Mesoscopic superconductivity and high spin polarization coexisting at metallic point contacts on Weyl semimetal TaAs

A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics.

[1]  Y. Tokura,et al.  Detection of Berry’s Phase in a Bulk Rashba Semiconductor , 2013, Science.

[2]  C. Felser,et al.  Chiral Weyl Pockets and Fermi Surface Topology of the Weyl Semimetal TaAs. , 2016, Physical review letters.

[3]  Sirshendu Gayen,et al.  Comment on "Tip induced unconventional superconductivity on Weyl semimetal TaAs" [arXiv:1607.00513] , 2016, 1607.01405.

[4]  Su-Yang Xu,et al.  Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs. , 2015, Physical review letters.

[5]  Sirshendu Gayen,et al.  Unexpected superconductivity at nanoscale junctions made on the topological crystalline insulator Pb0.6Sn0.4Te , 2016, 1607.01609.

[6]  C. T. Chen,et al.  Growth and properties of strained VOx thin films with controlled stoichiometry , 2003, cond-mat/0301263.

[7]  Su-Yang Xu,et al.  Tantalum Monoarsenide: an Exotic Compensated Semimetal , 2015, 1502.00251.

[8]  L. C. Gupta,et al.  High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb , 2014, 1407.6179.

[9]  Su-Yang Xu,et al.  Electron scattering in tantalum monoarsenide , 2017, 1702.01245.

[10]  G. F. Chen,et al.  Experimental discovery of Weyl semimetal TaAs , 2015 .

[11]  Michael Tinkham,et al.  Introduction to Superconductivity , 1975 .

[12]  Observation of Weyl nodes in TaAs , 2015, 1503.09188.

[13]  L. Cohen,et al.  Possibilities and limitations of point-contact spectroscopy for measurements of spin polarization , 2005 .

[14]  Su-Yang Xu,et al.  Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP. , 2016, Physical review letters.

[15]  Yukio Tanaka,et al.  Symmetry and Topology in Superconductors –Odd-Frequency Pairing and Edge States– , 2011, 1105.4700.

[16]  Su-Yang Xu,et al.  Signatures of the Adler–Bell–Jackiw chiral anomaly in a Weyl fermion semimetal , 2016, Nature Communications.

[17]  Run‐Wei Li,et al.  Pure spin-Hall magnetoresistance in Rh/Y3Fe5O12 hybrid , 2015, Scientific Reports.

[18]  D. Shoenberg,et al.  Magnetic Oscillations in Metals , 1984 .

[19]  Xiong-Jun Liu,et al.  Discovery of tip induced unconventional superconductivity on Weyl semimetal. , 2016, Science bulletin.

[20]  Role of critical current on the point-contact Andreev reflection spectra between a normal metal and a superconductor , 2003, cond-mat/0311648.

[21]  X. Dai,et al.  Observation of the Chiral-Anomaly-Induced Negative Magnetoresistance in 3D Weyl Semimetal TaAs , 2015, 1503.01304.

[22]  X. Dai,et al.  Weyl Semimetal Phase in Noncentrosymmetric Transition-Metal Monophosphides , 2014, 1501.00060.

[23]  Sumathi Rao,et al.  Weyl semi-metals : a short review , 2016, 1603.02821.

[24]  I. I. Mazin.  How to Define and Calculate the Degree of Spin Polarization in Ferromagnets , 1999 .

[25]  Ashvin Vishwanath,et al.  Subject Areas : Strongly Correlated Materials A Viewpoint on : Topological semimetal and Fermi-arc surface states in the electronic structure of pyrochlore iridates , 2011 .

[26]  A. Ganguli,et al.  Unconventional superconductivity at mesoscopic point contacts on the 3D Dirac semimetal Cd3As2. , 2014, Nature materials.

[27]  T. M. Klapwijk,et al.  Transition from metallic to tunneling regimes in superconducting microconstrictions: Excess current, charge imbalance, and supercurrent conversion , 1982 .

[28]  Shuang Jia,et al.  Discovery of a Weyl fermion semimetal and topological Fermi arcs , 2015, Science.

[29]  Xiong-Jun Liu,et al.  Observation of superconductivity induced by a point contact on 3D Dirac semimetal Cd3As2 crystals. , 2015, Nature materials.

[30]  J. Moodera,et al.  Measuring the spin polarization of a metal with a superconducting point contact , 1998, Science.

[31]  C. Felser,et al.  Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP , 2015, Nature Physics.

[32]  Su-Yang Xu,et al.  A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class , 2015, Nature Communications.

[33]  A. Kandala,et al.  Giant anisotropic magnetoresistance in a quantum anomalous Hall insulator , 2015, Nature Communications.

[34]  T. Yokoyama,et al.  Topology of Andreev bound states with flat dispersion , 2011, 1102.1322.

[35]  Leon Balents,et al.  Weyl semimetal in a topological insulator multilayer. , 2011, Physical review letters.

[36]  I. Mazin,et al.  Andreev spectra and subgap bound states in multiband superconductors. , 2008, Physical review letters.

[37]  Su-Yang Xu,et al.  Experimental discovery of a topological Weyl semimetal state in TaP , 2015, Science Advances.

[38]  E. Parthé,et al.  The transposition structure of NbAs and of similar monophosphides and arsenides of niobium and tantalum , 1963 .

[39]  Xi Dai,et al.  Chern semimetal and the quantized anomalous Hall effect in HgCr2Se4. , 2011, Physical review letters.

[40]  C. Felser,et al.  Chiral Quasiparticles at the Fermi Surface of the Weyl Semimetal TaAs , 2016, 1603.08846.