5 TABLE II. Superconducting parameters of Se-39 and Se-11 obtained from the analysis of µ$_{0}$H c 2 ,onset ( T ). µ$_{0}$H ∗ c $_{2}$(0), µ$_{0}$H p c $_{2}$(0) and µ$_{0}$H p (0) are the zero-temperature orbital, paramagnetically, and Pauli limited upper critical fields, respectively. α is the fitted Maki parameter ( λ so =0). ξ ab (0) and ξ c (0) are the ab-plane and c-axis zero-temperature coherence length calculated using µ$_{0}$H p c $_{2}$(0), respectively. µ$_{0}$H ∗ c 2 $_{,ab}$(0) µ$_{0}$H ∗ c 2 $_{,c}$(0) µ$_{0}$H p c 2 $_{,ab}$(0) µ$_{0}$H p c 2 $_{,c}$(0) µ$_{0}$H p,ab (0) µ$_{0}$H p,c (0) α$_{H}$$_{‖}$$_{ab}$ α$_{H}$$_{‖}$$_{c}$ ξ ab (0) ξ c (0) (T) (T) (T) (T) (T) (T) (nm) (nm) Fe$_{1}$$_{.}$$_{02(3)}$Te$_{0}$$_{.}$$_{61(4)}$Se$_{0}$$_{.}$$_{39(4)}$ 98.8 57.9 39.8 43.3 61.5 92.2 2.271 0.888 2.76 3.00 Fe$_{1}$$_{.}$$_{05(3)}$Te$_{0}$$_{.}$$_{89(2)}$Se$_{0}$$_{.}$$_{11(2)}$ 83.1 59.0 35.4 35.9 55.3 63.8 2.127 1.307 3.03 3.07 GLYPH<s48> GLYPH<s46>GLYPH<s48> GLYPH<s48> GLYPH<s46>GLYPH<s49> GLYPH<s48> GLYPH<s46>GLYPH<s50> GLYPH<s48> GLYPH<s46>GLYPH<s51> GLYPH<s48> GLYPH<s46>GLYPH<s52> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s48> GLYPH<s46>GLYPH<s54> GLYPH<s48> GLYPH<s46>GLYPH<s55> GLYPH<s48> GLYPH<s46>GLYPH<s48> GLYPH<s48> GLYPH<s46>GLYPH<s49> GLYPH<s48> GLYPH<s46>GLYPH<s50> GLYPH<s48> GLYPH<s46>GLYPH<s51> GLYPH<s48> GLYPH<s46>GLYPH<s52> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s48> GLYPH<s46>GLYPH<s54> GLYPH<s48> GLYPH<s46>GLYPH<s55> GLYPH<s48> GLYPH<s46>GLYPH<s48> GLYPH<s48> GLYPH<s46>GLYPH<s49> GLYPH<s48> GLYPH<s46>GLYPH<s50> GLYPH<s48> GLYPH<s46>GLYPH<s51> GLYPH<s48> GLYPH<s46>GLYPH<s52> GLYPH<s48> GLYPH<s46>GLYPH<s53> GLYPH<s48> GLYPH<s46>GLYPH<s54> GLYPH<s48> GLYPH<s46>GLYPH<s55> GLYPH<s48> GLYPH<s46>GLYPH<s56> GLYPH<s48> GLYPH<s46>GLYPH<s57> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s48> GLYPH<s46>GLYPH<s57> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s49> GLYPH<s46>GLYPH<s49> GLYPH<s49> GLYPH<s46>GLYPH<s50> GLYPH<s49> GLYPH<s46>GLYPH<s51> GLYPH<s49> GLYPH<s46>GLYPH<s52> GLYPH<s49> GLYPH<s46>GLYPH<s53> GLYPH<s49> GLYPH<s46>GLYPH<s54> GLYPH<s87> GLYPH<s72>GLYPH<s72> GLYPH<s61>GLYPH<s48>GLYPH<s44> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s72> GLYPH<s99> GLYPH<s61>GLYPH<s48>GLYPH<s46>GLYPH<s56>GLYPH<s56>GLYPH<s56>GLYPH<s44> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s72> GLYPH<s99> GLYPH<s50> GLYPH<s47>GLYPH<s91>GLYPH<s84> GLYPH<s99> GLYPH<s40>GLYPH<s45>GLYPH<s100> GLYPH<s72> GLYPH<s99> GLYPH<s50> GLYPH<s47>GLYPH<s100> GLYPH<s84> GLYPH<s41> GLYPH<s84> GLYPH<s99> GLYPH<s93> GLYPH<s72> GLYPH<s97>GLYPH<s98> GLYPH<s61>GLYPH<s50>GLYPH<s46>GLYPH<s50>GLYPH<s55>GLYPH<s49>GLYPH<s44> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s70>GLYPH<s101> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s50> GLYPH<s40>GLYPH<s51> GLYPH<s41> GLYPH<s84> GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s54> GLYPH<s49> GLYPH<s40>GLYPH<s52> GLYPH<s41> GLYPH<s83>GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s51> GLYPH<s57> GLYPH<s40>GLYPH<s52> GLYPH<s41> GLYPH<s40>GLYPH<s97> GLYPH<s41> GLYPH<s72> GLYPH<s99> GLYPH<s50> GLYPH<s47>GLYPH<s91>GLYPH<s84> GLYPH<s99> GLYPH<s40>GLYPH<s45>GLYPH<s100> GLYPH<s72> GLYPH<s99> GLYPH<s50> GLYPH<s47>GLYPH<s100> GLYPH<s84> GLYPH<s41> GLYPH<s84> GLYPH<s99> GLYPH<s93> GLYPH<s87> GLYPH<s72>GLYPH<s72> GLYPH<s61>GLYPH<s48>GLYPH<s44> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s72> GLYPH<s99> GLYPH<s61>GLYPH<s49>GLYPH<s46>GLYPH<s51>GLYPH<s48>GLYPH<s55>GLYPH<s44> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s32> GLYPH<s72> GLYPH<s97>GLYPH<s98> GLYPH<s61>GLYPH<s50>GLYPH<s46>GLYPH<s49>GLYPH<s50>GLYPH<s55>GLYPH<s44>GLYPH<s32> GLYPH<s115> GLYPH<s111> GLYPH<s61>GLYPH<s48> GLYPH<s70>GLYPH<s101> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s53> GLYPH<s40>GLYPH<s51> GLYPH<s41> GLYPH<s84> GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s56> GLYPH<s57> GLYPH<s40>GLYPH<s50> GLYPH<s41> GLYPH<s83>GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s49> GLYPH<s49> GLYPH<s40>GLYPH<s50> GLYPH<s41> GLYPH<s40>GLYPH<s98> GLYPH<s41> GLYPH<s116>GLYPH<s32>GLYPH<s40>GLYPH<s61> GLYPH<s84> GLYPH<s47>GLYPH<s84> GLYPH<s99> GLYPH<s41> GLYPH<s32>GLYPH<s40>GLYPH<s61> GLYPH<s72> GLYPH<s99> GLYPH<s50>GLYPH<s44>GLYPH<s97>GLYPH<s98> GLYPH<s47>GLYPH<s72> GLYPH<s99> GLYPH<s50>GLYPH<s44>GLYPH<s99> GLYPH<s41> GLYPH<s32> GLYPH<s32>GLYPH<s70>GLYPH<s101> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s50> GLYPH<s40>GLYPH<s51> GLYPH<s41> GLYPH<s84> GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s54> GLYPH<s49> GLYPH<s40>GLYPH<s52> GLYPH<s41> GLYPH<s83>GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s51> GLYPH<s57> GLYPH<s40>GLYPH<s52> GLYPH<s41> GLYPH<s32>GLYPH<s70>GLYPH<s101> GLYPH<s49> GLYPH<s46>GLYPH<s48> GLYPH<s53> GLYPH<s40>GLYPH<s51> GLYPH<s41> GLYPH<s84> GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s56> GLYPH<s57> GLYPH<s40>GLYPH<s50> GLYPH<s41> GLYPH<s83>GLYPH<s101> GLYPH<s48> GLYPH<s46>GLYPH<s49> GLYPH<s49> GLYPH<s40>GLYPH<s50> GLYPH<s41> GLYPH<s40>GLYPH<s99> GLYPH<s41> where η$_{Δ}$ describes the strong coupling intraband cor- rection for the gap, I is the Stoner factor I = N ( E$_{F}$ ) J , N ( E$_{F}$ ) is the electronic density of states (DOS) per spin at the Fermi level E$_{F}$ , J is an effective exchange integral, η$_{ib}$ is introduced to describe phenomenologically the ef- fect of the gap anisotropy, λ is electron – boson coupling constant and ε =0.5 or 1. It can be seen that µ$_{0}$H$_{p}$ (0) can decrease if the Stoner factor increases via enhance- ment of J or N ( E$_{F}$ ). Excess Fe in Fe(2) site with local magnetic moment could interact with itinerant electron in Fe layer, resulting in exchange enhanced Pauli para- magnetism or Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, thus enhancing J . Hence, higher content of excess Fe in Se-11, could lead to larger α$_{H}$$_{‖}$$_{c}$ than in Se-39. Another possibility may be that the N ( E$_{F}$ ) is de- creased with increasing the content of Se. 14 This trend will also enhance the Pauli limited field, i.e. suppress the spin-paramagnetic effect, according to above formula. This could be why the µ$_{0}$H$_{p}$ (0) of Se-39 is higher than that of Se-11 if we assume other parameters in eq. (6) are not changed. Finally, we discuss the anisotropy of µ$_{0}$H$_{c}$$_{2}$ ( T ). The temperature dependence of anisotropy of µ$_{0}$H$_{c}$$_{2}$ ( T ), γ (= H$_{c}$$_{2}$$_{,ab}$ ( T ) /H$_{c}$$_{2}$$_{,c}$ ( T )), obtained from the µ$_{0}$H$_{c}$$_{2}$$_{,onset}$ ( T ) data is shown in Fig. 6(c) as a function of reduced temperature t = T/T$_{c}$ . The γ of Se-11 is smaller than that of Se-39. The difference in γ between the two samples decreases gradually. Both γ values decrease to about 1 with decreasing temperature, larger than in Fe(Te,S) and similar to previously reported in Fe(Te,Se). 27 , 43 These results show that Fe(Te,Se) is a high-field isotropic superconductor. fore another effect must compete with disorder. This may be the effect of excess Fe in Fe(2) position. Excess Fe in Fe(2) position is the unique feature of 11-system, different from other Fe pnictide superconduc- tors. The Fe(2) has larger local magnetic moment than Fe(1) in Fe-(Te,Se) layers. The Fe(2) moment is present even if the SDW antiferromagnetic ordering of the Fe plane is suppressed by doping or pressure, contributing to N ( E$_{F}$ ). 16 According to the expression of µ$_{0}$H$_{p}$ (0) with strong coupling correction considering e-boson and e-e interaction: 41 , 46 , 47 In summary, the anisotropy in the upper critical field of Fe$_{1}$$_{.}$$_{02(3)}$Te$_{0}$$_{.}$$_{61(4)}$Se$_{0}$$_{.}$$_{39(4)}$ and Fe$_{1}$$_{.}$$_{05(3)}$Te$_{0}$$_{.}$$_{89(2)}$Se$_{0}$$_{.}$$_{11(2)}$ single crystals was studied in high and stable magnetic fields up to 35 T. It is found that the zero-temperature upper critical field is much smaller than the predicted result of WHH theory without the spin-paramagnetic ef- fect. The anisotropy of the upper critical field decreases with decreasing temperature, becoming nearly isotropic at low temperature. The spin-paramagnetic effect is the dominant pair-breaking mechanism for both of H ‖ ab and H ‖ c. V. CONCLUSION µ$_{0}$H$_{p}$ (0)=1 . 86(1 + λ ) $^{ε}$η$_{Δ}$ η$_{ib}$ (1 − I ) (6) FIG. 6. Normalized upper critical field h ∗ vs. reduced tem- perature t = T/T c for (a) Se-39 and (b) Se-11 for H ‖ ab (closed circle) and H ‖ c (open circle). Solid lines: WHH model with α =0, λ =0; Dotted and dash lines: fitted h $^{∗}$( t ) including spin- paramagnetic effect for H ‖ ab and H ‖ c, respectively. (c) The anisotropy in the upper critical field, γ = H c 2 ,ab ( T ) /H c 2 ,c ( T ), as a function of reduced temperature t = T/T c .