Superconducting properties of the ternary boride YRh4B4

Abstract

The low number of physical parameters for superconductivity has motivated researchers to perform bulk measurements in YRh4B4, discovered four decades ago, with superconducting transition temperature () of approximately 11 K. We performed electrical resistivity, magnetic susceptibility, and specific heat measurements to investigate the superconducting properties of the ternary borides YRh4B4 with CeCo4B4-type tetragonal structure. The nearly single-phase YRh4B4 had a moderately high of 10.6 K. The lower and upper critical fields were determined to be 1.5 and 32 kOe, respectively, by magnetic susceptibility and electrical resistivity measurements. The Ginzburg-Landau parameter was approximately 4.35, which is greater than , implying that YRh4B4 is a type-II superconductor. Because of specific heat measurements, the Debye temperature , , and 2 were determined to be 505 K, 1.56, and 3.91, respectively, where the specific heat jump at and the superconducting gap at 0 K are expressed by ΔC and . The electrical resistivity at low temperatures showed quadratic temperature dependence, and its coefficient A was determined to be 0.004426 µΩ· cm K−2, indicating a large density of states at Fermi energy. The electron-phonon coupling constant was derived to be 0.69. These results strongly suggest that YRh4B4 is a conventional s-wave superconductor described by the Bardeen–Cooper–Shriefer theory, and that the moderately high- in YRh4B4 is attributable to a high due to vibrations of boron with a light mass and a large A-value originating from the large density of states at Fermi energy. These results will facilitate microscopic investigations and provide clues to develop a novel high- metal superconductor.