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Trabajo presentado en la 3rd Conference on Statistical Physics (2021), celebrada en Miramare (Italia) del 8 al 10 de septiembre de 2021., The stochastic nature of games at the casino allows lucky players to make profit by means of gambling. Like games of chance and stocks, small physical systems are subject to fluctuations, thus their energy and entropy become stochastic, following an unpredictable evolution. In this context, information about the evolution of a thermodynamic system can be used by Maxwell's demons to extract work using feedback control. This is not always the case, and a challenging task is then to develop efficient thermodynamic protocols achieving work extraction in situations where feedback control cannot be realized, in the same spirit as it is done on a daily basis in casinos and financial markets. We introduce and realize gambling demons who, following a customary gambling strategy to stop a nonequilibrium process at stochastic times, are able to extract more average work than the free energy change. We derive second laws in the presence of gambling, and a set of universal stopping-time fluctuation relations for the work done in classical and quantum stochastic non-stationary processes. We test experimentally our results in a single-electron box, where an electrostatic potential is used to drive the dynamics of individual electrons tunneling into a metallic island.

In this work we aim to analyze the effect of a strong antisymmetric spin-orbit coupling (ASOC) on the superconductivity of noncentrosymmetric LaPtSi. We study the energy gap structure of polycrystalline LaPtSi by using magnetic penetration depth measurements down to 0.02T c. We observed a dirty s-wave behavior, which provides compelling evidence that the spin-singlet component of the mixed pairing state is highly dominant. This is consistent with previous results in the sense that the mere presence of a strong ASOC does not lead to unconventional behaviors. Our result also downplays LaPtSi as a good candidate for realizing time-reversal invariant topological superconductivity.

In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors ${\mathrm{CeIrSi}}_{3}$ and ${\mathrm{CeRhSi}}_{3}$ carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in ${\mathrm{CeIrSi}}_{3}$ shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, ${\mathrm{CeRhSi}}_{3}$ does not possess a $T=0$ quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in ${\mathrm{CeIrSi}}_{3}$ and ${\mathrm{CeRhSi}}_{3}$ and maybe in other heavy fermions.

Superconductivity in noncentrosymmetric LaNiC$_2$ is expected to be induced by electron--phonon interactions due to its lack of magnetic instabilities. The non-Bardeen-Cooper-Schrieffer (BCS) behaviors found in this material call into question the long-standing idea that relates unconventional superconductivity with magnetic interactions. Here we report magnetic penetration-depth measurements in a high-purity single crystal of LaNiC$_2$ at pressures up to 2.5 GPa and temperatures down to 0.04 K. At ambient pressure and below 0.5$T_c$ the penetration depth goes as $T^4$ for the in-plane and $T^2$ for the out-of-plane component, firmly implying the existence of point nodes in the energy gap and the unconventional character of this superconductor. The present study also provides first evidence of magnetism in LaNiC$_2$ by unraveling a pressure-induced antiferromagnetic phase inside the superconducting state at temperatures below 0.5 K, with a quantum critical point around ambient pressure. The results presented here maintain a solid base for the notion that unconventional superconductivity only arises near magnetic order or fluctuations., Comment: 12 pages, 4 figures

We measured the temperature dependence of the magnetic penetration depth of La3Pd4Si4 down to 0.02 Tc. We observe a temperature-independent behaviour below 0.25 Tc, which is firm evidence for a nodeless superconducting gap in this material. The data display a very small anomaly around 1 K which we attribute to the possible presence of a superconducting impurity phase. The superfluid density is well described by a two-phase model, considering La3Pd4Si4 and the impurity phase. The present analysis suggests that the superconducting energy gap of La3Pd4Si4 is isotropic, as expected for conventional BCS superconductors.