Detection of a coherent boson current in the normal state of a high-temperature superconductorYBa2Cu3Oyfilm patterned to micrometer-sized rings

The key to clarifying the mechanism of the appearance of high $T_c$ in the high-temperature superconductor seems to be related to the anomalous 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. Campuzano, T. Takahashi, M. Randeria, M. R. Norman, T. Mochiki, K. Kadowaki, and J. Giapintzakis, Nature (London) 382, 51 (1996); and T. Ito, K. Takenaka, and S. Uchida, Phys. Rev. Lett. 70, 3995 (1993)]. Related to this is the presence of Bose-electron-type species such as paired holes [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 species in the normal state of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y.$ The idea [L. P. Levy, G. Dolan, J. Dunsmuir, and H. Bouchiat, Phys. Rev. Lett. 64, 2074 (1990)] of having 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 ${\mathrm{YB}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ film. The sensitivity of our detection system is not high enough to detect fermions, but it is high enough for detecting coherent bosons if they exist. Oscillations with flux periods corresponding to $h/2e$ have been found at $T>Tc,$ even at temperatures 30 K or more above $T_c$ inserted in the patterned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ film, but have not been found in the patterned Au or Pd films. To explain the coherent current circulating in a ring with a circumference as long as 40 μm, presumably in the prestage to the superconducting stage, the possible coexistence of a minority of coherent bosons and a majority of incoherent bosons is discussed. The detection of minority coherent bosons in the background of a majority of incoherent species is possible in this method.