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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. 

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 

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 

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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 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 

