NMR study of spin ladder compound (CPA)2CuBr4

Abstract We performed a nuclear magnetic resonance experiment on 1 H in ( CPA ) 2 CuBr 4 ( CPA = cyclopentylammonium ) which is considered as two-leg spin ladder system antiferromagnetic compound. Applied field range up to 8.7 T covers the critical field H c ( = 1.7 T ) where the energy gap disappears. In the field range H H c , the nuclear spin-lattice relaxation rate T 1 - 1 showed a thermal activation-type behavior, reflecting the presence of the finite spin gap at low temperature. As increasing the magnetic field across the H c , the temperature dependence of T 1 - 1 gradually changed from the thermal activation-type to the power-law type in the temperature range between 5 and 2 K. Further, we found a maximum of T 1 - 1 around 2 K for H > H c .