Evidence for multiple gaps in the specific heat of LiFeAs crystals

Abstract

The zero-field specific heat of LiFeAs was measured on several single crystals selected from a bulk sample. A sharp ⌬C p / T c anomaly Ϸ20 mJ/ mole K 2 was observed. The value appears to be between those of SmFeAs͑O 0.9 F 0.1 ͒ and ͑Ba 0.6 K 0.4 ͒Fe 2 As 2 but bears no clear correlation with their Sommerfeld coefficients. The electronic specific heat below T c further reveals a two-gap structure with the narrower one only on the order of 0.7 meV. While the results are in rough agreement with the H c1 ͑T͒ previously reported on both LiFeAs and ͑Ba 0.6 K 0.4 ͒Fe 2 As 2 , they are different from the published specific-heat data of a ͑Ba 0.6 K 0.4 ͒Fe 2 As 2 single crystal.

Strong-coupling superconductivity in NaFe1−xCoxAs: Validity of Eliashberg theory

“…(1) and (2). The thermodynamic properties of the Fe-based superconductors have been measured in many systems [10][11][12][13][14][15][16][17][18][19][20][21] . In Ba 0.6 K 0.4 Fe 2 As 2 , a calculation based on the Eliashberg model considering multiple bands is able to quantitatively reproduce the experimental results based on the assumption that spin fluctuations are electron pairing mediating bosons 13 .…”

Crossover from weak to strong pairing in unconventional superconductors

“…A closer look at the Fe-based superconductors reveals a wide spread of gap ratios, from weak BCS-like values in nonmagnetic LiFeAs [37][38][39][40][41][42] to twice larger values in high-T c ferropnictides with strong antiferromagnetic (AFM) correlations, such as optimally-doped Ba 1−x K x Fe 2 As 2 (BKFA) [15][16][17][43][44][45][46][47][48] or various 1111-compounds. 14,[49][50][51][52][53][54] We would like to emphasize that despite all the uncertainties in the published values, these differences are established beyond any doubt, as they have been confirmed by many complementary experiments, at least for several most studied materials (Table I).…”

“…Despite its relatively high T c , LiFeAs is characterized by weak coupling barely above the BCS limit, [37][38][39][40][41][42]80,81 possibly related to the absence of notable Fermi surface nesting in its band structure 37 or even a different pairing mechanism. 82,83 In NaFeAs, on the contrary, superconductivity with T c ≈ 10 K coexists with antiferromagnetism.…”

“…2, we compare the specific-heat-jump ratio reported in some Fe-based superconductors. 4,15,41,42,[88][89][90][91][92][93][94] For optimally doped BKFA with a relatively high value of T c , the ∆C /γ n T c ratio lies 75 % above the BCS limit. 15 It exceeds all other val- Table IV), as compared to the BCS prediction of 1.43.…”

Carrier contribution to the specific heat coefficient of Sr1−xKxFeWei1, Lv2, Chen3 et al. 2011Phys. Rev. BSelf Cite4110View full textAdd to dashboardCite

“…Both the ratio ΔC e /γ L T c ≈ 3 and the obvious kink, marked as A in the figure, around 6-8 K ≈ 0.2T c strongly suggest a two-gap structure similar to that of LiFeAs. 17 The same phonon baseline was then applied for all other samples. Bumps/dips up to 10 mJ/mol K 2 occasionally appear.…”