Critical point for Bose-Einstein condensation of excitons in graphite

Abstract

An exciton is an electron-hole pair bound by attractive Coulomb interaction. Short-lived excitons have been detected by a variety of experimental probes in numerous contexts. An excitonic insulator, a collective state of such excitons, has been more elusive. Here, thanks to Nernst measurements in pulsed magnetic fields, we show that in graphite there is a critical temperature (T = 9.2 K) and a critical magnetic field (B = 47 T) for Bose-Einstein condensation of excitons. At this critical field, hole and electron Landau sub-bands simultaneously cross the Fermi level and allow exciton formation. By quantifying the effective mass and the spatial separation of the excitons in the basal plane, we show that the degeneracy temperature of the excitonic fluid corresponds to this critical temperature. This identification would explain why the field-induced transition observed in graphite is not a universal feature of three-dimensional electron systems pushed beyond the quantum limit.

arXiv comment5 pages, 4 figures, supplemental Material included.To be published in PNAS

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• A comprehensive study of complex non-adiabatic exciton dynamics in MoSi${}_2$N${}_4$
• Antiferromagnetic ordering and excitonic pairing in the AA-stacked bilayer graphene
• Wide critical fluctuations of the field-induced phase transition in graphite
• First-principles design of excitonic insulators: A review
• A field-induced reentrant insulator state of a gap-closed topological insulator (Bi_{1-x}Sb_x) in quantum-limit states
• 0D-2D Heterostructure for making very Large Quantum Registers using itinerant Bose-Einstein Condensate of Excitons
• Spin-Triplet Excitonic Insulator in the Ultra-Quantum Limit of HfTe5
• Thermal Hall conductivity of semimetallic graphite dominated by ambipolar phonon drag
• High-field immiscibility of electrons belonging to adjacent twinned bismuth crystals
• Stabilization of sliding ferroelectricity through exciton condensation