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College Park, Maryland      June 6 - 10 , 2004

M4-A4 (4:45 PM): Novel Dynamic Scaling Regime in Hole-Doped Cuprates (Invited)

Ying Chen, Wei Bao (Los Alamos National Laboratory), J. E Lorenzo (Laboratoire de Cristallographie, CNRS, B.P. 166, 38042 Grenoble, France), Y. Qiu, S. Park (NIST Center for Neutron Research; University of Maryland, College Park), S.-H. Lee (NIST Center for Neutron Research), J. Sarrao (Los Alamos National Laboratory)

Only 3 % hole doping by Li is sufficient to suppress the long-range 3-dimensional antiferromagnetic order in La2CuO4, thus allowing experimental study of quantum spin dynamics of 2-dimensional (2D) spin liquid in a wide temperature range. The spin dynamics of such 2D quantum spin liquid was investigated with measurements of the dynamic magnetic structure factor S(ω,q), using cold neutron spectroscopy, for single crystalline La2Cu1-xLixO4 (x = 0.04, 0.06 and 0.1). The S(ω,q) peaks sharply at (π, π) for all these samples, suggesting that the (π, π) correlated dynamic spin clusters in Li-doped La2CuO4 have developed to substantial size below 150 K. Furthermore, S(ω,q) shows a crossover from the quantum critical (QC), ω/T scaling, at high temperatures to a novel low temperature regime characterized by a constant energy scale upon cooling, which is observed first time experimentally. The observed crossover possibly corresponds to the theoretically expected crossover from the QC to the quantum-disordered regime of the 2D Heisenberg antiferromagnetic spin liquid. Possible role played by doped holes in modifying spin fluctuation spectrum will be discussed.

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