Degenerate Ground State in a Mesoscopic <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mrow><msub><mrow><mi>YBa</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow><mrow><msub><mrow><mi>Cu</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow><mi>O</mi></mrow><mrow><mn>7</mn><mo>−</mo><mi mathvariant="italic">x</mi></mrow></msub></mrow></math></span> Grain Boundary Josephson Junction

E. Il'ichev; M. Grajcar; R. Hlubina; R. P. J. IJsselsteijn; H. E. Hoenig; H.-G. Meyer; A. Golubov; M. H. S. Amin; A. M. Zagoskin; A. N. Omelyanchouk; M. Yu. Kupriyanov

doi:10.1103/PhysRevLett.86.5369

Degenerate Ground State in a Mesoscopic ${{YBa}_{2} {Cu}_{3} O}_{7 - x}$ Grain Boundary Josephson Junction

E. Il'ichev, M. Grajcar, R. Hlubina, R. P. J. IJsselsteijn, H. E. Hoenig, H.-G. Meyer, A. Golubov, M. H. S. Amin, A. M. Zagoskin, A. N. Omelyanchouk, and M. Yu. Kupriyanov

Phys. Rev. Lett. 86, 5369 – Published 4 June 2001

Abstract

We have measured the current-phase relationship $I (ϕ)$ of symmetric 45° ${YBa}_{2} {Cu}_{3} O_{7 - x}$ grain boundary Josephson junctions. Substantial deviations of the Josephson current from conventional tunnel-junction behavior have been observed: (i) The critical current exhibits, as a function of temperature $T$ , a local minimum at a temperature $T^{*}$ . (ii) At $T \approx T^{*}$ , the first harmonic of $I (ϕ)$ changes sign. (iii) For $T < T^{*}$ , the second harmonic of $I (ϕ)$ is comparable to the first harmonic, and (iv) the ground state of the junction becomes degenerate. The results are in good agreement with a microscopic model of Josephson junctions between $d$ -wave superconductors.

Received 22 February 2001

DOI:https://doi.org/10.1103/PhysRevLett.86.5369

Authors & Affiliations

E. Il'ichev¹, M. Grajcar^1,2, R. Hlubina², R. P. J. IJsselsteijn¹, H. E. Hoenig¹, H.-G. Meyer¹, A. Golubov³, M. H. S. Amin⁴, A. M. Zagoskin^4,5, A. N. Omelyanchouk^4,6, and M. Yu. Kupriyanov⁷

¹Department of Cryoelectronics, Institute for Physical High Technology, P.O. Box 100239, D-07702 Jena, Germany
²Department of Solid State Physics, Comenius University, Mlynská Dolina F2, 842 48 Bratislava, Slovakia
³Department of Applied Physics, University of Twente, 7500 AE Enschede, The Netherlands
⁴D-Wave Systems Inc., 320-1985 W. Broadway, Vancouver, British Columbia, Canada V6J 4Y3
⁵Physics and Astronomy Department, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia, Canada V6T 1Z1
⁶B. I. Verkin Institute for Low Temperature Physics and Engineering, 47 Lenin Avenue, 310 164 Kharkov, Ukraine
⁷Institute of Nuclear Physics, Moscow State University, 119 899 Moscow, Russia