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Journal Article

Quadrupole spin polarization as signature of second-order topological superconductors


Kennes,  D. M.
Institut für Theorie der Statistischen Physik, RWTH Aachen;
Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;

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Plekhanov, K., Müller, N., Volpez, Y., Kennes, D. M., Schoeller, H., Loss, D., et al. (2021). Quadrupole spin polarization as signature of second-order topological superconductors. Physical Review B, 103(4): L041401. doi:10.1103/PhysRevB.103.L041401.

Cite as: https://hdl.handle.net/21.11116/0000-0007-CFAC-F
We study theoretically second-order topological superconductors characterized by the presence of pairs of zero-energy Majorana corner states. We uncover a quadrupole spin polarization at the system edges that provides a striking signature to identify topological phases, thereby complementing standard approaches based on zero-bias conductance peaks due to Majorana corner states. We consider two different classes of second-order topological superconductors with broken time-reversal symmetry and show that both classes are characterized by a quadrupolar structure of the spin polarization that disappears as the system passes through the topological phase transition. This feature can be accessed experimentally using spin-polarized scanning tunneling microscopes. We study different models hosting second-order topological phases, both analytically and numerically, and using Keldysh techniques we provide numerical simulations of the spin-polarized currents probed by scanning tips.