Probing charge-density waves and superconductivity in low-dimensional systems

Abstract

The recent advent of two-dimensional materials has led to the discovery of materials with fascinating phase diagrams. These systems have exciting electronic phases which coexist or compete with each other. Here in this thesis, we have looked into two such electron-phonon mediated many-body states { charge density wave and superconductivity. We start with a novel, dynamically modulated quantum phase transition between two distinct charge density wave (CDW) phases in 2-dimensional 2H-NbSe2. There is recent spectroscopic evidence for the presence of these two quantum phases, but its evidence in bulk measurements remained elusive [1]. We studied suspended, ultra-thin NbSe2 devices fabricated on piezoelectric substrates - with tunable akes thickness, disorder level, and strain. We find that over a certain range of temperature, the conductance

fluctuates between two precise values separated by the quantum of conductance, e2=h. These observations could be explained as arising from strain-induced dynamical phase transition between the two CDW states [2]. To affirm this, we vary the lateral strain across the device and map out the phase diagram near the critical point