Onset of the vortexlike Nernst signal above Tc in La2xSrxCuO4 and Bi2Sr2yLayCuO6

Yayu Wang, Z. A. Xu, T. Kakeshita, S. Uchida, S. Ono, Yoichi Ando, and N. P. Ong
Phys. Rev. B 64, 224519 – Published 21 November 2001
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Abstract

The diffusion of vortices down a thermal gradient produces a Josephson signal which is detected as a vortex Nernst effect. In a recent report by Xu et al. [Nature 406, 486 (2000)], an enhanced Nernst signal identified with vortex-like excitations was observed in a series of La2xSrxCuO4 (LSCO) crystals at temperatures 50–100 K above Tc. To pin down the onset temperature Tν of the vortexlike signal in the lightly doped regime (0.03<~x<~0.07), we have reanalyzed the carrier contribution to the Nernst signal in detail. By supplementing Nernst measurements with thermopower and Hall-angle data, we isolate the off-diagonal Peltier conductivity αxy and show that its profile provides an objective determination of Tν. With the results, we revise the phase diagram for the fluctuation regime in LSCO to accommodate the lightly doped regime. In the cuprate Bi2Sr2yLayCuO6, we find that the carrier contribution is virtually negligible for y in the range 0.4–0.6. The evidence of an extended temperature interval with vortexlike excitations is even stronger in this system. Finally, we discuss how Tν relates to the pseudogap temperature T* and the implications of strong fluctuations between the pseudogap state and the d-wave superconducting state.

  • Received 16 August 2001

DOI:https://doi.org/10.1103/PhysRevB.64.224519

©2001 American Physical Society

Authors & Affiliations

Yayu Wang1, Z. A. Xu1,*, T. Kakeshita2, S. Uchida2, S. Ono3, Yoichi Ando3, and N. P. Ong1

  • 1Joseph Henry Laboratories of Physics, Princeton University, Princeton, New Jersey 08544
  • 2School of Frontier Sciences, University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan
  • 3Central Research Institute of Electric Power Industry (CRIEPI), Komae, Tokyo 201-8511, Japan

  • *Present address of ZAX. Department of Physics, Zhejiang University, Hangzhou 310027, China.

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Vol. 64, Iss. 22 — 1 December 2001

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