Excitonic instability of three-dimensional gapless semiconductors: Large- N theory
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Contributors
Abstract
Three-dimensional gapless semiconductors with quadratic band touching, such as HgTe, α-Sn, or Pr2Ir2O7, are believed to display a non-Fermi-liquid ground state due to long-range electron-electron interaction. We argue that this state is inherently unstable towards spontaneous formation of a (topological) excitonic insulator. The instability can be parameterized by a critical fermion number Nc. For N<Nc the rotational symmetry is spontaneously broken, the system develops a gap in the spectrum, and features a finite nematic order parameter. To leading order in the 1/N expansion and in the static approximation, the analogy with the problem of dynamical mass generation in (2+1)-dimensional quantum electrodynamics yields Nc=16/[3π(π-2)]. Taking the important dynamical screening effects into account, we find that Nc≥2.6(2) and therefore safely above the physical value of N=1. Some experimental consequences of the nematic ground state are discussed.
Details
Original language | English |
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Article number | 165109 |
Journal | Physical Review B |
Volume | 93 |
Issue number | 16 |
Publication status | Published - 6 Apr 2016 |
Peer-reviewed | Yes |
Externally published | Yes |