Spin Fluctuations in the Underdoped High-T_c Cuprate La_<1.93>Sr_<0.07>CuO_4 : Condensed Matter: Electronic Properties, etc.

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We performed magnetic inelastic neutron-scattering experiments on La_<1.93>Sr_<0.07>CuO_4 over a wide range of ω and T; 2 ≤ ω ≤ 44 meV and 1.5 ≤ T < 300K. The dynamic susceptibility X"(q,ω) of this underdoped high-T_c. superconductor (T_c = 17K) is characterized by broad, incommensurate peaks. Here, the incommensurate wavevector δ_ω is approximately 0.07 reciprocal lattice units at low T and ω. The superconducting phase does not possess an observable gap in the spin excitation spectrum down to at least 2 meV. Scaling behavior is demonstrated for the Q-integrated energy spectrum X"(ω)_T with respect to (ω/k_BT). This scaling establishes a connnection between the magnetic excitations of the compositions on either side of the insulator-superconductor boundary in the La_<2-x>Sr_xCu0_4 phase diagram. We note a possible cross-over from an incommensurate to a commensurate response for ω> 20 meV or T > 300 K.
社団法人日本物理学会の論文
2001-03-15