Linear temperature term of heat capacity in insulating and superconducting La-Ba-Cu-O systems

Abstract

The heat capacity of ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ba}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$ was investigated between 0.8 and 10 K. The linear temperature term γT of the heat capacity is absent in the antiferromagnetic-ordered region of x≤0.02. γ increases abruptly from x=0.02 to x=0.04 where the system is still insulating at low temperature, and seems to saturate at the order of 5 mJ/mol ${\mathrm{K}}^2$ in the superconducting region of x≥0.05. The correlation between magnetic order and vanishing γT term and the existence of a finite γT term for Ba doping give support to the resonating-valence-bond picture.