Ultrasonic Studies of a Single Crystalline La_<1.85>Sr_<0.15>CuO_4 in High Magnetic Fields(Transport and Fermiology)

Temperature dependence of the sound velocity of a single crystalline La_Sr_CuO_4 has been measured in high magnetic fields. An increase of the sound velocity due to the flux line lattice (FLL) pinning is observed at a temperature below the superconducting transition temperature T_C. Anisotropic activation energies to depin flux lines are evaluated separately from measurements under various settings of the directions of wave vector k, polarization vector u and magnetic fields H using the analysis based oh the thermally assisted flux flow model. Besides the FLL elasticity, anomalous temperature dependence of elastic constants of c_ and (c_-c_)/2 (softening at low temperatures and hardening at lower temperatures below 10K) is observed in high magnetic fields

Upper Critical Field of Superconducting Amorphous Alloy Zr_<85>Si_<15>

The upper critical field H_ is measured for the amorphous superconductor Zr_Si_ (T_c=2.70 K, ρ_n=270 μΩ・cm) in the wide temperature range down to 50 mK. The conventional V-H recording in sweeping magnetic field and measurements of the flux flow resistivity defined by the I-V curve at constant field are done in order to clarify the resistive transition of the superconducting mixed-to-normal state in an amorphous superconductor with extreme softness in the flux pinning interaction. The results show the strong suppression of H_ at low temperatures, which is quite different from the upward deviation from the theoretical values H_^* due to the orbital pair breaking effect in the dirty limit, reported for some amorphous alloys. Analysis with the Werthamer-Helfand-Hohenberg theory which takes into account the effects of the orbital pair breaking, spin paramagnetism and spin-orbit interaction gives 1.51≤α≤1.77 and 1.0≤λ_≤1.7, where α is the impurity parameter and λ_ the spin orbit interaction parameter. This is the first implication for the superconductivity in amorphous alloys that the spin paramagnetic effect plays an important role in determining the low temperature H_ and the spin-orbit (spin-flip) scattering enhances H_ moderately. The counterevidence is produced to the previous observation that the upward deviation anomaly (H_>H_^*) is an intrinsic property in amorphous metals with high resitivity

Magnetic Flux Jumps in Superconducting 3Nb-Zr Alloy Wires

The magnetic field strength in the center of three kinds of superconducting solenoids wound with 3Nb-Zr alloy wire was measured through the course of a gradual variation of the external magnetic field. The manner of a discontinuous change of a magnetic field, viz. the flux jump which gives a clue to clarify the behavior of penetration and trapping of magnetic filaments through the solenoid was studied. In general, the step height of flux jumps becomes smaller as the external magnetic field becomes stronger

Design and Performance of Remote Controlled ^3He Refrigerator in Hybrid Magnet(Part II. Several Instruments and Techniques Developed in HFLSM)

A remote controlled ^3He refrigerator for use in a hybrid magnet is described. Temperatures between 1.3 K and 0.43 K can be remote controlled by ^3He vapor pressure within the temperature drift of 0.01 K in magnetic fields up to 23 T. Using this refrigerator, several kinds of physical measurements, such as electrical resistance, capacitance and ultrasonic attenuation, have been carried out without being disturbed by noise peculiar to the hybrid magnet system. Additionally, magnetic field dependence of capacitance thermometers at liquid ^3He temperatures is discussed

The de Haas-van Alphen Effect of n-Type Cd_3As_2

A study of the de Haas-van Alphen (dHvA) effect of Cd_3As_2 by the torque method is presented. One kind of the dHvA oscillations was observed in the (100) plane with fields up to 20 KG in the temperature range between 1.5 and 4.2°K. From the analysis of the dHvA oscillations, it was revealed that the Fermi surface of electrons is a revolution ellipsoid elongated along the c-(4-fold) axis. The effective mass ratio, m_〓^*/m_〓 of 0.034, 0.040 and 0.052 and the anisotropy factor m_〓^*/m_〓^* of 1.22, 1.18 and 1.13 have been obtained for the electron concentration of 2.05×10^, 2.20×10^ and 4.44×10^ cm^, respectively. These effective mass ratio and the anisotropy factor dependences on the electron concentration may suggest a non-parabolicity in the conduction band

Giant Quantum Oscillations in the Magneto-Acoustic Attenuation and the Spin Splitting of Arsenic

Giant quantum oscillations of the magneto-acoustic attenuation in arsenic have been studied for the 140 Mc/sec longitudinal wave and in the magnetic fields up to 93 kG. The observed attenuation peaks are spike shaped with spin splittings. The energy surface parameters and spin splitting parameters for holes on the γ-neck were determined from the attenuation peaks. The splitting above mentioned shows that for the field which is parallel to the trigonal axis, the effective g-factor is found to be 75. The line shape of the giant quantum attenuation peak has been interpreted in terms of the nonparabolic energy band model and it revealed the hole-mass character typical of the saddle point on the γ-neck

Role of Insulations in a Superconducting Magnet

Two types of the superconducting magnets, whose insulating layers inserted between every successive superconducting winding layer consist of the usual insulator named Mylar sheets in the one and of the metallic copper foils in the other, were examined. The former gives a comparatively definite magnetic field with regard to the exciting current but is liable to be damaged. The latter shows a large magnetic hysteresis owing to the intra- and inter-layer persistent eddy currents between successive layers of windings, but is not damaged by the super- to normal-phase transition