The generic nonequilibrium evolution of a strongly interacting fermionic system is studied. For strong quenches, a collective collapse-and-revival phenomenon is found to extend over the whole Brillouin zone. A qualitatively distinct behavior occurs for weak quenches where only weak wiggling occurs. Surprisingly, no evidence for prethermalization is found in the weak-coupling regime. In both regimes, indications for relaxation beyond oscillatory or power-law behavior are found and used to estimate relaxation rates without resorting to a probabilistic ansatz. The relaxation appears to be fastest for intermediate values of the quenched interaction.

This work probes the relevance of oxygen vacancies in the formation of local ferromagnetic coupling between Fe ions at octahedral sites in zinc ferrites. This coupling gives rise to a ferrimagnetic ordering with the Curie temperatures above room temperature in an otherwise antiferromagnetic compound. This conclusion is based on experimental results from x-ray magnetic circular dichroism measurements at the $\mathrm{Fe}{\mathrm{L}}_{2,3}$ edges and magnetization measurements performed on zinc ferrites, nanoparticles, and films, with different cation distributions and oxygen vacancy concentrations. Our observations are confirmed by density-functional-theory calculations and indicate that the enhanced ferrimagnetic response observed in some nominally nonmagnetic or antiferromagnetic ferrites can be taken as a further example of the defect-induced magnetism phenomenon.

We report here on the electrical detection of the ferromagnetic resonance in a notched Py stripe using the spin rectification effect. A lock-in detection technique is used to measure the rectified voltage generated when applying a radio-frequency field. The multiple peaks associated with the presence of a domain wall, observed during field scans, are properly identified with the help of dynamical micromagnetic simulations. It is found that at any frequency below 6 GHz some specific areas of the inhomogeneous magnetization within the domain wall can find a resonant condition and generate a voltage by rectification of the induction currents in the circuit.

The iron platinum arsenides ${\mathrm{Ca}}_{10}\left({\mathrm{Fe}}_{1-x}{\mathrm{Pt}}_x\mathrm{As}{)}_{10}\right({\mathrm{Pt}}_n{\mathrm{As}}_8)$ are the first Fe-based superconductors with metallic spacer layers. Furthermore they display a large variation in their critical temperatures depending on the amount of Pt in their spacer layers: $(n=3,4)$. To gain more insight into the role of the spacer layer the electronic structures of the iron platinum arsenides are represented in the momentum space of the underlying Fe sublattice using a first-principles unfolding method. We find that ${\mathrm{Ca}}_{10}\left(\mathrm{Fe}\mathrm{As}{)}_{10}\right({\mathrm{Pt}}_4{\mathrm{As}}_8)$, contrary to ${\mathrm{Ca}}_{10}\left(\mathrm{Fe}\mathrm{As}{)}_{10}\right({\mathrm{Pt}}_3{\mathrm{As}}_8)$, shows a net electron doping and a non-negligible interlayer coupling. Both effects could account for the difference in the critical temperatures.

The $d$-band shape of a metal site, governed by the local geometry and composition of materials, plays an important role in determining trends of the surface reactivity of transition-metal alloys. We discuss this phenomenon using the chemisorption of various adsorbates such as C, N, O, and their hydrogenated species on Pd bimetallic alloys as an example. For many alloys, the $d$-band center, even with consideration of the $d$-band width and $\mathit{sp}$ electrons, can not describe variations in reactivity from one surface to another. We investigate the effect of the $d$-band shape, represented by higher moments of the $d$ band, on the local electronic structure of adsorbates, e.g., energy and filling of adsorbate-metal antibonding states. The upper $d$-band edge ${\varepsilon }_u$, defined as the highest peak position of the Hilbert transform of the density of states projected onto $d$ orbitals of an active metal site, is identified as an electronic descriptor for the surface reactivity of transition metals and their alloys, regardless of variations in the $d$-band shape. The utilization of the upper $d$-band edge with scaling relations enables a considerable reduction of the parameter space in search of improved alloy catalysts and further extends our understanding of the relationship between the electronic structure and chemical reactivity of metal surfaces.

The dressing of quasiparticles in solids is investigated by changes in the electronic structure $E$($k$) driven by femtosecond laser pulses. Employing time- and angle-resolved photoemission on an optimally doped cuprate above $T_{\mathrm{c}}$, we observe two effects with different characteristic temporal evolutions and, therefore, different microscopic origins. First, a marked change in the effective mass due to the 70-meV kink in $E$($k$) is found to occur during the experiment's 100-fs temporal resolution and is assigned to laser-driven perturbation of an electronic interaction dressing the bare band. Second, a change in $k_{\mathrm{F}}$ is explained by effective photodoping due to particle-hole asymmetry and offers opportunities for ultrafast optoelectronic switches based on an optically driven insulator-superconductor transition.

We investigate the effect of a scanning gate tip on the nonlinear quantum transport properties of nanostructures. Generally, we predict that the symmetry of the current-voltage characteristic in reflection-symmetric samples is broken by a tip-induced rectifying conductance correction. Moreover, in the case of a quantum point contact (QPC), the tip-induced rectification term becomes dominant as compared to the change of the linear conductance at large tip-QPC distances. Calculations for a weak tip probing a QPC modeled by an abrupt constriction show that these effects are experimentally observable.

We have investigated the temperature ($T$)-dependent evolution of orbital states in a typical spin-orbital-lattice-coupled $2p$ electron Mott system $\mathrm{K}{\mathrm{O}}_2$, based on the electronic structures obtained by the dynamical mean-field theory as well as the density functional theory. We have shown that $\mathrm{K}{\mathrm{O}}_2$ exhibits the orbital fluctuation feature at high $T$ due to degenerate ${\pi }_g^{*}$ orbitals. Upon cooling, the orbital fluctuation is suppressed by the Jahn-Teller-type crystal field that becomes stronger with the lowering of structural symmetry, and then the ferro-orbital (FO) ordering emerges at low $T$. This FO ordering feature distinguishes $\mathrm{K}{\mathrm{O}}_2$ from $\mathrm{Rb}{\mathrm{O}}_2$ and $\mathrm{Cs}{\mathrm{O}}_2$ in that the latter two seem to have antiferro-orbital orderings at low $T$, indicating that the underlying physics is different between them. We propose that the suppression of the orbital fluctuation in $\mathrm{K}{\mathrm{O}}_2$ can be observed by thermal-conductivity measurement, as observed in spin-orbital-lattice-coupled $3d$ transition-metal oxides such as $\mathrm{LaV}{\mathrm{O}}_3$.

We study the quantum point contact between the topological superconductor and the helical Luttinger liquid. The effects of the electron-electron interactions in the helical Luttinger liquid on the low-energy physics of this system are analyzed by the renormalization group. Among the various couplings at the point contact which arises from the tunneling via the Majorana edge channel, the induced backscattering in the helical Luttinger liquid is the most relevant for repulsive interactions. Hence, at low temperatures, the helical Luttinger liquid is effectively cut into two separated half wires. As a result, the low-temperature physics is described by a fixed point consisting of two leads coupled to the topological superconductor, and the electrical transport properties through the point contact at low temperature and low bias are dominated by the tunneling via the Majorana edge channel. We compute the temperature dependence of the zero-bias tunneling conductance and study the full counting statistics for the tunneling current at zero temperature.

This paper reports on magnetometry and magnetoresistance measurements of MnSi epilayers performed in out-of-plane magnetic fields. We present a theoretical analysis of the chiral modulations that arise in confined cubic helimagnets where the uniaxial anisotropy axis and magnetic field are both out-of-plane. In contrast to in-plane field measurements [Wilson et al., Phys. Rev. B 86, 144420 (2012)], the hard-axis uniaxial anisotropy in MnSi/Si(111) increases the energy of (111)-oriented skyrmions and in-plane helicoids relative to the cone phase, and it makes the cone phase the only stable magnetic texture below the saturation field. While induced uniaxial anisotropy is important in stabilizing skyrmion lattices and helicoids in other confined cubic helimagnets, the particular anisotropy in MnSi/Si(111) entirely suppresses these states in an out-of-plane magnetic field. However, it is predicted that isolated skyrmions with enlarged sizes exist in MnSi/Si(111) epilayers in a broad range of out-of-plane magnetic fields. These results reveal the importance of the symmetry of the anisotropies in bulk and confined cubic helimagnets in the formation of chiral modulations, and they provide additional evidence of the physical nature of the $A$-phase states in other B20 compounds.

It was recently established that spin injection from a ferromagnetic metal into an organic semiconductor depends largely on the formation of hybrid interface states. Here we investigate whether the magnetic properties of the interface between cobalt and tris(8-hydroxyquinolinato)-Al(III) (${\text{Alq}}_3$), the most prominent molecular candidate for organic spin-valve devices, can be modified by substituting the aluminum atom with either gallium or indium. The electronic structure of ${\text{Alq}}_3$, ${\text{Gaq}}_3$, and ${\text{Inq}}_3$ and the properties of their interfaces with ferromagnetic cobalt are probed experimentally, by using different photoemission spectroscopy methods, and theoretically, through density functional theory calculations. For all cases, the results highlight the presence of spin-polarized interface states. However no striking difference between the properties of the various molecules and interfaces is observed. This is a consequence of the fact that the molecules frontier orbitals are mainly localized on the ligands and they show only a negligible contribution coming from the metal ion.

Epitaxial ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4/{\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3$ (LSCO/LCMO) superlattices on $\left(001\right)$-oriented ${\mathrm{LaSrAlO}}_4$ substrates have been grown with pulsed laser deposition technique. Their structural, magnetic, and superconducting properties have been determined with in situ reflection high-energy electron diffraction, x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy, electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO ($a=0.3779$ nm) and LCMO ($a=0.387$ nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the ${\mathrm{LaSrAlO}}_4$ substrate, a sizable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of $T_c^{\text{onset}}\approx 36$ K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for $H$ $\parallel$ $ab$ and a sizable paramagnetic shift for $H$ $\parallel$ $c$ that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of $T^{\text{Curie}}\approx 190$ K and a large low-temperature saturation moment of about 3.5(1) ${\mu }_B$ per Mn ion. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-x}/{\text{La}}_{2/3}{\text{Ca}}_{1/3}{\text{MnO}}_3$ superlattices, may allow one to identify the relevant mechanisms.

We revisit the atomic structure and microstructure of the so-called supertetragonal phases of highly strained epitaxial ${\text{BiFeO}}_3$ thin films. Quantitative atomic resolution scanning transmission electron microscopy is used to directly image the atomic positions. A crystallographic phase suggested by electron diffraction and predicted by ab initio calculations is evidenced. Microtwins are reported in thickest films. Electron energy loss spectroscopy is further employed to reveal subtle electronic structure features, which, interpreted in a framework of antiferrodistortive distortions coupling with the substrate, point towards a phase closer to the $P$4mm purely tetragonal phase.

An antiferromagnetic ordering in ${\mathrm{Pb}}_3{\mathrm{TeCo}}_3{V}_2{\mathrm{O}}_{14}$ takes place through formation of a short-range correlation regime with $T^{*}$ ∼ 10.5 K and the succession of a second-order phase transition at $T_{\mathrm{N}1}$ = 8.9 K and a first-order phase transition at $T_{\mathrm{N}2}$ = 6.3 K. An external magnetic field rapidly destroys magnetic structure at $T$ < $T_{\mathrm{N}2}$ and influences the magnetic order at $T_{\mathrm{N}2}$ < $T$ < $T_{\mathrm{N}1}$, resulting in a complex magnetic phase diagram of ${\mathrm{Pb}}_3{\mathrm{TeCo}}_3{V}_2{\mathrm{O}}_{14}$ as derived from magnetization and specific heat measurements. The first-principles calculations indicate that, in variance with a layered crystal structure, the magnetic subsystem of ${\mathrm{Pb}}_3{\mathrm{TeCo}}_3{V}_2{\mathrm{O}}_{14}$ is quasi-one-dimensional and highly unusual, consisting of weakly coupled triangular tubes.

Thermally activated magnetization decay is studied in ensembles of clusters of interacting dipolar moments by applying the master-equation formalism, as a model of thermal relaxation in systems of interacting single-domain ferromagnetic particles. Solving the associated master equation reveals a breakdown of the energy barrier picture depending on the geometrical symmetry of structures. Deviations are most pronounced for reduced symmetry and result in a strong interaction dependence of relaxation rates on the memory of system initialization. A simple two-state system description of an ensemble of clusters is developed, which accounts for the observed anomalies. These results follow from a semianalytical treatment, and are fully supported by kinetic Monte Carlo simulations.

Motivated by recent neutron scattering experiments in Fe-based superconductors, we study how the magnetic resonance in the superconducting state is affected by the simultaneous presence of either static or fluctuating magnetic orders using the random phase approximation. We find that for the underdoped materials with coexisting superconducting and antiferromagnetic orders, spin rotational symmetry is explicitly broken at the ordering momentum ${\mathit{Q}}_1=(\pi ,0)$. Only the longitudinal susceptibility exhibits the resonance mode, whereas a spin-wave Goldstone mode develops in the transverse component. Meanwhile, at the frustrated momentum ${\mathit{Q}}_2=(0,\pi )$, the susceptibility becomes isotropic in spin space and the magnetic resonance exists for both components. Furthermore, the resonance energies at ${\mathit{Q}}_1$ and ${\mathit{Q}}_2$ have distinct scales, which provide a natural explanation for the recently observed double resonance peaks. In addition, we show that near optimal doping the existence of strong magnetic fluctuations, which are modeled here via a Gaussian mode, can still induce the spin anisotropy in the magnetic susceptibility.

We solve the sign problem in a particle-hole symmetric spin-polarized fermion model on bipartite lattices using the idea of fermion bags. The solution can be extended to a class of models at half filling but without particle-hole symmetry. Attractive Hubbard models with an odd number of fermion species can also be solved. Our solutions should allow us to study quantum phase transitions that have remained unexplored so far due to sign problems.

We study the effects of heavy hole–light hole (HH-LH) mixing on fine-structure and polarization properties of neutral excitons (${\text{X}}^0$) confined in single GaAs/AlGaAs quantum dots (QDs) under the application of anisotropic biaxial stress. In the large HH-LH mixing regime, these properties are substantially different from the usually observed properties in the case of small or no mixing. By varying the applied stress, the mixing in the initially strain-free QDs changes from $\sim$0 to $\sim$70$\%$ and an anomalous anticrossing of the ${\text{X}}^0$ bright states is observed. The latter is attributed to stress-induced rotation of the in-plane principal axis of the QD confinement potential. We show that the analysis of free-excitonic emission of bulk GaAs surrounding the QDs not only allows estimation of the stress and mixing in the QDs, but also provides the quantum-confinement-induced HH-LH splitting of the as-grown QDs.

We find that the flow of direct electric current (dc) through graphene on substrate enhances surface optical second-harmonic generation (SHG) from the graphene/substrate system. The current can enhance surface SHG by about 300% for a chemical-vapor-deposition (CVD) graphene monolayer on a SiO${}_2/\mathrm{Si}\left(001\right)$ substrate, and by about 25% for an epitaxial four-layer-graphene film on a 3.5°-miscut vicinal SiC(0001) substrate. The enhancement in both the CVD and epitaxial graphene samples is due to electric field-induced SHG, which is produced by the current-associated vertical electric field at the SiO${}_2/$Si interface or at the graphene/SiC interface. Measurements of rotational-anisotropy SHG (RA-SH) from both samples revealed that the current-induced SHG varies strongly with the measurement location along the current flow direction. By measuring RA-SH from the vicinal SiC(0001) substrate, we determined all three second-order susceptibility tensor elements ($d_{33}$ = −52.0 pm/V, $d_{15}$ = 20.0 pm/V, and $d_{31}$ = 18.7 pm/V) that characterize the SHG response of hexagonal SiC at the fundamental wavelength of 740 nm. We further determined the three effective susceptibility tensor elements ($d_{33}$ = −135.8 pm/V, $d_{15}$ = 18.5 pm/V, and $d_{31}$ = 14.6 pm/V) that characterize the surface SHG from the graphene/vicinal-SiC(0001) sample and finally showed that the current-dependent tensor element $d_{33}$ can be enhanced to a large value of $d_{33}$ = −199.0 pm/V by electric current in epitaxial graphene.

There are various quantum chemical approaches for an ab initio description of transfer integrals within the framework of Marcus theory in the context of electron transfer reactions. In our paper, we aim to calculate transfer integrals in redox-active single molecule junctions, where we focus on the coherent tunneling limit with the metal leads taking the position of donor and acceptor and the molecule acting as a transport mediating bridge. This setup allows us to derive a conductance, which can be directly compared with recent results from a nonequilibrium Green's function approach. Compared with purely molecular systems we face additional challenges due to the metallic nature of the leads, which rules out some of the common techniques, and due to their periodicity, which requires k-space integration. We present three different methods, all based on density functional theory, for calculating the transfer integral under these constraints, which we benchmark on molecular test systems from the relevant literature. We also discuss many-body effects and apply all three techniques to a junction with a Ruthenium complex in different oxidation states.