No abstract

The thermal conductivity of the spin-Peierls ͑SP͒ compound CuGeO 3 was measured in magnetic fields up to 16 T. Above the SP transition, the heat transport due to spin excitations causes a peak at ϳ22 K, while below the transition the spin excitations rapidly diminish and the heat transport is dominated by phonons; however, the main scattering process of the phonons is with spin excitations, which demonstrates itself in an unusual peak in at ϳ5.5 K. This low-temperature peak is strongly suppressed with magnetic fields in excess of 12.5 T. RAPID COMMUNICATIONS R2914PRB 58 YOICHI ANDO et al. RAPID COMMUNICATIONS R2916PRB 58 YOICHI ANDO et al.

No abstract

The magnetic field dependence of the specific heat of Zn-doped single crystals of YBa 2 Cu 3 O 6.95 was measured between 2 and 10 K and up to 8 T. Doping levels of 0, 0.15%, 0.31%, and 1% were studied and compared. In particular we searched for the Schottky anomaly associated with the Zn-induced magnetic moments.

At high flux-flow velocities in the mixed state of a type-II superconductor the nonequilibrium distribution of the quasiparticles is shifted to higher energies. As shown theoretically by Larkin and Ovchinnikov, a distinct signature of this nonequilibrium effect is an electronic instability, resulting in a sharp kink in the currentvoltage characteristic at a critical vortex velocity v * . From measurements of v * the quasiparticle-energy relaxation rate Ϫ1 can be found. We have measured this instability point for epitaxial c axis oriented films of La 1.85 Sr 0.15 CuO 4Ϫx and YBa 2 Cu 3 O 7Ϫ␦ . In both cuprates the observed temperature dependence of Ϫ1 could be well fitted with the function Ϫ1 ϭa exp͓Ϫ2⌬(T)/k B T͔, suggesting that the electron-electron recombination process, perhaps in combination with the emission of another excitation, is crucial. As an example of a low-T c superconductor we have also studied amorphous Mo 3 Si films and found that Ϫ1 can be fitted by a function similar to that we have used for the cuprates, again indicating the importance of the electron-electron interaction. ͓S0163-1829͑97͒07745-X͔