Generic Finite Size Enhancement of Pairing in Mesoscopic Fermi Systems

The finite size dependent enhancement of pairing in mesoscopic Fermi systems is studied under the assumption that the BCS approach is valid and that the two body force is size independent. Different systems are investigated such as superconducting metallic grains and films as well atomic nuclei. It is shown that the finite size enhancement of pairing in these systems is in part due to the presence of a surface which accounts quite well for the data of nuclei and explains a good fraction of the enhancement in Al grains.Comment: Updated version 17/02/0

Calculation of Optical Conductivity of YbB12_{12} using Realistic Tight-Binding Model

Based on the previously reported tight-binding model fitted to the LDA+U band calculation, optical conductivity of the prototypical Kondo insulator YbB$_{12}$ is calculated theoretically. Many-body effects are taken into account by the self-consistent second order perturbation theory. The gross shape of the optical conductivity observed in experiments are well described by the present calculation, including their temperature-dependences.Comment: 6 pages, 7 figures, use jpsj2.cls, to appear in J. Phys. Soc. Jpn. Vol.73, No.10 (2004

Toward mid-infrared, subdiffraction, spectral-mapping of human cells and tissue: SNIM (scanning near-field infrared microscopy) tip fabrication

Scanning near-field infrared microscopy (SNIM) potentially enables subdiffraction, broadband mid-infrared (MIR:3–25-μm wavelength range) spectral-mapping of human cells and tissue for real-time molecular sensing, with prospective use in disease diagnosis. SNIM requires an MIR-transmitting tip of small aperture for photon collection. Here, chalcogenide-glass optical fibers are reproducibly tapered at one end to form a MIR transmitting tip for SNIM. A wet-etching method is used to form the tip. The tapering sides of the tip are Al-coated. These Al-coated tapered-tips exhibit near-field power-confinement when acting either as the launch-end or exit-end of the MIR optical fiber. We report first time optimal cleaving of the end of the tapered tip using focused ion beam milling. A flat aperture is produced at the end of the tip, which is orthogonal to the fiber-axis and of controlled diameter. A FIB-cleaved aperture is used to collect MIR spectra of cells mounted on a transflection plate, under illumination of a synchrotron- generated wideband MIR beam

Physical Electronics

Contains reports on three research projects

Correlation Effects on Optical Conductivity of FeSi

Effects of electron correlation in FeSi are studied in terms of the two-band Hubbard model with the density of states obtained from the band calculation. Using the self-consistent second-order perturbation theory combined with the local approximation, the correlation effects are investigated on the density of states and the optical conductivity spectrum, which are found to reproduce the experiments done by Damascelli et al. semiquantitatively. It is also found that the peak at the gap edge shifts to lower energy region by correlation effects, as is seen in the experiments.Comment: 4 pages, 3 figure

Quantum Chaos Versus Classical Chaos: Why is Quantum Chaos Weaker?

We discuss the questions: How to compare quantitatively classical chaos with quantum chaos? Which one is stronger? What are the underlying physical reasons

Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields

We consider nonlinear dynamics of a single vortex in a superconductor in a strong rf magnetic field $B_0\sin\omega t$. Using the London theory, we calculate the dissipated power $Q(B_0,\omega)$, and the transient time scales of vortex motion for the linear Bardeen-Stephen viscous drag force, which results in unphysically high vortex velocities during vortex penetration through the oscillating surface barrier. It is shown that penetration of a single vortex through the ac surface barrier always involves penetration of an antivortex and the subsequent annihilation of the vortex antivortex pairs. Using the nonlinear Larkin-Ovchinnikov (LO) viscous drag force at higher vortex velocities $v(t)$ results in a jump-wise vortex penetration through the surface barrier and a significant increase of the dissipated power. We calculate the effect of dissipation on nonlinear vortex viscosity $\eta(v)$ and the rf vortex dynamics and show that it can also result in the LO-type behavior, instabilities, and thermal localization of penetrating vortex channels. We propose a thermal feedback model of $\eta(v)$, which not only results in the LO dependence of $\eta(v)$ for a steady-state motion, but also takes into account retardation of temperature field around rapidly accelerating vortex, and a long-range interaction with the surface. We also address the effect of pinning on the nonlinear rf vortex dynamics and the effect of trapped magnetic flux on the surface resistance $R_s$ calculated as a function or rf frequency and field. It is shown that trapped flux can result in a temperature-independent residual resistance $R_i$ at low $T$, and a hysteretic low-field dependence of $R_i(B_0)$, which can {\it decrease} as $B_0$ is increased, reaching a minimum at $B_0$ much smaller than the thermodynamic critical field $B_c$.Comment: 18 figure

Spin Orientation and Spin Precession in Inversion-Asymmetric Quasi Two-Dimensional Electron Systems

Inversion asymmetry induced spin splitting of the electron states in quasi two-dimensional (2D) systems can be attributed to an effective magnetic field B which varies in magnitude and orientation as a function of the in-plane wave vector k||. Using a realistic 8x8 Kane model that fully takes into account spin splitting because of both bulk inversion asymmetry and structure inversion asymmetry we investigate the spin orientation and the effective field B for different configurations of a quasi 2D electron system. It is shown that these quantities depend sensitively on the crystallographic direction in which the quasi 2D system was grown as well as on the magnitude and orientation of the in-plane wave vector k||. These results are used to discuss how spin-polarized electrons can precess in the field B(k||). As a specific example we consider GaInAs-InP quantum wells.Comment: 10 pages, 6 figure

Solid State Physics

Contains reports on nine research projects

Noncommutative quantum mechanics and Bohm's ontological interpretation

We carry out an investigation into the possibility of developing a Bohmian interpretation based on the continuous motion of point particles for noncommutative quantum mechanics. The conditions for such an interpretation to be consistent are determined, and the implications of its adoption for noncommutativity are discussed. A Bohmian analysis of the noncommutative harmonic oscillator is carried out in detail. By studying the particle motion in the oscillator orbits, we show that small-scale physics can have influence at large scales, something similar to the IR-UV mixing