By performing high-pressure single-crystal neutron-diffraction measurements, the evolution of structure and magnetic ordering in ${\mathrm{EuFe}}_2{\mathrm{As}}_2$ under hydrostatic pressure were investigated. Both the tetragonal-to-orthorhombic structural transition and the Fe spin-density-wave transition are gradually suppressed and become decoupled with increasing pressure. The antiferromagnetic order of the Eu sublattice is, however, robust against the applied pressure up to 24.7 kbar, without showing any change of the ordering temperature. Under the pressure of 24.7 kbar, the lattice parameters of ${\mathrm{EuFe}}_2{\mathrm{As}}_2$ display clear anomalies at 27(3) K, well consistent with the superconducting transition observed in previous high-pressure resistivity measurements. Such an anomalous thermal expansion around $T_c$ strongly suggests the appearance of bulk superconductivity and strong electron-lattice coupling in ${\mathrm{EuFe}}_2{\mathrm{As}}_2$ induced by the hydrostatic pressure. The coexistence of long-range ordered Eu antiferromagnetism and pressure-induced superconductivity is quite rare in the ${\mathrm{EuFe}}_2{\mathrm{As}}_2$-based iron pnictides.

The pinning/depinning of an antiferromagnetic (AFM) domain wall is certainly the core issue for AFM spintronic device operation. In this work, we study theoretically the Néel-type domain wall pinning/depinning at a notch in an AFM nanostructure (nanoribbon). The depinning field depending on the notch dimension and intrinsic material properties is deduced and also numerically calculated. Contrary to conventional conception, it is revealed that the depinning field is remarkably dependent on the damping constant and the time-dependent oscillation of domain wall position in the weakly damping regime benefits to the wall depinning, resulting in a gradual saturation of the depinning field with increasing damping constant. A one-dimensional model accounting of the internal dynamics of the domain wall is used to explain perfectly the simulated results. It is demonstrated that the depinning mechanism of an AFM domain wall differs from the ferromagnetic domain wall by exhibiting a depinning typically three orders of magnitude faster than the latter, unveiling another origin for ultrafast dynamics of an AFM system.

We have performed the measurements of the vapor pressure and heat capacity for inert layer ${}^4\mathrm{He}$ adsorbed on a mesoporous silica. The heat capacity was found to exhibit a Schottky peak, indicating the excitation of the localized solid to fluid. We analyzed the heat capacity over a wide temperature range according to a model that considers the contribution of the localized solid and excited fluid, and clarified that the excited fluid coexists with the localized solid at high temperatures. Based on the areal density dependence of the amount of excited fluid, we discuss the formation of an inert layer prior to the appearance of a superfluid layer.

The probability of success of quantum annealing can be improved significantly by pausing the annealer during its dynamics, exploiting thermal relaxation in a controlled fashion. In this paper, we investigate the effect of pausing the quantum annealing of the fully connected ferromagnetic $p$-spin model. This analytically solvable model has a searchlike behavior and is often used as a benchmark for the performances of quantum annealing. We numerically show that: (i) the optimal pausing point is 60% longer than the avoided crossing time for the analyzed instance, and (ii) at the optimal pausing point, we register a 45% improvement in the probability of success with respect to a quantum annealing with no pauses of the same duration. These results are in line with those observed experimentally for less connected models with the available quantum annealers. The observed improvement for the $p$-spin model can be up to two orders of magnitude with respect to an isolated quantum dynamics of the same duration.

Inelastic neutron scattering studies in single crystals of ${\mathrm{TbInO}}_3$ and ${\mathrm{TbIn}}_{0.95}{\mathrm{Mn}}_{0.05}{\mathrm{O}}_3$ with nearly triangular antiferromagnetic lattice are reported. At low energies, a broad and apparently gapless continuum of magnetic excitations, located at the triangular lattice (TL) Brillouin zone boundary, is observed. The data are well described by the uncorrelated nearest-neighbor valence bonds model. At higher energies, a broad excitation branch dispersing from the TL zone boundary is observed. No signs of static magnetic order are found down to the temperatures two orders of magnitude smaller than the effective interaction energy. The fluctuating magnetic moment exceeds two-thirds of the ${\mathrm{Tb}}^{3+}$ free-ion value and is confined to the TL plane. These observations are consistent with a TL-based spin liquid state in ${\mathrm{TbInO}}_3$.

We show that in the $SU\left(2\right)\times U\left(1\right)$ spin-charge gauge approach we developed earlier one can attribute consistently an exclusion statistics with parameter 1/2 to the spinless charge carriers of the $t\text{−}J$ model in two dimensions, as it occurs in one dimension. Like the one-dimensional case, the no-double occupation constraint is at the origin of this fractional exclusion statistics. With this statistics we recover a large Fermi volume of holes at high dopings, close to that of the tight binding approximation. Furthermore, the composite nature of the hole, made of charge and spin carriers only weakly bounded, can provide a natural explanation of many unusual experimental features of the hole-doped cuprates.

We investigate the quench dynamics of a quantum dot strongly coupled to spin-polarized ferromagnetic leads. The real-time evolution is calculated by means of the time-dependent density-matrix numerical renormalization group method implemented within the matrix product states framework. We examine the system's response to a quench in the spin-dependent coupling strength to ferromagnetic leads as well as in the position of the dot's orbital level. The spin dynamics is analyzed by calculating the time-dependent expectation values of the quantum dot's magnetization and occupation. Based on these, we determine the time dependence of a ferromagnetic-contact-induced exchange field and predict its nonmonotonic buildup. In particular, two timescales are identified, describing the development of the exchange field and the dot's magnetization sign change. Finally, we study the effects of finite temperature on the dynamical behavior of the system.

We investigate different types of time-dependently driven single-particle sources whose common feature is that they produce pulses of integer charge and minimally excite the Fermi sea. These sources are: a slowly driven mesoscopic capacitor, a Lorentzian-shaped time-dependent bias voltage, and a local gate-voltage modulation of a quantum Hall edge state. They differ by their specific driving protocols, e.g., they have a pure ac driving or a driving with a dc component. In addition, only in the first of these setups, strong confinement leading to a discrete energy spectrum of the conductor, is exploited for the single-particle emission. Here, we study if and how these basic differences impact transport properties. Specifically, we address time- and energy-resolved charge and energy currents, as well as their zero-frequency correlators (charge, energy, and mixed noise), as they are frequently used to characterize experiments in quantum optics with electrons. Beyond disparities due to a different number and polarity of particles emitted per period, we in particular identify differences in the impact, which temperature has on the observables for sources with and without energy-dependent scattering properties. We are able to characterize and quantify the effect of temperature by a small set of physically relevant parameter ratios.

Majorana zero modes are a promising platform for topologically protected quantum information processing. Their non-Abelian nature, which is key for performing quantum gates, is most prominently exhibited through braiding. While originally formulated for two-dimensional systems, it has been shown that braiding can also be realized using one-dimensional wires by forming an essentially two-dimensional network. Here, we show that in driven systems far from equilibrium, one can do away with the second spatial dimension altogether by instead using quasienergy as the second dimension. To realize this, we use a Floquet topological superconductor which can exhibit Majorana modes at two special eigenvalues of the evolution operator, 0 and $\pi$, and thus can realize four Majorana modes in a single, driven quantum wire. We describe and numerically evaluate a protocol that realizes a topologically protected exchange of two Majorana zero modes in a single wire by adiabatically modulating the Floquet drive and using the $\pi$ modes as auxiliary degrees of freedom.

We study one-dimensional Floquet topological insulators with chiral symmetry going beyond the standard rotating wave approximation. The occurrence of many anticrossings between Floquet replicas leads to a dramatic extension of phase diagram regions with stable topological edge states (TESs). We present an explicit construction of all TESs in terms of a truncated Floquet Hamiltonian in frequency space, prove the bulk-boundary correspondence, and analyze the stability of the TESs in terms of their localization lengths. We propose experimental tests of our predictions in curved bilayer graphene.

In this Rapid Communication, we discuss the characteristic features of one-dimensional topological insulators with inversion symmetry but noncentered inversion axis in the unit cell, for any choice of the unit cell. In these systems, the global inversion operation generates a $k$-dependent inversion operator within the unit cell and this implies a nonquantized Zak's phase both for the trivial and nontrivial topological phases. By relating the Zak's phase with the eigenvalues of modified parity operators at the inversion invariant momenta, a corrected quantized form of the Zak's phase is derived. We show that finite energy topological edge states of this family of chains are symmetry protected not by usual chiral symmetry but by a hidden sublattice chiral-like symmetry. A simple justification is presented for shifts in the polarization quantization relation for any choice of endings of these chains.

The low-energy Dirac and Weyl spectra are allowed to violate the Lorentz symmetry and thereby have a tilted energy dispersion. The tilt in the energy dispersion induces a Hall voltage in the plane spanned by the electric field and the tilt velocity. In the presence of a magnetic field the planar Hall conductivity and resistivity show Shubnikov–de Haas oscillations. The oscillations in the planar Hall effect can become a fingerprint to spot the anomalous transport in Dirac and Weyl semimetals.

Two-dimensional semiconductors feature valleytronics phenomena due to locking of the spin and momentum valley of the electrons. However, the valley polarization is intrinsically limited in monolayer crystals by the fast intervalley electron-hole exchange. Heterobilayer crystals have been shown to have a longer exciton lifetime and valley depolarization time. Yet most reported valley polarization was low; the valley selection rules and mechanisms of valley depolarization remain controversial. Here, we show that nearly pure valley polarizations are achievable in high-quality heterostructures with precise momentum-valley alignment. Together with time-resolved and temperature dependence measurements, we furthermore identify both singlet and brightened triplet interlayer excitons with opposite valley polarizations, which originate from direct band-gap transitions and are localized at the $H_h^h$ atomic registry—corresponding to the band minima of the heterostructure. Our results also reveal ultrafast interlayer electron transfer and strongly suppressed interlayer exciton valley depolarization. Our results pave the way for using semiconductor heterobilayers to control valley selection rules for valleytronic applications.

Motivated by the recent activities on the diamond lattice antiferromagnet ${\mathrm{NiRh}}_2{\mathrm{O}}_4$ with ${\mathrm{Ni}}^{2+}3d^8$ local moments, we theoretically explore on general grounds the unique spin and orbital physics for the diamond lattice antiferromagnet with $3d^8$ local moments. The superexchange interaction between the local moments usually favors magnetic orders. Due to the particular electron configuration of the $3d^8$ ion with a partially filled upper $t_{2g}$ level and a fully filled lower $e_g$ level, the atomic spin-orbit coupling becomes active at the linear order and would favor a spin-orbital-entangled singlet with quenched local moments in the single-ion limit. Thus, the spin-orbital entanglement competes with the superexchange and could drive the system to a quantum critical point that separates the spin-orbital singlet and the magnetic order. We further explore the effects of magnetic field and uniaxial pressure. The nontrivial response to the magnetic field is intimately tied to the underlying spin-orbital structure of the local moments. We discuss future experiments such as doping and pressure and point out the correspondence between different electron configurations.

By calculating the differential tunneling conductance spectra from the two ends of a Majorana nanowire with a quantum dot embedded at one end, we establish that a careful examination of the nonlocal correlations of the zero-bias conductance peaks, as measured separately from the two ends of the wire, can distinguish between topological Majorana bound states and trivial Andreev bound states. In particular, there will be identical correlated zero-bias peaks from both ends for Majorana bound states, and thus the presence of correlated zero-bias conductance from the two wire ends could imply the presence of topological Majorana zero modes in the system. On the contrary, there will not be identical correlated zero-bias peaks from both ends for Andreev bound states, so the absence of correlated zero-bias conductance from the two wire ends implies the absence of topological Majorana zero modes in the system. We present detailed results for the calculated conductance, energy spectra, and wave functions for different chemical potentials at the same magnetic field values to motivate end-to-end conductance correlation measurements in Majorana nanowires.

We investigate the decay of Ag islands on Cu(111) by variable low temperature scanning tunneling microscopy between 195 and 250 K. Such islands exhibit a misfit dislocation pattern forming $\left(8\times 8\right)$ to $\left(10\times 10\right)$ superstructures because of a major lattice mismatch between silver and copper. The decay of islands smaller than $200{\mathrm{nm}}^2$ alternates between a slower and a faster decay. It is slower for specific island sizes, in particular those with magic numbers of superstructure unit cells. We relate these changes to the complexity of the heteroepitaxial decay, involving a deconstruction of the misfit dislocation pattern and a simultaneous diffusion of several adspecies during decay.

In the last years, electric fields have been used to control the magnetic exchange interactions and anisotropies in nanometric devices. In this paper, we study the spin-spin exchange interaction between two magnetic impurities embedded in a three-dimensional nonrelativistic electron gas, namely the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. The gas is confined in an insulating structure, and an applied voltage produces local changes in the electron density, which modulates the Fermi level of the system. Using a simple model, we demonstrate that this voltage modifies the strength and wavelength of the coupling between the impurities. Depending on the voltage, the effective RKKY exchange can change from a ferro- to an antiferromagnetic coupling, and vice versa. The spin-spin coupling can also be switched on and off by the voltage.