Bulk and surface electronic states of ${\mathrm{MnPSe}}_3$ have been investigated by means of x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and theoretical calculations. In Mn $2p$ XPS, the main peak is accompanied by a charge-transfer satellite which is commonly observed in various Mn chalcogenides. The intensity of the charge-transfer satellite is considerably reduced by oxidization of the surface. The multiplet structure of Mn $2p$ XAS indicates the high spin ${\mathrm{Mn}}^{2+}$ configuration. The cluster model analyses of the XPS and XAS spectra indicate that the Se $4p$-to-Mn $3d$ charge-transfer energy $\mathrm{\Delta }$ is negative providing the strong $p-d$ hybridization. The magnetic interaction between the third nearest neighboring Mn spins is enhanced by the smallness of $\mathrm{\Delta }$ and the unique molecular orbitals of the ${\mathrm{P}}_2{\mathrm{Se}}_6$ cluster.

We discuss the implications of a small indium content (3%) in a GaAs epilayer on the electron and nuclear spin relaxation due to enhanced quadrupolar effects induced by the strain. Using the weakly perturbative spin noise spectroscopy, we study the electron spin relaxation dynamics without explicit excitation. The observed temperature dependence indicates the presence of localized states, which have an increased interaction with the surrounding nuclear spins. Time-resolved spin noise spectroscopy is then applied to study the relaxation dynamics of the optically pumped nuclear spin system. It shows a multi-exponential decay with time components, ranging from several seconds to hundreds of seconds. Further, we provide a measurement of the local magnetic field acting between the nuclear spins and discover a strong contribution of quadrupole effects. Finally, we apply the nuclear spin diffusion model, that allows us to estimate the concentration of the localized carrier states and to determine the nuclear spin diffusion constant characteristic for this system.

We study the deep-ultraviolet emission in Bernal boron nitride as a function of temperature. The quasidegeneracy of indirect and direct excitons in Bernal boron nitride leads to their simultaneous recombination, allowing a comparison of phonon-assisted broadening in the two cases. Temperature-dependent measurements reveal that below 200 K, the efficiency of phonon-assisted broadening is one order of magnitude lower for the direct transition at 6.035 eV than for the phonon replicas of the indirect exciton. This striking effect results from the inhibition of quasielastic acoustic phonon scattering in the strong-coupling regime of the light-matter interaction, where the density of final states is reduced by the curvature of the polaritonic dispersion.

We investigate the possibility of achieving valley filtering and enhanced negative differential resistance (NDR) in transition metal dichalcogenide (TMD)-based optoelectronic superlattice (SL). The multipeak NDR is predicted to occur in this system, the operation window of which is controlled successively by the resonant tunneling through miniband regime and the Wannier-Stark ladder regime. It is shown that the synergy of the electric and light stimulus can bring the pure valley current and pronounced peak-to-valley current ratio (PVCR). Our findings illustrate the origin of multipeak responses and provide a theoretical basis for designing devices that can generate pure valley current with complex NDR characteristics.

We derive two second-order exchange terms in the $GW$ electron-hole interaction kernel. The contributions of these terms have been neglected in the conventional $GW +$ Bethe-Salpeter method, and we implement them in an all-electron mixed basis program. To reveal the effect of these terms, we apply them to 28 molecules of Thiel's benchmark set and compare the $S_1$ excitation energies with those obtained from the conventional $GW +$ Bethe-Salpeter method. In addition, using the exciton analysis method with exciton wave functions, we estimate the expectation values for each term in the $GW$ electron-hole interaction kernel. The contribution of the two second-order exchange terms is approximately 0.1–0.2 eV at the exciton states of the $n\to {\pi }^{*}$ transition; however, the contributions are smaller for the $\pi \to {\pi }^{*}$ and $\pi \to$ Rydberg transitions. Our findings reveal that the errors of the conventional $GW +$ Bethe-Salpeter method are potentially reduced by considering these terms; however, the extent of the corrections is insufficient for the underestimated excitation energies. We believe that our findings are a significant step towards advancing the conventional $GW +$ Bethe-Salpeter method.

The band structure and magnetic properties of organic charge-transfer salt $\lambda \text{−}{\left(\text{BEDSe-TTF}\right)}_2{\mathrm{GaCl}}_4$ [BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $\lambda$-BEDSe] are investigated. The reported crystal structure is confirmed using x-ray diffraction measurements, and the transfer integrals are calculated. The degree of electron correlation $U/W$ ($U$: on-site Coulomb repulsion, $W$: bandwidth) of $\lambda$-BEDSe is larger than one and comparable to that of the isostructural Mott insulator $\lambda -({\mathrm{ET})}_2{\mathrm{GaCl}}_4$ (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as $\lambda$-ET), whereas the $U/W$ of the superconducting salt $\lambda -({\mathrm{BETS})}_2{\mathrm{GaCl}}_4$ [BETS: bis(ethylenedithio)tetraselenafulvalene] is smaller than one. ${}^{13}\mathrm{C}$-NMR and $\mu \mathrm{SR}$ measurements revealed that $\lambda$-BEDSe undergoes an antiferromagnetic (AF) ordering below $T_{\mathrm{N}}=22$ K. In the AF state, discrete ${}^{13}\mathrm{C}$-NMR spectra with a remaining central peak are observed, indicating the commensurate AF spin structure also observed in $\lambda$-ET. The similarity of the structural and magnetic properties between $\lambda$-BEDSe and $\lambda$-ET suggests that both salts are in the same electronic phase, i.e., the physical properties of $\lambda$-BEDSe can be understood by the universal phase diagram of bandwidth-controlled $\lambda$-type organic conductors obtained by donor molecule substitution.

The optical properties of monocrystalline, intrinsic silicon are of interest for technological applications as well as fundamental studies of atom-surface interactions. For an enhanced understanding, it is of great interest to explore analytic models which are able to fit the experimentally determined dielectric function $\epsilon (T_{\mathrm{\Delta }},\omega )$, over a wide range of frequencies and a wide range of the temperature parameter $T_{\mathrm{\Delta }}=(T-T_0)/T_0$, where $T_0=293\mathrm{K}$ represents room temperature. Here, we find that a convenient functional form for the fitting of the dielectric function of silicon involves a Lorentz-Dirac curve with a complex, frequency-dependent amplitude parameter, which describes radiation reaction. We apply this functional form to the expression $[\epsilon (T_{\mathrm{\Delta }},\omega )-1]/[\epsilon (T_{\mathrm{\Delta }},\omega )+2]$, inspired by the Clausius-Mossotti relation. With a very limited set of fitting parameters, we are able to represent, to excellent accuracy, experimental data in the (angular) frequency range $0<\omega <0.16\mathrm{a}.\mathrm{u}.$ and $0<T_{\mathrm{\Delta }}<2.83$, corresponding to the temperature range $293\mathrm{K}<T<1123\mathrm{K}$. Using our approach, we evaluate the short-range $C_3$ and the long-range $C_4$ coefficients for the interaction of helium atoms with the silicon surface. In order to validate our results, we compare to a separate temperature-dependent direct fit of $\epsilon (T_{\mathrm{\Delta }},\omega )$ to the Lorentz-Dirac model.

We demonstrate numerically that a robust and unusual multifractal regime can emerge in a one-dimensional quantum chain with maximally correlated disorder, above a threshold disorder strength. This regime is preceded by a mixed and an extended regime at weaker disorder strengths, with the former hosting both extended and multifractal eigenstates. The multifractal states we find are markedly different from conventional multifractal states in their structure, as they reside approximately uniformly over a continuous segment of the chain, and the lengths of these segments scale nontrivially with system size. This anomalous nature also leaves imprints on dynamics. An initially localized wave packet shows ballistic transport, in contrast to the slow, generally subdiffusive, transport commonly associated with multifractality. However, the timescale over which this ballistic transport persists again scales nontrivially with the system size.

Time evolution of an infinite two-dimensional (2D) many body quantum lattice system can be described by the Suzuki-Trotter decomposition applied to the infinite projected entangled pair state (iPEPS). Each Trotter gate increases the bond dimension of the tensor network, $D$, that has to be truncated back in a way that minimizes a suitable error measure. This paper goes beyond simplified error measures–like the one used in the full update, the simple update, and their intermediate neighborhood tensor update–and directly maximizes an overlap between the exact iPEPS with the increased bond dimension and the new iPEPS with the truncated one. The optimization is performed in a tangent space of the iPEPS variational manifold. This gradient tensor update is benchmarked by a simulation of a sudden quench of a transverse field in the 2D quantum Ising model and the quantum Kibble-Zurek mechanism in the same 2D system.

Surface curvature of magnetic systems can lead to many static and dynamic effects which are not present in flat systems of the same material. These emergent magnetochiral effects can lead to frequency nonreciprocity of spin waves, which has been shown to be a bulk effect of dipolar origin and is related to a curvature-induced symmetry breaking in the magnetic volume charges. So far, such effects have been investigated theoretically mostly for thin shells, where the spatial profiles of the spin waves can be assumed to be homogeneous along the thickness. Here, using a finite-element dynamic-matrix approach, we investigate the transition of the spin-wave spectrum from thin to thick curvilinear shells, at the example of magnetic nanotubes in the vortex state. With increasing thickness, we observe the appearance of higher-order radial modes which are strongly hybridized and resemble the perpendicular-standing spin waves (PSSWs) in flat films. Along with an increasing dispersion asymmetry, we uncover the curvature-induced nonreciprocity of the mode profiles. This is explained in a very simple, general picture for thick curvilinear shells, considering the inhomogeneity of the emergent geometric volume charges along the thickness of the shell. Such curvature-induced mode-profile asymmetry also leads to nonreciprocal hybridization, which can facilitate unidirectional spin-wave propagation. With that, we also show how curvature allows for nonlinear three-wave splitting of a higher-order radial mode into secondary modes which can also propagate unidirectionally. We believe that our study provides a significant contribution to the understanding of the spin-wave dynamics in curvilinear magnetic systems, and also advertises these for novel magnonic applications.

Samples of $\left({\mathrm{Mn}}_{1-x}{\mathrm{Co}}_x\right)\mathrm{Si}$ with $x=0.15$ and $x=0.17$ were grown, and their physical properties: magnetization, magnetic susceptibility, resistivity, and heat capacity were studied. The data analysis included previous results at $x=0.057,0.063,\mathrm{and}0.09$. The doping of MnSi with Co completely destroys the helical phase transition, but it saves the helical fluctuation area normally situated slightly above the phase-transition temperature. This area, spreading from $\sim 5$ to 0 K does not change much with doping and forms some sort of helical fluctuation cloud, revealing the quantum critical properties: $C_p/T\to \infty$ at $T\to 0$.

We report a comprehensive study of the ${\mathrm{Zr}}_5{\mathrm{Pt}}_3{\mathrm{C}}_x$ superconductors, with interstitial carbon between 0 and 0.3. At a macroscopic level, their superconductivity, with $T_c$ ranging from 4.5 to 6.3 K, was investigated via electrical-resistivity, magnetic-susceptibility, and specific-heat measurements. The upper critical fields ${\mu }_0{H}_{\mathrm{c}2}\sim 7$ T were determined mostly from measurements of the electrical resistivity in applied magnetic field. The microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($\mu \mathrm{SR}$) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electronic density of states at the Fermi level, dominated by the Zr $4d$ orbitals. The low-temperature superfluid density, obtained via transverse-field $\mu \mathrm{SR}$, suggests a fully gapped superconducting state in ${\mathrm{Zr}}_5{\mathrm{Pt}}_3$ and ${\mathrm{Zr}}_5{\mathrm{Pt}}_3{\mathrm{C}}_{0.3}$, with zero-temperature gap ${\mathrm{\Delta }}_0=1.20$ and 0.60 meV and magnetic penetration depth ${\lambda }_0$ = 333 and 493 nm, respectively. The exponential dependence of the NMR relaxation rates below $T_c$ further supports nodeless superconductivity. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field $\mu \mathrm{SR}$ measurements, confirms the preserved time-reversal symmetry in the superconducting state of ${\mathrm{Zr}}_5{\mathrm{Pt}}_3{\mathrm{C}}_x$. In contrast to a previous study, our $\mu \mathrm{SR}$ and NMR results suggest conventional superconductivity in the ${\mathrm{Zr}}_5{\mathrm{Pt}}_3{\mathrm{C}}_x$ family, independent of the C content.

The rapid irradiation and heating of matter can lead to material removal via a process known as ablation. While previous investigations have focused on ablation with optical and soft x-ray pulses, the process is not well understood for the high-energy x-rays delivered at current x-ray free electron laser facilities. In this paper, we use hybrid two-temperature model molecular dynamics simulations to determine the damage threshold and dynamics for tantalum foils under irradiation with x-rays in the range 1–5 keV. We report that damage occurs for foils with thickness $\ge 300$ nm when heated to around 1.25 eV/atom. This damage results from the combined processes of melting and cavitation, finally resulting in the removal of material layers. The predictions of this study, in terms of the cavitation threshold and underlying dynamics, could guide interpretation of experiments as well as applications including development of beamline optics for free-electron lasers. We report consistency between cavitation and ablation behavior in isochoric heating experiments and spall processes in hydrodynamic compression and release experiments, confirming the primary modes of damage are mechanical in nature for the x-ray energies investigated.

We investigate entanglement dynamics in continuously monitored open quantum systems featuring current-carrying nonequilibrium states. We focus on a prototypical one-dimensional model of boundary-driven noninteracting fermions with monitoring of the local density, whose average Lindblad dynamics features a well-studied ballistic to diffusive crossover in transport. Here we analyze the dynamics of the fermionic negativity, mutual information, and purity along different quantum trajectories. We show that monitoring this boundary-driven system enhances its entanglement negativity at long times, which otherwise decays to zero in the absence of measurements. This result is in contrast with the case of unitary evolution where monitoring suppresses entanglement production. For small values of $\gamma$, the stationary-state negativity shows a logarithmic scaling with system size, transitioning to an area-law scaling as $\gamma$ is increased beyond a critical value. Similar critical behavior is found in the mutual information, while the late-time purity shows no apparent signature of a transition, being $O\left(1\right)$ for all values of $\gamma$. Our work unveils the double role of weak monitoring in current-driven open quantum systems, simultaneously damping transport and enhancing entanglement.

We theoretically investigate a nonlinear spin Hall effect in $\mathcal{PT}$-symmetric antiferromagnetic metals, which serve as an efficient spin current generator. We elucidate that an emergent spin-dependent Berry curvature dipole is a microscopic origin of the nonlinear spin Hall effect, which becomes nonzero with neither relativistic spin-orbit coupling, uniform magnetization, nor spin-split band structure. By analyzing a microscopic antiferromagnetic model without spin-orbit coupling for an intuitive understanding of the phenomena, we elucidate essential hopping processes and a condition to enhance the nonlinear spin Hall conductivity. We also provide a complete table to include useful correspondence among the Néel vector, odd-parity multipoles, nonlinear spin conductivity tensor, and candidate materials in all the $\mathcal{PT}$-symmetric black-and-white magnetic point groups.

Magnetic frustration, arising from the competition of exchange interactions, has received great attention because of its relevance to exotic quantum phenomena in materials. In the current work, we report an unusual checkerboard-shaped scattering anomaly in ${\mathrm{FeGe}}_2$, far from the known incommensurate magnetic satellite peaks, by inelastic neutron scattering. More surprisingly, such phenomenon appears as spin dynamics at low temperature, but it becomes prominent above Néel transition as elastic scattering. A model Hamiltonian that includes an intraplane next-nearest neighbor was proposed and such anomaly is attributed to the near-perfect magnetic frustration and the emergence of unexpected two-dimensional magnetic order in the quasi-one-dimensional ${\mathrm{FeGe}}_2$.