Magnetic field effects on two-leg Heisenberg antiferromagnetic ladders: Thermodynamic properties

Abstract

Using the recently developed transfer-matrix renormalization group method, we have studied the thermodynamic properties of two-leg antiferromagnetic ladders in the magnetic field. Based on different behavior of magnetization, we found disordered spin liquid, Luttinger liquid, spin-polarized phases and a classical regime depending on magnetic field and temperature. Our calculations in Luttinger liquid regime suggest that both the divergence of the NMR relaxation rate and the anomalous specific heat behavior observed on Cu${}_2$(C${}_5$H${}_{12}$N${}_2$)${}_2$Cl${}_4$}are due to quasi-one-dimensional effect rather than three-dimensional ordering.

4 pages and 6 figures; some parts of the text has been revised in this version accepted by Phys. Rev. Lett