W0296

Magnetic Order and Superconductivity in Electron Doped Nd1.85Ce0.15CuO4. H.J. Kang¹, Pengcheng Dai^1,2, J.W. Lynn³, J.R. Thompson^1,2, Shou-Cheng Zhang⁴, Y. Onose⁵, and Y. Tokura ^5,6, ¹Dept. of Physics and Astronomy, Univ. of Tennessee, Knoxville, TN 37996, ²Solid State Div., Oak Ridge National Laboratory, Oak Ridge, TN 37831, ³NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, ⁴Dept. of Physics, McCullough Bldg., Stanford Univ., Stanford, CA 94305, ⁵Spin Superstructure Project, ERATO, Japan Science and Technology, Tsukuba 305-8562, Japan, Correlated Electron Research Center, Tsukuba 305-8562, Japan, ⁶Dept. of Applied Physics, Univ. of Tokyo, Tokyo13-8656, Japan.

High-transition-temperature (high-Tc) superconductivity in the copper oxides is a delicate phenomenon that competes with many other possible quantum ground states. Determining what the closest competing ground state is, and establishing if that state is universal amongst all high-Tc materials, will strongly constrain possible physical explanations for superconductivity. The competing ground state reveals itself when superconductivity is destroyed by application of a magnetic field, and antiferromagnetism has been theoretically predicted and observed in hole-doped materials upon application of modest fields. However, because none of these experiments probed the state where the upper critical field Bc₂ is reached, the quantum phase transition from the superconducting state to the antiferromagnetic state has never been experimentally observed. Here we report the first such example from transport and neutron scattering experiments on the electron-doped Nd_1.85Ce_0.15CuO₄, where Bc₂ is experimentally accessible. The applied field reveals a novel static, commensurate, insulating-like, long-range ordered antiferromagnetic state, in which the induced moment scales approximately linearly with the applied field and saturates at Bc₂. Our experiment therefore establishes antiferromagnetic order as the universal competing ground state in high-Tc copper oxides.