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.

We focus on the biorthogonal work statistics of the interacting many-body Hatano-Nelson model after switching on the imaginary vector potential. We introduce a generalized Loschmidt echo $G\left(t\right)$ using the biorthogonal metric operator whose Fourier transform yields the probability distribution of work done. The statistics of work displays several universal features, including an exponential decay with the square of both the system size and imaginary vector potential for the probability to stay in the ground state. Additionally, its high-energy tail follows a universal power law with exponent $-3$. This originates from the peculiar temporal power-law decay of $G\left(t\right)$ with a time-dependent exponent, corresponding to an unusual orthogonality catastrophe. The mean and the variance of work scale linearly and logarithmically with system size, while all higher cumulants are nonextensive. Our results are relevant for nonunitary field theories as well.

In twisted bilayer semiconductors with arbitrary twisting angles, a chiral excitonic system can arise from the interlayer electron-hole Coulomb exchange interaction (Förster coupling) that hybridizes the anisotropic intralayer excitons from individual layers. We present a general framework for the effective exciton Hamiltonian taking into account the electron-hole Coulomb exchange, using twisted homobilayer systems composed of transition metal dichalcogenides or black phosphorus as examples. We demonstrate that such chiral excitonic systems can feature unconventional Hall (Nernst) effects arising from quantum geometric properties characteristic of the layer hybridized wave functions under the chiral symmetry, for example, the time-reversal even-layer Hall counterflow and the crossed nonlinear dynamical Hall effect, when mechanical and statistical force (temperature or density gradient) drives the exciton flow.

The Wannier-Stark localization dynamically alters the entanglement behavior of non-Hermitian free fermions. Utilizing the single-particle correlation matrix technique, we analyze the effective Hamiltonian of these fermions with a Wannier-Stark ladder. Under open boundary conditions, we observe steady-state half-chain entanglement entropy (EE) and identify two distinct area-law regions and an algebraic scaling region. Finite-sized scaling analysis reveals critical scaling behavior of the half-chain EE. Notably, the system demonstrates unique entanglement characteristics under periodic boundary conditions, which diverge from the $(1+1)d$ conformal field theory predictions for Anderson localization. Our findings highlight entanglement phases emerging from the interplay between the non-Hermitian skin effect and disorder-free localization.

The low lattice thermal conductivity in tin selenide is key to its excellent thermoelectric properties. The dominant mechanism for this phononic property, however, is debated. Past lattice-dynamic calculations for SnSe consistently predicted the existence of a phonon bandgap, which is puzzling as it has not been observed in spectroscopic experiments and is typically associated with low phonon-scattering rates in contrast to the observed physical properties. In this work, we accurately investigate the size of the phonon bandgap in SnSe using a direct comparison between experimental neutron spectroscopy, lattice-dynamic calculations, and $abinitio$ molecular dynamics. We theoretically investigate the effects of van der Waals interactions in density functional theory calculations using the popular Grimme D2/D3 and semilocal methods and we also assess the effect of finite-temperature driven anharmonicity using Born-Oppenheimer $abinitio$ molecular dynamics. The D2/D3 lattice dynamics calculations, which assume 0 K, predict a phonon bandgap, although the size and structure depends on the details of the van der Waals correction. In contrast, both the experiment and $abinitio$ dynamics identify there is a valley in the density of states at finite temperature, ascribed to strong anharmonicity that shifts specific phonon modes. This finding highlights the need for great care when applying 0 K lattice dynamics and dispersion corrections to SnSe, with general implications for designing thermoelectric materials via computational methods.

Heterostructures comprising of ferromagnet and nonmagnetic metal (NM) interfaces capable of generating spin torque are crucial for next-generation ultrafast magnetic switching devices. Here we present the effect of change of NM underlayer with different spin-orbit coupling (SOC) strength on the spin-dependent electronic structure of quintessential heterostructures of CoFeB/NM. The results reveal deviations from the conventional expectation of the dependence on the strength of SOC of the NM layer. Dichroic photoemission measurements indicate that the spin polarization of the ferromagnetic CoFeB layer is higher with the weaker-SOC Cu underlayer than that with the stronger-SOC Ta, Pt, and W underlayers. The phase space of the unoccupied electronic states near the Fermi level is found more for the W underlayer system than that of the Cu and Ta underlayer systems.

We study the anomalous Hall effect arising from the altermagnetic order and spin-orbit interaction in doped ${\mathrm{FeSb}}_2$. To investigate the anomalous transport, we have constructed a tight-binding model of ${\mathrm{FeSb}}_2$. We separately considered the constraints imposed on the model parameters by the spin symmetry group and magnetic symmetry group at zero and finite spin-orbit interaction, respectively. The resulting model includes the effect of exchange splitting and is applicable at both zero and finite spin-orbit interaction. In the case of spin symmetry, the analysis covers the spin-only subgroup arising from collinear magnetism, as well as nontrivial symmetry elements. This allows us to explore changes in the hopping amplitudes as symmetry is reduced by spin-orbit interaction from the spin group to the magnetic group. While the anomalous Hall effect is forbidden by spin symmetry, it is allowed by the symmetries of the magnetic group. The intrinsic Hall conductivity is shown to vanish linearly with spin-orbit interaction. This nonanalytic behavior is universal to altermagnets. It originates from the singularity of the Berry curvature localized along lines on a Fermi surface confined to symmetry planes. These planes host spin degeneracy protected by spin symmetry, which is lifted by spin-orbit interaction.

Magnetotransport is often employed as an effective method to study the underlying quantum correction to classical Drude conductivity. Here, we report a rare cooperative correction phenomenon arising from both spin-singlet and spin-triplet channels, which is manifested by the coexistence of weak antilocalization (WAL) effects induced by strong spin-orbit coupling (SOC) of Pt and weak localization (WL) effects due to the Pt spontaneous magnetization in the $\mathrm{Pt/V}{\mathrm{I}}_3$ heterostructures. The magnetoresistance exhibits an unexpected field-independent response at low magnetic fields, which cannot be explained by traditional Lorentz scattering theory or interpreted as a cusplike WAL response. The anomalous Hall signal observed in the heterostructures indicates the emergence spontaneous magnetizations in Pt, and the density functional theory calculations confirm that SOC of Pt at the interface of heterostructures remains robust. Consequently, we reasonably deduce that the unusual magnetotransport behavior fundamentally originates from the quantum cooperative correction of WAL and WL in the heterostructures. However, it proposes a huge challenge for realizing quantum coexistence of two distinct symmetric channels in real materials, thereby highlighting the potential of artificial heterostructures in constructing complex electronic structures and multifunctional electronic devices.