arXiv subjects

F. J. Castro

Publications and source records attributed to F. J. Castro.

3 recordsLinked to original sources

arXiv2023

Enhanced weak superconductivity in trigonal $\gamma$-PtBi$_2$

Electrical resistivity experiments show superconductivity at $T_c = 1.1\,$K in a high-quality single crystal of trigonal $\gamma$-PtBi$_2$, with an enhanced critical magnetic field $\mu_0H_{c2}(0) \gtrsim 1.5\,$Tesla and a low critical current-density $J_c(0)\approx 40\,\mathrm{A}/\mathrm{cm}^2$ at $H=0$. Both $T_c$ and $H_{c2}(0)$ are the highest reported values for stoichiometric bulk samples at ambient pressure. We found a weak $H_{c2}$ anisotropy with $\Gamma=H_{c2}^{ab}/H_{c2}^{c} < 1$, which is unusual among superconductors. Under a magnetic field, the superconducting transition becomes broader and asymmetric. Along with the low critical currents, this observation suggests an inhomogeneous superconducting state. In fact, no trace of superconductivity is observed through field-cooling--zero-field-cooling magnetization experiments.

cond-mat.supr-con↗

arXiv2021

First-order phase transformation at constant volume: a continuous transition?

We describe a first-order phase transition of a simple system in a process where the volume is kept constant. We show that, unlike what happens when the pressure is constant, (i) the transformation extends over a finite temperature (and pressure) range, (ii) each and every extensive potential (internal energy $U$, enthalpy $H$, Helmholtz energy $F$ and Gibbs energy $G$), and the entropy $S$, is continuous across the transition, and (iii) the constant-volume heat capacity does not diverge during the transition, only exhibits discrete jumps. These non-intuitive results highlight the importance of controlling the correct variables in order to distinguish between continuous and discontinuous transitions. Additionally, they provide a didactic tool to further discuss the phase transitions phenomena. We apply our results to describe the transition between ice VI and liquid water using thermodynamic information available in the literature.

physics.class-ph↗

arXiv2001

Experimental evidence of stochastic resonance without tuning due to non Gaussian noises

In order to test theoretical predictions, we have studied the phenomenon of stochastic resonance in an electronic experimental system driven by white non Gaussian noise. In agreement with the theoretical predictions our main findings are: an enhancement of the sensibility of the system together with a remarkable widening of the response (robustness). This implies that even a single resonant unit can reach a marked reduction in the need of noise tuning.

cond-mat.stat-mech↗