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

TL;DR

This study investigates the Hall effect in Fe(Se0.5Te0.5) thin films, revealing how the Hall coefficient's temperature dependence correlates with superconducting transition temperatures and indicating electron dominance as key for superconductivity.

Contribution

It provides new insights into the relationship between electronic transport properties and superconductivity in Fe-chalcogenide thin films, highlighting the role of electron and hole densities.

Findings

Hall coefficient varies with temperature depending on T_c.

Sign reversal in Hall resistance indicates electron dominance.

Electronic state above T_c_ characterized by n_e_ > n_h_.

Abstract

The Hall effect is investigated for eight superconducting Fe(Se_0.5_Te_0.5_) thin films grown on MgO and LaSrAlO_4_ substrates with different transition temperatures (T_c_). The normal Hall coefficients (R_H_) have positive values with magnitude of 1 - 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 - 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 = 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 occurence of superconductivity in Fe-chalcogenide superconductors.