Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers

doi:10.1126/sciadv.1602579

Title: Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers

Abstract

Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of three-dimensional (3D) crystals with bulk inversion symmetry. We report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet.We propose a theoretical model where magnetic fluctuations in Ni induce the superconducting pairing of the d _xy ± id _x²-y² orbital symmetry between the electrons in Bi. In this model, the order parameter spontaneously breaks the TRS and has a nonzero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor.

Authors:

Gong, Xinxin ^[1]; Kargarian, Mehdi ^[2]; Stern, Alex ^[3];

^[4]; Zhou, Hexin ^[4]; Jin, Xiaofeng ^[4]; Galitski, Victor M. ^[2]; Yakovenko, Victor M. ^[2]; Xia, Jing ^[3]

Univ. of California, Irvine, CA (United States). Department of Physics and Astronomy; Fudan Univ., Shanghai (China). Department of Physics
Univ. of Maryland, College Park, MD (United States). Department of Physics, Condensed Matter Theory Center and Joint Quantum Institute
Univ. of California, Irvine, CA (United States). Department of Physics and Astronomy
Fudan Univ., Shanghai (China). Department of Physics

Publication Date:: Fri Mar 31 00:00:00 EDT 2017

Research Org.:: Univ. of Maryland, College Park, MD (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

OSTI Identifier:: 1424726

Grant/Contract Number:: SC0001911

Resource Type:: Journal Article: Accepted Manuscript

Journal Name:: Science Advances

Additional Journal Information:: Journal Volume: 3; Journal Issue: 3; Journal ID: ISSN 2375-2548

Publisher:: AAAS

Country of Publication:: United States

Language:: English

Subject:: 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats


                    Gong, Xinxin, Kargarian, Mehdi, Stern, Alex, Yue, Di, Zhou, Hexin, Jin, Xiaofeng, Galitski, Victor M., Yakovenko, Victor M., and Xia, Jing. Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers.  United States: N. p., 2017. 
        Web.  doi:10.1126/sciadv.1602579.

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                    Gong, Xinxin, Kargarian, Mehdi, Stern, Alex, Yue, Di, Zhou, Hexin, Jin, Xiaofeng, Galitski, Victor M., Yakovenko, Victor M., & Xia, Jing. Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers.  United States.  doi:10.1126/sciadv.1602579.

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                    Gong, Xinxin, Kargarian, Mehdi, Stern, Alex, Yue, Di, Zhou, Hexin, Jin, Xiaofeng, Galitski, Victor M., Yakovenko, Victor M., and Xia, Jing. Fri .  
        "Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers".  United States.  
        doi:10.1126/sciadv.1602579.  https://www.osti.gov/servlets/purl/1424726.

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@article{osti_1424726,

  title        = {Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers},

  author       = {Gong, Xinxin and Kargarian, Mehdi and Stern, Alex and Yue, Di and Zhou, Hexin and Jin, Xiaofeng and Galitski, Victor M. and Yakovenko, Victor M. and Xia, Jing},

  abstractNote = {Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of three-dimensional (3D) crystals with bulk inversion symmetry. We report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet.We propose a theoretical model where magnetic fluctuations in Ni induce the superconducting pairing of the dxy ± idx2-y2 orbital symmetry between the electrons in Bi. In this model, the order parameter spontaneously breaks the TRS and has a nonzero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor.},

  doi          = {10.1126/sciadv.1602579},

  journal      = {Science Advances},

  number       = 3,

  volume       = 3,

  place        = {United States},

  year         = {Fri Mar 31 00:00:00 EDT 2017},

  month        = {Fri Mar 31 00:00:00 EDT 2017}

}

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Journal Article:

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DOI: 10.1126/sciadv.1602579

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Works referenced in this record:

Role of Spin in Quasiparticle Interference
journal, November 2004

Pascual, J. I.; Bihlmayer, G.; Koroteev, Yu. M.
Physical Review Letters, Vol. 93, Issue 19, Article No. 196802
DOI: 10.1103/PhysRevLett.93.196802

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It is pointed out that erroneous Bardeen-Cooper-Schrieffer model equations have been used by Haranath Ghosh in his recent treatment of time-reversal symmetry-breaking superconductivity. Consequently, his numerical results are misleading, and his conclusions are not to the point.
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In the context of broken time-reversal states of d-wave superconductors, Adhikari disputes the use of the BCS gap equation for d{sub x{sup 2}{minus}y{sup 2}}+e{sup i{theta}}d{sub xy} superconductors for the case of {theta}=0 in Haranath Ghosh, Phys. Rev. B 59, 3357 (1999). We emphasize in this reply that such a conclusion is based on unphysical arguments. The results of Haranath Ghosh and conclusions are correct and to the point.
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Title: Time-reversal symmetry-breaking superconductivity in epitaxial bismuth/nickel bilayers

Abstract

Citation Formats

Role of Spin in Quasiparticle Interference journal, November 2004

Role of Spin in Quasiparticle Interference
journal, November 2004