3 GLYPH<s48>GLYPH<s46>GLYPH<s54> GLYPH<s48>GLYPH<s46>GLYPH<s52> GLYPH<s48>GLYPH<s46>GLYPH<s50> GLYPH<s48>GLYPH<s46>GLYPH<s48> GLYPH<s32>GLYPH<s40> GLYPH<s109>GLYPH<s41> GLYPH<s53> GLYPH<s52> GLYPH<s51> GLYPH<s50> GLYPH<s49> GLYPH<s48> GLYPH<s32>GLYPH<s35>GLYPH<s50>GLYPH<s32>GLYPH<s79>GLYPH<s114>GLYPH<s105>GLYPH<s103>GLYPH<s105>GLYPH<s110>GLYPH<s97>GLYPH<s108>GLYPH<s32> GLYPH<s32>GLYPH<s112>GLYPH<s111>GLYPH<s119>GLYPH<s101>GLYPH<s114>GLYPH<s45>GLYPH<s108>GLYPH<s97>GLYPH<s119>GLYPH<s32>GLYPH<s102>GLYPH<s105>GLYPH<s116>GLYPH<s32>GLYPH<s102>GLYPH<s111>GLYPH<s114>GLYPH<s32>GLYPH<s35>GLYPH<s50> GLYPH<s32>GLYPH<s65>GLYPH<s108>GLYPH<s32>GLYPH<s99>GLYPH<s111>GLYPH<s97>GLYPH<s116>GLYPH<s101>GLYPH<s100>GLYPH<s32>GLYPH<s35>GLYPH<s50> GLYPH<s32>GLYPH<s115>GLYPH<s45>GLYPH<s119>GLYPH<s97>GLYPH<s118>GLYPH<s101>GLYPH<s32>GLYPH<s66>GLYPH<s67>GLYPH<s83>GLYPH<s32>GLYPH<s102>GLYPH<s105>GLYPH<s116>GLYPH<s32>GLYPH<s102>GLYPH<s111>GLYPH<s114>GLYPH<s32>GLYPH<s65>GLYPH<s108> GLYPH<s84>$_{GLYPH<s99>}$GLYPH<s32>GLYPH<s32>GLYPH<s111>GLYPH<s102>GLYPH<s32> GLYPH<s98>GLYPH<s117>GLYPH<s108>GLYPH<s107>GLYPH<s32>GLYPH<s65>GLYPH<s108> GLYPH<s40>GLYPH<s32>GLYPH<s49>GLYPH<s46>GLYPH<s50>GLYPH<s48>GLYPH<s32>GLYPH<s75>GLYPH<s32>GLYPH<s41> GLYPH<s84>$_{GLYPH<s99>}$GLYPH<s32>GLYPH<s32>GLYPH<s111>GLYPH<s102>GLYPH<s32>GLYPH<s102>GLYPH<s105>GLYPH<s108>GLYPH<s109>GLYPH<s32>GLYPH<s65>GLYPH<s108>GLYPH<s32> GLYPH<s40>GLYPH<s32>GLYPH<s49>GLYPH<s46>GLYPH<s52>GLYPH<s53>GLYPH<s32>GLYPH<s75>GLYPH<s32>GLYPH<s41> FIG. 4: (Color online) Effective penetration depth in single crystal Fe(Te,Se) before (blue circles) and after (red triangles) coating with an Al layer. The curve is shifted up according to Eq. (1) and the data are extrapolated to T = 0 using a T 2 fit resulting in λ (0) ≈ 560 ± 20 nm. FIG. 3: (Color online) Exponent n and pre-factor A obtained by fitting to Δ λ ( T ) ∝ AT n for various upper temperature limits shown on the x-axis. The exponents in the upper panel were obtained with n and A both being free parameters. In the lower panel, A was acquired with a fixed n . gives an estimate of λ (0) ≈ 560 ± 20 nm for the penetra- tion depth of Fe(Te,Se). More details on the method can be found in Ref. 16. The upper panel of Fig. 3 shows the exponent n , which (i) does not depend much on the selection of the upper limit of the fitting range, (2) is somewhat smaller in Fe(Te,S), n ≈ 1 . 8, than in Fe(Te,Se) n ≈ 2. The pre-factor A obtained from the fit does not depend much on the fitting range either. The superfluid density, ρ$_{s}$ ( T ) = λ $^{2}$(0) /λ $^{2}$( T ), shown in Fig. 5, exhibits a noticeable positive curvature at el- evated temperatures, similar to MgB$_{2}$[21]. This sug- gests a multi-gap superconductivity, which we analyze in the framework of the self-consistent γ − model [17]. Although this s − wave model cannot explain the power- law behavior at the lowest temperatures, it should pro- vide a reasonable description at elevated temperatures, ∼ T$_{c}$/ 3 < T < T$_{c}$ , for which effects of gap anisotropy are smeared. Fitting in the temperature range from 0 . 45 T$_{c}$ to T$_{c}$ , shown by a solid (red) line in Fig. 5, produces a good agreement with the data. To limit the number of the fitting parameters, the partial densities of states were chosen to be equal in the two bands, n$_{1}$ = 0 . 5, and the first intra-band coupling parameter, λ$_{1}$ = 0 . 5, was chosen to produce a correct T$_{c}$ ≈ 12 K assuming a Debye tem- perature of 400 K. The variation of λ$_{1}$ does not affect the fitting quality or relative ratios of the fitting parame- ters. The parameters obtained in the fit are: λ$_{2}$ = 0 . 347, λ$_{12}$ = 0 . 096 and γ = 0. This result means that ρ$_{s}$ ( T ) at temperatures of the order of T$_{c}$ is fully described by only one component, determined by the band with a smaller gap. The existence of the larger gap and small interband coupling, λ$_{12}$ , are needed, however, to maintain a high T$_{c}$ . The fit over the entire temperature range reveals a clear deviation from this clean exponential model at low temperatures. The new fitting parameters of λ$_{2}$ = 0 . 281, λ$_{12}$ = 0 . 117 and γ = 0 . 157 are close to the previous set, albeit with small, but finite γ indicating 16 % contribu- tion of the larger gap to the total superfluid density. The temperature dependent gaps obtained self-consistently in where λ is the unknown penetration depth to be deter- mined. Figure 4 shows the measured λ$_{eff}$ ( T ) that is com- pared to the data without Al coating. The negative offset of 0.05 µ m accounts for the thickness of the Al layer and λ$_{Al}$ ( T ≪ T Al c ). According to Eq. (1), data plotted this way give the actual λ ( T ) and its extrapolation to T = 0 To calculate the superfluid density, we need to know the absolute value of the penetration depth, λ (0). We used the technique described in Ref. 16. A thin alu- minum layer was deposited using magnetron sputtering conducted in an argon atmosphere. The Al layer thick- ness, t = 100 ± 10 nm, was determined by using an Inficon XTC 2 with a 6 MHz gold quartz crystal and later di- rectly measured by using scanning electron microscopy on the edge of a broken sample. By measuring the fre- quency shift from T ≪ T Al c to T > T Al c and converting it into the effective penetration depth of the coated sam- ple, λ$_{eff}$ , one can extract the full penetration depth of the material under study from λ$_{eff}$ = λ$_{Al}$ λ + λ$_{Al}$ tanh ( t/λ$_{Al}$ ) λ$_{Al}$ + λ tanh ( t/λ$_{Al}$ ) (1)