Strain-Induced Topological Phase Transitions Covering the <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub></math> Indicator in Orthorhombic Li<sub>2</sub>AuBi.

Zhang, Tan; Coen, Frank; Rappe, Andrew M · Nano Lett · 2024

basic_science · Level V

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Abstract

The <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub></math> symmetry indicator is widely used to classify topological materials hosting inversion symmetry. We find orthorhombic Li<sub>2</sub>AuBi in space group <i>Cmcm</i> is a topological insulator with <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>=</mo><mn>1</mn></math> under no strain via first-principles calculations. Due to small band gaps in the <i>k</i><sub><i>z</i></sub> = 0 plane, the band inversions can be selectively induced by moderate external strains to realize phases covering all values of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub></math> = 1, 2, 3, and 0. Detailed <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub></math> phase diagrams are plotted under various moderate strains. The (001) surface states and their associated Fermi surfaces and spin textures are calculated. The topological surface states have different connectivities and different spin textures for the four different <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>Z</mi></mrow><mrow><mn>4</mn></mrow></msub></math> phases. The tunability of topological surface states via moderate strain suggests Li<sub>2</sub>AuBi as an attractive topological material for device applications.