INFLUENCE OF PRESSURE ON THE SUPERCONDUCTING STATE OF RNI(2)B(2)C (R=Y, HO, ER, AND TM) COMPOUNDS

Measurements of the superconducting transition temperature T-c under hydrostatically applied pressure have been carried out on single-crystalline RNi(2)B(2)C (R=Y, Ho, Er, Tm) superconductors. YNi2B2C and ErNi2B2C exhibit peaks in T-c(P) centered at approximate to 0.52 GPa and approximate to 0.94 GPa with initial slopes of dT(c)/dP approximate to + 0.03 K/GPa and dT(c)/dP approximate to + 0.17 K/GPa, respectively. T-c(P) of HoNi2B2C and TmNi2B2C decreases in a nearly linear fashion with dT(c)/dP approximate to-0.25 K/GPa and -0.45 K/GPa, respectively. The discussion of the T-c(P) results focuses on the shape of the density of states near the Fermi level. The strong negative dT(c)/dP value (as well as the low T-c(P = 0)) of TmNi2B2C is attributed to the existence of magnetic correlations above T-c.