Dirac Surface States and Nature of Superconductivity in Noncentrosymmetric BiPd

• Main Authors: Sun, Zhixiang, Enayat, Mostafa, Maldonado, Ana, Lithgow, Calum, Yelland, Ed, Peets, Darren C, Yaresko, Alexander, Schnyder, Andreas P, Wahl, Peter
• Format: Journal Article
• Language: English
• Published: 30-03-2015
• Subjects: Physics - Superconductivity
• DOI: 10.48550/arxiv.1407.5667

Nat. Commun. 6, 6633 (2015) In non-magnetic bulk materials, inversion symmetry protects the spin
degeneracy. If the bulk crystal structure lacks a centre of inversion, however,
spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal
whose Fermi surfaces exhibit an intricate spin texture. In superconducting
Rashba metals a pairing wavefunction constructed from these complex spin
structures will generally contain both singlet and triplet character. Here we
examine the possible triplet components of the order parameter in
noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric
superconductor macroscopic characterization, atomic-scale ultra-low-temperature
scanning tunnelling spectroscopy, and relativistic first-principles
calculations. While the superconducting state of BiPd appears topologically
trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order
parameter governed by a single isotropic s-wave gap, we show that the material
exhibits Dirac-cone surface states with a helical spin polarization.