Pressure dependence and non-universal effects of microscopic couplings on the spin-Peierls transition in CuGeO

Abstract

The theory by Cross and Fisher (CF) is by now commonly accepted for the description of the spinPeierls transition within an adiabatic approach. The dimerization susceptibility as the essential quantity, however, is approximated by means of a continuum description. Several important experimental observations can not be understood within this scope. Using density matrix renormalization group (DMRG) techniques we are able to treat the spin system exactly up to numerical inaccuracies. Thus we find the correct dependence of the equation of state on the spin-spin interaction constant J, still in an adiabatic approach. We focus on the pressure dependence of the critical temperature which is absent in the CF theory as the only energy scale with considerable pressure dependence is J which drops out completely. Comparing the theoretical findings to the experimentally measured pressure dependence of the spin-Peierls temperature we obtain information on the variation of the frustration parameter with pressure. Furthermore, the ratio of the spectral gap and the transition temperature is analyzed.

Magnetoelastic excitations in spin-Peierls systems

“…23 The prefactor 0 (k B T/J) is assumed constant in field theory but has been shown by Raupach et al using densitymatrix renormalization-group studies to be temperature dependent in the static case and for q z ϭ/c. 44 Recent numerical studies suggest that the approximate result Eq. ͑52͒ describes the exact dimer-dimer correlation function better when rescaling the energy as (q z ,)ϭ CF (q z ,g T ), where the scaling function g T depends on the NNN coupling FIG.…”

“…The amplitude of the potential is determined by 0 (k B T/J) of which the temperature dependence is shown in Ref. 44. It is enhanced for TϽJ/k B and appears to vanish for T→0 for J 2 ϭ0 while it might even diverge for J 2 /J у0.241.…”