TY - JOUR
T1 - Tunneling into high temperature superconductors
T2 - Andreev bound states and broken time-reversal symmetry
AU - Greene, L. H.
AU - Covington, M.
AU - Aprili, M.
AU - Paraoanu, E.
N1 - Funding Information:
Acknowledgements-We are grateful to J.A. Sauls for motivating this work, for many stimulating discussions and for a critical reading of this manuscript. We also acknowledge invaluable conversations with M. Fogelstrom, D. Ranier, R.B. Laughlin, A.J. Leggett, M.B. Weissman and M. Turlakov. The self-assembled monolayers used to form the insulating tunnel barrier were developed and applied by Professor C.A. Mirkin and his students F. Xu and J. Zhu. This research is supportedb y the National Science Foundation through the Science and Technology Center for Superconductivity (NSF-DMR 91-20000). Support is also received from NSF (DMR 94-21957) for EP and LHG.
PY - 1998/8/7
Y1 - 1998/8/7
N2 - Tunneling into high-temperature superconductors is shown to be a powerful spectroscopic probe of the unconventional superconducting state in YBa2Cu3O7 (YBCO). Planar tunneling is performed on low-leakage, ab-oriented YBCO/I/Cu junctions, where I is formed with a self-assembled organic monolayer. The reproducible dependence of the tunneling conductance on temperature, magnetic-field, doping and ion-induced disorder confirm that the zero-bias conductance peak (ZBCP) is an Andreev bound state, which arises directly from a d-wave order parameter. At temperatures below ∼8 K in zero applied magnetic field, the ZBCP splits, signifying a phase transition into a broken time-reversal symmetry state. An applied magnetic field induces further splitting that grows nonlinearly with increasing field. A theoretical model that invokes the formation of sub-dominant order parameter near the surface shows striking qualitative and quantitative agreement with our data.
AB - Tunneling into high-temperature superconductors is shown to be a powerful spectroscopic probe of the unconventional superconducting state in YBa2Cu3O7 (YBCO). Planar tunneling is performed on low-leakage, ab-oriented YBCO/I/Cu junctions, where I is formed with a self-assembled organic monolayer. The reproducible dependence of the tunneling conductance on temperature, magnetic-field, doping and ion-induced disorder confirm that the zero-bias conductance peak (ZBCP) is an Andreev bound state, which arises directly from a d-wave order parameter. At temperatures below ∼8 K in zero applied magnetic field, the ZBCP splits, signifying a phase transition into a broken time-reversal symmetry state. An applied magnetic field induces further splitting that grows nonlinearly with increasing field. A theoretical model that invokes the formation of sub-dominant order parameter near the surface shows striking qualitative and quantitative agreement with our data.
KW - A. high-T superconductors
KW - A. surfaces and interfaces
KW - A. thin films
KW - D. electronic transport
KW - D. tunnelling
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U2 - 10.1016/S0038-1098(98)00212-9
DO - 10.1016/S0038-1098(98)00212-9
M3 - Article
AN - SCOPUS:0032493541
SN - 0038-1098
VL - 107
SP - 649
EP - 656
JO - Solid State Communications
JF - Solid State Communications
IS - 11
ER -