Pressure dependence and non-universal effects of microscopic couplings on the spin-Peierls transition in CuGeO₃

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, involving however a continuum approximation for the relevant response function. Using density matrix renormalization group (DMRG) techniques we are able to treat the spin system on the lattice exactly up to numerical inaccuracies. Thus we find the correct dependence of the equation of state on the spin-spin interaction constant which in the CF theory drops out completely. With respect to CuGeO₃ we focus on the pressure dependence of the critical temperature and analyze the ratio of the spectral gap and the transition temperature.