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It is know that a paramagnetic phase is stabilized in integer spin systems with large easy-plane type single-ion anisotropy owing to the local singlet groundstate. In this case, applying pressure can collapse the excitation gap and induce a quantum phase transition into a magnetically ordered phase. We investigate how the magnetic excitation evolves with pressure on the basis of the extended spinwave theory. In the vicinity of the quantum critical point in the ordered phase, a longitudinal mode (Higgs mode) exists in the low-energy region. We report that the Higgs mode is observable as an electromagnon excitation.

A triangular triple quantum dot (TTQD) is an artificial variant of an orbitally-degenerate atomic system, which is expected to exhibit a novel Kondo physics. We focus on the emergence of electric polarization by the Kondo effect, owing to electron hopping in the triangular loop that is triggered by a point contact between the apex of TTQD and a metallic lead. Since the charge distribution depends on the spin correlation in TTQD, the electric dipole can be controlled by applying a magnetic field that suppresses the Kondo effect. We demonstrate this multiferroic behavior on the nanoscale using an impurity Anderson model for the TTQD Kondo system.

We demonstrate the existence of the spin-nematic interactions in an easy-plane type antiferromagnet Ba2CoGe2O7 by exploring the magnetic anisotropy and spin dynamics. The combination of neutron scattering and magnetic susceptibility measurements reveals that the origin of the in-plane anisotropy is an antiferro-type interaction of the spin-nematic operator. The relation between the nematic operator and the electric polarization in the ligand symmetry of this compound is presented. The introduction of the spin-nematic interaction is useful to understand the physics of spin and electric dipole in multiferroic compounds.

The adsorption and photoreaction of NO on Ag films deposited on Pt(1 1 1) were investigated at 90 K by reflection-absorption infrared spectroscopy (RAIRS). Similar to Ag(1 1 1), NO molecules were found to be converted into (NO) 2 and N 2 O on the Ag films. At an Ag thickness of 1 ML, however, a new adsorption state that reveals a RAIRS band at 1848 cm −1 is present on the surface. The (NO) 2 dimer species was found to react into N 2 O, while the reaction of the new species was substantially suppressed. Upon photon irradiation with a wavelength of 193 nm, the three adsorption species on Ag(1 ML)/Pt(1 1 1) were depleted from the surface. The origin of the newly found species and the photoreaction mechanism are discussed.

Orbital degrees of freedom of a Cooper pair play an important role in the unconventional superconductivity. To elucidate the orbital effect in the Kondo problem, we investigated a single magnetic impurity coupled to Cooper pairs with a $p_x +i p_y$ ($d_{x^2-y^2}+id_{xy}$) symmetry using the numerical renormalization group method. It is found that the ground state is always a spin doublet. The analytical solution for the strong coupling limit explicitly shows that the orbital dynamics of the Cooper pair generates the spin 1/2 of the ground state., Comment: 4 pages, 2 figures, JPSJ.sty, to be published in J. Phys. Soc. Jpn. 70 (2001) No. 10

The adsorption and initial absorption of hydrogen (H2) by Pd(1 0 0) at T=100–160 K are investigated by thermal desorption spectroscopy (TDS) and nuclear reaction analysis, which enables a depth-resolved determination of the hydrogen concentration at and below the Pd surface. Under 3×10−8 mbar H2 and T 130 K H-migration from such a near-surface hydride phase to the deeper bulk of the metal occurs and a solution of H in Pd is formed by means of facile diffusion. This bulk dissolved hydrogen emerges as a broad structure in TDS at T=200–260 K exhibiting a tailing at high temperatures characteristic of diffusion-controlled desorption kinetics.

The microscopic mechanism of circular currents induced in the vicinity of a non-magnetic impurity is analyzed for the (time-reversal symmetry breaking) chiral superconducting state ${\bf d}({\bf k}) = \hat{{\bf z}} (k_x \pm i k_y)$ which is very likely realized in Sr_2RuO_4. From the analytic, not self-consistent solution of the Bogolyubov-de Gennes equations we find two types of quasiparticle states, a bound state and the continuum state. Through impurity scattering the condensate transfers angular momentum to the quasiparticle states which generate a circular current. At low temperature the continuum part of the quasiparticle spectrum gives the main contribution. The non-selfconsistent solution yields a state of finite angular momentum. The comparison with the corresponding Ginzburg-Landau theory reveals the existence of a compensating counterflow created by the superconducting condensate. The currents and magnetic fields appearing around the impurity have possibly been observed by muon spin relaxation measurements., Comment: 16 page Latex, 3PS file, accepted by J.Phys.Soc.Jpn

Photoluminescence spectra and the reflectivity of incident light were examined in dye molecules in strongly scattering media. With increasing incident light intensity, the spectra show red- and blueshifts depending on the geometry of experiments, and the reflectivity increases nonlinearly. These excitation-power-dependent spectral shifts and nonlinear reflectivity are well explained when we consider saturation absorption in the excitation process and the reabsorption in the luminescence process in dyes.

The tunneling probability for a positive muon in high-purity tantalum is significantly enhanced by the onset of superconductivity. This establishes the predominant influence of low energy infrared couplings to the conduction electrons in the quantum tunneling motion of a charged interstitial atom in metals.

In a previous paper a possibility of coexistence of two superconducting order parameters was discussed for the (1, 1, 0) surface of d x 2 - y 2 -wave superconductors. In the present report physical properties are examined particularly for the time-reversal-breaking state ( s ± i d ) near the (1, 1, 0) surface. The nature of coexisting order parameters shows up in the local density of states. It is also shown that the superconducting current flows along the surface due to the time reversal breaking and induces the magnetic field. The induced magnetic field can be used to detect the time-reversal-breaking states experimentally.

Magnetic excitation in a spin dimer system on a bilayer honeycomb lattice is investigated in the presence of a zigzag edge, where disordered and ordered phases can be controlled by a quantum phase transition. In analogy with the case of graphene with a zigzag edge, a flat edge magnon mode appears in the disordered phase. In an ordered phase, a finite magnetic moment generates a mean-field potential to the magnon. Since the potential is nonuniform on the edge and bulk sites, it affects the excitation, and the dispersion of the edge mode deviates from the flat shape. We investigate how the edge magnon mode evolves when the phase changes through the quantum phase transition and discuss the similarities to ordered spin systems on a monolayer honeycomb lattice., Comment: 17 pages, 13 figures

The boundary effect in d -wave superconductors is studied for specular and rough surfaces. In particular, the local density of states near the boundary is examined to see how the d -wave symmetry shows up in the direction dependence of the surface relative to the order parameter.

We study an orbitally degenerate Kondo effect in a triangular triple quantum dot (TTQD), where the three dots are connected vertically with a single metallic lead through electron tunneling. Both spin and orbital degrees of freedom play an important role in the SU(4) Kondo effect. This is demonstrated by an equilateral TTQD Kondo system at half-filling, by Wilson's numerical renormalization group method. We show how an emergent electric polarization of the TTQD is associated with a crossover from SU(4) to SU(2) symmetry in the low-temperature state. A marked sign reversal of the electric polarization is generated by the fine-tuning of Kondo coupling with degenerate orbitals, which can be utilized to reveal orbital dynamics in the SU(4) Kondo effect., 5 pages, 5 figures

We investigate general structure of Landau free energy for stabilizing a novel superconducting state with both even-frequency and odd-frequency components in gap function. On the basis of the Luttinger-Ward functional, we elucidate an emergent mixing between different "parities" in time. The simplest case of the conventional s-wave singlet mixed with the odd-frequency triplet state under broken time-reversal symmetry is examined to demonstrate the anomalous structure of the free-energy functional. The induced odd-frequency component alters behaviors of physical quantities from those obtained by neglecting the odd-frequency component. The novel mixed state may also be relevant to strong-coupling superconductivity coexisting with ferromagnetism., 11 pages, 7 figures

A novel superconducting state under the broken time-reversal symmetry is studied in conventional phonon-mediated superconductors. By solving the Eliashberg equation self-consistently with the mass renormalization effect, it is found that the even- and odd-frequency components of the order parameter coexist in the bulk system as a consequence of the broken time-reversal symmetry. This finding would direct more attention to the odd-frequency pairing that affects physical quantities, especially in strong coupling superconductors., 5 pages, 4 figures

We measure Raman scattering in an interacting spin-dimer system KCuCl3 under hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced quantum phase, we observe a one-magnon Raman peak, which originates from the longitudinal magnetic excitationand is observable through the second-order exchange interaction Raman process. We report the pressure dependence of the frequency, halfwidth and Raman intensity of this mode., Comment: 4 pages, 3 figures, inpress in JPCS as a proceeding of LT26

A new type of Kondo effect in unconventional superconductors is studied theoretically by using the Wilson's numerical renormalization group method. In this case, orbital degrees of freedom of a Cooper pair play an important role. It produces multichannel exchange couplings with a magnetic impurity, although the impurity is just a local spin. Here we focus on a p x +i p y -wave state which is a fully gapped system. In this case, the ground state is always a spin doublet in all the T K /Δ region, and the local spin is shrunk by the Kondo effect in the strong coupling region ( T K /Δ→∞). Here T K and Δ are the Kondo temperature and the superconducting energy gap, respectively. It indicates that the spin of the ground state is generated by the orbital effect of the Cooper pairs. This is completely different from the s -wave pairing case where a Kondo singlet is stabilized for large T K /Δ values. This type of Kondo effect reflects the symmetry of the conduction electron system.

The Kondo effect strongly depends on spin and orbital degrees of freedom of Cooper pairs. We focus on the Kondo effect in a p x +i p y -wave superconductor with a full energy gap. The numerical renormalization study shows that the ground state is always a spin doublet for a S imp =1/2 local spin and that it is always a spin singlet for S imp =1. The latter is due to uniaxial spin anisotropy of the Cooper pair. We also compare these results with a case of the d x 2 - y 2 +i d x y -wave superconductivity having the same energy-gap structure.

We study inelastic (dynamical) impurity scattering effects in two-band superconductors with the same ($s_{++}$ wave) or different ($s_\pm$ wave) sign order parameters. We focus on the enhancement of the superconducting transition temperature $T_{\rm c}$ by magnetic interband scattering with the interchange of crystal-field singlet ground and multiplet excited states. Either the $s_{++}$-wave or $s_\pm$-wave state is favored by the impurity-mediated pairing, which depends on the magnetic and nonmagnetic scattering strengths derived from the hybridization of the impurity states with the conduction bands. The details are examined for the singlet-triplet configuration that is suggestive of Pr impurities in the skutterudite superconductor LaOs$_4$Sb$_{12}$., 14 pages, 5 figures, to appear in J. Phys. Soc. Jpn. Vol. 79, No. 9 (2010)

Ortho-para (o-p) conversion of ${\text{H}}_{2}$ and para-ortho (p-o) conversion of ${\text{D}}_{2}$ were investigated on a Ag surface coadsorbed with ${\text{O}}_{2}$ by resonance-enhanced multiphoton ionization combined with photostimulated desorption. Compared with a bare Ag surface, both ${\text{H}}_{2}$ o-p conversion and ${\text{D}}_{2}$ p-o conversion were accelerated on ${\text{O}}_{2}$-covered surfaces, and the conversion time was found to decrease with increasing ${\text{O}}_{2}$ coverage. In order to analyze the conversion kinetics, Monte Carlo simulations taking account of hydrogen diffusion on the surfaces were performed and compared with the experimental data. The conversion time of ${\text{H}}_{2}$ and ${\text{D}}_{2}$ in the vicinity of adsorbed ${\text{O}}_{2}$ was estimated to be 8.3 and 53.4 s, respectively. The isotope dependence of the conversion is discussed.

A single impurity problem is investigated for multiband s-wave superconductors with different sign order parameters (+-s-wave superconductors) suggested in Fe-pnictide superconductors. Not only intraband but also interband scattering is considered at the impurity. The latter gives rise to impurity-induced local boundstates close to the impurity. We present an exact form of the energy of the local boundstates as a function of strength of the two types of impurity scattering. The essential role of the impurity is unchanged in finite number of impurities. The main conclusions for a single impurity problem help us understand effects of dense impurities in the +-s-wave superconductors. Local density of states around the single impurity is also investigated. We suggest impurity site nuclear magnetic resonance as a suitable experiment to probe the local boundstates that is peculiar to the +-s-wave state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave, reflecting the unconventional nature of the sign reversing order parameter. For a quantum magnetic impurity, interband scattering destabilizes the Kondo singlet., Comment: 23 pages, 7 figures, to be published in J. Phys. Soc. Jpn. (2009) No. 8

We report the observation of the $A_{\rm g}$-symmetric one-magnon Raman peak in the magnon Bose-Einstein condensation phase of TlCuCl$_{3}$. Its Raman shift traces the one-magnon energy at the magnetic $\Gamma$ point, and its intensity is proportional to the squared transverse magnetization. The appearance of the one-magnon Raman scattering originates from the exchange magnon Raman process and reflects the change of the magnetic-state symmetry. Using the bond-operator representation, we theoretically clarify the Raman selection rules, being consistent with the experimental results.

We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point., 4 pages, 4 figures

Since a symmetric spin-dependent electric polarization makes quantum spin systems couple to an electric field, it is one of a possible origin of electromagnon excitations in noncollinear (spiral) magnetically ordered states. In collinear ordered states, however, it is believed that the electromagnon excitation is difficult to realize. In the present study, we focus on the symmetric spin-dependent electric polarization and study the electromagnon excitation in both collinear and noncollinear states. In one-magnon excitation process, it is found that the symmetric spin-dependent polarization couples to a longitudinal fluctuation of the ordered moment and that the electromagnon measurements probe the longitudinal (Higgs) mode selectively. In noncollinear states, we report that both Higgs and Nambu-Goldstone (transverse) modes are observable.

The Kondo effect plays an important role in emergence of electric polarization in a triangular triple-quantum-dot system, where one of the three dots is point-contacted with a single lead, and a magnetic flux penetrates through the triangular loop. The Kondo-induced electric polarization exhibits an Aharonov-Bohm type oscillation as a function of the magnetic flux. Our theoretical study shows various oscillation patterns associated with the field-dependent mixing of twofold orbitally degenerate ground states and their sensitivity to the point contact.

Magnetic excitation in the interacting spin dimer system NH4CuCl3 is investigated on the basis of an extended spin-wave theory, assuming a doubled unit cell with four dimer sublattices of inequivalent intradimer interactions as suggested by neutron scattering measurements. In the magnetically ordered phase, there are both transverse (Nambu–Goldstone) and longitudinal (Higgs) excitation modes as in the pressure-induced ordered phase of the isostructural spin dimer compounds TlCuCl3 and KCuCl3. The inequivalent dimer model is consistent with the magnon dispersion relation at zero magnetic field and with the field dependence of the excitation energies obtained by neutron scattering and ESR measurements. This supports the existence of four dimer sublattices with inequivalent dimers in NH4CuCl3.

The compound TlCuCl3 represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Wuertz [Phys. Rev. B 50, 13515 (1994)] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important., 4 pages, 4 figures, to appear in Physical Review Letters

The most important character of the exotic superconductor PrOs4Sb12 is the existence of low-lying excitations (excitons) with a finite energy gap and it appears as the magnetic field-induced order above 4.5 T. We focus on the a_u conduction band, which hybridizes with a Pr 4f^2 state strongly, coupled to the excitons. It results in an attractive interaction between the conduction electrons. The symmetry of the superconducting order parameter is determined by dispersion relation of the exciton. For the bcc system PrOs4Sb12, a d-wave state [kx ky + omega ky kz + omega^2 kz kx, omega=exp(pm i 2 pi/3)] is stabilized with broken time reversal symmetry., 4 pages

Magnetoelastic properties in field-induced magnetic ordered phases are studied theoretically based on a Ginzburg-Landau theory. A critical field for the field-induced ordered phase is obtained as a function of temperature and pressure, which determine the phase diagram. It is found that magnetic field dependence of elastic constant decreases discontinuously at the critical field, Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We found an Ehrenfest relation between the field dependence of the elastic constant and the pressure dependence of critical field. Our theory provides the theoretical form for magnetoelastic properties in field- and pressure-induced ordered phases., 7 pages, 3 figures

We study the ground-state phase transitions of quasi-one-dimensional quantum Heisenberg antiferromagnets by the quantum Monte Carlo method with the continuous-time loop algorithm and finite-size scaling. For a model which consists of S = 1 chains with bond alternation coupled on a square lattice, we determine the ground state phase diagram and the universality class of the quantum phase transitions.

A simple model consisting of three distinct dimer sublattices is proposed to describe the magnetism of NH 4 CuCl 3 . It explains the occurrence of magnetization plateaus only at 1/4 and 3/4 of the saturation magnetization. The field dependence of the excitation modes observed by electron-spin-resonance measurements is also explained by the model. The model predicts that the magnetization plateaus should disappear under high pressure.

Thallium copper chloride is a quantum spin liquid of S = 1/2 Cu^2+ dimers. Interdimer superexchange interactions give a three-dimensional magnon dispersion and a spin gap significantly smaller than the dimer coupling. This gap is closed by an applied hydrostatic pressure of approximately 2kbar or by a magnetic field of 5.6T, offering a unique opportunity to explore the both types of quantum phase transition and their associated critical phenomena. We use a bond-operator formulation to obtain a continuous description of all disordered and ordered phases, and thus of the transitions separating these. Both pressure- and field-induced transitions may be considered as the Bose-Einstein condensation of triplet magnon excitations, and the respective phases of staggered magnetic order as linear combinations of dimer singlet and triplet modes. We focus on the evolution with applied pressure and field of the magnetic excitations in each phase, and in particular on the gapless (Goldstone) modes in the ordered regimes which correspond to phase fluctuations of the ordered moment. The bond-operator description yields a good account of the magnetization curves and of magnon dispersion relations observed by inelastic neutron scattering under applied fields, and a variety of experimental predictions for pressure-dependent measurements., 20 pages, 17 figures

The flux flow resistivity ${\ensuremath{\rho}}_{f}$ associated with purely viscous motion of vortices in high-quality ${\mathrm{MgB}}_{2}$ was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different ${\ensuremath{\rho}}_{f}$ slopes was clearly observed in $\mathit{H}\ensuremath{\Vert}\mathrm{ab}$ plane. The unusual H dependence indicates that two very differently sized superconducting gaps in ${\mathrm{MgB}}_{2}$ manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat-capacity and thermal-conductivity results.

Photostimulated desorption and change of the ortho-para ratio of H2 physisorbed on Ag at 7 K are reported. After pump laser excitation at 193 nm neutral H2 desorbing in a nonthermal process is state selectively detected by resonance-enhanced multiphoton ionization. At weak pump laser fluence the natural ortho-para conversion of H2 on Ag was monitored to proceed with a conversion time of approximately 780 s, which is in good agreement with predictions based on an electron-exchange-hyperfine-contact model. With increasing pump laser fluence, the ortho-para ratio decreases faster, suggesting photoassisted ortho-para H2 conversion.

The phase transition of Si(001) surface below 40 K was studied by low-energy electron diffraction (LEED). The temperature dependence of the intensities and widths of the quarter order diffraction spots and LEED intensity versus electron energy curves (I-V curves) were obtained in the temperature region from 20 to 300 K. While the spot intensities of the quarter order spots decrease and the widths broaden, the I-V curves do not change so much below 40 K. This clearly shows that a phase transition occurs from an ordered phase above 40 K to a disordered phase below 40 K.

The magnetic properties of the interacting dimer system ${\mathrm{T}\mathrm{l}\mathrm{C}\mathrm{u}\mathrm{C}\mathrm{l}}_{3}$ are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

The magnetic properties of the interacting dimer system TlCuCl3 are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

Electromagnon excitation is investigated on the basis of the symmetric spin-dependent electric polarization in both collinear and noncollinear magnetically ordered states. We focus on quantum spin systems with a large easy-plane single-ion anisotropy, where both massive longitudinal (Higgs) and massless transverse (Nambu–Goldstone) modes exist in the magnetic excitations. In the one-magnon excitation, it is found that the symmetric spin-dependent electric polarization is connected with the longitudinal fluctuation of the ordered moment and that the Higgs mode appears as the electromagnon excitation in collinear states. In noncollinear states, both the Higgs and Nambu–Goldstone modes are observable as the electromagnon excitation.

A magnetic flux effect is studied theoretically on an electric polarization induced by the Kondo effect in a triangular triple-quantum-dot system, where one of the three dots is connected to a metallic lead. This electric polarization exhibits an Aharonov–Bohm oscillation as a function of the magnetic flux penetrating through the triangular loop. The numerical renormalization group analysis reveals how the oscillation pattern depends on the Kondo coupling of a local spin with lead electrons, which is sensitive to the point contact with the lead. It provides an experimental implication that the Kondo effect is the origin of the emergent electric polarization.

Hydrogen atoms buried at the interface between Pb layers and the Si(111) surface were investigated by resonant nuclear reaction analysis (NRA) using ${}^{1}\mathrm{H}{(}^{15}\mathrm{N},\ensuremath{\alpha}\ensuremath{\gamma}{)}^{12}\mathrm{C}$ in grazing incidence geometry. Pb atoms were deposited on the H-terminated Si(111) surface at 110 K, and the H depth was clearly distinguished with a depth scale of one monolayer. The NRA spectrum revealed a monotonous shift to higher energy with increasing Pb coverage indicating H remains at the interface between Pb and the Si substrate. The dependence of the spectral shift on the Pb coverage was found to have an offset corresponding to a depth of about 0.1 nm. This offset suggests a model for the Pb/H/Si(111) interface structure implying that the initial Pb layer resides in the preadsorbed H layer.

Quasiparticle states around a single vortex in a ${p}_{x}\ifmmode\pm\else\textpm\fi{}{\mathrm{ip}}_{y}$-wave superconductor are studied on the basis of the Bogoliubov--de Gennes (BdG) theory, where both charge and current screenings are taken into account. Due to the violation of time-reversal symmetry, there are two types of vortices which are distinguished by their winding orientations relative to the angular momentum of the chiral Cooper pair. The BdG solution shows that the charges of the two types of vortices are quite different, reflecting the rotating Cooper pair of the ${p}_{x}\ifmmode\pm\else\textpm\fi{}{\mathrm{ip}}_{y}$-wave paring state.

The Kondo effect strongly depends on spin and orbital degrees of freedom of unconventional superconductivity. We focus on the Kondo effect in the $p_x + i p_y$-wave and $d_{x^2 - y^2} + i d_{xy}$-wave superconductors to compare the magnetic properties of the spin-triplet and spin-singlet Cooper pairs. The difference appears when both of the paired electrons couple to a local spin directly. For the $p_x + i p_y$-wave, the ground state is always a spin doublet for a $S_{\rm imp} = 1/2$ local spin, and it is always a spin singlet for $S_{\rm imp} = 1$. The latter is due to uniaxial spin anisotropy of the triplet Cooper pair. For the $d_{x^2 - y^2} + i d_{xy}$-wave, the interchange of ground states occurs, which resembles a competition between the Kondo effect and the superconducting energy gap in s-wave superconductors. Thus the internal degrees of freedom of Cooper pairs give a variety to the Kondo effect., 7 pages, 6 figures, RevTex, to be published in Phys. Rev. B

Hydrogen atoms adsorbed on Si(111) and Pt(111) were investigated by nuclear reaction analysis (NRA) using 1H(15N,alphagamma)12C. From measurements of the NRA spectrum at normal and tilted ion incidences the zero-point vibrational energies of H on Si(111) in the perpendicular and parallel directions were found to be 123.4+/-4.6 and 44.6+/-6.2 meV, respectively, which are consistent with harmonic potentials. The zero-point energies obtained for Pt(111)-H were 80.8+/-3.9 and 62.1+/-6.0 meV for perpendicular and parallel directions, respectively. These results indicate that the stretching mode is harmonic, while the bending mode is strongly anharmonic.

In a chiral superconductor with broken time-reversal symmetry a ``spontaneous Hall effect'' may be observed. We analyze this phenomenon by taking into account the surface properties of a chiral superconductor. We identify two main contributions to the spontaneous Hall effect. One contribution originates from the Bernoulli (or Lorentz) force from spontaneous currents running along the surfaces of the superconductor. The other contribution has a topological origin and is related to the intrinsic angular momentum of Cooper pairs. The latter can be described in terms of a Chern-Simons-like term in the low-energy field theory of the superconductor and has some similarities with the quantum Hall effect. The spontaneous Hall effect in a chiral superconductor is, however, non-universal. Our analysis is based on three approaches to the problem: a self-consistent solution of the Bogoliubov-de Gennes equation, a generalized Ginzburg-Landau theory, and a hydrodynamic formulation. All three methods consistently lead to the same conclusion that the spontaneous Hall resistance of a two-dimensional superconducting Hall bar is of order h/(e k_F\lambda)^2, where k_F is the Fermi wave vector and \lambda is the London penetration depth; the Hall resistance is substantially suppressed from a quantum unit of resistance. Experimental issues in measuring this effect are briefly discussed., Comment: 22 pages including 12 figures