DETECTION OF A COHERENT BOSON CURRENT IN THE NORMAL-STATE OF A HIGH-TEMPERATURE SUPERCONDUCTOR YBA2CU3OY FILM PATTERNED TO MICROMETER-SIZEDRINGS

The key to clarifying the mechanism of the appearance of high T-c in t he high-temperature superconductor seems to be related to the anomalou s properties in its normal state [H. Yasuoka, S. Kambe, Y. Itoh, and T . Machi, Physica B 199-200, 278 (1994); H. Ding T. Yokoya, J. C. Campu zano, T. Takahashi, hi. Randeria, M. R. Norman, T. Mochiki, K. Kadowak i, and J. Giapintzakis, Nature (London) 382, 51 (1996); and T. Ito, K. Takenaka, and S. Uchida, Phys. Rev. Lett. 70, 3995 (1993)]. Related t o this is the presence of Bose-electron-type species such as paired ho les [V. J. Emery and S. A. Kivelson, Nature (London) 374, 434 (1995)] and holons [P. W. Anderson, G. Bakaran, Z. Zou, and T. Hsu, Phys. Rev. Lett. 58, 2790 (1987)] in the normal state which has been proposed by theoreticians. We have succeeded in detecting the coherent Bose speci es in the normal state of YBa2Cu3Oy,. The idea [L. P. Levy, G. Dolan, J. Dunsmuir, and H. Bouchiat, Phys. Rev. Lett. 64, 2074 (1990)] of hav ing the detected oscillation of a fermion persisting current caused by the Aharanov-Bohm effect on magnetic field scanning in the assemblage of the mesoscopic rings of metal was employed in the assemblage of a ring patterned in the YB2Cu3Oy film. The sensitivity of our detection system is not high enough to detect fermions, but it is high enough fo r detecting coherent bosons if they exist. Oscillations with flux peri ods corresponding to h/2e have been found at T > Tc, even at temperatu res 30 K or more above T-c inserted in the patterned YBa2Cu3Oy, film, but have not been found in the patterned Au or Pd films. To explain th e coherent current circulating in a ring with a circumference as long as 40 mu m, presumably in the prestage to the superconducting stage, t he possible coexistence of a minority of coherent bosons and a majorit y of incoherent bosons is discussed. The detection of minority coheren t bosons in the background of a majority of incoherent species is poss ible in this method. [S0163-1829(98)08129-6].