Pressure evolution of the normal- and superconducting-state properties of the line-nodal material CaSb2 revealed by Sb123 nuclear quadrupole resonance
H. Takahashi, S. Kitagawa, K. Ishida, A. Ikeda, S. R. Saha, S. Yonezawa, J. Paglione, Y. Maeno
DOI 10.1103/PhysRevB.109.L100501 · Physical Review B
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Abstract
CaSb2 is the Dirac line-nodal material that exhibits a superconducting (SC) transition at 1.7 K. In spite of its conventional SC state at ambient pressure, the transition temperature Tc shows a peak structure against hydrostatic pressure. We performed ac magnetic susceptibility and Sb123 nuclear quadrupole resonance (NQR) measurements on single-crystalline CaSb2 under pressures up to 2.08 GPa. Tc monotonically increased in this pressure region, which is consistent with a previous study. We observed continuous broadening of the NQR spectrum against pressure, which is a sign of unique compression behavior of the lattice. In the normal state, the nuclear spin-lattice relaxation rate 1/T1 is proportional to temperature in all pressure values, typical of a metal. However, 1/T1T in the normal state is independent of pressure, indicating that the density of states at the Fermi energy N(EF), which is one of the parameters governing Tc, is insensitive to pressure. From these results, we conclude that N(EF) does not govern the origin of the enhancement in Tc. This is unusual for a weak electron-phonon coupling superconductor. In the SC state, we revealed that the SC gap becomes larger and more isotropic under pressure.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| CaSb2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 1.7 | Pressure unresolved | onset |
| CaSb2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 1.7 | 1.68 GPa | onset |
| NaAlSi Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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