Pressure dependence and non-universal effects of microscopic couplings on the spin-Peierls transition in CuGeO_3

TL;DR

This paper uses DMRG techniques to improve the understanding of the pressure dependence of the spin-Peierls transition in CuGeO_3, revealing non-universal effects of microscopic couplings beyond traditional theories.

Contribution

It introduces an exact numerical approach to study pressure effects on the spin-Peierls transition, highlighting the limitations of the adiabatic CF theory.

Findings

Pressure significantly affects the critical temperature.

The frustration parameter varies with pressure.

The spectral gap to transition temperature ratio is analyzed.

Abstract

The theory by Cross and Fisher (CF) is by now commonly accepted for the description of the spin-Peierls 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.