SPECIFIC HEAT AND SUPERCONDUCTIVITY OF LA-GE SYSTEM

The low temperature specific heat of orthorohmbically distorted Cc-type La-Ge compounds have been measured in order to investigate the origin of an anomalously small specific heat jump, (ΔC/γT)T=Tc of LaGe2 at the superconducting transition temperature. LaGex has orthorohmbically distorted Cc-type crystal structure in the composition range 2.0≤ x≤1.78. For 2.0≤ × ≤1.85, (ΔC/γT)T=Tc is anomalously small as in LaGe2. (ΔC/γT)T=Tc approaches the B.C.S. value at x =1.78. In the intermediate range, 1.85< × <1.78, there appears two close specific heat jumps as if samples were of two-phase crystal structure. According to the detailed X-ray study of the crystal structure these curious behaviour of (ΔC/γT)T=Tc seems to be due to some intrinsic origin and a possible model is discussed. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.