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

The heat capacity of La_2-x{Ba}ₓCuO₄ was investigated between 0.8 and 10 K. The linear temperature term {γ}T 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 K² in the superconducting region of x{≥}0.05. The correlation between magnetic order and vanishing {γ}T term and the existence of a finite {γ}T term for Ba doping give support to the resonating-valence-bond picture.