The in-plane London penetration depth, λ (T), was measured in single crystals of the iron-chalcogenide superconductors Fe1.03 (Te 0.63 Se0.37) and Fe1.06 (Te0.88 S0.14) by using a radio-frequency tunnel diode resonator. Similar to the iron-arsenides and in stark contrast to the iron-phosphides, iron-chalcogenides exhibit a nearly quadratic temperature variation of λ (T) at low temperatures. The absolute value of the penetration depth in the T→0 limit was determined for Fe1.03 (Te0.63 Se 0.37) by using an Al coating technique, giving λ (0) 560±20 nm. The superfluid density ρs (T) = λ2 (0) / λ2 (T) was fitted with a self-consistent two-gap γ model. While two different gaps are needed to describe the full-range temperature variation in ρs (T), a nonexponential low-temperature behavior requires pair-breaking scattering, and therefore an unconventional (e.g., s± or nodal) order parameter.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 10 2010|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics