Evidence of high-temperature exciton condensation in a two-dimensional semimetal

Abstract

Electrons and holes can spontaneously form excitons and condense in a semimetal or semiconductor, as predicted decades ago. This type of Bose condensation can happen at much higher temperatures in comparison with dilute atomic gases. Two-dimensional (2D) materials with reduced Coulomb screening around the Fermi level are promising for realizing such a system. Here we report a change in the band structure accompanied by a phase transition at about 180 K in single-layer ZrTe2 based on angle-resolved photoemission spectroscopy (ARPES) measurements. Below the transition temperature, gap opening and development of an ultra-flat band top around the zone center are observed. This gap and the phase transition are rapidly suppressed with extra carrier densities introduced by adding more layers or dopants on the surface. The results suggest the formation of an excitonic insulating ground state in single-layer ZrTe2, and the findings are rationalized by first principles calculations and a self-consistent mean-field theory. Our study provides evidence for exciton condensation in a 2D semimetal and demonstrates strong dimensionality effects on the formation of intrinsic bound electron-hole pairs in solids.

References in corpus (12)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Evidence of high-temperature exciton condensation in 2D atomic double layers
• Evidence for an excitonic insulator phase in 1T-TiSe${}_2$
• Unfolding spinor wavefunctions and expectation values of general operators: Introducing the unfolding-density operator
• Strongly correlated excitonic insulator in atomic double layers
• Fermi surface evolution and Luttinger theorem in Na${}_x$CoO${}_2$: a systematic photoemission study
• Evidence for equilibrium excitons and exciton condensation in monolayer WTe2
• Direct observation of excitonic instability in Ta2NiSe5
• Evidence of ideal excitonic insulator in bulk MoS2 under pressure
• Semiconductor-metal phase transition and emergent charge density waves in 1T-ZrX${}_2$ (X = Se, Te) at the two-dimensional limit
• Evolution of the electronic structure in Ta${}_2$NiSe${}_5$ across the structural transition revealed by resonant inelastic x-ray scattering

Cited by in corpus (18)

• A New Era of Excitonic Insulators
• Observation of possible excitonic charge density waves and metal-insulator transitions in atomically thin semimetals
• Spontaneous gap opening and potential excitonic states in an ideal Dirac semimetal Ta${}_2$Pd${}_3$Te${}_5$
• A gate-tunable quantum phase transition in a topological excitonic insulator
• Excitonic Instability in Ta2Pd3Te5 Monolayer
• Unusual ferromagnetic band evolution and high Curie temperature in monolayer 1T-CrTe2 on bilayer graphene
• Spectroscopic evidence for possible quantum spin liquid behavior in a two-dimensional Mott insulator
• Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe${}_2$
• Electronic and Optical Properties of Ta${}_2$NiSe${}_5$ Monolayer: A First-principles Study
• First-principles design of excitonic insulators: A review
• Spin-Triplet Excitonic Insulator in the Ultra-Quantum Limit of HfTe5
• Gate tuning of coupled electronic and structural phase transition in atomically thin Ta${}_2$NiSe${}_5$
• Unusual temperature dependence of the band structure associated with local atomic distortion in monolayer 1T'-WTe2
• Engineering excitonic metal-insulator transitions in ultra-thin doped copper sulfides
• Excitons and Optical Response in Excitonic Insulator Candidate TiSe${}_2$
• Long-lived relaxation channel and exciton-phonon coupling in Ta2NiSe5 via non-degenerate pump-probe spectroscopy
• Raman spectroscopy of van der Waals topological magnet GdGaI
• Emergent quantum phenomena in two-dimensional 1T-TaS2