arXiv subjects

R. Ocaña

Publications and source records attributed to R. Ocaña.

3 recordsLinked to original sources

arXiv2003

Magnetothermal Conductivity of Highly Oriented Pyrolytic Graphite in the Quantum Limit

We report on the magnetic field (0T$ \le B \le 9$T) dependence of the longitudinal thermal conductivity $κ(T,B)$ of highly oriented pyrolytic graphite in the temperature range 5 K $\le T\le$ 20 K for fields parallel to the $c-$axis. We show that $κ(T,B)$ shows large oscillations in the high-field region (B > 2 T) where clear signs of the Quantum-Hall effect are observed in the Hall resistance. With the measured longitudinal electrical resistivity we show that the Wiedemann-Franz law is violated in the high-field regime.

cond-mat.str-el↗

arXiv2001

Angle Dependence of the Transverse Thermal Conductivity in YBa$_2$Cu$_3$O$_7$ single crystals: Doppler Effect vs. Andreev scattering

We have measured the transverse thermal conductivity $κ_{xy}$ of twinned and untwinned YBa$_2$Cu$_3$O$_7$ single crystals as a function of angle $θ$ between the magnetic field applied parallel to the CuO$_2$ planes and the heat current direction, at different magnetic fields and temperatures. For both crystals we observed a clear twofold variation in the field-angle dependence of $κ_{xy}(θ) = - κ^0_{xy}(T,B) \sin(2θ)$. We have found that the oscillation amplitude $κ^0_{xy}$ depends on temperature and magnetic field. Our results show that $κ^0_{xy} = a B \ln(1/(bB))$ with the temperature- and sample-dependent parameters $a$ and $b$. We discuss our results in terms of Andreev scattering of quasiparticles by vortices and a recently proposed theory based on the Doppler shift in the quasiparticle spectrum.

cond-mat.supr-con↗

arXiv2001

Nonmonotonic Temperature Dependence of the Thermal Hall Angle of a YBa$_{2}$Cu$_{3}$O$_{6.95}$ Single Crystal

We have performed high-resolution measurements of the magnetic field (0~T~$ \le B \le 9~$T) and temperature (10 K~$\le T < 140~$K) dependence of the longitudinal and transverse Hall thermal conductivity of a twinned YBa$_{2}$Cu$_{3}$O$_{6.95}$ single crystal. We have used and compared two recently published methods to extract the thermal Hall angle $θ_H(T,B)$. Our results indicate that $\cot(θ_H)$ varies quite accurately as $T^4$ in the intermediate temperature range $\sim 0.3 < T/T_c$. It shows a well defined minimum at $T_m \simeq 20~$K which resembles that observed in the $c$-axis microwave conductivity. The electronic part of the longitudinal and the transverse thermal conductivity show the scaling behavior for transport properties predicted for d-wave superconductors in the temperature range $\sim 18~$K~$\le T \le 30~$K.

cond-mat.supr-con↗