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Partial Lattice Defects in Higher-Order Topological Insulators.

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Higher-order topological insulators (HOTIs) can host helical modes at dislocations without weak topological indices. These modes appear at fractional Burgers vector dislocations, common in stacking faults, impacting material conductivity.

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Area of Science:

  • Condensed matter physics
  • Topological materials science
  • Materials science

Background:

  • Weak topological indices were previously considered essential for binding helical modes to lattice dislocations.
  • Higher-order topological insulators (HOTIs) represent a distinct class of topological materials with unique electronic properties.

Purpose of the Study:

  • To investigate the possibility of hosting helical modes in HOTIs at dislocations even without weak topological indices.
  • To characterize the nature of these helical modes and their relationship to specific dislocation types.

Main Methods:

  • Theoretical analysis of helical modes in HOTIs.
  • Investigation of dislocations characterized by fractional Burgers vectors and stacking faults.
  • Adiabatic transformation to demonstrate the robustness of helical modes.

Main Results:

  • HOTIs can host single helical modes at screw or edge dislocations without requiring weak topological indices.
  • These helical modes are bound to dislocations with fractional Burgers vectors, often associated with stacking faults.
  • The helical modes exhibit robustness, as demonstrated by adiabatic transformations.

Conclusions:

  • The findings challenge the necessity of weak topological indices for helical mode localization at dislocations.
  • Helical modes at partial dislocations in HOTIs, linked to stacking faults, are a significant phenomenon.
  • The presence of these modes can influence the measurable conductivity of bulk crystals, offering new avenues for material design and application.