We investigate the effects of charged impurity distributions and carrier-carrier interactions on electronic transport in graphene on ${\mathrm{SiO}}_2$ by employing a self-consistent coupled simulation of carrier transport and electrodynamics. We show that impurity clusters of characteristic width 40–50 nm generate electron-hole puddles of experimentally observed sizes. The residual conductivity and the linear-region slope of the conductivity versus carrier density dependence are determined by the impurity distribution, and the measured slope can be used to estimate the impurity density in experiment. Furthermore, we show that the high-density sublinearity in the conductivity stems from carrier-carrier interactions.

Near-field and resonance effects have a strong influence on nanoscale electromagnetic energy transfer, and detailed understanding of these effects is required for the design of new, optimized nano-optical devices. We provide a comprehensive microscopic view of electromagnetic energy transfer phenomena by introducing quantum Langevin heat baths as local noise sources in the equations of motion for the thermally fluctuating electric dipoles forming dielectric bodies. The theory is, in a sense, the microscopic generalization of the well-known fluctuational electrodynamics theory and thereby provides an alternative and conceptually simple way to calculate the local emission and absorption rates from the local Langevin bath currents. We apply the model to study energy transfer between silicon carbide nanoparticles located in a microcavity formed of two mirrors and next to a surface supporting propagating surface modes. The results show that the heat current between dipoles placed in a cavity oscillates as a function of their position and separation and can be enhanced by several orders of magnitude as compared to the free-space heat current with a similar interparticle distance. The predicted enhancement can be viewed as a many-body generalization of the well-known cavity Purcell effect. Similar effects are also observed in the interparticle heat transfer between dipoles located next to a surface of a polar material supporting surface phonon polaritons.

We studied single crystals of $\text{BaV}{}_{13}$$\text{O}{}_{18}$, in which V ions with an average valence of +2.62 ($3d^{2.38}$) form a quasi-fcc lattice. We found that the ground state of the stoichiometric crystal is insulating, whereas that of the off-stoichiometric crystal is metallic with a large effective mass. This metallic state can be explained by the Kondo coupling between the magnetic moment existing at the lone V ion and itinerant carriers in the V tetramers.

The presence of electric field–induced polarization reversal behavior just below Néel's antiferromagnetic ordering temperature ($T_{\mathrm{N}}$) is demonstrated in polycrystalline orthorhombic ${\mathrm{LuCrO}}_3$, which crystallizes in the centrosymmetric space group (Pbnm) at room temperature. This result on ${\mathrm{LuCrO}}_3$ is compared with ${\mathrm{ErCrO}}_3$, another orthochromite. The single phase nature and the quality of both polycrystalline samples were checked by x-ray diffraction and transmission electron microscopy (TEM). The high-resolution TEM images of ${\mathrm{LuCrO}}_3$ and ${\mathrm{ErCrO}}_3$ brought out the presence of twin boundaries. Detailed magnetic, dielectric, and polarization studies were carried out on both systems. As the presence of ferroelectric-like characteristics is found below $T_{\mathrm{N}}$ in both ${\mathrm{LuCrO}}_3$ and ${\mathrm{ErCrO}}_3$, this rules out the condition for the rare earth cation to be paramagnetic for observing possible signatures of multiferroicity in this family of compounds. Also, we report a much stronger magnetodielectric effect in the case of ${\mathrm{ErCrO}}_3$ compared with ${\mathrm{LuCrO}}_3$ reflecting the different magnetism of their $A$-site cations.

Defects intentionally introduced into magnetic materials often have a profound effect on the physical properties. Specifically tailored neutron spectroscopic experiments can provide detailed information on both the local exchange interactions and the local distances between the magnetic atoms around the defects. This is demonstrated for manganese dimer excitations observed for the magnetically diluted three- and two-dimensional compounds ${\mathrm{KMn}}_x{\mathrm{Zn}}_{1-x}$F${}_3$ and K${}_2$Mn${}_x{\mathrm{Zn}}_{1-x}$F${}_4$, respectively. The resulting local exchange interactions deviate up to 10% from the average, and the local Mn-Mn distances are found to vary stepwise with increasing internal pressure due to the Mn/Zn substitution. Our analysis qualitatively supports the theoretically predicted decay of atomic displacements according to 1/$r^2$, 1/$r$, and constant (for three-, two-, and one-dimensional compounds, respectively) where $r$ denotes the distance of the displaced atoms from the defect.

‘‘Bad metals” are known to have a large linear resistivity at high $T$ that is universally seen near the Mott-Hubbard insulating phase. Less well known is that the thermopower $\alpha \left(T\right)$ of the Mott-Hubbard systems also exhibits simple universal features: (i) close to the insulating phase, where the resistivity has a low-temperature upturn, $\alpha \left(T\right)$ has a pronounced low-$T$ peak that shifts to higher $T$ with doping; (ii) when the resistivity is nearly linear, which occurs at moderate doping, $\alpha \left(T\right)$ has a small low-$T$ peak that shifts to lower $T$ with doping and has a high-$T$ sign change; and (iii) at the highest doping, where the resistivity acquires a $T^2$ term, $\alpha \left(T\right)$ is negative and depends monotonically on $T$. The universality $\alpha \left(T\right)$ can be understood using the Kelvin formula and the fact that the chemical potential for doped Mott insulators displays similar behavior at high $T$. The universality is illustrated with the exact solution of the simplest model for a doped Mott insulator at high $T$.

The behavior of a ${}^4\text{He}$ monolayer on a single graphene sheet in which the zero-point energy of the carbon atoms was taken into account was calculated. It was found that the ground state was a liquid of density $\sim$0.030 Å${}^{-2}$, instead of the $\sqrt{3}\times \sqrt{3}$ commensurate arrangement found previously for flat graphene. Helium absorption on both sides of the carbon layer left the phase diagram unchanged with respect to the case in which only one of the two surfaces was available for coating.

The electronic structures of supercells of ${\text{CeO}}_{2-\delta }$ have been calculated within the density functional theory (DFT). The equilibrium properties such as lattice constants, bulk moduli, and magnetic moments are well reproduced by the generalized gradient approximation (GGA). Electronic excitations are simulated by robust total-energy calculations for constrained states with atomic core holes or valence holes. Pristine ceria ${\text{CeO}}_2$ is found to be a nonmagnetic insulator with magnetism setting in as soon as oxygens are removed from the structure. In the ground state of defective ceria, the Ce-$f$ majority band resides near the Fermi level but appears at about 2 eV below the Fermi level in photoemission spectroscopy experiments due to final-state effects. We also tested our computational method by calculating threshold energies in Ce-M${}_5$ and O-K x-ray absorption spectroscopy and comparing theoretical predictions with the corresponding measurements. Our result that $f$ electrons reside near the Fermi level in the ground state of oxygen-deficient ceria is crucial for understanding the catalytic properties of ${\text{CeO}}_2$ and related materials.

We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multiple scattering phenomena can strongly depend on the transport measurement geometry. This eventually yields the coexistence of a ballistic waveguide and a highly resistive channel (Anderson insulator) in the same two-dimensional platform, evidenced by a ${\sigma }_{yy}/{\sigma }_{xx}$ ratio varying over several orders of magnitude, and suggesting the possibility of building graphene electronic circuits based on the unique properties of chiral massless Dirac fermions in graphene.

The formation energies and charge transition levels of the most relevant $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ intrinsic point defects, i.e., Nb antisites and Li as well Nb vacancies, are studied from first principles. Thereby isolated defects are modeled in the framework of the density functional theory with local and hybrid exchange-correlation functionals. The inclusion of nonlocal exchange opens the $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ fundamental band gap by nearly 2 eV and modifies considerably the relative stability of the investigated defects with respect to values calculated with local functionals. On the other hand, supercell symmetry and finite-size errors in calculations using periodic boundary conditions are found to have a major influence on the outcome of the simulations. It is found that, in particular, the Nb vacancy causes a long-range strain field and requires very large supercells for its adequate modeling. Compared to previous theoretical results we find an enhanced stability of the Nb vacancy with respect to the other defects. The V${}_{\mathrm{Nb}}^{-5}$ is predicted to be stable for Fermi level positions in the upper part of the band gap.

Recent advances in cold atom experimentation suggest that studies of quantum two-dimensional melting of dipolar molecules, with dipoles aligned perpendicular to ordering plane, may be on the horizon. An intriguing aspect of this problem is that two-dimensional classical aligned dipoles (already studied in great detail in soft matter experiments on magnetic colloids) are known to melt via a two-stage process, with an intermediate hexatic phase separating the usual crystal and isotropic fluid phases. We estimate here the effect of quantum fluctuations on this hexatic phase, for both dipolar systems and charged Wigner crystals. Our approximate phase diagrams rely on a pair of Lindemann criteria, suitably adapted to deal with the effects of thermal fluctuations in two dimensions. As part of our analysis, we determine the phonon spectra of quantum particles on a triangular lattice interacting with repulsive $1/r^3$ and $1/r$ potentials. A large softening of the transverse and longitudinal phonon frequencies, due to both lattice effects and quantum fluctuations, plays a significant role in our analysis. The hexatic phase is predicted to survive down to very low temperatures.

We investigate spatial adiabatic passage processes for sound wave propagation in sonic crystals, consisting of steel cylinders embedded in a water host medium, that present two linear defects. This work constitutes an extension of the well-known quantum optical rapid adiabatic passage technique to the field of sound propagation. Several spatial adiabatic passage devices are proposed by appropriately designing the geometry of the two linear defects along the propagation direction to work as a coherent multifrequency adiabatic splitter, a phase difference analyzer, and a coherent multifrequency adiabatic coupler. These devices are robust in front of fluctuations of the geometric parameter values.

The total and magnetically resolved Compton profiles are analyzed within the combined density functional and dynamical mean-field theory for the transition-metal elements Fe and Ni. A rather good agreement between the measured and computed magnetic Compton profiles of Fe and Ni is obtained with the standard local spin-density approximation (LSDA). By including local but dynamic many-body correlations captured by dynamical mean-field theory (DMFT), the calculated magnetic Compton profile is further improved when compared with experiment. The second moment of the difference of the total Compton profiles between the LSDA and DMFT, along the same momentum direction, has been used to discuss the strength of electronic correlations in Fe and Ni.

The influence of an electrical current on the propagation of magnetostatic surface waves is investigated in a relatively thick (40 nm) permalloy film both experimentally and theoretically. Contrary to previously studied thinner films where the dominating effect is the current-induced spin-wave Doppler shift, the magnetic field generated by the current (Oersted field) is found to induce a strong nonreciprocal frequency shift which overcompensates the Doppler shift. The measured current-induced frequency shift is in agreement with the developed theory. The theory relates the sign of the frequency shift to the spin-wave modal profiles. The good agreement between the experiment and the theory confirms a recent prediction of a counterintuitive mode localization for magnetostatic surface waves in the dipole-exchange regime.

Magneto-optical Kerr effect measurements of epitaxial AFM/FM bilayers and FM/AFM/FM trilayers on ${\mathrm{Cu}}_3$Au(001), where “AFM” stands for a Ni${}_{25}$Mn${}_{75}$ antiferromagnetic layer, and “FM” for ferromagnetic layers that are either Ni or Ni/Co with out-of-plane or in-plane easy axis of magnetization, show that trilayers with collinear magnetization directions of both FM layers exhibit always a much lower exchange bias field $H_{\mathrm{eb}}$ at a fixed temperature compared to bilayers of the same Ni${}_{25}$Mn${}_{75}$ thickness. At the same time, the blocking temperature for exchange bias $T_b$ is strongly reduced. In trilayers with orthogonal easy axes of the two FM layers (in-plane and out-of-plane), in contrast, both $H_{\mathrm{eb}}$ and $T_b$ are nearly identical to that of the corresponding bilayers. Such a behavior can be explained by pinned magnetic moments inside the bulk of the AFM layer that coexist independently for orthogonal spin directions, but have to be equally shared between both interfaces in the case of collinear spin directions. This result thus also confirms a 3Q-like noncollinear spin structure of Ni${}_{25}$Mn${}_{75}$.

Spin angular momentum transfer into an antiferromagnetic (AFM) insulator is observed in a single-crystalline Fe/CoO/MgO(001) heterostructure by time-resolved magneto-optical Kerr effect. The transfer process is mediated by the Heisenberg exchange coupling between Fe and CoO spins. Spin angular momentum transfer to ordered AFM spins is independent of the external magnetic field and enhances the spin precession damping in Fe, which remains nearly invariant with temperature.

The transmon superconducting qubit is being intensely investigated as a promising approach for the physical implementation of quantum information processing, and high-quality factors of order ${10}^6$ have been achieved both in two- and three-dimensional architectures. These high-quality factors enable detailed investigations of decoherence mechanisms. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom and the quasiparticles that tunnel across Josephson junctions. In a transmon, tunneling of a single quasiparticle is associated with a change in parity. Here we present the theory of the parity-switching rates in single-junction transmons and compare it with recent measurements. We also show that parity switching can have an important role in limiting the coherence time.

As in ${{\mathrm{YBa}}_2{\mathrm{Cu}}_3\mathrm{O}}_{6+x}$ and ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{8+\delta }$, the pseudogap state in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ is characterized by the existence of an intra-unit-cell magnetic order revealed by polarized neutron scattering technique. We report here a supplementary set of polarized neutron scattering measurements for which the direction of the magnetic moment is determined and the magnetic intensity is calibrated in absolute units. These data allow a close comparison between bilayer systems ${{\mathrm{YBa}}_2{\mathrm{Cu}}_3\mathrm{O}}_{6+x}$ and ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ and raise important questions concerning the range of the magnetic correlations and the role of disorder around optimal doping.

Starting from the London-type model, we study the domain structures in ferromagnetic superconductors taking account of the nucleation of vortices and antivortices coupled to the magnetic texture. We predict that the coupling between domains and vortices results in the formation of two energetically favorable domain configurations: (i) a Meissner-type vortex-free configuration with strong domain shrinking and (ii) a more rare domain configuration with a dense vortex-antivortex lattice. The switching between these configurations is shown to result in the first-order phase transitions which could be observable in superconducting uranium-based compounds.