Hall effect in superconducting Fe(Se0.5Te0.5) thin films

The Hall effect is investigated for eight superconducting Fe(Se0.5Te0.5) thin films grown on MgO and LaSrAlO4 substrates with different transition temperatures (T-c). The normal Hall coefficients (R-H) have positive values with magnitude of 1 similar to 1.5 x 10(-3) cm(3)/C at room temperature for the all samples. With decreasing temperature, we find two characteristic types of behavior in R-H(T) depending on T-c. For thin films with lower T-c (typically T-c < 5 K), R-H start decreasing approximately below T=250 K toward a negative side, some of which shows sign reversal at T=50 similar to 60 K, but turns positive toward T=0 K. On the other hand, for the films with higher T-c (typically T-c > 9 K), R-H leaves almost unchanged down to T approximate to 100 K, and then starts decreasing toward a negative side. Around the temperatures when R-H changes its sign from positive to negative, obvious nonlinearity is observed in the field-dependence of Hall resistance as to keep the low-field R-H positive while the high-field R-H negative. Thus, the electronic state just above T-c is characterized by n(e) (electron density) > n(h) (hole density) with keeping mu(e) < mu(h). These results suggest the dominance of electron density to the hole density is an essential factor for the occurrence of superconductivity in Fe-chalcogenide superconductors.