title: Exponential temperature dependence of the penetration depth in single crystal MgB2.
abstract: The temperature dependence of the London penetration depth, lambda(T), was measured in both single crystal and polycrystalline MgB2 samples by a high-resolution, radio frequency technique. A clear exponential temperature dependence of lambda(T) was observed at low temperature, indicating s-wave pairing. A BCS fit to the lowest temperature data gives an in-plane energy gap Delta of 30+/-2 K (2Delta/T(c) = 1.5+/-0.1), which is significantly smaller than the standard BCS weak coupling value of 3.5. We find that the data are best described by a two-gap model.
authors.affiliation: H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England.
authors.forename: F
authors.initials: F
authors.lastname: Manzano
authors.forename: A
authors.initials: A
authors.lastname: Carrington
authors.forename: N E
authors.initials: NE
authors.lastname: Hussey
authors.forename: S
authors.initials: S
authors.lastname: Lee
authors.forename: A
authors.initials: A
authors.lastname: Yamamoto
authors.forename: S
authors.initials: S
authors.lastname: Tajima