Valley selective hybridization and residual coupling of electronic states in commensurate van der Waals (vdW) heterobilayers enable the control of the orbital character of interlayer excitons. We demonstrate electric field control of layer index, orbital character, lifetime, and emission energy of indirect excitons in ${\mathrm{MoS}}_2/{\mathrm{WS}}_2$ heterobilayers embedded in an vdW field-effect structure. Different excitonic dipoles normal to the layers are found to stem from bound electrons and holes located in different valleys of ${\mathrm{MoS}}_2/{\mathrm{WS}}_2$ with a valley selective degree of hybridization. For the energetically lowest emission lines, coupling of electronic states causes a field-dependent level anticrossing that goes along with a change of the interlayer exciton lifetime from 400 to 100 ns. In the hybridized regime the exciton is delocalized between the two constituent layers, whereas for large positive or negative electric fields, the layer index of the bound hole is field dependent. Our results demonstrate the design of van der Waals solids with the possibility to $\mathit{in}$ situ control their physical properties via external stimuli such as electric fields.

Despite the growing interest in topological materials, the difficulty of experimentally synthesizing and integrating them with other materials has been one of the main barriers restricting access to their unique properties. Recent advances in synthesizing metastable phases of crystalline materials can help to overcome this barrier and offer new platforms to experimentally study and manipulate band topology. Because III-V semiconductors have a wide range of functional material applications (including optoelectronic devices, light-emitting diodes, and highly efficient solar cells) and because Bi-doped III-V materials can be synthesized by ion plantation and ion-cutoff methods, we revisit the effect of bismuth substitution in metastable III-V semiconductors. Through first-principles calculation methods, we show that in wurtzite structure III-V materials, Bi substitution can lead to band inversion phenomena and induce nontrivial topological properties. Specifically, we identify that GaBi and InBi are Dirac-Weyl semimetals, characterized by the coexistence of Dirac points and Weyl points, and ${\text{GaAs}}_{0.5}{\text{Bi}}_{0.5},{\text{GaSb}}_{0.5}{\text{Bi}}_{0.5},{\text{InSb}}_{0.5}{\text{Bi}}_{0.5}$ are triple-point semimetals, characterized by two sets of “near-Dirac” triple points on the Fermi level. These experimentally accessible bismuth-based topological semimetals can be integrated into the large family of functional III-V materials for experimental studies of heterostructures and future optoelectronic applications.

Massive Dirac fermions break the chiral symmetry explicitly and also make the Berry curvature of the band structure non-Abelian. By utilizing the Green's function technique, we develop a microscopic theory to establish a set of quantum diffusive equations for massive Dirac materials in the presence of electric and magnetic fields. It is found that the longitudinal magnetoresistance is always negative and quadratic in the magnetic field, and decays quickly with the mass. The theory is applicable to the systems with non-Abelian Berry curvature and resolves the puzzles of anomalous magnetotransport properties measured in topological materials.

We present time-resolved conductance measurements and charge spectra for the conduction-band states of InAs quantum dots after creating metastable holes by illumination. We demonstrate an electrical way of measuring the conduction-band energy offset and inverse tunnel rates of electrons from a two-dimensional electron gas into neutral ($X^0$), single positively ($X^{1+}$), and double positively ($X^{2+}$) charged exciton states. The experiment also gives information about the metastable hole storage time and discharge dynamics.

We demonstrate that nonequilibrium nanoscopic systems with Majorana zero modes admit a special kind of universality which cannot be classified as strictly transport or strictly thermodynamic in nature. To reveal such a type of Majorana universality we explore purely thermal nonequilibrium states of a quantum dot whose low-energy degrees of freedom are governed by Majorana zero modes. Specifically, the quantum dot is coupled to a topological superconductor, supporting Majorana zero modes, as well as to two normal metallic contacts with the same chemical potentials but different temperatures. It is shown that the Majorana universality in this setup is dual: it is stored inside both the response of the electric current, excited exclusively by the temperature difference, and the quantum dot compressibility. The latter is defined as the derivative of the quantum dot particle number with respect to the chemical potential and forms a universal Majorana ratio with a proper derivative of the electric current that flows in nonequilibrium states of a purely thermal nature.

Non-Hermitian topological systems have been shown to exhibit many interesting properties. However, due to the presence of complex energy spectra and non-Hermitian skin effect (NHSE), the topological edge states will be dynamically unstable and unresolvable from the bulk states which are also localized at the boundaries. Here we propose a one-dimensional nonreciprocal superlattice model in which topological phases are solely induced by the modulated asymmetric hopping amplitude. Most importantly, we can obtain robust real energy spectra, and in the meanwhile, eliminate the NHSE both in the commensurate and incommensurate lattices by tuning the modulation. Thus the topological zero and nonzero energy edge states are stable and distinguishable from the bulk states, which would definitely facilitate the experimental identifications of non-Hermitian topological phases. We further propose a practical scheme to realize this nonreciprocal model by exploiting electrical circuits.

In the present work, we propose an ionic Hamiltonian for describing the interaction of graphene with an adsorbed Co atom. In this approach, the electronic correlation effects, related to the many $d$ orbitals involved in the interaction, are taken into account by selecting appropriate electronic configurations of the adsorbed atom. The Hamiltonian parameters are calculated considering the localized and extended features of the atom-surface interacting system. The physical quantities of interest are calculated by using a Green functions formalism, solved by means of the equations of motion method closed up to a second order in the atom-band coupling term. The charge and spin fluctuations in the adsorbed Co atom are inferred from density functional theory calculations and assuming that the lower energy configurations obey Hund's rules. The calculated spectral densities and the occurrence probabilities of the different atomic configurations are analyzed as a function of the Co energy level positions and the surface temperature. In addition, the conductance spectra are calculated by using the Keldysh formalism and compared with existing measurements. We analyze the behavior, under variable bias and gate potentials, of resonancelike features in the conductance spectra which can be related to transitions between atomic configurations of low occurrence probability.

To separate the motion of the center of mass for the exciton in a constant magnetic field, Donk et al. [Phys. Rev. B 97, 195408 (2018)] considered the case of zero angular momentum and assumed the equality of the electron and hole masses. Within these approximations, they removed the angular momentum operator from the Schrödinger equation and were able to obtain a Hamiltonian describing the electron-hole relative motion. In this Comment paper, we show that the assumptions mentioned above are not justified, and, as a consequence, the given Hamiltonian for the relative motion is incorrect. In addition, we present an analytical procedure (without any assumptions) to separate the center of mass and obtain the exact Hamiltonian for the relative motion, which agrees with the previous theoretical studies.

In the Comment, the authors state that the separation of the relative and center of mass variables in our work is not correct. Here we point out that there is a typographical error, i.e., $q_i$ instead of $-e$, in two of our equations which, when corrected, makes the Comment redundant. Within the ansatzes mentioned in our paper all our results are correct, in contrast to the claims of the Comment.

The localized β-relaxation process is critical for understanding the complex dynamics and controlling the properties of glasses. However, the β-relaxation in most metallic glasses only appears in a form of excess wing or shoulder in dynamic mechanical spectra while the underlying mechanism of the β-relaxation remains elusive. In the present work, the β-relaxation of metallic glasses is systematically studied by calorimetry where the glass-transition temperature ($T_{\mathrm{g}}$) is resolved. The key finding is that the long-time sub-$T_{\mathrm{g}}$ annealing induces an endothermic peak upon heating prior to $T_{\mathrm{g}}$ with an activation energy of $\sim 26R{T}_{\mathrm{g}}$. By using an annealing-scanning-annealing thermal protocol, we show that this distinct endothermic sub-$T_{\mathrm{g}}$ peak is a reversible β-relaxation, indicating that the β-relaxation has both reversible and irreversible parts, which can be refined by the combination of calorimetry and the designed thermal protocol. The results might deepen our understanding of relaxation and the aging of metallic glasses.

From a theoretical perspective, we demonstrate that nanometric magnetic skyrmions are created by application of a circularly polarized microwave magnetic field to a thin-plate Dzyaloshinskii-Moriya ferromagnet with fabricated rectangular holes. This phenomenon is caused by an effective steady magnetic field perpendicular to the microwave-polarization plane induced by the rotating magnetic field and the intense interference of spin waves excited by this magnetic field due to the hole structure, which causes reversals of local magnetizations and results in the formation of skyrmions. Our proposal provides an option to write or create magnetic textures the sizes of which are much smaller than the spot size of the external stimulus such as magnetic field, light, and microwave.

Skyrmions are localized solitonic spin textures with protected topology, which are promising as information carriers in ultradense and energy-efficient logic and memory devices. Recently, magnetic skyrmions have been observed in magnetic thin films, and are stabilized by the extrinsic interfacial Dzyaloshinskii-Moriya interaction (DMI) and/or external magnetic fields. The specific effects in magnetic monolayer materials have not been thoroughly studied. Here, we investigate the intrinsic magnetic skyrmions in a family of monolayer Janus van der Waals magnets, MnSTe, MnSeTe, VSeTe, and MnSSe, by the first-principles calculations combined with the micromagnetic simulations. The monolayer Janus MnSTe, MnSeTe, and VSeTe with out-of-plane geometric asymmetry and strong spin-orbit coupling have a large intrinsic DMI, which could stabilize a sub-50-nm intrinsic skyrmions in monolayer MnSTe and MnSeTe at zero magnetic field. Whereas a monolayer VSeTe with an in-plane easy axis forms a magnetic domain rather than skyrmions. Moreover, the size and shape of skyrmions can be tuned by an external magnetic field. Therefore, our work motivates a vista for seeking intrinsic skyrmions in atomic-scale magnets.

The Nd magnet ${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$ is an indispensable permanent magnet for high-technology commercial products. We study magnetization reversal in hard-soft-hard magnet systems of the atomistic model of the Nd magnet at zero and room temperatures. We present the nucleation and pinning fields as a function of the strength of the anisotropy energy of the soft magnet, estimated by using the stochastic Landau-Lifshitz-Gilbert equation. In the Nd magnet, reflecting the lattice structure, the properties of domain walls (DWs) depend on their moving directions. Bloch and Néel DWs move along the $a$ (or $b$) and $c$ axes, respectively. We investigate the difference in the nucleation and pinning fields between the Bloch and Néel DWs. We also analyze the dependence of the threshold fields on the thickness of the soft magnet. We find that the thermal fluctuation effect affects the threshold fields in the Nd magnet model more significantly than those in the simple anisotropic Heisenberg model [Mohakud et al., Phys. Rev. B 94, 054430 (2016)]. We also find that the strength of the anisotropy energies of the soft magnet phase is not so important for the pinning field, while it is essential for the nucleation field, etc. We discuss the detailed features of the dependencies and their microscopic mechanisms.

Interfacial spin-orbit coupling in Josephson junctions offers an intriguing way to combine anomalous Hall and Josephson physics in a single device. We study theoretically how the superposition of both effects impacts superconductor/ferromagnetic-insulator/superconductor junctions' transport properties. Transverse-momentum-dependent skew tunneling of Cooper pairs through the spin-active ferromagnetic-insulator interface creates sizable transverse Hall supercurrents, to which we refer as anomalous Josephson Hall effect currents. We generalize the Furusaki-Tsukada formula, which got initially established to quantify usual (tunneling) Josephson current flows, to evaluate the transverse current components and demonstrate that their amplitudes are widely adjustable by means of the spin-orbit coupling strengths or the superconducting phase difference across the junction. As a clear spectroscopic fingerprint of Josephson junctions, well-localized subgap bound states form around the interface. By analyzing the spectral properties of these states, we unravel an unambiguous correlation between spin-orbit coupling-induced asymmetries in their energies and the transverse current response, founding the currents' microscopic origin. Moreover, skew tunneling simultaneously acts like a transverse spin filter for spin-triplet Cooper pairs and complements the discussed charge-current phenomena by their spin-current counterparts. The junctions' universal spin-charge-current cross ratios provide valuable possibilities to experimentally detect and characterize interfacial spin-orbit coupling.

The localization tensor is a measure of distinguishability between insulators and metals. This tensor is related to the quantum metric tensor associated with the occupied bands in momentum space. In two dimensions and in the thermodynamic limit, it defines a flat Riemannian metric over the twist-angle space, topologically a torus, which endows this space with a complex structure, described by a complex parameter $\tau$. It is shown that the latter is a physical observable related to the anisotropy of the system. The quantity $\tau$ and the Riemannian volume of the twist-angle space provide an invariant way to parametrize the flat quantum metric obtained in the thermodynamic limit. Moreover, if, by changing the couplings of the theory, the system undergoes quantum phase transitions in which the gap closes, the complex structure $\tau$ is still well defined, although the metric diverges (metallic state), and it is fixed by the form of the Hamiltonian near the gap closing points. The Riemannian volume is responsible for the divergence of the metric at the phase transition.

The fractional Josephson effect remains one of the decisive hallmarks of topologically protected Majorana zero modes. We analyze the effects of parity violating quasiparticle poisoning onto the current voltage characteristics of topological Josephson junctions. We include poisoning events directly within the resistively shunted junction (RSJ) model in the overdamped limit both in the short- and long-junction regime. We calculate the current voltage characteristics numerically where poisoning is modeled either via additional rates in the Fokker-Planck equations or by a time dependent parity and compare them to the limits of no and strong poisoning rates which we obtain analytically. Combining the tilted washboard potential with poisoning events, we show that the critical current of the long junction limit can be used as a probe of the junction topology even in the high temperature poisoning case where relaxation and excitation processes are equally likely. Using the tilted washboard potential model we develop three different schemes to measure the poisoning rate thereby also extending the consideration to two pairs of helical edge states containing a constriction that allows for tunneling between the two pairs of edge states.

Integrated circuits of photonic components are the goal of applied polaritonics. Here, we propose a compact clock generator based on an exciton-polariton micropillar, providing optical signal with modulation frequency up to 100 GHz. This generator can be used for driving polariton devices. The clock frequency can be controlled by the driving laser frequency. The device also features low power consumption (1 pJ/pulse).

We measured the optical reflectivity spectra under applied uniaxial strain for bulk single crystals of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$, which exhibits orbital ordering at 130 K. We found that, with compressive strain, particularly, along the $b$ axis, the reflectivity spectrum at room temperature changes almost in an isotropic manner as if it changes to that at lower temperatures. This experimental result indicates a strong coupling between the orbital degree of freedom and the strain in this compound.

The paper investigates the interaction of femtosecond laser pulses with the thin films of copper, gold, and platinum. It considers electron-phonon relaxation processes and melting in the metal system nonequilibrium heated by laser radiation. Instead of the approximated formula by Wang et al. [Phys. Rev. B 50, 8016 (1994)], which is widely used to determine the temperature dependence of the electron-phonon coupling factor, we propose an improved approach for its more accurate calculation from first principles. Comparison with experiments and other calculations shows our approach to provide good calculation accuracy. Melting time versus absorbed energy density was estimated for the films and shown to be markedly sensitive to latent heat at low absorbed energy densities $(<1$ MJ/kg). Our calculations taken to study the temporal evolution of the (220) diffraction peak intensity after femtosecond irradiation show good agreement between experimental and theoretical data, which was attained due to higher accuracy in our determination of the temperature dependence electron-phonon coupling factor.