DYNAMICAL PROPERTIES OF AN ANTIFERROMAGNET NEAR THE QUANTUM CRITICAL-POINT - APPLICATION TO LACUO2.5

LaCuO2.5 is composed of coupled, two-chain cuprate ladders. The interl adder coupling is very close to the value at the quantum critical poin t between spin liquid and antiferromagnetic (AF) ground states, and th e material shows AF order with a weak moment and low Neel temperature. For such a nearly critical AF we show the existence of a low-lying, l ongitudinal spin-fluctuation mode, and illustrate its possible observa tion in experiment. (C) 1998 Published by Elsevier Science B.V. All ri ghts reserved.