ON THE NATURE OF CHARGE DENSITY WAVES, SUPERCONDUCTIVITY AND THEIR INTERPLAY IN 1T-TiSe2

Abstract

This thesis presents mainly analytical theoretical studies on the interplay between charge density waves (CDW) and superconductivity (SC) in 1T-TiSe2 From mean field and DFT calculation, it is shown that an excitonic mechanism is capable of reproducing with very good quantitative agreement the experimental phase diagram for the CCDW transition temperature as a function of carrier density. A Ginzburg-Landau phenomenological theory was developed to understand the experimentally observed transition from commensurate to incommensurate CDW (ICDW) order with doping or pressure, and the emergence of a superconducting dome that coexists with ICDW. A microscopic theory provides a description of CDW fluctuations beyond mean-field. The result indicates that SC order in TiSe2 can be either driven by fluctuation-induced pairing or, at least, enhanced by CDW fluctuations. Finally, collaborating with experimental groups, we discovered that, with increasing magnetic field, an anomalous quantum metal phase emerges between the SC to normal metal transition.