Magnetic textures in the ferromagnetic phases of $\mathrm{L}{\mathrm{a}}_{1-x}\mathrm{S}{\mathrm{r}}_x\mathrm{Mn}{\mathrm{O}}_3$ for $0.15<x<0.30$ have been investigated by Lorentz microscopy combined with small-angle electron diffraction experiments. Various types of magnetic textures characterized by stripe, plate-shaped, and cylindrical (magnetic bubble) domains were found. Two distinct types of magnetic stripe domains appeared in the orthorhombic structure with an inversion symmetry of $\mathrm{L}{\mathrm{a}}_{0.825}\mathrm{S}{\mathrm{r}}_{0.175}\mathrm{Mn}{\mathrm{O}}_3$, depending significantly on magnetocrystalline anisotropy. Based on in situ observations as functions of temperature and the strength of the external magnetic field, a magnetic field-temperature phase diagram was constructed, showing the stabilization of magnetic bubbles in the ferromagnetic phase of $\mathrm{L}{\mathrm{a}}_{0.825}\mathrm{S}{\mathrm{r}}_{0.175}\mathrm{Mn}{\mathrm{O}}_3$.

We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates ${\mathrm{Eu}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ and ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of ${\mathrm{Eu}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures ($\sim 6$ to 300 K) and pressures ($\sim 0.1$ to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of ${\mathrm{Eu}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ and ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ using high-resolution Ir ${\mathrm{L}}_3$-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at $\sim 3–5$ eV, spin-orbit excitations at $\sim 0.5–1$ eV, and broad low-lying excitations below $\sim 0.15$ eV. In single-crystal samples of “Eu-rich” ${\mathrm{Eu}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ (found to possess an actual stoichiometry of ${\mathrm{Eu}}_{2.18}{\mathrm{Ir}}_{1.82}{\mathrm{O}}_{7.06})$ we observe highly damped magnetic excitations at $\sim 45$ meV, which display significant momentum dependence. We compare these results with recent dynamical structure factor calculations.

Cubic ${\mathrm{SrTiO}}_3$ becomes tetragonal below 105 K. The antiferrodistortive (AFD) distortion leads to clockwise and counterclockwise rotation of adjacent ${\mathrm{TiO}}_6$ octahedra. This insulator becomes a metal upon the introduction of extremely low concentration of $n$-type dopants. However, signatures of the structural phase transition in charge conduction have remained elusive. Employing the Montgomery technique, we succeed in resolving the anisotropy of charge conductivity induced by the AFD transition, in the presence of different types of dopants. We find that the slight lattice distortion ($<6\times {10}^{-4}$) gives rise to a 20% anisotropy in charge conductivity, in agreement with the expectations of band calculations. Application of uniaxial strain amplifies the detectable anisotropy by disfavoring one of the three possible tetragonal domains. In contrast with all other known anisotropic Fermi liquids, the anisotropy has opposite signs for elastic and inelastic scattering. Increasing the concentration of dopants leads to a drastic shift in the temperature of the AFD transition either upward or downward. The latter result puts strong constraints on any hypothetical role played by the AFD soft mode in the formation of Cooper pairs and the emergence of superconductivity in ${\mathrm{SrTiO}}_3$.

Two-dimensional quantum spin Hall (QSH) insulators with reasonably wide band gaps are imperative for the development of various innovative technologies. Through systematic density functional calculations and tight-binding simulations, we found that stanene on an $\alpha$-alumina surface may possess a sizeable topologically nontrivial band gap $\left(\sim 0.25\mathrm{eV}\right)$ at the $\mathrm{\Gamma }$ point. Furthermore, stanene is atomically bonded to but electronically decoupled from the substrate, providing high structural stability and isolated QSH states to a large extent. The underlying physical mechanism is rather general, and this finding may lead to the opening of a new vista for the exploration of QSH insulators for room temperature device applications.

Despite its huge successes in total-energy-related applications, the Kohn-Sham scheme of density functional theory cannot get reliable single-particle excitation energies for solids. In particular, it has not been able to calculate the ionization potential (IP), one of the most important material parameters, for semiconductors. We illustrate that an approximate exact-exchange optimized effective potential (EXX-OEP), the Becke-Johnson exchange, can be used to largely solve this long-standing problem. For a group of 17 semiconductors, we have obtained the IPs to an accuracy similar to that of the much more sophisticated $GW$ approximation (GWA), with the computational cost of only local-density approximation/generalized gradient approximation. The EXX-OEP, therefore, is likely as useful for solids as for finite systems. For solid surfaces, the asymptotic behavior of the $v_{xc}$ has effects similar to those of finite systems which, when neglected, typically cause the semiconductor IPs to be underestimated. This may partially explain why standard GWA systematically underestimates the IPs and why using the same GWA procedures has not been able to get an accurate IP and band gap at the same time.

In zero magnetic field, the famous neutron spin resonance in the $f$-electron superconductor ${\mathrm{CeCoIn}}_5$ is similar to the recently discovered exciton peak in the nonsuperconducting ${\mathrm{CeB}}_6$. A magnetic field splits the resonance in ${\mathrm{CeCoIn}}_5$ into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in ${\mathrm{CeB}}_6$. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a nonmonotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.

We demonstrate that the highly stable valley-polarized electron states in ultrapure single-crystalline diamond allow for investigation of charge transport, magnetoresistivity, and determination of the dominant scattering mechanism. The Hall effect gives rise to nonisotropic contributions in the mobility tensor that were measured at a temperature of 70 K in a time-of-flight setup with an added magnetic field. The observations of the magnetotransport of valley-polarized electrons in diamond are compared with both Monte Carlo simulations and an analytical model based on the Boltzmann transport equation. We establish that acoustic phonon scattering is the dominant electron scattering mechanism at 70 K for each of the valley polarizations in the investigated samples.

Recent experiments find the signal of giant nonlocal resistance $R_{\mathrm{NL}}$ in $\mathsf{H}$-shaped graphene samples due to the spin/valley Hall effect. Interestingly, when the Fermi energy deviates from the Dirac point, $R_{\mathrm{NL}}$ decreases to zero much more rapidly compared with the local resistance $R_L$, and the well-known relation of $R_{\mathrm{NL}}\propto R_L^3$ is not satisfied. In this work, based on the nonequilibrium Green's function method, we explain such transport phenomena in $\mathsf{H}$-shaped graphene with Rashba spin-orbit coupling. When the Fermi energy is near the Dirac point, the nonlocal resistance is considerably large and is much sharper than the local one. Moreover, the relationship between the Rashba effect and the fast decay of $R_{\mathrm{NL}}$ compared with $R_L$ is further investigated. We find that the Rashba effect contributes neither to the fast decay nor to the peak of $R_{\mathrm{NL}}$ itself. Actually, it is the extremely small density of states near the Dirac point that leads to the large peak of $R_{\mathrm{NL}}$, while the fast decay results from the quasiballistic mechanism. Finally, we revise the classic formula $R_{\mathrm{NL}}\propto R_L^3$ by replacing $R_{\mathrm{NL}}$ with $R_{\mathrm{Hall}}$, which represents the nonlocal resistance merely caused by the spin Hall effect, and the relation holds well.

Current vertex correction (CVC), the backflowlike correction to the current, comes from conservation laws, and the CVC due to electron correlation contains information about many-body effects. However, it has been little understood how the CVC due to electron correlation affects the charge transports of a correlated multiorbital system. To improve this situation, I studied the in-plane resistivity ${\rho }_{ab}$ and the Hall coefficient in the weak-field limit $R_{\mathrm{H}}$, in addition to the magnetic properties and the electronic structure, for a $t_{2g}$-orbital Hubbard model on a square lattice in a paramagnetic state away from or near an antiferromagnetic (AF) quantum-critical point (QCP) in the fluctuation-exchange (FLEX) approximation with the CVCs arising from the self-energy ($\mathrm{\Sigma }$), the Maki-Thompson (MT) irreducible four-point vertex function, and the main terms of the Aslamasov-Larkin (AL) one. Then, I found three main results about the CVCs. First, the main terms of the AL CVC do not qualitatively change the results obtained in the FLEX approximation with the $\mathrm{\Sigma }$ CVC and the MT CVC. Second, ${\rho }_{ab}$ and $R_{\mathrm{H}}$ near the AF QCP have a high-temperature region, governed mainly by the $\mathrm{\Sigma }$ CVC, and a low-temperature region, governed mainly by the $\mathrm{\Sigma }$ CVC and the MT CVC. Third, in case away from the AF QCP, the MT CVC leads to a considerable effect on only $R_{\mathrm{H}}$ at low temperatures, although $R_{\mathrm{H}}$ at high temperatures and ${\rho }_{ab}$ at all temperatures considered are sufficiently described by including only the $\mathrm{\Sigma }$ CVC. Those findings reveal several aspects of many-body effects on the charge transports of a correlated multiorbital system. I also achieved the qualitative agreement with several experiments of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ or ${\mathrm{Sr}}_2{\mathrm{Ru}}_{0.975}{\mathrm{Ti}}_{0.025}{\mathrm{O}}_4$. Moreover, I showed several better points of this theory than other theories.

Electrically detected magnetic resonance (EDMR) spectroscopy is employed to study the influence of triplet excitons on the photocurrent in state-of-the-art microcrystalline silicon thin-film solar cells. These triplet excitons are used as sensitive spin probes for the investigation of their electronic and nuclear environment in this mixed-phase material. According to low-temperature EDMR results obtained from solar cells with different ${}^{29}\mathrm{Si}$ isotope concentrations between $0.01\%$ and $50\%$, the triplet excitons reside at extended defects in the crystallites of microcrystalline silicon that give rise to shallow states in the silicon band gap. The excitons possess a rather delocalized wave function, couple to electron spins in conduction band tail states nearby, and take part in a spin-dependent recombination process. Our study shows that extended defects such as grain boundaries or stacking faults in the crystalline part of the material act as charge carrier traps that can influence the material conductivity.

We study a polarizer-analyzer mounting for the terahertz regime with perfectly conducting metallic polarizers made of a periodic subwavelength pattern. With a renewed Jones formalism, we analytically investigate the influence of the multiple reflections, which occur between the polarizer and the analyzer, on the transmission response. We demonstrate that this interaction leads to a modified transmission response: the extended Malus law. In addition, we show that the transmission response can be controlled by the distance between the polarizer and the analyzer. For particular setups, the mounting exhibits extremely sensitive transmission responses. This interesting feature can be employed for high-precision sensing and characterization applications. We specifically propose a general design for measuring the electro-optical response of materials in the terahertz domain allowing detection of refractive index variations as small as ${10}^{-5}$.

We present a structural and magnetic phase diagram of the solid solution ${\text{LaCo}}_x{\text{Mn}}_{1-x}{\text{O}}_3$. We show by neutron diffraction that the monoclinic structure previously observed for the elpasolite form ${\text{La}}_2{\text{CoMnO}}_6$ (${\text{LaCo}}_{0.5}{\text{Mn}}_{0.5}{\text{O}}_3$) is also observed for another member of the solid solution $x=0.35$. We also present the transition temperatures for the orthorhombic/monoclinic structures of the series to the rhombohedral structure and determine the expected transition temperatures from rhombohedral to cubic symmetry. We present the magnetic structures as determined by neutron diffraction for materials with lower cobalt content and provide evidence, including ac and dc susceptibility measurements, for the possible glassy nature of the magnetism in the cobalt-rich materials in the series. Based on high-resolution neutron diffraction, we also suggest that there is a limit to the ${\text{LaCo}}_x{\text{Mn}}_{1-x}{\text{O}}_3$ solid solution at $x=0.85$. Finally we present a possible, previously unreported, low-temperature monoclinic structure for the sample ${\text{LaCo}}_{0.75}{\text{Mn}}_{0.25}{\text{O}}_3$.

The short-range structure of liquid carbon dioxide is investigated at pressures $\left(P\right)$ up to 10 GPa and temperatures $\left(T\right)$ from 300 to 709 K by means of x-ray diffraction experiments in a diamond anvil cell (DAC) and classical molecular dynamics (MD) simulations. The molecular x-ray structure factor could be measured up to $90{\mathrm{nm}}^{-1}$ thanks to the use of a multichannel collimator which filters out the large x-ray scattered signal from the diamond anvils. The experimental data show that the short-range structure of fluid ${\mathrm{CO}}_2$ is anisotropic and continuously changes from a low density to a high density form. The MD simulations are used to extract a detailed three-dimensional analysis of the short-range structure over the same P-T range as the experiment. This reveals that upon compression, a fraction of the molecules in the first-neighbor shell change orientation from the (distorted) T shape to the slipped parallel configuration, accounting for the observed structural changes. The local arrangement is found similar to that of the $Pa\overline{3}$ solid at low density and to that of the $Cmca$ crystal at high density. The comparison with other simple quadrupolar liquids, either diatomic $\left({\mathrm{I}}_2\right)$ or triatomic $\left({\mathrm{CS}}_2\right)$, suggests that this structural evolution with density is a general one for these systems.

I introduce a dynamical field theory to describe the glassy behavior in supercooled liquids. The mean-field approximation of the theory predicts a dynamical arrest transition, as in the ideal mode-coupling theory and mean-field discontinuous spin-glass models. Instead, beyond the mean-field approximation, the theory predicts that the transition is avoided and transformed into a crossover, as observed in experiments and simulations. To go beyond mean-field, a standard perturbative loop expansion is performed at first. Approaching the ideal critical point this expansion is divergent at all orders and I show that the leading divergent term at any given order is the same as a dynamical stochastic equation, called stochastic-beta relaxation (SBR) in Europhys. Lett. 106, 56003 (2014). At variance with the original theory, SBR can be studied beyond mean-field directly, without the need to resort to a perturbative expansion. Thus it provides a qualitative and quantitative description of the dynamical crossover. For consistency reasons, it is important to establish the connection between the dynamical field theory and SBR beyond perturbation theory. This can be done with the help of a stronger result: the dynamical field theory is exactly equivalent to a theory with quenched disorder. Qualitatively, the nonperturbative mechanism leading to the crossover is therefore the same as the mechanism of SBR. Quantitatively, SBR is equivalent to making the mean-field approximation once the quenched disorder has been generated.

Incorporation of strong electron correlations into the density functional theory (DFT) for the electronic structure calculations of light lanthanides leads to a modification of interatomic forces and consequently the lattice dynamics. Using first-principles theory we demonstrate the substantial influence of the $4f$ electron correlations on the phonon dispersion relations of Nd. The calculations are verified by an inelastic x-ray scattering experiment performed on a single-crystalline Nd(0001) film. We show that very good agreement between the calculated and measured data is achieved when electron-electron interactions are treated by the $\mathrm{DFT}+U$ approach.

We study the coexistence of strain- and charge-mediated magnetoelectric coupling in a cobalt (0–7 nm) wedge on ferroelectric (011)-oriented ${\left[\mathrm{Pb}({\mathrm{Mg}}_{1/3}/{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3\right]}_{0.68}\text{−}{\left[{\mathrm{PbTiO}}_3\right]}_{0.32}$ using surface-sensitive x-ray magnetic circular dichroism spectroscopy at the Co $L_{3,2}$ edges. Three distinct electric field driven remanent magnetization states can be set in the Co film at room temperature. Ab initio density functional theory calculations unravel the relative contributions of both strain and charge to the observed magnetic anisotropy changes illustrating magnetoelectroelastic coupling at artificial multiferroic interfaces.

We report on in-plane magnetic anisotropy in epitaxial bcc Co/Fe(110) bilayers on W(110). The magnetic surface anisotropy in the Co/Fe(110) bilayers exhibited a strong nonmonotonic dependence on Co coverage. Magneto-optical studies revealed a sharp maximum of the magnetic surface anisotropy, $2.44\mathrm{mJ}/{\mathrm{m}}^2$, at $d_{\mathrm{Co}}=5\AA$. This giant interfacial magnetic anisotropy allowed a small fraction of a Co monolayer to reorient the magnetization of the bulk-like Fe film. We conclude that the mono- and double-layer bcc Co(110) exhibited in-plane magnetic anisotropy with a $\left[1\overline{1}0\right]$ easy axis.

Spin current injection and spin accumulation near a ferromagnetic insulator (FI)/nonmagnetic metal (NM) bilayer film under a thermal gradient is investigated theoretically. By using the Fermi golden rule and the Boltzmann equations, we find that FI and NM can exchange spins via interfacial electron-magnon scattering because of the imbalance between magnon emission and absorption caused by either the deviation of the magnon number from the equilibrium Bose-Einstein distribution or the difference in magnon temperature and electron temperature. A temperature gradient in FI and/or a temperature difference across the FI/NM interface generates a spin current which carries angular momenta parallel to the magnetization of FI from the hotter side to the colder one. Interestingly, the spin current induced by a temperature gradient in NM is negligibly small due to the nonmagnetic nature of the nonequilibrium electron distributions. The results agree well with all existing experiments.

Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The $1.23-\mathrm{nm}$ ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$ recording layer coercivity exhibits a size dependence which suggests single-domain behavior for diameters $\le 100$ nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy $K_{\text{eff}}$ using two different techniques. $K_{\text{eff}}$ is extracted both from distributions of the switching fields of the recording and reference layers and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that $K_{\text{eff}}$ increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that $K_{\text{eff}}$ can be controlled with a voltage down to the smallest size measured, 64 nm.

We study the influence of nonmagnetic impurity scatterings on the tunneling conductance of a junction consisting of a normal metal and a disordered unconventional superconductor by solving the quasiclassical Eilenberger equation self-consistently. We find that the impurity scatterings in both the Born and the unitary limits affect the formation of the Andreev bound states and modify strongly the tunneling spectra around zero bias. Our results are interpreted well by the appearance of odd-frequency Cooper pairs near the interface and by the divergent behavior of the impurity self-energy. The present paper provides a useful tool to identify the pairing symmetry of unconventional superconductors in experiments.