Magnetic Resonance in Electron-doped Cuprate Superconductors
In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations. In high-transition temperature copper oxides superconductors it is generally believed that magnetic excitations play the fundamental role in the superconducting mechanism because superconductivity occurs when mobile carriers are doped into the antiferromagnetic parent compounds. Indeed, a sharp magnetic excitation termed "resonance" has been observed by neutron scattering in a number of hole-doped materials. The resonance is intimately related to superconductivity and its interaction with the mobile carriers observed by photoemission, optical conductivity, and tunneling suggests a similar role to lattice vibrations in conventional superconductors. However, the relevance of the resonance to high-Tc superconductivity has been in doubt because so far it has been found only in the hole-doped class of high-TC materials. We have recently discovered the resonance in the electron-doped class of superconductors, for the material Pr0.88LaCe0.12CuO4-d (Tc=24 K). The resonance energy (Er) is found to obey the universal relation Er=5.8kBTc for all high-Tc superconductors irrespective of carrier type (see Figure). These results unify our understanding of copper oxide superconductors and demonstrate that the resonance is a fundamental property of the superconducting copper oxides.
Complete details can be found in:
Resonance in the Electron-doped high TC Superconductor Pr0.88LaCe0.12CuO4-y, S. D. Wilson, P. Dai, S. Li, S. Chi, H. J. Kang, and J. W. Lynn, Nature 442, 59 (2006).
See also, Antiferromagnetic Order as the Competing Ground State in Electron Doped Nd1.85Ce0.15CuO4, H. J. Kang, P. Dai, J. W. Lynn, M. Matsuura, J. R. Thompson, S-C. Zhang, D. N. Argyriou, Y. Onose, and Y. Tokura, Nature 423, 522 (2003).
Quantum Spin Correlations through the Superconducting-to-normal Phase Transition in Electron-doped Superconducting Pr0.88LaCe0.12CuO4-δ, Stephen D. Wilson, Shiliang Li, Jun Zhao, Gang Mu, Hai-hu Wen, Jeffrey W. Lynn, Paul G. Freeman, Louis-Pierre Regnault, Klaus Habicht, Pengcheng Dai, Proceedings of the National Academy of Sciences 104, 15259 (2007).
Impact of Oxygen Annealing on the Heat Capacity and Magnetic Resonance of Superconducting Pr0.88LaCe0.12CuO4-y, S. Li, S. Chi, J. Zhao, H.-H. Wen, M. B. Stone, J. W. Lynn, and P. Dai, Phys. Rev. B78, 014520 (2008).