Charge carrier dynamics of FeSe thin film investigated by terahertz magneto-optical spectroscopy

We performed terahertz magneto-optical spectroscopy of FeSe thin film to elucidate the charge carrier dynamics. The measured diagonal (longitudinal) and off-diagonal (Hall) conductivity spectra are well reproduced by a two-carrier Drude model, from which the carrier densities, scattering times, and effective masses of electron and hole carriers are determined in a wide range of temperature. The hole density decreases below the structural transition temperature while electron density increases, which is attributed to the band-structure modification in the electronic nematic phase. The scattering time of the hole carrier becomes substantially longer than that of the electron at lower temperature, which accounts for the increase of the positive dc Hall coefficient at low temperature.

Figure 1

(a) Temperature dependence of dc resistivity $\rho$ (red line) and $d\rho /dT$ (blue line) of the FeSe thin film. A kink anomaly at $T_{\mathrm{s}}$ is indicated by black arrow. Inset shows an enlarged view of the resistivity curve around $T_{\mathrm{c}}\sim 3$ K. (b) Schematic of our THz magnetospectroscopy. (c) Faraday rotation spectrum and (d) ellipticity spectrum induced by FeSe film at 7 K with the magnetic field of 7 T.

Figure 2

(a) Real- and (b) imaginary part of the longitudinal optical conductivity spectrum, and (c) real- and (d) imaginary part of the optical Hall conductivity spectrum, respectively, of FeSe at $T=7\mathrm{K}$ with $B=7\mathrm{T}$. Green open square represents experimental result, blue dashed, red dashed, and gray solid line indicate, respectively, the contribution of the hole carrier, electron carrier, and sum of them given by the two-carrier Drude fitting described in the text.

Figure 3

(a) Real- and (b) imaginary part of the optical Hall conductivity spectrum with various magnetic-field strength of 1–7 T. (c), (d) Magnetic-field dependence of calculated curves by the two-carrier Drude model. Dashed vertical lines indicate the spectral range of the experiment.

Figure 4

Temperature dependence of (a) real- and (b) imaginary part of the longitudinal optical conductivity, and (c) real- and (d) imaginary part of the optical Hall conductivity of FeSe thin film with $B=7\mathrm{T}$.

Figure 5

(a) Real- and (b) imaginary part of the longitudinal optical conductivity spectrum, and (c) real- and (d) imaginary part of the optical Hall conductivity spectrum, respectively, of FeSe at $T=140\mathrm{K}$ with $B=7\mathrm{T}$. Green open squares represent the experimental data. Blue dashed, red dashed, and black solid lines show, respectively, the contribution of the hole carrier, electron carrier, and sum of them given by the two-carrier Drude fitting.

Figure 6

Temperature dependence of (a) scattering times, (b) carrier densities, (c) mobilities of the electron and hole of FeSe thin film given by THz magnetospectroscopy. The structural transition temperature $T_{\mathrm{s}}$ is indicated by arrows. (d) Hall coefficient of FeSe thin film as a function of temperature, obtained by THz magnetospectroscopy (red circles) and dc transport measurement (gray line).