Excitonic Gap Formation in Pumped Dirac Materials

Abstract

Recent pump-probe experiments demonstrate the possibility that Dirac materials may be driven into transient excited states describable by two chemical potentials, one for the electrons and one for the holes. Given the Dirac nature of the spectrum, such an inverted population allows the optical tunability of the density of states of the electrons and holes, effectively offering control of the strength of the Coulomb interaction. Here we discuss the feasibility of realizing transient excitonic instabilities in optically-pumped Dirac materials. We demonstrate, theoretically, the reduction of the critical coupling leading to the formation of a transient condensate of electron-hole pairs and identify signatures of this state. Furthermore, we provide guidelines for experiments by both identifying the regimes in which such exotic many-body states are more likely to be observed and estimating the magnitude of the excitonic gap for a few important examples of existing Dirac materials. We find a set of material parameters for which our theory predicts large gaps and high critical temperatures and which could be realized in future Dirac materials. We also comment on transient excitonic instabilities in three-dimensional Dirac and Weyl semimetals. This study provides the first example of a transient collective instability in driven Dirac materials.

12 pages, 6 figures

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• Dirac materials
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• Floquet topological phase of nondriven $p$-wave nonequilibrium excitonic insulators
• Excitons and carriers in transient absorption and time-resolved ARPES spectroscopy: an abinitio approach
• Excitonic instability in optically-pumped three-dimensional Dirac materials
• Excitonic instability of two-dimensional tilted Dirac cones
• Relativistic suppression of Auger recombination in Weyl semimetals
• Non-Hermitian BCS-BEC crossover of Dirac fermions
• Dynamic spin-triplet order induced by alternating electric fields in superconductor-ferromagnet-superconductor Josephson junctions
• Identification of strongly interacting organic semimetals
• Ultrafast creation and melting of nonequilibrium excitonic condensates in bulk WSe${}_2$
• Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: an ab-initio perspective
• Nanosecond dynamics in intrinsic topological insulator ${\text{Bi}}_{2-x}{\text{Sb}}_x{\text{Se}}_3$ revealed by time-resolved optical reflectivity
• Dirac node engineering and flat bands in doped Dirac materials
• Research on topological materials using ultrafast spectroscopy