Evidences for the exciton gas phase and its condensation in monolayer 1T-ZrTe2

Abstract

The excitonic insulator (EI) is a Bose-Einstein condensation (BEC) of excitons bound by electron-hole interaction in a solid, which could support high-temperature BEC transition. The material realization of EI has been elusive, which is further challenged by the difficulty of distinguishing it from a conventional charge density wave (CDW) state. In the BEC limit, the pre-condensation exciton gas phase is a hallmark to distinguish EI from conventional CDW, yet direct experimental evidence has been lacking. Here we report a distinct correlated phase beyond the $2\times 2$ CDW ground state emerging in epitaxially grown monolayer 1T-ZrTe2 and its investigation by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The results show novel band- and energy-dependent folding behavior in a two-step process, evidenced by an exciton gas phase prior to its condensation into the final CDW state. The excellent agreement between experiments and theoretical predictions on the recovery of the pristine band structure by carrier-density-dependent suppression of the CDW state further corroborates the monolayer 1T-ZrTe2 as an EI. Our findings provide a versatile two-dimensional platform that allows tuning of the excitonic effect.

22 pages, 4 figures

References in corpus (11)

• Quantum ESPRESSO toward the exascale
• Observation of giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
• Probing Excitonic Dark States in Single-layer Tungsten Disulfide
• Evidence for an excitonic insulator phase in 1T-TiSe${}_2$
• Strongly correlated excitonic insulator in atomic double layers
• Evidence for a Monolayer Excitonic Insulator
• Evidence for equilibrium excitons and exciton condensation in monolayer WTe2
• Semiconductor-metal phase transition and emergent charge density waves in 1T-ZrX${}_2$ (X = Se, Te) at the two-dimensional limit
• Possible Excitonic Insulating Phase in Quantum-Confined Sb Nanoflakes
• Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3
• Detecting photoelectrons from spontaneously formed excitons

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