Spec. Condensed Matter, SuYang Xu, PU & LBNL, "2D Topological Superconductors based on 3D Topological Insulators with Helical Pairing"

Thu, Feb 26, 2015, 1:30 pm to 2:30 pm
PCTS Seminar Room
Research on topological insulators and Dirac materials have opened the door to search for related topological states of quantum matter. Superconductivity involving topological Dirac electrons has recently been proposed as a platform between concepts in high-energy and condensed-matter physics. It has been predicted that SUSY (supersymmetry), Weyl fermions, axions or Majorana fermions, all of which remain elusive in particle physics, may be realized through emergent particles in topological insulator based magnets or superconducting systems [1,2]. Using artificially fabricated 3D topological-insulator–superconductor heterostructures, we present direct spectroscopic evidence for the existence of helical Cooper pairing in a half Dirac gas [3]. Our experimental studies reveal that 2D topological superconductivity (TSC) in a helical Dirac gas is distinctly different from that in an ordinary superconductor in terms of the spin degrees of the Dirac electrons. We further show that the pairing of Dirac electrons can be suppressed by time-reversal symmetry-breaking impurities, thereby removing the distinction. Our first demonstration and momentum-space imaging of Cooper pairing in a half-Dirac-gas 2D topological superconductor serve as a critically important platform for future testing of fundamental physics predictions such as emergent SUSY (supersymmetry) and topological quantum criticality (QCP) [3-5]. References: 1 M.Z. Hasan & C. L. Kane ; Rev. Mod. Phys. 82, 3045 (2010) and Qi & Zhang, RMP 83, 1057 (2011) 2 J.E. Moore; Nature 464, 194 (2010) and Fu & Kane, Phys. Rev. Letts. 100, 096407 (2008). 3 S.-Y. Xu, N. Aldoust, I. Belopolski et al., Nature Physics 10, 943 (2014). 4 T. Grover et.al., Science 344, 280 (2014). 5 S.-Y. Xu, C. Liu, S. Kushwaha et al., Science 347, 294 (2015).