Superconductivity mediated by a soft phonon mode: Specific heat, resistivity, thermal expansion, and magnetization of YB6
R. Lortz, Y. Wang, U. Tutsch, S. Abe, C. Meingast, P. Popovich, W. Knafo, N. Shitsevalova, Yu. B. Paderno, A. Junod
DOI 10.1103/PhysRevB.73.024512 · Physical Review B
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Abstract
The superconductor YB6 has the second highest critical temperature Tc among the boride family MBn. We report measurements of the specific heat, resistivity, magnetic susceptibility, and thermal expansion from 2to300K, using a single crystal with Tc=7.2K. The superconducting gap is characteristic of medium-strong coupling. The specific heat, resistivity, and expansivity curves are deconvolved to yield approximations of the phonon density of states F(ω), the spectral electron-phonon scattering function αtr2F(ω), and the phonon density of states weighted by the frequency-dependent Grüneisen parameter γG(ω)F(ω), respectively. Lattice vibrations extend to high frequencies >100meV, but a dominant Einstein-like mode at ∼8meV, associated with the vibrations of yttrium ions in oversized boron cages, appears to provide most of the superconducting coupling and gives rise to an unusual temperature behavior of several observable quantities. A surface critical field Hc3 is also observed.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YB6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 7.2 | Pressure not reported | midpoint |
| YB6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 7.24 | Pressure not reported | midpoint |
| YB6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 7.13 | Pressure not reported | midpoint |
| YB6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 7.15 | Pressure not reported | midpoint |
| MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 40 | Pressure not reported | unknown |
| ZrB12 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 6 | Pressure not reported | unknown |
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