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Area of Science:

  • Condensed matter physics
  • Materials science
  • Quantum mechanics

Background:

  • Two-dimensional topological insulators (TIs) possess unique edge states protected by time-reversal symmetry.
  • These helical edge states are predicted to exhibit quantized conductance, robust against scattering.

Purpose of the Study:

  • To investigate the paradoxical breaking of time-reversal symmetry by the current-carrying state in TIs.
  • To elucidate the mechanism behind the loss of protection against elastic backscattering.

Main Methods:

  • Theoretical analysis of electron-electron interactions and spin polarization in helical edge states.
  • Investigation of the system's current-voltage (I-V) characteristics.

Main Results:

  • Applied current induces a gap in the edge state dispersion through a feedback mechanism.
  • This current-induced gap opening breaks the protection against elastic backscattering.
  • A nonlinear contribution to the I-V characteristic, observable down to zero temperature, confirms this phenomenon.

Conclusions:

  • Electron-electron interactions and spin polarization are crucial for current-induced gap opening in 2D TIs.
  • This mechanism offers insights into the behavior of topological states under electrical bias.
  • Potential for similar effects in three-dimensional TIs' surface states was discussed.