High Pressure Synthesis and Spin Gap of Quasi One Dimensional System Sr_n-1Cu_n+1O_2n(n=3, 5)

Abstract

SrCu₂O₃ and Sr₂Cu₃O₅ containing two-leg and three-leg S=1/2 ladders made of antiferromagnetic Cu-O-Cu linear bonds, respectively, were synthesized at high pressure, and their crystallographic and magnetic properties were investigated. Susceptibility of the 2-leg ladder system, SrCu₂O₃, showed a thermal excitation from the nonmagnetic ground state with a large spin gap of 420 K, while Sr₂Cu₃O₅ containing 3-leg ladders had a finite susceptibility at the lowest temperature reflecting its gapless nature in the spin excitation spectrum. SrCu₂O₃ has thus been found to be the first 2-leg ladder compound having a well-defined spin gap.