Large surface conductance and superconductivity in topological insulator microstructures

Abstract

Controllable geometric manipulation via micromachining techniques provides a promising tool for enhancing useful topological electrical responses relevant to future applications such as quantum information science [P. J. W. Moll, "Focused ion beam microstructuring of quantum matter," Annu. Rev. Condens. Matter Phys. 9, 147 (2018); Jang et al., "Observation of half-height magnetization steps in Sr2RuO4," Science 331, 186 (2011); Moll et al., "Transport evidence for Fermi-arc-mediated chirality transfer in the Dirac semimetal Cd3As2," Nature 535, 266 (2016); Moll et al., "Evidence for hydrodynamic electron flow in PdCoO2," Science 351, 1061 (2016)]. Here, we present microdevices fabricated with a focused ion beam from an indium-doped topological insulator Pb1-xSnxTe. With the device thickness on the order of 1 μm and an extremely large bulk resistivity, we achieve an unprecedented enhancement of the surface contribution to about 30% of the total conductance near room temperature. The surface contribution increases as the temperature is reduced, becoming dominant below approximately 180 K, compared to 30 K in millimeter-thickness crystals. In addition to the enhanced surface contribution to normal-state transport, we observe the emergence of surface superconductivity below 6 K. Measurements of magnetoresistivity at high magnetic fields reveal a weak antilocalization behavior in the normal-state magnetoconductance at low temperatures and a variation in the power-law dependence of resistivity on temperature with the field. These results demonstrate that interesting electronic responses relevant to practical applications can be achieved by suitable engineering of single crystals.