Temperature dependence of the spin and orbital magnetization density in Sm1−xGdxAl2Sm_{1-x}Gd_{x} Al_{2} around the spin-orbital compensation point

Non-resonant ferromagnetic x-ray diffraction has been used to separate the spin and orbital contribution to the magnetization density of the proposed zero-moment ferromagnet $Sm_{0.982}Gd_{0.018} Al_{2}$. The alignment of the spin and orbital moments relative to the net magnetization shows a sign reversal at 84K, the compensation temperature. Below this temperature the orbital moment is larger than the spin moment, and vice versa above it. This result implies that the compensation mechanism is driven by the different temperature dependencies of the $4f$ spin and orbital moments. Specific heat data indicate that the system remains ferromagnetically ordered throughout

Modulated Vortex Lattice in High Fields and Gap Nodes

The mean field vortex phase diagram of a quasi two dimensional superconductor with a nodal d-wave pairing and with strong Pauli spin depairing is examined in the parallel field case in order to examine an effect of gap nodes (or minima) on the stability of a FFLO-like vortex lattice. We find through a heuristic argument and a model calculation with a four-fold anisotropic Fermi velocity that the FFLO-like state is relatively suppressed as the field approaches a nodal direction. When taking account of a couple of experimental results altogether, the present result strongly suggests that a node or gap minimum of the pairing function of CeCoIn$_5$ is located along the [100]-direction.Comment: 5 pages, 2 figures, References were added. To appear in Phys. Rev.

Precise measurements of electron and hole g-factors of single quantum dots by using nuclear field

We demonstrated the cancellation of the external magnetic field by the nuclear field at one edge of the nuclear polarization bistability in single InAlAs quantum dots. The cancellation for the electron Zeeman splitting gives the precise value of the hole g-factor. By combining with the exciton g-factor that is obtained from the Zeeman splitting for linearly polarized excitation, the magnitude and sign of the electron and hole g-factors in the growth direction are evaluated.Comment: 3 pages, 2 figure

S-wave bottom tetraquarks

The relativistic four-quark equations are found in the framework of coupled-channel formalism. The dynamical mixing of the meson-meson states with the four-quark states is considered. The four-quark amplitudes of the tetraquarks, including $u$, $d$, $s$ and bottom quarks, are constructed. The poles of these amplitudes determine the masses and widths of $S$-wave bottom tetraquarks.Comment: 8 pages, late

Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots

A systematic variation of the exciton fine-structure splitting with quantum dot size in single InAs/GaAs quantum dots grown by metal-organic chemical vapor deposition is observed. The splitting increases from -80 to as much as 520 $\mu$eV with quantum dot size. A change of sign is reported for small quantum dots. Model calculations within the framework of eight-band k.p theory and the configuration interaction method were performed. Different sources for the fine-structure splitting are discussed, and piezoelectricity is pinpointed as the only effect reproducing the observed trend.Comment: 5 pages, 5 figure

Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field

We report measurements of the temperature dependent components of the magnetic penetration depth {\lambda}(T) in single crystal samples of YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We observe a downturn in {\lambda}(T) at low temperatures for currents flowing along the b and c axes but not along the a axis. The downturn in {\lambda}_b is suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy of {\lambda}(T) likely result from proximity induced superconducting on the CuO chains, however we also discuss the possibility that a significant part of the anisotropy might originate from the CuO2 planes.Comment: 5 page

The monitoring system for the aerogel Cherenkov counter of the BELLE detector

We report on a design and performances of a monitoring system developed for the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists of blue LEDs, a diffuser box, and optical distributors which distribute the LED light to the ACC modules. The employed LED (NSPB series) has been observed to have high reliability on the long term stability and the temprature dependence. The diffuser box is employed to reduce the intrinsic non-uniformity of the LED light intensity. The overall performances of the present monitoring system on uniformity and intensity of the light output have been found to satisfy all the requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum. and Meth. A. Postscript file (4.5 MB) is available at http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p

Microscopic modelling of perpendicular electronic transport in doped multiple quantum wells

We present a microscopic calculation of transport in strongly doped superlattices where domain formation is likely to occur. Our theoretical method is based on a current formula involving the spectral functions of the system, and thus allows, in principle, a systematic investigation of various interaction mechanisms. Taking into account impurity scattering and optical phonons we obtain a good quantitative agreement with existing experimental data from Helgesen and Finstad (J. Appl. Phys. 69, 2689, (1991)). Furthermore the calculated spectral functions indicate a significant increase of the average intersubband spacing compared to the bare level differences which might explain the experimental trend.Comment: 10 pages 5 figure