To investigate the origin of the enhanced Tc ({approx} 110 K) of the trilayer cuprate superconductor Bi2Sr2Ca2Cu3O10+{delta} (Bi-2223), its underdoped single crystals are a critical requirement. Here, we demonstrate the first successful in-plane resi
stivity measurements of heavily underdoped Bi-2223 (zero-resistivity temperatures {approx} 20~35 K). Detailed crystal growth methods, the annealing process, as well as X-ray diffraction (XRD) and magnetic susceptibility measurement results are also reported.
The pentaquark $Theta^+$ has been searched for via the $pi^-p to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on
the production cross section averaged over the scattering angle from 2$^{circ}$ to 15$^{circ}$ in the laboratory frame were found to be less than 0.28 $mu$b/sr at the 90% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10%. Constraints on the $Theta^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.
We report the first results of a search for real photon-photon scattering using X rays. A novel system is developed to split and collide X-ray pulses by applying interferometric techniques. A total of $6.5times10^{5}$ pulses (each containing about $1
0^{11}$ photons) from an X-ray Free-Electron Laser are injected into the system. No scattered events are observed, and an upper limit of $1.7times 10^{-24}$ ${rm m^{2}}$ (95% C.L.) is obtained on the photon-photon elastic scattering cross section at 6.5 keV.
The $Theta^+$ pentaquark baryon was searched for via the $pi^-pto K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No
peak structure corresponding to the $Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{circ}$ to 15$^{circ}$ in the laboratory frame was obtained to be 0.26 $mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{Theta}=1/2^+$ and $J^P_{Theta}=1/2^-$, respectively.
The spin interaction between an electron and nuclei was investigated optically in a single self-assembled InAlAs quantum dot (QD). In spin dynamics, the correlation time of the coupled electron-nuclear spin system and the electron spin relaxation tim
e play a crucial role. We examined on a positively charged exciton in a QD to evaluate these key time constants directly via the temporal evolution measurements of the Overhauser shift and the degree of circular polarization. In addition, the validity of our used spin dynamics model was discussed in the context of the experimentally obtained key parameters.
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.
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.
We report the hysteresis of optically-pumped nuclear spin polarization and the degree of circular polarization of photoluminescence on the excitation power and electron spin polarization in single InAlAs quantum dots. By increasing (or decreasing) th
e excitation power at a particular excitation polarization, an abrupt rise (or drop) and a clear hysteretic behavior were observed in the Overhauser shift of the photoluminescence of the exciton and exciton complexes from the same single quantum dot under an external magnetic field of 5 T. However, the degree of circular polarization shows different behaviors between a positively charged exciton and a neutral exciton or biexciton; further, only positively charged exciton exhibits the precisely synchronized change and hysteretic behavior. It is suggested that the electron spin distribution is affected by the flip-flop of electron-nuclear spins. Further, the hysteresis is observed as a function of the degree of circular polarization of the excitation light and its dependence on the excitation power is studied. The saturation of the Overhauser shift after the abrupt rise indicates the almost complete cancellation of the external magnetic field by the nuclear field created within the width that is decided by the correlation time between the electron and the nuclei spin system.
