Emergence of Fermi pockets in an excitonic CDW melted novel superconductor

TL;DR

This study reveals how copper doping in TiSe2 transforms its charge density wave state into a superconductor, characterized by the emergence of Fermi pockets and altered electronic structures, highlighting an unconventional CDW-SC crossover.

Contribution

First identification of momentum space locations of doped electrons forming Fermi pockets in Cu-doped TiSe2 and analysis of the CDW to SC transition through photoemission spectroscopy.

Findings

Emergence of large electron pockets near the L-point in the Brillouin zone.

Increase in nesting volume with doping and sharp drop in CDW coherence.

Observation of a narrow electron pocket with d-like character in the superconducting state.

Abstract

A superconducting (SC) state (Tc ~ 4.2K) has very recently been observed upon successful doping of the CDW ordered triangular lattice TiSe$_2$, with copper. Using high resolution photoemission spectroscopy we identify, for the first time, the momentum space locations of the doped electrons that form the Fermi sea of the parent superconductor. With doping, we find that the kinematic nesting volume increases whereas the coherence of the CDW order sharply drops. In the superconducting doping, we observe the emergence of a large density of states in the form of a narrow electron pocket near the \textit{L}-point of the Brillouin Zone with \textit{d}-like character. The \textit{k}-space electron distributions highlight the unconventional interplay of CDW to SC cross-over achieved through non-magnetic copper doping.