Time-reversal symmetry breaking and gapped surface states due to spontaneous emergence of new order in d-wave nanoislands
Author(s)Nagai, Yuki; Ota, Yukihiro; Tanaka, K.
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We solve the Bogoliubov-de Gennes equations self-consistently for the d-wave order parameter in nanoscale d-wave systems with  surfaces and show that spontaneous time-reversal symmetry (TRS) breaking occurs at low temperatures due to a spontaneously induced complex order parameter of extended s-wave symmetry. The Andreev surface bound states, which are protected by a one-dimensional (1D) topological invariant in the presence of TRS, are gapped by the emergence of this new order parameter. The extended s-wave order parameter is localized within a narrow region near the surfaces, which is consistent with the fact that topological protection of the gapless Andreev surface states is characterized by the 1D topological invariant. In this TRS-breaking phase, not only is the complex order parameter induced, but also the d-wave order parameter itself becomes complex. Furthermore, the disappearance of topological protection brings about novel vortex phenomena near the surfaces. We show that vortex-antivortex pairs are formed in the extended s-wave order parameter along the surfaces if the side length of a nanoisland or the width of an infinitely long nanoribbon is relatively large.
DepartmentMassachusetts Institute of Technology. Department of Physics
Physical Review B
American Physical Society
Nagai, Yuki; Ota, Yukihiro andTanaka, K. "Time-reversal symmetry breaking and gapped surface states due to spontaneous emergence of new order in d-wave nanoislands." Physical Review B 96, 6 (August 2017): 060503(R) © 2017 American Physical Society
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