Origin of the anomalous magnetic circular dichroism spectral shape in ferromagnetic (Ga,Mn)As: Impurity bands inside the band gap

The electronic structure of a prototype dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We prove that the optical transitions originated from impurity bands cause the strong positive MCD background. The MCD signal due to the E0 transition from the valence band to the conduction band is negative indicating that the p-d exchange interactions between the p-carriers and d-spin is antiferromagnetic. The negative E0 MCD signal also indicates that the hole-doping of the valence band is not so large as previously assumed. The impurity bands seem to play important roles for the ferromagnetism of Ga1-xMnxAs.Comment: 13 pages, 3 figure

Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals

We report the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane resistivity and the Hall angle, we demonstrate that the nature of the low-temperature normal state in the Zn-doped samples is significantly altered from that in the pristine samples under high magnetic fields. In particular, we observe nearly-isotropic negative magnetoresistance as well as an increase in the Hall coefficient at very low temperatures in non-superconducting Zn-doped samples, which we propose to be caused by the Kondo scattering from the local moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in Phys. Rev.

Shock Theory of a Bubbly Liquid in a Deformable Tube

Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. Quasi-one-dimensional bubbly flow equations that include fluid-structure interaction are formulated, and the steady shock relations are derived. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material are measured. The experimental data indicate that the linear theory cannot properly predict the propagation speeds of shock waves in mixture-filled tubes; the shock theory is found to more accurately estimate the measured wave speeds

Assessment study of infrared detector arrays for low-background astronomical research

The current state-of-the-art of infrared detector arrays employing charge coupled devices (CCD) or charge injection devices (CID) readout are assessed. The applicability, limitations and potentials of such arrays under the low-background astronomical observing conditions of interest for SIRFT (Shuttle Infrared Telescope Facility) are determined. The following are reviewed: (1) monolithic extrinsic arrays; (2) monolithic intrinsic arrays; (3) charge injection devices; and (4) hybrid arrays

Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}

We measure the normal-state in-plane resistivity of La-doped Bi-2201 single crystals at low temperatures by suppressing superconductivity with 60-T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR

Shock propagation through a bubbly liquid in a deformable tube

Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid–structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure on the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves in a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds

Gauge field for edge state in graphene

By considering the continuous model for graphene, we analytically study a special gauge field for the edge state. The gauge field explains the properties of the edge state such as the existence only on the zigzag edge, the partial appearance in the $k$-space, and the energy position around the Fermi energy. It is demonstrated utilizing the gauge field that the edge state is robust for surface reconstruction, and the next nearest-neighbor interaction which breaks the particle-hole symmetry stabilizes the edge state.Comment: 9 pages, 5 figure

Charge Localization from Local Destruction of Antiferromagnetic Correlation in Zn-doped YBa2Cu3O7-d

The in-plane normal-state resistivity of Zn-doped YBa2Cu3O7-d single crystals is measured down to low temperatures by suppressing superconductivity with magnetic fields up to 18 T. Substitution of Cu with Zn in the CuO2 planes is found to induce carrier localization at low temperatures in "clean" samples with kF l > 5, where the mean free path l is larger than the electron wave length and thus localization is not normally expected. The destruction of the local antiferromagnetic correlation among Cu spins by Zn is discussed to be the possible origin of this unusual charge localization.Comment: 4 pages of LaTeX (revtex and epsf) including 4 postscript figure