Magnetic Field-Induced Phase Transitions in theS=1/2 Two-Leg Spin-Ladder Material Cu(DEP)Br2

Abstract

From heat capacity ( C p ) measurements on a single crystal sample of the spin ( S ) 1/2 two-leg spin-ladder material Cu(DEP)Br 2 above a critical magnetic field ( H c0 ) where the energy gap between the singlet ground state and the excited magnetic state closes, we have observed a peak anomaly, which is indicative of a magnetic long-range ordering. We have examined how the position of the anomaly in C p changes with temperature ( T ) and magnetic field ( H ) to obtain the experimental H – T phase diagram of this S =1/2 two-leg spin ladder material. From the low-temperature specific heat below H c0 , we have evaluated the field-dependent energy gap that vanishes at about 7.6 T.