AVS 59th Annual International Symposium and Exhibition
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeM

Paper MI-WeM11
Scanning Tunneling Microscopy Observation of the Superconducting Gap in CuxBi2Se3

Wednesday, October 31, 2012, 11:20 am, Room 006

Session: Topological Insulators and Rashba
Presenter: J. Ha, Center for Nanoscale Sci. and Tech. / NIST and Seoul National Univ.
Authors: J. Ha, Center for Nanoscale Sci. and Tech. / NIST and Seoul National Univ.
N. Levy, Center for Nanoscale Sci. and Tech. / NIST
T. Zhang, Center for Nanoscale Sci. and Tech. / NIST and Maryland NanoCenter / Univ. of Maryland
R.L. Kallaher, Center for Nanoscale Sci. and Tech. / NIST
F. Sharifi, Center for Nanoscale Sci. and Tech. / NIST
A.A. Talin, Center for Nanoscale Sci. and Tech. / NIST
Y. Kuk, Seoul National Univ., Republic of Korea
J.A. Stroscio, Center for Nanoscale Sci. and Tech. / NIST
Correspondent: Click to Email
The discovery of topological insulators has triggered the search for new topological states of matter. A topological superconductor is one such state, characterized by the existence of an unconventional superconducting gap in the bulk, and gapless Andreev bound states on the surface. Recently, Cu intercalated Bi2Se3 (CuxBi2Se3) was found to be superconducting with TC ≈ 3.8 K [1], and is considered a prime candidate for topological superconductivity due to its peculiar band structure and strong spin-orbit coupling. A recent point contact measurement observed zero-bias conductance peaks, claiming these as evidence of surface Andreev bound states, and angle resolved photoemission spectroscopy has revealed the preservation of the topological surface states at the Fermi level [2, 3]. However, direct measurement of the superconducting gap in this material has not been reported.

In this work, we use an ultra-low temperature scanning tunneling microscope [4] to investigate the superconducting properties of a cleaved CuxBi2Se3 bulk crystal. The crystal was synthesized by electrochemical intercalation of Cu atoms into a previously synthesized Bi2Se3 crystal. We observe a superconducting gap in scanning tunneling spectroscopy (STS) measurements. We estimate the size of the gap to be 0.35 meV from a preliminary BCS fit of the superconducting gap. STS measurements under a magnetic field show a complete suppression of the superconducting gap at a critical field of ≈ 1.5 T. Significant inhomogeneity is observed in the material with spatial variations of the superconducting gap. We will discuss these observations in the context of current theories of topological superconductors.

[1] Y. S. Hor et al., Phys. Rev. Lett. 104, 057001 (2010)

[2] L. A. Wray et al., Nat. Phys. 6, 855–859 (2010)

[3] S. Sasaki et al., Phys. Rev. Lett. 107, 217001 (2011)

[4] Y. J. Song et al., Rev. Sci. Instrum. 81, 121101 (2010)