The low-temperature specific heat anomaly of the isotropic one-dimensional Heisenberg antiferromagnet (S=¹/₂) in a magnetic field

The specific heat of the isotropic S=1/2 Heisenberg antiferromagnetic chain is proportional to the temperature at low T. The proportionality constant gamma is a function of field. The authors show that the low-field limit is anomalous in the sense that lim_{H to 0}lim_{T to 0} gamma =(1+ square root e/ pi )/3 differs from lim_{T to 0}lim_{H to 0} gamma =²/₃. They also obtain an approximate interpolation formula between these two limits for situations in which H and T tend to zero simultaneously.