Berry's phase contribution to the anomalous Hall effect of gadolinium

When conduction electrons are forced to follow the local spin texture, the resulting Berry phase can induce an anomalous Hall effect (AHE). In gadolinium, as in double-exchange magnets, the exchange interaction is mediated by the conduction electrons and the AHE may therefore resemble that of chromium dioxide and other metallic double-exchange ferromagnets. The Hall resistivity, magnetoresistance, and magnetization of single crystal gadolinium were measured in fields up to 30 T. Measurements between 2 K and 400 K are consistent with previously reported data. A scaling analysis for the Hall resistivity as a function of the magnetization suggests the presence of a Berry's-phase contribution to the anomalous Hall effect.Comment: 6 pages, 7 figures, submitted to Phys. Rev.

A Numerical Renormalization Group approach to Green's Functions for Quantum Impurity Models

We present a novel technique for the calculation of dynamical correlation functions of quantum impurity systems in equilibrium with Wilson's numerical renormalization group. Our formulation is based on a complete basis set of the Wilson chain. In contrast to all previous methods, it does not suffer from overcounting of excitation. By construction, it always fulfills sum rules for spectral functions. Furthermore, it accurately reproduces local thermodynamic expectation values, such as occupancy and magnetization, obtained directly from the numerical renormalization group calculations.Comment: 13 pages, 7 figur

Rotating vortex core: An instrument for detecting the core excitations

Effects of fermionic zero modes (bound states in a vortex core) on the rotational dynamics of vortices with sponaneously broken axisymmetry are considered. The results are compared with the Helsinki experiments where the vortex cores were driven to a fast rotation and torsional oscillations by an NMR r.f. field (Kondo et al, Phys. Rev. Lett. 67, 81 (1991)). We predict a resonance NMR absorption on localized states at the external frequency comparable with the interelevel distance, which is similar to the cyclotron Landau damping. The resonances can experimentally resolve the localized levels in vortex cores. For a pure rotation of the core, the effect depends on the relative signs of the vortex winding number and of the core rotation; thus it is sensitive to the direction of rotation of the container. The similarity with the fermionic zero modes on the fundamental strings, which simulate the thermodynamics of black holes, is discussed.Comment: RevTex file, 7 pages, 1 Figure, extended and clarified after referee Reports, to appear in Phys. Rev.

Greater V˙O2peak is correlated with greater skeletal muscle deoxygenation amplitude and hemoglobin concentration within individual muscles during ramp-incremental cycle exercise.

It is axiomatic that greater aerobic fitness (V˙O2peak) derives from enhanced perfusive and diffusive O2 conductances across active muscles. However, it remains unknown how these conductances might be reflected by regional differences in fractional O2 extraction (i.e., deoxy [Hb+Mb] and tissue O2 saturation [StO2]) and diffusive O2 potential (i.e., total[Hb+Mb]) among muscles spatially heterogeneous in blood flow, fiber type, and recruitment (vastus lateralis, VL; rectus femoris, RF). Using quantitative time-resolved near-infrared spectroscopy during ramp cycling in 24 young participants (V˙O2peak range: ~37.4-66.4 mL kg-1 min-1), we tested the hypotheses that (1) deoxy[Hb+Mb] and total[Hb+Mb] at V˙O2peak would be positively correlated with V˙O2peak in both VL and RF muscles; (2) the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) during submaximal exercise would not differ among subjects differing in V˙O2peak Peak deoxy [Hb+Mb] and StO2 correlated with V˙O2peak for both VL (r = 0.44 and -0.51) and RF (r = 0.49 and -0.49), whereas for total[Hb+Mb] this was true only for RF (r = 0.45). Baseline deoxy[Hb+Mb] and StO2 correlated with V˙O2peak only for RF (r = -0.50 and 0.54). In addition, the deoxy[Hb+Mb] slopes were not affected by aerobic fitness. In conclusion, while the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) did not differ between fitness groups the capacity to deoxygenate [Hb+Mb] (index of maximal fractional O2 extraction) correlated significantly with V˙O2peak in both RF and VL muscles. However, only in the RF did total[Hb+Mb] (index of diffusive O2 potential) relate to fitness

Kondo Effect in a Quantum Antidot

We report Kondo-like behaviour in a quantum antidot (a submicron depleted region in a two-dimensional electron gas) in the quantum-Hall regime. When both spin branches of the lowest Landau level encircle the antidot in a magnetic field ($\sim 1$ T), extra resonances occur between extended edge states via antidot bound states when tunnelling is Coulomb blockaded. These resonances appear only in alternating Coulomb-blockaded regions, and become suppressed when the temperature or source-drain bias is raised. Although the exact mechanism is unknown, we believe that Kondo-like correlated tunnelling arises from skyrmion-type edge reconstruction. This observation demonstrates the generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let

Local Interstellar Medium. International Astronomical Union Colloquium No. 81

Helium and hydrogen backscattering; ultraviolet and EUV absorption spectra; optical extinction and polarization; hot gases; soft X-ray observations; infrared and millimeter wavelengths; radio wavelengths and theoretical models of the interstellar matter within about 150 parsecs of the Sun were examined

Zero-bias anomalies of point contact resistance due to adiabatic electron renormalization of dynamical defects

We study effect of the adiabatic electron renormalization on the parameters of the dynamical defects in the ballistic metallic point contact. The upper energy states of the ``dressed'' defect are shown to give a smaller contribution to a resistance of the contact than the lower energy ones. This holds both for the "classical" renormalization related to defect coupling with average local electron density and for the "mesoscopic" renormalization caused by the mesoscopic fluctuations of electronic density the dynamical defects are coupled with. In the case of mesoscopic renormalization one may treat the dynamical defect as coupled with Friedel oscillations originated by the other defects, both static and mobile. Such coupling lifts the energy degeneracy of the states of the dynamical defects giving different mesoscopic contribution to resistance, and provides a new model for the fluctuator as for the object originated by the electronic mesoscopic disorder rather than by the structural one. The correlation between the defect energy and the defect contribution to the resistance leads to zero-temperature and zero-bias anomalies of the point contact resistance. A comparison of these anomalies with those predicted by the Two Channel Kondo Model (TCKM) is made. It is shown, that although the proposed model is based on a completely different from TCKM physical background, it leads to a zero-bias anomalies of the point contact resistance, which are qualitatively similar to TCKM predictions.Comment: 6 pages, to be published in Phys. Rev.

Hyperfine Interactions and Spin Transport in Ferromagnet-Semiconductor Heterostructures

Measurements and modeling of electron spin transport and dynamics are used to characterize hyperfine interactions in Fe/GaAs devices with $n$-GaAs channels. Ga and As nuclei are polarized by electrically injected electron spins, and the nuclear polarization is detected indirectly through the depolarization of electron spins in the hyperfine field. The dependence of the electron spin signal on injector bias and applied field direction is modeled by a coupled drift-diffusion equation, including effective fields from both the electronic and nuclear polarizations. This approach is used to determine the electron spin polarization independently of the assumptions made in standard transport measurements. The extreme sensitivity of the electron spin dynamics to the nuclear spin polarization also facilitates the electrical detection of nuclear magnetic resonance.Comment: Submitted to Phys. Rev.

Low-lying optical phonon modes in the filled skutterudite CeRu4Sb12

The phonon dynamics of filled skutterudite CeRu4Sb12 have been studied at room temperature by inelastic neutron scattering. Optical phonons associated with a large vibration of Ce atoms are observed at a relatively low energy of E = 6 meV, and show anticrossing behavior with acoustic phonons. We propose that the origin of the low lattice thermal conductivity in filled skutterudites can be attributed to intensive Umklapp scattering originating from low-lying optical phonons. By an analysis based on a Born-von Karman force model, the longitudinal force constants of the nearest Ce-Sb and Ce-Ru pairs are estimated to be 0.025 mdyn/A, while that of the nearest Ru-Sb pair is estimated to be 1.4 mdyn/A, indicating that the Ce atoms are bound very weakly to the surrounding rigid RuSb6-octahedron cages.Comment: 4pages, 5 figures, J. Phys. Soc. Jpn. (2006) in pres