Specific-heat analysis of rare-earth transition-metal borocarbides: An estimation of the electron-phonon coupling strength

Journal Article · Fri Dec 01 00:00:00 EST 1995 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.52.16165· OSTI ID:147775

Michor, H; Holubar, T; Dusek, C; Hilscher, G ^[1]

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1. Institut fuer Experimentalphysik, Technische Universitaet Wien, Wiedner Hauptstrasse 8-10, A-1040 Wien (Austria)

We analyzed the superconducting and normal-state heat capacity of superconducting YNi{sub 2}B{sub 2}C, LuNi{sub 2}B{sub 2}C, LaPt{sub 1.5}Au{sub 0.5}B{sub 2}C and the nonsuperconducting reference compounds LaNi{sub 2}B{sub 2}C, YCo{sub 2}B{sub 2}. The deviations of the thermodynamic ratios as {Delta}{ital C}/{gamma}{ital T}{sub {ital c}}, {gamma}{ital T}{sup 2}{sub {ital c}}/{ital H}{sup 2}{sub {ital c}}(0), {ital H}{sub {ital c}}{sup {prime}}({ital T}{sub {ital c}})/{ital T}{sub {ital c}}{ital H}{sub {ital c}}(0), and {Delta}(0)/{ital k}{sub B}{ital T}{sub {ital c}} from their BCS values give an estimate for the strong-coupling parameter {ital T}{sub {ital c}}/{omega}{sub ln } which is in the range of 0.06--0.1 and indicates that the phonon mediated superconductivity can be classified in the moderately strong-coupling limit. From the normal-state specific heat between 2 and 300 K we constructed model phonon spectra to determine the moments of the phonon density of states {ital F}({omega}) and calculated the electron-phonon enhancement factor {lambda} with the Allen and Dynes formula which yields {lambda} values in the range of 0.95--1.15 for the three superconducting compounds. The comparison of these {lambda} values with the electron mass enhancement derived from the ratio of the Sommerfeld parameter {gamma} and the calculated density of states at the Fermi level, {ital N}({ital E}{sub {ital F}}), shows that band structure calculations overestimate {ital N}({ital E}{sub {ital F}}). Furthermore we determined the upper critical field {ital H}{sub {ital c}2}({ital T}) from specific-heat measurements up to 11 T and the normalized Ginzburg-Landau parameter {ital k}({ital T}) which both show BCS-type behavior for LaPt{sub 1.5}Au{sub 0.5}B{sub 2}C, but a significant upward curvature for YNi{sub 2}B{sub 2}C and especially for LuNi{sub 2}B{sub 2}C.

• OSTI ID: 147775
• Journal Information: Physical Review, B: Condensed Matter, Vol. 52, Issue 22; Other Information: PBD: 1 Dec 1995
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BORON CARBIDES
SPECIFIC HEAT
SUPERCONDUCTIVITY
NICKEL CARBIDES
PLATINUM CARBIDES
GOLD COMPOUNDS
YTTRIUM CARBIDES
LUTETIUM CARBIDES
LANTHANUM CARBIDES
ELECTRON-PHONON COUPLING
ELECTRONIC SPECIFIC HEAT
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0013-0065 K
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
BCS THEORY
CRITICAL FIELD