Superconductivity and electrical properties in single-crystalline ultrathin Nb films grown by molecular-beam epitaxy

K. Yoshii; H. Yamamoto; K. Saiki; A. Koma

doi:10.1103/PhysRevB.52.13570

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Superconductivity and electrical properties in single-crystalline ultrathin Nb films grown by molecular-beam epitaxy

K. Yoshii, H. Yamamoto, K. Saiki, A. Koma

DOI 10.1103/PhysRevB.52.13570 · Physical Review B

T1

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Abstract

High-quality superconducting ultrathin Nb films were grown on sapphire single-crystal substrates by molecular-beam epitaxy, of which thicknesses ranged from 1.2 to 9.0 nm. They were found to be single crystalline by reflection high-energy electron diffraction. Size effects appeared remarkably in the normal conduction range. Superconducting transition temperatures (Tc’s) of these films were higher than in the past reports for the same thicknesses. The thickness (d) dependence of Tc was ln[Tc(d)]∝-1/d, which could be explained in terms of the proximity effect. A theory of localization effects in two-dimensional superconductors by Maekawa and Fukuyama, on the other hand, could not be applied to the present experiments, since the prepared ultrathin films had better crystallinity than those discussed in the theory.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.13	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.84	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	6.99	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	6.3	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.4	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.83	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	3.9	Pressure not reported	onset
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.73	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.66	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.88	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.69	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.51	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	4.06	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.1	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.21	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.61	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.24	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	6.97	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.47	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.05	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	6.72	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	4.88	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	2.91	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.4	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	4.6	Pressure not reported	midpoint
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.79	Pressure not reported	midpoint