Contrasts in electron correlations and inelastic scattering between LiFeP and LiFeAs revealed by charge transport

By using high-quality single crystals, we quantitatively compare the transport properties between LiFeP and LiFeAs superconductors with compensated electron and hole carriers. The low-temperature resistivity follows the Fermi-liquid $A{T}^2$ dependence with a factor of $\sim 3$ difference in the coefficient $A$. This highlights weaker electron correlations in LiFeP, which is consistent with its $\sim 70$ times lower upper critical field than that of LiFeAs. Our analysis of the magnetotransport data indicates that in LiFeP, the electron carriers with lighter masses exhibit stronger temperature dependence of inelastic scattering rate than the holes, which is the opposite to the LiFeAs case. This stark difference in the band-dependent inelastic scattering may be relevant to the recently reported contrasting superconducting gap structures in these two superconductors.

Figure 1

In-plane resistivity ${\rho }_{xx}\left(T\right)$ in single crystals of (a) LiFeP and (b) LiFeAs at zero magnetic field. The insets show the expanded view plotted against $T^2$ at low temperatures. Also shown are the calculated Fermi surfaces of (c) LiFeP and (d) LiFeAs with the shades illustrating the magnitude of the Fermi velocity $v_F$.

Figure 2

Upper critical field $H_{c2}\left(T\right)$ curves in LiFeP (a) and LiFeAs (b) determined from the ${\rho }_{xx}\left(T\right)$ curves under the magnetic field applied parallel (insets) and perpendicular to the $c$ axis. For the determination of $H_{c2}\left(T\right)$, we used the midpoint of the resistive transition (big circles) as well as the resistive onset and the zero resistivity point (small circles). (c) $H_{c2}$ anisotropy ${\gamma }_{\xi }=H_{c2}(\perp c)/H_{c2}(\parallel c)={\xi }_{ab}/{\xi }_c$ as a function of temperature.

Figure 3

MR at different temperatures and the Kohler's plot in single crystals of (a) LiFeP and (b) LiFeAs. (c) $R_H\left(T\right)$ curves defined by the field derivative of the Hall resistivity $d{\rho }_{xy}/dH$ in the zero-field limit.[39] (d) Electron and hole carrier mobilities ${\mu }_e\left(T\right),{\mu }_h\left(T\right)$ in LiFeP and LiFeAs derived by using Eqs. (1) and (2). The crossing of the two curves in LiFeP at $T\approx 170$ K corresponds to the sign change of the Hall effect (c).