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and 10% of ρ$_{n}$ ( T, H )( T$_{c,zero}$ ) in low fields. The normal- state resistivity ρ$_{n,ab}$ ( H, T ) was determined by linearly extrapolating the normal-state behavior above the onset of superconductivity transition in ρ$_{ab}$ ( T ) curves (same as for ρ$_{ab}$ ( H ) curves). Because the curves of µ$_{0}$H$_{c}$$_{2}$ ( T ) for all defined temperatures are almost linear except for µ$_{0}$H$_{c}$$_{2}$ ( T$_{c,zero}$ ) of Se-39 with slightly upturn cur- vature near 0 T, we use the linear fitting results at low field near T$_{c}$ as the slopes of µ$_{0}$H$_{c}$$_{2}$ ( T$_{c}$ ). This is shown by solid and dotted lines in Fig. 2 and the val- ues are listed in Table 1. According to the conven- tional one-band Werthamer-Helfand-Hohenberg (WHH) theory, which describes the orbital limited upper critical field of dirty type-II superconductors, 40 the µ$_{0}$H ∗ c $_{2}$(0) can be described by 

and the values corresponding to three defined tempera- tures are also listed in Table 1. 

The magnetic-field dependence of resistivity ρ$_{ab}$ ( H ) of Se-39 and Se-11 are presented in Fig. 3. It can be clearly seen that superconductivity is suppressed by increasing magnetic field at the same temperature and the transi- tion of ρ$_{ab}$ ( H ) curves are shifted to lower magnetic fields at higher measuring temperature. Comparing with Se- 11, the superconductivity of Se-39 still appears under field up to 35 T when temperature is below 1.47 K, in- dicating Se-39 has a higher µ$_{0}$H$_{c}$$_{2}$ (0) than Se-11 in both directions. 

Fig. 4 shows the temperature dependence of resistivity at high magnetic fields. For Se-11, the superconductivity above 0.3 K is suppressed at µ$_{0}$H =35 T, irrespective of the direction of field. However it still survives below 1.5 K for Se-39. This is consistent with the results of ρ$_{ab}$ ( H ) 

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measurement. The superconducting transition widths of both samples are only slightly broader even at 35 T. It indicates that the vortex-liquid state in Fe(Te,Se) is much narrow or even absent in both low field high temperature region and high field low temperature region. On the other hand, the ρ$_{ab}$ ( T ) curves for H ‖ c and H ‖ ab approach each other gradually with increasing filed. This trend is more pronounced for Se-11 sample. The anisotropy of upper critical field is decreasing with increasing field. 

By combining the magnetotransport results in low and high magnetic fields we show phase diagrams in Fig. 5. Both samples show linear increase in µ$_{0}$H$_{c}$$_{2}$ ( T ) with de- creasing temperature near T$_{c}$ . For Se-11 there is a sat- uration trend at temperatures far below T$_{c}$ irrespective of field direction. It can also be seen clearly that the µ$_{0}$H$_{c}$$_{2}$ ( T ) of Se-39 is higher than that of Se-11 for both field directions. Data above 35 T were extracted by lin- ear extrapolation of ρ$_{ab}$ ( H ) at µ$_{0}$H < 35 T to ρ$_{ab}$ ( H ) =0.9 ρ$_{n,ab}$ ( T$_{c}$, H ). The upper critical fields from high magnetic field measurement are much smaller than those predicted using the conventional WHH model (Table 1), especially for H ‖ ab. 

In what follows we analyze the possible reasons for the deviation of µ$_{0}$H$_{c}$$_{2}$ (0) from the conventional WHH model. Only the µ$_{0}$H$_{c}$$_{2}$$_{,onset}$ ( T ) were chosen for further analysis. 18 , 41 In the conventional BCS model, orbital ef- fect arising from the Lorentz force acting on paired elec- trons with opposite momenta is the main cause of pair breaking. The superconductivity is destroyed when the kinetic energy exceeds the condensation energy of the Cooper pairs. On the other hand, superconductivity can also be eliminated via breaking the singlet pair into un- bound triplet. In other words, the Pauli spin suscepti- bility energy exceeding the condensation energy leads to the partial alignment of the spins. This is spin Zeeman effect, also called spin-paramagnetic effect. The effects of Pauli spin paramagnetism and spin-orbit interaction were included in the WHH theory through the Maki parame- ters α and λ$_{so}$ . 42 For an isotropic type-II superconductor in the dirty limit, µ$_{0}$H$_{c}$$_{2}$ ( T ) can be calculated using the 

## IV. DISCUSSION 

