Magnetic excitations in the strong-leg quantum spin ladder compound ${\left({\mathrm{C}}_7{\mathrm{H}}_{10}\mathrm{N}\right)}_2{\mathrm{CuBr}}_4$ (known as DIMPY) in the field-induced Tomonaga-Luttinger spin-liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual nonlinear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact-diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2 Heisenberg antiferromagnetic ladder and owe their ESR observability to the uniform Dzyaloshinskii-Moriya interaction.

The coupled kinetic equation for density and spin Wigner functions is derived including spin-orbit coupling, electric and magnetic fields, and self-consistent Hartree mean fields suited for SU(2) transport. The interactions are assumed to be with scalar and magnetic impurities as well as scalar and spin-flip potentials among the particles. The spin-orbit interaction is used in a form suitable for solid state physics with Rashba or Dresselhaus coupling, graphene, extrinsic spin-orbit coupling, and effective nuclear matter coupling. The deficiencies of the two-fluid model are worked out consisting of the appearance of an effective in-medium spin precession. The stationary solution of all these systems shows a band splitting controlled by an effective medium-dependent Zeeman field. The self-consistent precession direction is discussed and a cancellation of linear spin-orbit coupling at zero temperature is reported. The precession of spin around this effective direction caused by spin-orbit coupling leads to anomalous charge and spin currents in an electric field. Anomalous Hall conductivity is shown to consist of the known results obtained from the Kubo formula or Berry phases and a symmetric part interpreted as an inverse Hall effect. Analogously the spin-Hall and inverse spin-Hall effects of spin currents are discussed which are present even without magnetic fields showing a spin accumulation triggered by currents. The analytical dynamical expressions for zero temperature are derived and discussed in dependence on the magnetic field and effective magnetizations. The anomalous Hall and spin-Hall effect changes sign at higher than a critical frequency dependent on the relaxation time.

The spin and density response functions in the random phase approximation are derived by linearizing the kinetic equation including a magnetic field, the spin-orbit coupling, and mean fields with respect to an external electric field. Different polarization functions appear describing various precession motions showing Rabi satellites due to an effective Zeeman field. The latter turns out to consist of the mean-field magnetization, the magnetic field, and the spin-orbit vector. The collective modes for charged and neutral systems are derived and a threefold splitting of the spin waves dependent on the polarization and spin-orbit coupling is shown. The dielectric function including spin-orbit coupling, polarization, and magnetic fields is presented analytically for long wavelengths and in the static limit. The dynamical screening length as well as the long-wavelength dielectric function shows an instability in charge modes, which are interpreted as spin segregation and domain formation. The spin response describes a crossover from damped oscillatory behavior to exponentially damped behavior dependent on the polarization and collision frequency. The magnetic field causes ellipsoidal trajectories of the spin response to an external electric field and the spin-orbit coupling causes a rotation of the spin axes. The spin-dephasing times are extracted and discussed in dependence on the polarization, magnetic field, spin-orbit coupling, and single-particle relaxation times.

The structural and the magnetic properties of ${\mathrm{CeCu}}_{6-x}{\mathrm{Ag}}_x$ $\left(0\le x\le 0.85\right)$ and ${\mathrm{CeCu}}_{6-x}{\mathrm{Pd}}_x$ $\left(0\le x\le 0.4\right)$ have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of ${\mathrm{CeCu}}_{6-x}{\mathrm{Ag}}_x$ and ${\mathrm{CeCu}}_{6-x}{\mathrm{Pd}}_x$ as a function of Ag/Pd composition are reported. The end member, ${\mathrm{CeCu}}_6$, undergoes a structural phase transition from an orthorhombic $\left(Pnma\right)$ to a monoclinic $\left(P{2}_1/c\right)$ phase at 240 K. In ${\mathrm{CeCu}}_{6-x}{\mathrm{Ag}}_x$, the structural phase transition temperature $\left(T_s\right)$ decreases linearly with Ag concentration and extrapolates to zero at $x_S$ $\approx 0.1$. The structural transition in ${\mathrm{CeCu}}_{6-x}{\mathrm{Pd}}_x$ remains unperturbed with Pd substitution within the range of our study. The lattice constant $b$ slightly decreases with Ag/Pd doping, whereas $a$ and $c$ increase with an overall increase in the unit cell volume. Both systems, ${\mathrm{CeCu}}_{6-x}{\mathrm{Ag}}_x$ and ${\mathrm{CeCu}}_{6-x}{\mathrm{Pd}}_x$, exhibit a magnetic quantum critical point (QCP), at $x\approx 0.2$ and $x\approx 0.05$, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector $({\delta }_{1}0$ ${\delta }_2)$, where ${\delta }_1\sim 0.62,{\delta }_2\sim 0.25,x=0.125$ for ${\mathrm{CeCu}}_{6-x}{\mathrm{Pd}}_x$ and ${\delta }_1\sim 0.64,{\delta }_2\sim 0.3,x=0.3$ for ${\mathrm{CeCu}}_{6-x}{\mathrm{Ag}}_x$. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the $c$ axis of the orthorhombic unit cell.

We show that the fully polarized triplet $s$-wave component is characterized not only by the spin direction, but also by chirality. Interaction of a polarized triplet component and a singlet one results in creation of triplet Cooper pairs with opposite spin direction or of different chiralities. Such spin transformation leads to interesting phenomena in multiterminal magnetic Josephson junctions. We calculate the dc Josephson current $I_{\text{J}}$ in a multiterminal Josephson contact of the $S_{\text{m}}/n/S_{\text{m}}^{\prime }$ type with “magnetic” superconductors $S_{\text{m}}$ that generate fully polarized triplet components. The superconductors $S_{\text{m}}$ are attached to magnetic insulators (filters) which let pass electrons with a fixed spin direction only. The filter axes are assumed to be oriented antiparallel to each other. The Josephson current is zero in two-terminal Josephson junction, i.e., in $S/n/S_{\text{m}}$ or in $S_{\text{m}}/n/S_{\text{m}}^{\prime }$ contact. But in the three-terminal Josephson junction, with another $S$ superconductor attached to the normal wire, the finite current $I_{\text{J}}$ appears flowing from the $S$ superconductor to $S_{\text{m}}$ superconductors. The currents through the right (left) superconductors $S_{\text{m}}$ are opposite in sign, $I_{\text{R}}\equiv I_{\text{J}}=I_{\text{c}}sin({\chi }_{\text{R}}+{\chi }_{\text{L}}-2\chi )=-I_{\text{L}}$, where ${\chi }_{\text{L/R}}$ and $\chi$ are the phases of superconductors $S_{\text{m}},S_{\text{m}}^{\prime }$, and $S$, respectively. We discuss possibilities of experimental observation of the effect.

Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by $3d$ transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

The superconducting pairing state of ${\mathrm{LaPt}}_4{\mathrm{Ge}}_{12}$ is studied by measuring the magnetic penetration depth $\lambda (T,B)$ and superfluid density ${\rho }_s\left(T\right)$ using a tunnel-diode-oscillator (TDO)-based method and transverse-field muon-spin rotation $\left(\mathrm{TF}\text{−}\mu \mathrm{SR}\right)$ spectroscopy. The penetration depth follows an exponential-type temperature dependence at $T\ll T_c$, but increases linearly with magnetic field at $T=1.5$ K. A detailed analysis demonstrates that both ${\lambda }_L\left(T\right)$ and ${\rho }_s^{\mathrm{TDO}}\left(T\right)$, measured in the Meissner state using the TDO method, are well described by a two-gap $\gamma$ model with gap sizes of ${\mathrm{\Delta }}_1\left(0\right)=1.31k_B{T}_c$ and ${\mathrm{\Delta }}_2\left(0\right)=1.80k_B{T}_c$, and weak interband coupling. In contrast, ${\rho }_s^{\mu \mathrm{SR}}\left(T\right)$, derived from the $\mu \mathrm{SR}$ data, can be fitted by a single-gap BCS model with a gap close to ${\mathrm{\Delta }}_2\left(0\right)$. We conclude that ${\mathrm{LaPt}}_4{\mathrm{Ge}}_{12}$ is a marginal two-gap superconductor and the small gap ${\mathrm{\Delta }}_1$ seems to be suppressed by a small magnetic field applied in the $\mu \mathrm{SR}$ experiments. In comparison, the $4f$ electrons in ${\mathrm{PrPt}}_4{\mathrm{Ge}}_{12}$ may enhance the interband coupling and, therefore, give rise to more robust multiband superconductivity.

We investigate the impact of longitudinal thermal spin fluctuations on the temperature dependence of the elastic constants of paramagnetic body-centered-cubic (bcc) and face-centered-cubic (fcc) Fe. Based on a series of constrained local magnetic moment calculations, the spin fluctuation distribution is established using Boltzmann statistics and involving the Jacobian weight, and a temperature-dependent quadratic mean moment is introduced that accurately represents the spin fluctuation state as a function of temperature. We show that with increasing temperature, $c^{\prime }$ and $c_{44}$ for the fcc phase and $c_{44}$ for the bcc phase decrease at different rates due to different magnetoelastic coupling strengths. In contrast, $c^{\prime }$ in the bcc phase exhibits relatively high thermal stability. Longitudinal thermal spin fluctuations diminish the softening of both elastic constants in either phase and have comparatively large contributions in the fcc phase. In both bcc and fcc Fe, $c_{44}$ has a larger temperature factor than $c^{\prime }$. On the other hand, $c^{\prime }$ is more sensitive to the longitudinal thermal spin fluctuations, which balance the volume-induced softening by 21.6% in fcc Fe.

The effect of ordering on the galvanomagnetic properties such as the anomalous Hall conductivity (AHC) and the anisotropic magnetoresistance (AMR) ratio is studied using recently developed formalism which takes into account both the Fermi surface and Fermi sea contributions to the conductivity tensor. As a case study we have considered Pd-rich $L{1}_2\text{−}{\mathrm{Pd}}_{70}{\mathrm{Fe}}_{30}$ alloy and disordered fcc-${\mathrm{Pd}}_{1-x}{\mathrm{Co}}_x$ alloy with a weak partial $L{1}_0$ and $L{1}_2$ orderings which can exist around stoichiometric compositions. We have found a nonnegligible effect of the Fermi sea term for the Pd-rich PdFe alloys while its effect for completely disordered fcc-PdCo alloy is small. The most important effect of inclusion of a weak partial order for fcc-PdCo alloys in theoretical calculations is improvement of the agreement between theory and experiment for the resistivity but first of all for the AMR ratio. An enhancement of the AMR ratio due to the layerlike $L{1}_0$ ordering brings calculated and experimental values into a good agreement missing in the disordered alloy. The effect of the isotropic $L{1}_2$ ordering on the AMR values is weak. Finally, the effect of the ordering on the resistivity and the AHC is much weaker, although observable.

We discuss the appearance of odd-frequency Cooper pairs in two-band superconductors by solving the Gor'kov equation analytically. We introduce the equal-time $s$-wave pair potentials as realized in ${\mathrm{MgB}}_2$ and iron pnictides. Although the order parameter symmetry is conventional, the band degree of freedom enriches the symmetry variety of pairing correlations. The hybridization and the asymmetry between the two conduction bands induce odd-frequency pairs as a subdominant pairing correlation in the uniform ground state. To study the magnetic response of odd-frequency Cooper pairs, we analyze the Meissner kernel represented by the Gor'kov Green function. In contrast to the even-frequency pairs linked to the pair potential, the induced odd-frequency Cooper pairs indicate a paramagnetic property. We also discuss the relation between the amplitude of the odd-frequency pairing correlation and the stability of superconducting states in terms of the self-consistent equation for the pair potential.

We introduce a supersymmetric Chern-Simons theory whose low energy physics is that of the fractional quantum Hall effect. The supersymmetry allows us to solve the theory analytically. We quantize the vortices and, by relating their dynamics to a matrix model, show that their ground state wave function is in the same universality class as the Laughlin state. We further construct coherent state representations of the excitations of a finite number of vortices. These are quasiholes. By an explicit computation of the Berry phase, without resorting to a plasma analogy, we show that these excitations have fractional charge and spin.

On a road towards applications and devices based on functional oxides with correlated electrons, the crucial element is uncovering the effects of the reduced dimensionality on the electronic phase transition into a multiordered ground state. Towards this goal, we present a study of reduced dimensionality on charge and antiferromagnetic orderings in ultrathin ${\mathrm{EuNiO}}_3$ films on ${\mathrm{NdGaO}}_3$ substrates using hard and soft resonant x-ray scattering to investigate the presence of electronic and magnetic orderings. Despite the ultrathin nature of the films, they exhibit the bulklike order parameters up to room temperature, suggesting that the spontaneously coherent Mott ground state in the highly distorted rare-earth nickelates can be successfully sustained even when constrained towards two-dimensionality. The presence of charge ordering at room temperature and below opens prospects for their use in novel electric-field-controlled devices.

We investigate the orbital origin of the Fano-Kondo line shapes measured in STM spectroscopy of magnetic adatoms on metal substrates. To this end we calculate the low-bias tunnel spectra of a Co adatom on the (001) and (111) Cu surfaces with our density functional theory-based ab initio transport scheme augmented by local correlations. In order to associate different $d$ orbitals with different Fano line shapes we only correlate individual $3d$ orbitals instead of the full Co $3d$ shell. We find that Kondo peaks arising in different $d$ levels indeed give rise to different Fano features in the conductance spectra. Hence, the shape of measured Fano features allows us to draw some conclusions about the orbital responsible for the Kondo resonance, although the actual shape is also influenced by temperature, effective interaction, and charge fluctuations. Comparison with a simplified model shows that line shapes are mostly the result of interference between tunneling paths through the correlated $d$ orbital and the $sp$-type orbitals on the Co atom. Very importantly, the amplitudes of the Fano features vary strongly among orbitals, with the $3z^2$ orbital featuring by far the largest amplitude due to its strong direct coupling to the $s$-type conduction electrons.

Using femtosecond pump-probe spectroscopy, we identify excitation-induced dephasing as a major mechanism responsible for the breakdown of the strong coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed on the transmitted probe-pulse spectrum as a density-dependent broadening of the exciton-polariton resonances and the emergence of a third resonance at high excitation density. A striking asymmetry in the energy shift between the upper and the lower polaritons is also evidenced. Using the excitonic Bloch equations, we quantify the respective contributions to the energy shift of many-body effects associated with Coulomb fermion exchange and photon assisted exchange processes and the contribution to collisional broadening.

Metallic nanostructures characterized by multiple geometric length scales support low-frequency surface-plasmon modes, which enable strong light localization and field enhancement. We suggest studying such configurations using singular perturbation methods and demonstrate the efficacy of this approach by considering, in the quasistatic limit, a pair of nearly touching metallic nanospheres subjected to an incident electromagnetic wave polarized with the electric field along the line of sphere centers. Rather than attempting an exact analytical solution, we construct the pertinent (longitudinal) eigenmodes by matching relatively simple asymptotic expansions valid in overlapping spatial domains. We thereby arrive at an effective boundary eigenvalue problem in a half space representing the metal region in the vicinity of the gap. Coupling with the gap field gives rise to a mixed-type boundary condition with varying coefficients, whereas coupling with the particle-scale field enters through an integral eigenvalue selection rule involving the electrostatic capacitance of the configuration. By solving the reduced problem we obtain accurate closed-form expressions for the resonance values of the metal dielectric function. Furthermore, together with an energy like integral relation, the latter eigensolutions yield also closed-form approximations for the induced dipole moment and gap-field enhancement under resonance. We demonstrate agreement between the asymptotic formulas and a seminumerical computation. The analysis, underpinned by asymptotic scaling arguments, elucidates how metal polarization together with geometrical confinement enables a strong plasmon-frequency redshift and amplified near field at resonance.

We describe a Josephson device composed of two superconductors separated by two interacting quantum dots in parallel, where clear manifestations of Cooper pair splitting and subsequent recombination occur. Indeed, in addition to sequential tunneling of electrons through each dot, an additional transport channel exists in this system: crossed Andreev reflection, where a Cooper pair from the source is split between the two dots and recombined in the drain superconductor. Unlike nonequilibrium scenarios for Cooper pair splitting which involve superconducting/normal metal “forks”, our proposal relies on an Aharonov-Bohm measurement of the DC Josephson current when a flux is inserted between the two dots. We provide a path integral approach to treat arbitrary transparencies, and we explore all contributions for the individual phases (0 or $\pi$) of the quantum dots. We propose a definition of the Cooper pair splitting efficiency (the fraction of the electron transfer processes which involve the splitting of a Cooper pair) for arbitrary transparencies, which allows us to find the phase associations which favor the crossed Andreev process. Possible applications to experiments using nanowires as quantum dots are discussed.

The noncentrosymmetric semiconductors $\mathrm{BiTe}X(X=\text{Cl},\text{Br},\text{I})$ show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single-crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), and density functional theory calculations to systematically investigate the structural and electronic properties of $\mathrm{BiTe}X\left(0001\right)$ surfaces. For $X=\text{Cl}$, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.

It is shown that quantum interference can be employed to create an exciton transistor. An applied potential gates the quasiparticle motion and also discriminates between quasiparticles of differing binding energy. When implemented within nanoscale assemblies, such control elements could mediate the flow of energy and information. Quantum interference can also be used to dissociate excitons as an alternative to using heterojunctions. A finite molecular setting is employed to exhibit the underlying discrete, two-particle, mesoscopic analog to Fano antiresonance. Selected entanglement measures are shown to distinguish regimes of behavior which cannot be resolved from population dynamics alone.

We study the polarization response of the emission from type-II GaAsSb capped InAs quantum dots. The theoretical prediction based on the calculations of the overlap integrals of the single-particle states obtained in the $\vec{k}·\vec{p}$ framework is given. This is verified experimentally by polarization resolved photoluminescence measurements on samples with the type-II confinement. We show that the polarization anisotropy might be utilized to find the vertical position of the hole wave function and its orientation with respect to crystallographic axes of the sample. A proposition for usage in the information technology as a room temperature photonic gate operating at the communication wavelengths as well as a simple model to estimate the energy of fine-structure splitting for type-II GaAsSb capped InAs QDs are given.

We study the Fermi energy level dependence of the nonlinear terahertz (THz) transmission of gated multilayer and single-layer graphene transferred onto sapphire and quartz substrates. The two samples represent two limits of low-field impurity scattering: short-range neutral and long-range charged impurity scattering, respectively. We observe an increase in the transmission as the field amplitude is increased due to intraband absorption bleaching starting at THz fields above 8 kV/cm. This effect arises from a field-induced reduction in THz conductivity that depends strongly on the Fermi energy. We account for intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. We find that although the Fermi-level dependence in the monolayer and five-layer samples is quite different due to the dominance of long- and short-range momentum scattering, respectively, both exhibit a strong dependence on the field amplitude that cannot be explained on the basis of an increase in the lattice temperature alone. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths where nonlinearities exist.