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Momentum-space imaging of Cooper pairing in a half-Dirac-gas topological superconductor

Nature Physics volume 10, pages 943–950 (2014)Cite this article

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Abstract

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 supersymmetry and Majorana fermions, both of which remain elusive in particle physics, may be realized through emergent particles in these particular superconducting systems. Using artificially fabricated topological-insulator–superconductor heterostructures, we present direct spectroscopic evidence for the existence of Cooper pairing in a weakly interacting half Dirac gas. Our studies reveal that two dimensional topological superconductivity in a helical Dirac gas is distinctly different from that in an ordinary two-dimensional superconductor in terms of the spin degrees of freedom of electrons. We further show that the pairing of Dirac electrons can be suppressed by time-reversal symmetry-breaking impurities, thereby removing the distinction. Our demonstration and momentum-space imaging of Cooper pairing in a half-Dirac-gas two-dimensional topological superconductor serve as a critically important platform for future testing of fundamental physics predictions such as emergent supersymmetry and topological quantum criticality.

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Figure 1: Sample layout and characterization.
Figure 2: Spectroscopically resolved proximity-induced topological superconductivity.
Figure 3: Topological superconducting gap and helical Cooper pairing.
Figure 4: Hybridization dependence of the superconducting gap.
Figure 5: Point-contact interface transport and conditions for predicted emergent supersymmetry.

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Acknowledgements

The work at Princeton and Princeton-led synchrotron-based ARPES measurements is supported by US DOE DE-FG-02-05ER46200. MBE growth of Bi2Se3/NbSe2 samples at Penn State was supported by ARO through ARO-MURI (W911NF-12-1-0461). The point-contact measurements were supported by US DOE DE- FG02-08ER4653 (Q.L.). C.F. and M.J.G. are supported by the ONR under grant N00014-11-1-0728 and N00014-14-1-0123 and B.D. and M.J.G. are supported by the AFOSR under grant FA9550-10-1-0459. Initial materials work was supported by MRSEC Program Grant DMR-0819860. M.J.G. is supported by NSF CAREER Award ECCS 13-51871. F.C.C. acknowledges the support provided by MOST-Taiwan under project number NSC-102-2119-M-002-004. We gratefully acknowledge E. Rienks for assistance at the BESSY facility. We also thank J. Denlinger, S-k. Mo, A. Fedorov, and M. Hashimoto for beamline support at the beamlines 4.0.3, 10.0.1, 12.0.1 at the ALS, and the beamline 5–4 at the SSRL, respectively.

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Authors and Affiliations

  1. Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA

    Su-Yang Xu, Nasser Alidoust, Ilya Belopolski, Chang Liu, Madhab Neupane, Guang Bian, Chen Fang & M. Zahid Hasan

  2. Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA

    Anthony Richardella, Wenqing Dai, Qi Li & Nitin Samarth

  3. Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan

    Song-Hsun Huang, Raman Sankar & Fangcheng Chou

  4. Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, USA

    Chen Fang, Brian Dellabetta & Matthew J. Gilbert

  5. Princeton Center for Complex Materials, Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, USA

    M. Zahid Hasan

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  1. Su-Yang Xu
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Contributions

S-Y.X., N.A., I.B., C.L., M.N., and G.B. conducted the ARPES experiments with the assistance from M.Z.H.; A.R. and N.S. performed the Bi2Se3 MBE growth; S-H.H., R.S., and F.C. prepared the NbSe2 single crystalline samples; W.D. and Q.L. conducted the point-contact Andreev-reflection transport measurements; C.F., B.D., and M.J.G. performed theoretical calculations. M.Z.H. was responsible for the conception, overall direction, planning and integration among the research units.

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Correspondence to M. Zahid Hasan.

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Xu, SY., Alidoust, N., Belopolski, I. et al. Momentum-space imaging of Cooper pairing in a half-Dirac-gas topological superconductor. Nature Phys 10, 943–950 (2014). https://doi.org/10.1038/nphys3139

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