We grew single-crystal thin films of a topological crystalline insulator (TCI) SnTe with a smooth surface at the atomic scale by molecular beam epitaxy (MBE). In the magnetoresistance (MR) measurement, we observed both positive and negative components near zero magnetic field at lowest temperatures of 2 - 3 K, while we observed only a negative MR at elevated temperatures of 6 - 10 K. The positive MR is attributed to the weak antilocalization (WAL) in the transport through the topological surface state (SS), demonstrating π berry phase which is essential to the topological SS, while the negative MR to the weak localization (WL) in the transport through the bulk state (two-dimensional bulk subbbands). The absolute value of the prefactor a deduced from the fitting of the observed positive MR to the Hikami-Larkin-Nagaoka equation was much smaller than expected from the number of transport channel of the SS, suggesting the coupling of the SS to the bulk state.
We have developed 1310 nm high power quantum dot distributed feedback lasers. Optical output power of >40 m W at $85^{\circ}\mathrm{C}$ was achieved with sidemode suppression ratio of >50 dB. Stable relative intensity noise against external optical feedback was observed under high power operation.
In the previous paper, we used a semiconductor laser and a position sensing detector(PSD) to measure two DOF position of spherical ultrasonic motor(SUSM) and the effectiveness was confirmed. However, we have not realized three DOF position detection and control. Therefore, in this paper, we develop a new spherical rotor with two built-in semiconductor lasers to measure three DOF position of SUSM. Experiments are examined and the precision of the system is investigated.
Abstract The effect of low-temperature InGaAs/GaAs cover layer growth of InAs quantum dots on their optical and structural properties was investigated. Photoluminescence intensity depended heavily on the growth temperature and thickness of the low-temperature cover layer and decreased as the number of dislocations formed directly above InAs quantum dots increased. These dislocations are formed at the initial stage of high-temperature GaAs growth, originating from pits that remain on the surface after the growth of the low-temperature cover layer and subsequent annealing. To ensure a high-quality InAs quantum dot structure free from dislocations, it is important to obtain a highly flat surface with suppressed pits after low-temperature cover layer growth and subsequent annealing.
Abstract InAs quantum dots with InGaAs strain-reducing layer on GaAs(001) grown at three different temperatures were investigated from the aspect of both structural and optical properties. Dislocations originated from the InAs quantum dot (QD) layer were observed at growth temperatures of 490 °C, 500 °C, and 510 °C. Their densities are relatively larger in the cases of 490 °C and 510 °C, where they are caused by strain accumulation at larger-size InAs quantum dots during cover layer growth. Photoluminescence lifetimes at 6 K are almost the same in the three samples. On the other hand, that of the 500 °C-grown sample is an order of magnitude larger than the other two samples at 300 K. This indicates that dislocations act as a non-radiative center to deteriorate optical characteristics. Growth around 500 °C suppresses the growth of larger-size InAs QDs and reduces the InAs strain accumulation, which leads to the dislocation formation at the cover layer.
Several chemokine receptors are expressed selectively on the surface of T cells depending on their polarization. The aim of this study was to characterize chemokine receptor expression in peripheral blood memory T cells in Crohn's disease (CD) and ulcerative colitis (UC), and to correlate the expression with disease activity. Peripheral blood mononuclear cells (PBMCs) were obtained from 24 patients with CD, 30 patients with UC, 24 normal controls and 10 disease controls. PBMCs were stained by anti-CCR3, CCR4, CCR5, CXCR3, CD4, CD8, CD45RO and beta 7 integrin, and the expression of the chemokine receptors were determined by flow cytometry. CCR4 expression on memory T cells was significantly lower in UC than in CD or normal controls, and that of memory CD4+ T and beta 7(high) memory CD4+ T cells was significantly higher in CD than in UC or normal controls. CCR4 expression on memory CD4+ T cells exhibited significant positive correlation with disease activity in CD, and this decreased significantly after treatment. Such a decrease was not found in the disease controls. CCR5 and CXCR3 expression on memory CD8+ T cells was significantly lower in CD than in normal controls. CXCR3 expression on beta 7(high) memory CD4+ T and CXCR3 expression on memory CD8+ T cells were lower in UC than in normal controls. These findings suggest that in peripheral blood memory T cells, chemokine receptor expression is different between CD and UC. Enhancement of CCR4 and suppression of CCR5 and CXCR3 seem to be the characteristic chemokine receptor profile in peripheral blood memory T cells of CD.
