Effect of Cu intercalation and pressure on excitonic interaction in 1T-TiSe2

TL;DR

This study investigates how Cu intercalation and pressure influence excitonic interactions and phase transitions in 1T-TiSe2, revealing different structural and electronic behaviors and highlighting the role of excitons in the phase diagram.

Contribution

It provides detailed structural analysis of Cu-intercalated and pressurized 1T-TiSe2, clarifying how these methods differently affect excitonic interactions and phase transitions.

Findings

Cu intercalation and pressure differently affect structural parameters.

The relationship between CDW suppression and superconductivity varies for the two methods.

Excitonic interactions are significant in the pressure-temperature phase diagram, but not in the doping-temperature phase diagram.

Abstract

1T-TiSe2 has a semimetallic band structure at room temperature and undergoes phase transition to a triple-q charge density wave (CDW) state with a commensurate superlattice structure (2a * 2a * 2c) below Tc ~ 200 K at ambient pressure. This phase transition is caused by cooperative phenomena involving electron-phonon and electron-hole (excitonic) interactions, and cannot be described by a standard CDW framework. By Cu intercalation or the application of pressure, this phase transition temperature is suppressed and superconductivity (SC) appears. However, it is not clear what kind of order parameters are affected by these two procedures. We investigated the crystal structure of CuxTiSe2 and pressurized 1T-TiSe2 around the SC state by synchrotron x-ray diffraction on single crystals. In the high-temperature phase, the variation of structural parameters for the case of Cu intercalation and application of pressure are considerably different. Moreover, the relationship between the critical points of the CDW phase transition and the SC dome are also different for the two cases. The excitonic interaction appears to play an important role in the P-T phase diagram of 1T-TiSe2, but not in the x-T phase diagram.