Exploring dissipation dynamics in low-dimensional superconductor

Abstract

Technological advances in the past decade in fabricating two-dimensional superconducting materials with low disorder have enabled exploring many exciting phases. In recent times, two-dimensional superconductors have been the focus of research in condensed matter physics, with theories predicting such systems to be a suitable platform to observe not only exotic phases but a medium to test several statistical phenomena which are somewhat challenging to probe in other arrangements. In this thesis, my discussion has revolved around two Type II superconducting systems in which we have investigated several low-dimensional phenomena through transport studies. Ising superconductors are predicted to host several unconventional phases through a topological pairing of electrons that arises due to spin-momentum locking. An ideal system to observe such superconductivity are the transition metal dichalcogenide (TMD) materials which show a strong Ising spin-orbit coupling (SOC) in the monolayer limit owing to the lack of in-plane inversion symmetry. In the first part of the colloquium, I will present a study of van der Waals heterostructure comprising of monolayer MoS2 – a semiconducting TMD with high Ising SOC and few-layer NbSe2 – a conventional superconducting TMD. Through systematic magnetotransport measurement, we found that the superconductivity in the heterostructure region is of 2D Ising in nature in contrast to the 3D behavior of the few-layer NbSe2. We establish that the observed phenomena can be attributed to the hybridization of the bands of an effectively thinned NbSe2 and the monolayer MoS2 on top of it. Following this, I will discuss the study of the carrier dynamics of this heterostructure around the transition temperature at zero magnetic fields through resistance fluctuation spectroscopy. We establish the universal BKT-type behavior of the superconductivity in the heterostructure region. In the second part of the thesis, I discussed the results of our study of the dynamics of the hexatic phase in the two-dimensional vortex lattice of a weakly pinned superconducting thin film (MoGe). The hexatic phase is an intermediate phase that arises in the melting process of a two-dimensional crystalline solid. We specifically studied the effect of an external drive on the phase through fluctuation spectroscopy. We observe low-frequency oscillations in the vortex velocity that are exclusive to the thermally assisted flux flow (TAFF) regime. We also observed a long-term memory effect of the vortex motion in the Hexatic regime of the vortex lattice. Lastly, we uncovered a current-induced dynamical instability in the Hexatic phase, where the system toggles between two defined levels in the presence of a constant external drive.