mass countersigns for neighboring edge states. Our proposed strategy for inducing corner state through interlayer coupling is versatile and applicable to both ${\mathbb{Z}}_2$ topological insulators and quantum anomalous Hall effects. We demonstrate this approach using several representative models including the seminal Kane-Mele model, the Bernevig-Hughes-Zhang model, and the Rashba graphene model to explicitly exhibit the formation of corner states via interlayer coupling. Moreover, we also observe that the stacking of the coupled ${\mathbb{Z}}_2$ topological insulating systems results in the formation of the time-reversal invariant three-dimensional second-order nodal ring semimetals. Remarkably, the three-dimensional system from the stacking of the Bernevig-Hughes-Zhang model can be transformed into second-order Dirac semimetals, characterized by one-dimensional hinge Fermi arcs. Our strategy of engineering second-order topological phases via simple interlayer coupling promises to advance the exploration of higher-order topological insulators in two-dimensional spinful systems.

In view of tunable and nonreciprocal terahertz devices, we study electromagnetic wave scattering from a cluster of gyroelectric core–dielectric shell cylinders. In particular, we consider InSb core-Ge shell cylinders under magnetic fields less than 2.4 T. We expand the electromagnetic fields in terms of the vector cylindrical wave functions and relate the expansion of the scattered field to that of the incident field. We show that a cluster exhibits distinct scattering cross sections upon illumination by oppositely directed waves. The excitation of nondipolar modes in a cluster even as simple as a dimer enables magnetic field switching between highly forward and highly backward scattering patterns. Moreover, nearly complete simultaneous suppression of both forward and backward scattering is feasible. A finite array of cylinders may serve as a magnetic field controlled terahertz beam steerer.

In quantum materials, basic observables such as spectral functions and susceptibilities are determined by Green's functions and their complex quasiparticle spectrum rather than by bare electrons. Even in closed many-body systems, this makes a description in terms of effective non-Hermitian (NH) Bloch Hamiltonians natural and intuitive. Here, we discuss how the abundance and stability of nodal phases is drastically affected by NH topology. While previous work has mostly considered complex degeneracies known as exceptional points as the NH counterpart of nodal points, we propose to relax this assumption by only requiring a crossing of the real part of the complex quasiparticle spectra, which entails a band crossing in the spectral function, i.e., a nodal spectral function. Interestingly, such real crossings are topologically protected by the braiding properties of the complex Bloch bands, and thus generically occur already in one-dimensional systems without symmetry or fine tuning. We propose and study a microscopic lattice model in which a sublattice-dependent interaction stabilizes nodal spectral functions. Besides the gapless spectrum, we identify nonreciprocal charge transport properties after a local potential quench as a key signature of nontrivial band braiding. Finally, in the limit of zero interaction on one of the sublattices, we find a perfectly ballistic unidirectional mode in a nonintegrable environment, reminiscent of a chiral edge state known from quantum Hall phases. Our analysis is corroborated by numerical simulations both in the framework of exact diagonalization and within the conserving second Born approximation.

Quantum materials whose atoms are arranged on a lattice of corner-sharing triangles, i.e., the kagome lattice, have recently emerged as a captivating platform for investigating exotic correlated and topological electronic phenomena. Here, we combine ultralow temperature angle-resolved photoemission spectroscopy (ARPES) with scanning tunneling microscopy and density functional theory calculations to reveal the fascinating electronic structure of the bilayer-distorted kagome material $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$, where Ln stands for Nd and Yb. Distinct from other kagome materials, $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ exhibits twofold, rather than sixfold, symmetries, stemming from the distorted kagome lattice, which leads to a unique electronic structure. Combining experiment and theory we map out the electronic structure and discover double flat bands as well as multiple Van Hove singularities (VHSs), with one VHS exhibiting higher-order characteristics near the Fermi level. Notably, in the magnetic version ${\mathrm{NdTi}}_3{\mathrm{Bi}}_4$, the ultralow base temperature ARPES measurements unveil an unconventional band splitting in the band dispersions which is induced by the ferromagnetic ordering. These findings reveal the potential of bilayer-distorted kagome metals $Ln{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ as a promising platform for exploring novel emergent phases of matter at the intersection of strong correlation and magnetism.