Analysis of the Ghost and Mirror Fields in the Nernst Signal Induced by Superconducting Fluctuations

Observation of the ghost critical field for superconducting fluctuations in a disordered TaN thin film

We experimentally study the ghost critical field (GCF), a magnetic field scale for the suppression of superconducting fluctuations, using Hall effect and magnetoresistance measurements on a disordered superconducting thin film near its transition temperature $T_c$. We observe an increase in the Hall effect with a maximum in field that tracks the upper critical field below $T_c$, vanishes near $T_c$, and returns to higher fields above $T_c$. Such a maximum has been observed in studies of the Nernst effect and identified as the GCF. Magnetoresistance measurements near $T_c$ indicate quenching of…

Nernst effect in the phase-fluctuating superconductor InO$_x$

We present a study of the Nernst effect in amorphous 2D superconductor InO$_x$, whose low carrier density implies low phase rigidity and strong superconducting phase fluctuations. Instead of presenting the abrupt jump expected at a BCS transition, the Nernst signal evolves continuously through the superconducting transition as previously observed in underdoped cuprates. This contrasts with the case of Nb$_{0.15}$Si$_{0.85}$, where the Nernst signal due to vortices below T$_{c}$ and by Gaussian fluctuations above are clearly distinct. The behavior of the ghost critical field in InO$_x$ points t…

Nernst effect as a probe of superconducting fluctuations in disordered thin films

In amorphous superconducting thin films of $Nb_{0.15}Si_{0.85}$ and $InO_x$, a finite Nernst coefficient can be detected in a wide range of temperature and magnetic field. Due to the negligible contribution of normal quasi-particles, superconducting fluctuations easily dominate the Nernst response in the entire range of study. In the vicinity of the critical temperature and in the zero-field limit, the magnitude of the signal is in quantitative agreement with what is theoretically expected for the Gaussian fluctuations of the superconducting order parameter. Even at higher temperatures and fin…

超导体中的粒子-空穴鬼影干涉

Particle-Hole Ghost Interference in Superconductors

本文提出超导体中由单个杂质靠近线缺陷、台阶边缘或相边界产生的粒子-空穴干涉，形成结合传统$2k_F$弗里德尔振荡与双曲条纹的鬼影干涉图样，可作为超导电子序的局域探针。

Thermoelectric properties of iron-based superconductors and parent compounds

Herewith, we review the available experimental data of thermoelectric transport properties of iron-based superconductors and parent compounds. We discuss possible physical mechanisms into play in determining the Seebeck effect, from whence one can extract information about Fermi surface reconstruction and Lifshitz transitions, multiband character, coupling of charge carriers with spin excitations and its relevance in the unconventional superconducting pairing mechanism, nematicity, quantum critical fluctuations close to the optimal doping for superconductivity, correlation. Additional informat…

A global inversion-symmetry-broken phase inside the pseudogap region of YBa$_2$Cu$_3$O$_y$

The phase diagram of cuprate high-temperature superconductors features an enigmatic pseudogap region that is characterized by a partial suppression of low energy electronic excitations. Polarized neutron diffraction, Nernst effect, THz polarimetery and ultrasound measurements on YBa$_2$Cu$_3$O$_y$ suggest that the pseudogap onset below a temperature T* coincides with a bona fide thermodynamic phase transition that breaks time-reversal, four-fold rotation and mirror symmetries respectively. However, the full point group above and below T* has not been resolved and the fate of this transition as…