2013/10/03 by Jason Cornelius Pillay, Keola Wierschem, Pinaki Sengupta
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.88.054416
published as Physical Review B 88, 054416 (2013) · 7 pages, 5 figures, updated and extended version of arXiv:cond-mat/0307746
arxiv created 2013/10/03 · arxiv updated 2013/10/04
The zero and finite temperature spin-Peierls transitions in a quasi-one-dimensional spin-1/2 Heisenberg model coupled to adiabatic bond phonons is investigated using the Stochastic Series Expansion (SSE) Quantum Monte Carlo (QMC) method. The quantum phase transition from a gapless Neel state to a spin-gapped Peierls state is studied in the parameter space spanned by spatial anisotropy, inter-chain coupling strength and spin-lattice coupling strength. It is found that for any finite inter-chain coupling, the transition to a dimerized Peierls ground state only occurs when the spin-lattice coupling exceeds a finite, non-zero critical value. This is in contrast to the pure 1D model (zero inter-chain coupling), where adiabatic/classical phonons lead to a dimerized ground state for any non-zero spin-phonon interaction. The phase diagram in the parameter space shows that for a strong inter-chain coupling, the relation between the inter-chain coupling and the critical value of the spin-phonon interaction is linear whereas for weak inter-chain coupling, this behavior is found to have a natural logarithm-like relation. No region was found to have a long range magnetic order and dimerization occurring simultaneously. Instead, the Neel state order vanishes simultaneously with the setting in of the spin-Peierls state. For the thermal phase transition, a continuous heat capacity with a peak at the critical temperature, Tc, shows a second order phase transition. The variation of the equilibrium bond length distortion, δeq, with temperature showed a power law relation which decayed to zero as the temperature was increased to Tc, indicating a continuous transition from the dimerized phase to a paramagnetic phase with uniform bond length and zero antiferromagnetic susceptibility.