Quantum spin excitations through the metal-to-insulator crossover in YBa2Cu3O6+y

Shiliang Li, Zahra Yamani, Hye Jung Kang, Kouji Segawa, Yoichi Ando, Xin Yao, H. A. Mook, and Pengcheng Dai
Phys. Rev. B 77, 014523 – Published 25 January 2008

Abstract

We use inelastic neutron scattering to study the temperature dependence of the spin excitations of a detwinned superconducting YBa2Cu3O6.45 (Tc=48K). In contrast to earlier work on YBa2Cu3O6.5 (Tc=58K), where the prominent features in the magnetic spectra consist of a sharp collective magnetic excitation termed “resonance” and a large (ω15meV) superconducting spin gap, we find that the spin excitations in YBa2Cu3O6.45 are gapless and have a much broader resonance. Our detailed mapping of magnetic scattering along the a*b*-axis directions at different energies reveals that spin excitations are unisotropic and consistent with the “hourglasslike” dispersion along the a*-axis direction near the resonance, but they are isotropic at lower energies. Since a fundamental change in the low-temperature normal state of YBa2Cu3O6+y when superconductivity is suppressed takes place at y0.5 with a metal-to-insulator crossover (MIC), where the ground state transforms from a metallic to an insulatinglike phase, our results suggest a clear connection between the large change in spin excitations and the MIC. The resonance therefore is a fundamental feature of metallic ground state superconductors and a consequence of high-Tc superconductivity.

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  • Received 2 November 2007

DOI:https://doi.org/10.1103/PhysRevB.77.014523

©2008 American Physical Society

Authors & Affiliations

Shiliang Li1,*, Zahra Yamani2, Hye Jung Kang3,4, Kouji Segawa5, Yoichi Ando6, Xin Yao7, H. A. Mook8, and Pengcheng Dai1,8,†

  • 1Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
  • 2Canadian Neutron Beam Centre, National Research Council, Chalk River Laboratories, Chalk River, Ontario K0J 1J0, Canada
  • 3NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA
  • 4Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-6393, USA
  • 5Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
  • 6Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
  • 7Department of Physics, Shanghai Jiaotong University, Shanghai 200030, People’s Republic of China
  • 8Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA

  • *slli@utk.edu
  • daip@ornl.gov

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Vol. 77, Iss. 1 — 1 January 2008

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