Néel to spin-Peierls transition in a quasi-one-dimensional Heisenberg model coupled to bond phonons

Jason Cornelius Pillay, Keola Wierschem, and Pinaki Sengupta
Phys. Rev. B 88, 054416 – Published 22 August 2013

Abstract

The zero and finite temperature spin-Peierls transitions in a quasi-one-dimensional spin-12 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 Néel state to a spin-gapped Peierls state is studied in the parameter space spanned by spatial anisotropy, interchain coupling strength, and spin-lattice coupling strength. It is found that for any finite interchain coupling, the transition to a dimerized Peierls ground state only occurs when the spin-lattice coupling exceeds a finite, nonzero critical value. This is in contrast to the pure 1D model (zero interchain coupling), where adiabatic/classical phonons lead to a dimerized ground state for any nonzero spin-phonon interaction. The phase diagram in the parameter space shows that for a strong interchain coupling, the relation between the interchain coupling and the critical value of the spin-phonon interaction is linear whereas for weak interchain coupling, this behavior is found to have a natural logarithmlike relation. No region was found to have a long range magnetic order and dimerization occurring simultaneously. Instead, the Néel 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.

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  • Received 11 April 2013

DOI:https://doi.org/10.1103/PhysRevB.88.054416

©2013 American Physical Society

Authors & Affiliations

Jason Cornelius Pillay, Keola Wierschem, and Pinaki Sengupta

  • School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371

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Issue

Vol. 88, Iss. 5 — 1 August 2013

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