We derive the current response to the linearly polarized electromagnetic field incident normally on the specular surface of a clean nonconventional superconductor with orbital spontaneous magnetization parallel to the crystal axis and perpendicular to the crystal surface. The result includes the usual part known from the theory of conventional superconductivity, as well as the magneto-optical term typical for superconductors with spontaneous time-reversal breaking. As an application of the basic current-field relation, we consider the Kerr effect for the rotation of the polarization of infrared light reflected from the superconductor surface.

Since the discovery of high-$T_c$ ${\mathrm{LaO}}_{1-x}{\mathrm{F}}_x\mathrm{FeAs}$ and other such systems based on $\mathrm{FeAs}$ layers, several proposals have been made for the superconducting order parameter ${\Delta }_{\mathbf{k}}$, on both phenomenological and microscopic grounds. Here we discuss how the symmetry of ${\Delta }_{\mathbf{k}}$ in the bulk can be determined, assuming that single crystals will soon be available. We suggest that a measurement of the dependence of the low-temperature specific heat on the angle of a magnetic field in the $\mathrm{FeAs}$ plane is the simplest such method, and calculate representative specific heat vs field angle oscillations for the various candidate states, using a phenomenological band structure fitted to the density functional theory Fermi surface.

Unlike the broadly studied influence of the in-plane magnetic fields on magnetic domain structures in thin-film elements, not much is known to date, on the changes of the domain structure driven by external magnetic fields applied perpendicular to the plane. Using high-resolution transmission electron microscopy studies combined with micromagnetic modeling, we investigated the effect of static, strong perpendicular fields on square and disk-shaped mesoscopic permalloy elements with a vortex flux-closure magnetization structure. In the case of square elements, we discovered an unexpected, pronounced, and reversible bending of the $90°$ domain walls, which increases with the field strength and changes direction when the field direction is reversed. By means of micromagnetic simulations and atomic force microscopy studies, we demonstrate that this effect is connected with the minute curvatures of the sample surface. The slight curvature arises from surface tensions in the membrane on which the microstructures are fabricated.

We study theoretically the charge transport pumped by magnetization dynamics through epitaxial FIF and FNIF magnetic tunnel junctions (F, ferromagnet; I, insulator; N, normal metal). We predict a small but measurable dc pumping voltage under ferromagnetic resonance conditions for collinear magnetization configurations, which may change sign as a function of barrier parameters. A much larger ac pumping voltage is expected when the magnetizations are at right angles. Quantum size effects are predicted for an FNIF structure as a function of the normal layer thickness.

We extend the Hertz–Millis theory of quantum phase transitions in itinerant electron systems to phases with broken discrete symmetry. By using a set of coupled flow equations derived within the functional renormalization group framework, we compute the second order phase transition line $T_c\left(\delta \right)$, where $\delta$ is a nonthermal control parameter, near a quantum critical point. We analyze the interplay and relative importance of quantum and classical fluctuations at different energy scales, and we compare the Ginzburg temperature $T_G$ to the transition temperature $T_c$, the latter being associated with a non-Gaussian fixed point.

We develop a theory of anomalous quantum Hall effects in graphene. We demonstrate that the Landau level structure by itself is not sufficient to determine the form of the quantum Hall effect. It is only a special symmetry of disorder that gives rise to anomalous quantization of Hall conductivity in graphene. We analyze the symmetries of disordered single- and double-layer graphene samples in magnetic field and identify the conditions for anomalous Hall quantization.

We have examined time-averaged charges of the molecular donors around the phase boundary between the insulating, superconducting, and metal phases for ${\beta }^{″}$-type ET [$\mathrm{ET}=\text{bis}$-ethelenedithio-tetrathiafulvalene] salts with one (two) hole(s) per two (three) molecules by using vibrational spectroscopy. Around the phase boundary, the site charges are neither those expected for a well-developed charge-ordered (CO) state nor a homogeneous distribution. The molecular charges exhibit an inhomogeneous distribution just above the insulator-superconductor transition temperature. We have analyzed the distribution of the site charges from the viewpoint of the alternation of intersite Coulomb interactions along the stacking direction. The closeness in the energy of several CO patterns mostly contributes to the inhomogeneous distribution, whereas a large difference (no difference) in the energy levels contributes to the CO (homogeneous) state. Our observations indicate that the instability due to the closeness in the energy of several distributions correlates with the insulator-superconductor transition in nondimerized or weakly dimerized molecular conductors.

Motivated by the recent controversy surrounding the Kerr effect measurements in strontium ruthenate [J. Xia et al., Phys. Rev. Lett. 97, 167002 (2006)], we examine the electromagnetic response of a clean chiral $p$-wave superconductor. When the contributions of the collective modes are accounted for, the Hall response in a clean chiral superconductor is smaller by several orders of magnitude than previous theoretical predictions and is too small to explain the experiment. We also uncover some unusual features of the collective modes of a chiral superconductor, namely, that they are not purely longitudinal and couple to external transverse fields.

Motivated by recent experiments on $\mathrm{Zn}{\mathrm{Cu}}_3{\left(\mathrm{O}\mathrm{H}\right)}_6{\mathrm{Cl}}_2$, we study the inhomogeneous Knight shifts (local susceptibilities) of a spin-$1∕2$ kagome antiferromagnet in the presence of nonmagnetic impurities. Using high temperature series expansion, we calculate the local susceptibility and its histogram down to about $T=0.4J$. At low temperatures, we explore a Dirac spin liquid proposal and calculate the local susceptibility in the mean field and beyond mean field using Gutzwiller projection, finding the overall picture to be consistent with the NMR experiments.

An ion-radical salt, ${\left(\text{ESBN}\right)}_2{\text{ClO}}_4$, obtained from the electrochemical crystallization of an organic donor radical, ESBN, exhibited giant negative magnetoresistance ($-70\%$ at 2 K in 9 T) in spite of the absence of metal ions. Furthermore, it was found that the conductivity of ${\left(\text{ESBN}\right)}_2{\text{ClO}}_4$ was characterized by a distinct nonlinear temperature dependence and a nonlinear power law of $I\propto V^n$ $\left(n=12\right)$. We speculated that such correlated spin-dependent electron transportation is derived from the charge-ordered electronic structure and the strong intramolecular ferromagnetic coupling between $\pi$-conduction electrons and $\pi$-localized spins in the “spin-polarized donor.”

We address the electronic structure and magnetic properties of vacancies and voids both in graphene and graphene ribbons. By using a mean-field Hubbard model, we study the appearance of magnetic textures associated with removing a single atom (vacancy) and multiple adjacent atoms (voids) as well as the magnetic interactions between them. A simple set of rules, based on the Lieb theorem, link the atomic structure and the spatial arrangement of the defects to the emerging magnetic order. The total spin $S$ of a given defect depends on its sublattice imbalance, but some defects with $S=0$ can still have local magnetic moments. The sublattice imbalance also determines whether the defects interact ferromagnetically or antiferromagnetically with one another and the range of these magnetic interactions is studied in some simple cases. We find that in semiconducting armchair ribbons and two-dimensional graphene without global sublattice imbalance, there is a maximum defect density above which local magnetization disappears. Interestingly, the electronic properties of semiconducting graphene ribbons with uncoupled local moments are very similar to those of diluted magnetic semiconductors, presenting giant Zeeman splitting.

An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been carried out on $\mathrm{Li}\mathrm{B}{\mathrm{H}}_4$. The phase diagram of $\mathrm{Li}\mathrm{B}{\mathrm{H}}_4$ is mapped to $10\mathrm{GPa}$ and $500\mathrm{K}$, and four phases are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal a nontrivial layered structure of $\mathrm{Li}\mathrm{B}{\mathrm{H}}_4$. The layers and their deformations define the structural stability of the observed phases.

The topographic image of dynamic force microscopy (DFM) keeping the frequency shift $\left(\Delta f_z\right)$ constant at tiny cantilever oscillation amplitudes corresponds to the constant-vertical force $\left(F_z\right)$ gradient surface, while the interpretation becomes complicated at larger oscillation amplitudes. We discuss how $F_z$ and the potential energy $\left(U\right)$ act on the tip during DFM topographic scan at various cantilever oscillation amplitudes by measuring the $\Delta f_z$ map on the $\mathrm{Si}\left(111\right)\text{−}(7\times 7)$ surface at room temperature. The $\Delta f_z$ map is numerically converted into $F_z$ and $U$ maps. DFM topographic curves at various cantilever oscillation amplitudes are numerically derived by using the experimentally obtained $F_z$ map. In addition, we discuss how the lateral force $\left(F_x\right)$ acts on the tip at various tip-surface distances on various surface sites by an $F_x$ map converted from a $U$ map. The positions at which $F_x$ becomes zero are identified as $U$ minimum sites, such as the top of adatom sites, and $U$ maximum sites (equilibrium positions of $F_x$), such as the center positions among three center adatoms. The tip deviated from these sites is then laterally attracted toward the $U$ minimum sites. It is also demonstrated that lateral force microscopy performed at $1\mathrm{\AA }$ cantilever oscillation enables direct measurement of the lateral force gradient by numerically deriving the frequency shift $\left(\Delta f_x\right)$ caused by $F_x$.

Ice films as many as 30 molecular layers thick can be imaged with scanning tunneling microscopy (STM) when negative sample biases $<-6(\pm 1)\text{V}$ and subpicoamp tunneling currents are used. We observe that water deposited onto Pt(111) below 120 K forms amorphous films, whereas metastable cubic ice appears between 120 and 150 K. To determine the mechanisms of ice growth, we investigate the thickness-dependent film morphology. Cubic ice emerges from screw dislocations in the crystalline ice film that are caused by the mismatch in the atomic Pt- step height and the ice-bilayer separation.

The spin- and charge-density-wave order parameters of the itinerant antiferromagnet chromium are directly measured with nonresonant x-ray diffraction as the system is driven toward its quantum critical point with high pressure using a diamond anvil cell. The exponential decrease of the spin and charge diffraction intensities with pressure confirms the harmonic scaling of spin and charge, while the evolution of the incommensurate ordering vector provides important insight into the difference between pressure and chemical doping as means of driving quantum phase transitions. Measurement of the charge density wave over more than two orders of magnitude of diffraction intensity provides the clearest demonstration to date of a weakly coupled BCS-type ground state. Evidence for the coexistence of this weakly coupled ground state with high-energy excitations and pseudogap formation above the ordering temperature in chromium, the charge-ordered perovskite manganites, and the blue bronzes, among other such systems, raises fundamental questions about the distinctions between weak and strong coupling.

The deposition of Au onto thin Xe films at a low temperature leads to cluster formation. The subsequent Xe sublimation results in cluster aggregation and delivery to the substrate in a process known as buffer-layer-assisted growth. Previously, this process was described in terms of a diffusion-limited cluster-cluster aggregation process during layer-by-layer desorption of the buffer. Instead, significant diffusion, restructuring, and dewetting of the Xe occur prior to desorption, and this leads to cluster aggregation. Cluster motion and aggregation are driven by capillary forces as the dewetting film retreats and sublimes. Kinetic Monte Carlo simulations reproduce the experimentally observed particle shapes and size distributions, and they provide additional insight into the interaction of the particles with the dewetting front. The presence of nanoscale particles on the film inhibits dewetting and significantly alters the shape of the front.

The description of realistic strongly correlated systems has recently advanced through the combination of density functional theory in the local density approximation (LDA) and dynamical mean field theory (DMFT). This $\text{LDA}+\text{DMFT}$ method is able to treat both strongly correlated insulators and metals. Several interfaces between LDA and DMFT have been used, such as ($N\text{th}$ order) linear muffin-tin orbitals or maximally localized Wannier functions. Such schemes are, however, either complex in use or additional simplifications are often performed (i.e., the atomic sphere approximation). We present an alternative implementation of $\text{LDA}+\text{DMFT}$, which keeps the precision of the Wannier implementation, but which is lighter. It relies on the projection of localized orbitals onto a restricted set of Kohn–Sham states to define the correlated subspace. The method is implemented within the projector augmented wave and within the mixed-basis pseudopotential frameworks. This opens the way to electronic structure calculations within $\text{LDA}+\text{DMFT}$ for more complex structures with the precision of an all-electron method. We present an application to two correlated systems, namely, ${\text{SrVO}}_3$ and $\beta$-NiS (a charge-transfer material), including ligand states in the basis set. The results are compared to calculations done with maximally localized Wannier functions, and the physical features appearing in the orbitally resolved spectral functions are discussed.

We study the effects of quenched height fluctuations (ripples) in graphene on the density of states (DOS). We show that at strong ripple disorder, a divergence in the DOS can lead to an ordered ground state. We also discuss the formation of dislocations in corrugated systems, buckling effects in suspended samples, and the changes in the Landau levels due to the interplay between a real magnetic field and the gauge potential induced by ripples.

Due to recent successes of a statistical-based nonlocal continuum crystal plasticity theory for single-glide in explaining various aspects such as dislocation patterning and size-dependent plasticity, several attempts have been made to extend the theory to describe crystals with multiple-slip systems using ad hoc assumptions. We present here a mesoscale continuum theory of plasticity for multiple-slip systems of parallel edge dislocations. We begin by constructing the Bogolyubov–Born–Green–Yvon–Kirkwood integral equations relating different orders of dislocation correlation functions in a grand canonical ensemble. Approximate pair correlation functions are obtained for single-slip systems with two types of dislocations and, subsequently, for general multiple-slip systems of both charges. The effect of the correlations manifests itself in the form of an entropic force in addition to the external stress and the self-consistent internal stress. Comparisons with a previous multiple-slip theory based on phenomenological considerations shall be discussed.

The surface phase $\mathrm{Sn}∕\mathrm{Cu}\left(100\right)\text{−}(3\sqrt{2}\times \sqrt{2})R45°$ exhibits a temperature induced phase transition to a $(\sqrt{2}\times \sqrt{2})R45°$ phase above $360\mathrm{K}$. We report an angle-resolved photoemission study of the two-dimensional Fermi surface of the low-temperature phase. The Fermi surface is formed by folding of a quasi-two-dimensional surface band and presents three contours. It is characterized by gaps appearing in optimally nested regions of one of the contours, whereas other sections remain ungapped. We address the origin of the folding and of the surface phase transition, which is attributed to the formation of a surface charge density wave.