We present an exhaustive study of the coherent heat transport through superconductor-ferromagnet (SF) Josephson junctions including a spin-filter (I${}_{\mathrm{sf}}$) tunneling barrier. By using the quasiclassical Keldysh Green's function technique we derive a general expression for the heat current flowing through a SF-I${}_{\mathrm{sf}}$-FS junction and analyze the dependence of the thermal conductance on the spin-filter efficiency, the phase difference between the superconductors and the magnetization direction of the ferromagnetic layers. In the case of noncollinear magnetizations we show explicitly the contributions to the heat current stemming from the singlet and triplet components of the superconducting condensate. We also demonstrate that the magnetothermal resistance ratio of a SF-I${}_{\mathrm{sf}}$-FS heat valve can be increased by the spin-filter effect under suitable conditions.

KFe${}_2$As${}_2$ single crystals are studied using specific-heat, high-resolution thermal-expansion, magnetization, and magnetostriction measurements. The magnetization and magnetostriction data provide clear evidence for strong Pauli-limiting effects of the upper critical field for magnetic fields parallel to the FeAs planes, suggesting that KFe${}_2$As${}_2$ may be a good candidate to search for the Fulde-Ferrell-Larkin-Ovchinnikov state. Using standard thermodynamic relations, the uniaxial pressure derivatives of the critical temperature $T_c$, the normal-state Sommerfeld coefficient ${\gamma }_n$, the normal-state susceptibility $\chi$, and the thermodynamic critical field $H_c$ are calculated from our data. We find that the close relationship between doping and pressure as found in other Fe-based systems does not hold for KFe${}_2$As${}_2$.

We have presented evidence for composition-driven rhombohedral-to-cubic and cubic-to-tetragonal morphotropic phase transitions in (1 − $x$)BiFeO${}_3$-$x$BaTiO${}_3$ (BF-$x$BT) solid solutions at $x$ ≈ 0.35 and 0.85, respectively. It is shown that these transitions lead to the appearance of two peaks in the composition variation of dielectric constant, similar to that in well-known piezoelectric ceramics. The existing controversies about the true structure of the so-called cubic phase of BF-$x$BT are resolved using high-energy synchrotron x-ray powder diffraction data. It is shown that the ferroelectric cubic phase of BF-$x$BT has got locally monoclinic structure of $M_A$ type in the $Cm$ space group whose polarization vector rotates on its mirror plane on increasing the concentration of BaTiO${}_3$ ($x$). The ferroelectric-to-paraelectric phase transition in pseudocubic monoclinic phase is shown to be of tricritical nature.

We study the quantum corrections to the polarizability of isolated metallic mesoscopic systems using the loop expansion in diffusive propagators. We show that the difference between connected (grand-canonical ensemble) and isolated (canonical ensemble) systems appears only in subleading terms of the expansion, and can be neglected if the frequency of the external field, $\omega$, is of the order of (or even slightly smaller than) the mean level spacing, $\Delta$. If $\omega \ll \Delta$, the two-loop correction becomes important. We calculate it by systematically evaluating the ballistic parts (the Hikami boxes) of the corresponding diagrams and exploiting electroneutrality. Our theory allows one to take into account a finite dephasing rate, $\gamma$, generated by electron interactions, and it is complementary to the nonperturbative results obtained from a combination of random matrix theory (RMT) and the $\sigma$-model, valid at $\gamma \to 0$. Remarkably, we find that the two-loop result for isolated systems with moderately weak dephasing, $\gamma \sim \Delta$, is similar to the result of the RMT+$\sigma$-model even in the limit $\omega \to 0$. For smaller $\gamma$, we discuss the possibility to interpolate between the perturbative and the nonperturbative results. We compare our results for the temperature dependence of the polarizability of isolated rings to the experimental data of Deblock et al. [Phys. Rev. Lett. 84, 5379 (2000); Phys. Rev. B 65, 075301 (2002)], and we argue that the elusive 0D regime of dephasing might have manifested itself in the observed magneto-oscillations. Besides, we thoroughly discuss possible future measurements of the polarizability, which could aim to reveal the existence of 0D dephasing and the role of the Pauli blocking at small temperatures.

The geometrically frustrated double-perovskite Ba${}_2$YRuO${}_6$ has magnetic $4d^3$ Ru${}^{5+}$ ions decorating an undistorted face-centered-cubic lattice. This material has been previously reported to exhibit commensurate long-range antiferromagnetic order below $T_N\sim$ 36 K, a factor $f\sim 15$ times lower than its Curie-Weiss temperature ${\Theta }_{\text{CW}}=-522$ K, and purported short-range order to $T^{*}=47$ K. We report new time-of-flight neutron spectroscopy of Ba${}_2$YRuO${}_6$ which shows the development of a $\sim$5 meV spin gap in the vicinity of the [100] magnetic ordering wave vector below $T_N=36$ K, with the transition to long-range order occurring at $T^{*}=47$ K. We also report spin waves extending to $\sim$14 meV, a surprisingly small bandwidth in light of the large ${\Theta }_{\text{CW}}$. We compare the spin gap and bandwidth to relevant neutron studies of the isostructural 4$d^1$ material Ba${}_2$YMoO${}_6$, and discuss the results in the framework of relatively strong spin-orbit coupling expected in 4$d$ magnetic systems.

We propose a possible realization of the overscreened Kondo impurity problem by a magnetic $s=1/2$ impurity embedded in a two-dimensional $S=1$ $U\left(1\right)$ spin liquid with a Fermi surface. This problem contains an interesting interplay between non-Fermi-liquid behavior induced by a $U\left(1\right)$ gauge field coupled to fermions and a non-Fermi-liquid fixed point in the overscreened Kondo problem. Using a large-$N$ expansion together with an expansion in the dynamical exponent of the gauge field, we find that the coupling to the gauge field leads to weak but observable changes in the physical properties of the system at the overscreened Kondo fixed point. We discuss the extrapolation of this result to a physical case and argue that the realization of overscreened Kondo physics could lead to observations of effects due to gauge fields.

We study sequential tunneling of magnetic excitations in nonitinerant systems through triangular molecular magnets. It is known that the quantum state of these molecular magnets can be controlled by application of an electric or a magnetic field. Here, we use this fact to control the flow of a pure magnetization current through the molecular magnet by electric or magnetic means. This allows us to design a system that behaves as a magnon transistor. We show how to combine three magnon transistors to form a nand gate, and give several possible realizations of the latter, one of which could function at room temperature using transistors with an 11 ns switching time.

Frequency modulation experiments were performed on a spin torque vortex oscillator for a wide range of modulation frequencies, up to 10$\%$ of the oscillator frequency. A thorough analysis of the intermodulation products shows that the key parameter that describes these experiments is the deviation sensitivity, which is the dynamical frequency-current dependence. It differs significantly from the oscillator tunability discussed so far in the context of spin-transfer oscillators. The essential difference between these two concepts is related to the response time of the vortex oscillator, driven either in quasisteady state or in a transient regime.

Spin-transfer torque (STT) provides key mechanisms for current-induced phenomena in ferromagnets. While it is widely accepted that STT involves both adiabatic and nonadiabatic contributions, their underlying physics and range of validity are quite controversial. By computing microscopically the response of conduction electron spins to a time varying and spatially inhomogeneous magnetic background, we derive the adiabatic and nonadiabatic STT in a unified fashion. Our result confirms the macroscopic theory [Phys. Rev. Lett. 93, 127204 (2004)] with all coefficients matched exactly. Our derivation also reveals a benchmark on the validity of the result, which is used to explain three recent measurements of the nonadiabatic STT in quite different settings.

Measurements of temperature and field dependent bulk properties have been carried out on ${\{\mathrm{Ce},\mathrm{La}\}}_3{\mathrm{Pd}}_4{\mathrm{Si}}_4$. Rietveld refinements of x-ray powder intensity data confirm the orthorhombic ${\mathrm{U}}_3{\mathrm{Ni}}_4{\mathrm{Si}}_4$-type structure for both compounds. While ${\mathrm{La}}_3{\mathrm{Pd}}_3{\mathrm{Si}}_4$ exhibits superconductivity below 2 K together with some indications of a two gap scenario, the former can be characterized as a Kondo lattice system in presence of crystalline electric field splitting. Due to the closeness of a quantum critical point, distinct non-Fermi-liquid features dominate the low temperature physics of ${\mathrm{Ce}}_3{\mathrm{Pd}}_4{\mathrm{Si}}_4$.

The evolution with carrier concentration of the electrical properties of amorphous indium oxide (InO${}_x$) thin films has been studied using electric double-layer transistor configurations. Carrier variations of up to $7\times {10}^{14}\text{carriers}/{\text{cm}}^2$ were achieved using an ionic liquid as a gate dielectric. The superconductor-insulator transition was traversed, and the magnitude and position of the large magnetoresistance peak found in the insulating regime were modified. The systematic variation of the magnetoresistance peak with charge concentration was found to be qualitatively consistent with a simulation based on a model involving granularity.

The nanoscopic magnetoelectronic phase separation in doped La${}_{1-x}$Sr${}_x$CoO${}_3$ perovskites was studied with local probes. The phase separation is directly observed by Mössbauer spectroscopy in the studied doping range of 0.05 $\le$ $x$ $\le$ 0.25 both at room temperature and in the low-temperature magnetic phase. Extended with current synchrotron-based x-ray spectroscopies, these data help to characterize the volume as well as the local electric and magnetic properties of the distinct phases. A simple model based on a random distribution of the doping Sr ions describes well both the evolution of the separated phases and the variation of the Co spin state. The experiments suggest that Sr doping initiates small droplets and a high degree of doping-driven cobalt spin-state transition, while the Sr-free second phase vanishes rapidly with increasing Sr content.

The effect of substitutional doping of fluorographene with boron and nitrogen atoms on its electronic and magnetic properties is investigated using first-principles calculations. It is found that boron dopants can be readily incorporated in the fluorographene crystal where they act as shallow acceptors and cause hole doping, but no changes in the magnetic properties are observed. Nitrogen dopants act as deep donors and give rise to a magnetic moment, but the resulting system becomes chemically unstable. These results are opposite to what was found for substitutional doping of graphane, i.e., hydrogenated graphene, in which case B substituents induce magnetism and N dopants do not.

The phase diagram of $para$-H${}_2$ on both one-layer and bilayer graphene was calculated by means of the diffusion Monte Carlo method. The zero-point energy of the carbon atoms in the substrate was taken into account. That inclusion had minor effects on the liquidlike or incommensurate branches of the phase diagram, but it raised appreciably the energy per hydrogen molecule of the $\sqrt{3}\times \sqrt{3}$ commensurate solid with respect to the case of a perfectly flat substrate. That meant that the ground state of $para$-H${}_2$ on bilayer graphene was a $\sqrt{3}\times \sqrt{3}$ registered structure, but on a single graphene layer, both this arrangement and a triangular incommensurate phase of density $0.077\pm 0.001$ Å${}^{-2}$ were found to be in equilibrium at $T=0$ K.

We have grown the uranium compound URhIn${}_5$ with the tetragonal HoCoGa${}_5$-type by the In self-flux method. In contrast to the nonmagnetic ground state of the isoelectronic analog URhGa${}_5$, URhIn${}_5$ is an antiferromagnet with antiferromagnetic transition temperature $T_{\mathrm{N}}=98$ K. The moderately large electronic specific heat coefficient $\gamma =50$ mJ/K${}^2$mol demonstrates the contribution of 5$f$ electrons to the conduction band. On the other hand, magnetic susceptibility in the paramagnetic state roughly follows a Curie-Weiss law with a paramagnetic effective moment corresponding to a localized uranium ion. The crossover from localized to itinerant character at low temperature may occur around the characteristic temperature 150 K where the magnetic susceptibility and electrical resistivity show a marked anomaly.

An accurate, fully automated, theoretical ab initio scheme is presented for the calculation of elasto-optic constants of crystalline systems of any space group of symmetry. The approach is developed within periodic boundary conditions, exploits both translational and point symmetry, and allows for the use of several one-electron Hamiltonians, such as Hartree-Fock, Kohn-Sham, or hybrids. Generalized-gradient functionals are found to improve the agreement with experiments by a factor of 2 with respect to simple local-density ones, commonly used in the literature so far. The explicit dependence of elasto-optic constants from the electric field frequency can be evaluated as well, thus allowing for a closer comparison with experimental data that usually refer to finite frequencies. The relatively large uncertainty associated with experimental measurements, and the use of an electric field with finite wavelength, make the availability of a predictive theoretical scheme particularly helpful in interpreting the photoelastic response of crystals. The proposed scheme, which has been implemented in the crystal program, proves numerically stable with regard to its computational parameters and accurate with respect to elasto-optic constants of a set of eight crystals for which consolidated experimental values have been reported.

We perform ab initio calculations for the equation of state of dense liquid hydrogen and deuterium using quantum molecular dynamics simulations based on finite-temperature density functional theory. This extensive data set allows us to determine specific density-temperature-pressure tracks such as the cold curve, precompressed and principal Hugoniot curves, and isentropes which are essential for the analysis and interpretation of high-pressure experiments. In this study we focus on conditions probed by recent quasi-isentropic shock compression experiments that have reached a so-far unprecedented 108-fold compression of gaseous deuterium. As these states of matter are relevant for the deep interior of Jupiter-like exoplanets we simultaneously give predictions for their isentropes.

The antiferromagnet URhIn${}_5$ with the Néel temperature $T_{\mathrm{N}}=98$ K has been investigated by nuclear magnetic/quadrupole resonance (NMR/NQR). ${}^{115}$In-NQR spectra in the paramagnetic state give the respective electrical field gradient parameters for the locally tetragonal and orthorhombic In(1) and In(2) sites. In the antiferromagnetic state at 4.5 K, ${}^{115}$In-NMR spectra in the zero external field indicate a commensurate antiferromagnetic structure. The internal field at In(1) sites is found to be zero and that at In(2) sites is 21.1 kOe at 4.5 K. The temperature ($T$) dependence of the nuclear relaxation rates $1/T_1$ in the paramagnetic state shows a distinct site dependence: Korringa-type constant ${\left(T_{1}T\right)}^{-1}$ behavior below $\sim$150 K for In(1) sites and a divergent behavior of $1/T_1$ toward $T_{\mathrm{N}}$ for In(2). The plausible antiferromagnetic structure is discussed based on these observations.

The archetype of half-metallic magnetism, NiMnSb, has been reported to show an anomaly at low temperature. The high degree of spin polarization of the conduction electrons, characteristic of a half metal, is lost above this temperature. Recently reported experiments show that this anomaly is not an intrinsic property of NiMnSb: it requires an excess of (interstitial) manganese. Electronic structure calculations reported here show that the excess manganese orders antiferromagnetically with respect to the host magnetization, reduces the half-metallic band gap, and pushes the top of the valence band up to 36 meV below the Fermi level. Thermal excitations from minority to majority spin channel induce an avalanche effect, leading to the disordering of the magnetic moments of the excess manganese. This mechanism is supported by measurements of the magnetization as a function of temperature on NiMn${}_{1.05}$Sb: It shows a maximum in the magnetization measured in a field of 400 Oe.

To extend the applicability of density functional theory for superconductors (SCDFT) to systems with significant particle-hole asymmetry, we construct an improved exchange-correlation kernel entering the gap equation. We show that the kernel is numerically stable and does not diverge even in the low-temperature limit. Solving the gap equation for model systems with the present kernel analytically and numerically, we find that the asymmetric component of electronic density of states, which has not been considered with the previous kernel, systematically decreases transition temperature ($T_{\mathrm{c}}$). We present a case where the decrease of $T_{\mathrm{c}}$ amounts to several tens of percent.