Cu NMR Study in DCNQI-Cu System

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Abstract
Cu-NMR measurement was made to investigate the electronic property of the counterion site in (DMe-DCNQI) 2 Cu and (DMeO-DCNQI) 2 Cu where the metallic state is stabilized down to low- T , (DBr-DCNQI) 2 Cu which exhibits the Metal-Insulator (M-I) transition and partially deutrated (DMe-DCNQI- d 2 [1,1;0]) 2 Cu which experiences a re-entrant (M-I-M) transition. In the metallic state, the nuclear-spin-lattice relaxation rate, 63 (1/ T 1 ) is found to follow nearly T 1 T =const. law for all compounds except for (DMe-DCNQI) 2 Cu where ( T 1 T ) -1 is T-dependent above 100 K being scaled to the square of the d-spin part of the Knight shift, K 3d ( T ) 2 . From the analyses of 63 (1/ T 1 ), it is shown microscopically that the metallic state is usual, unaffected by the correlation effect among d -electrons. At the M-I transition, the value of 63 ( T 1 T ) -1 and the Knight shift both being T -independent change discontinuously without any clear enhancement in the metallic region. The Cu-NMR results suggest that the d -electron correlation effect does not play a primary role for the M-I transition.

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