Combined resistivity and Hall effect study on ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ single crystals

Electrical transport measurements are used to study the Rh-doped NaFeAs superconductor series with a focus on the tetragonal phase. The resistivity curvature has an anomalous temperature dependence evidencing in the phase diagram two crossover regions of changes in the scattering rate, the effective mass as well as of the charge carrier density. The first crossover region is directly connected to the structural transition and resembles the onset of resistivity anisotropy. The second crossover region can as well be deduced from the temperature-dependent Hall coefficient. A comparison to literature nuclear magnetic resonance data suggests this region to be connected with nematic fluctuations far above the tetragonal to orthorhombic phase transition.

Figure 1

Temperature dependence of the resistivity of the ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ single crystals, taken from Ref. [1]. For clarity, the data have been normalized with respect to their room temperature value and shifted. The solid lines which have been obtained from extrapolated linear fits to the high-temperature region $T\gtrsim 250$ K are guides to the eye.

Figure 2

Color-coded phase diagram of ${\mathrm{NaFe}}_{1-x}{T}_x$ with $T=\text{Co}$ and Rh. The curvature of the resistivity of the ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ single crystals is shown. Red marks a positive, yellow nearly no curvature, and blue a negative curvature of the resistivity data sets. The gray dotted lines are guides to the eye to mark the transition regions $T^{*1}$ and $T^{*2}$. The gray solid and green lines mark the phase transition temperatures from Ref. [1]. The gray open triangles mark the nematic transition temperature found by Ref. [11] by analyzing the resistivity anisotropy of detwinned ${\mathrm{NaFe}}_{1-y}{\mathrm{Co}}_y\mathrm{As}$ single crystals with the nominal Co-doping level $y$. The dark yellow triangles mark the same transition temperatures with $y$ rescaled to match vanishing of $T_S$ of our samples with $x\sim 0.017$. The half-open turquoise diamonds mark the $1/T_{1}T=0.22$ (sK)${}^{-1}$ data points from NMR measurements [17, 32] on ${\mathrm{NaFe}}_{1-x}{\mathrm{Co}}_x\mathrm{As}$ single crystals (see Discussion). The black squares mark the deviation temperature $T_{R_H}$ at which the Hall coefficient deviates from the high-temperature phenomenological fit.

Figure 3

Hall coefficient $R_H$ from the underdoped ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ crystals. The arrow marks the structural transition temperature $T_S$ from Ref. [1]. The inset shows the diagonal resistivity ${\rho }_{xy}$ in dependence of the absolute magnetic field of the $x=0.013$ underdoped sample.

Figure 4

Hall coefficient $R_H$ from the optimal and overdoped ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ crystals. The inset shows the diagonal resistivity ${\rho }_{xy}$ in dependence of the absolute magnetic field of the $x=0.018$ optimally doped sample.

Figure 5

The negative cotangent of the Hall angle ${\theta }_H$ for all ${\mathrm{NaFe}}_{1-x}{\mathrm{Rh}}_x\mathrm{As}$ single crystals in a semilogarithmic plot (a). On the right side (b)–(e), for selected compositions, the deviation from the high temperature fit by Eq. (1), plotted as $b=(cot{\theta }_H-a)/T^{\beta }$. The fit range was chosen as $T\ge 100$ K. $T_{R_H}$ marks the temperature where the data points deviate from the high-temperature fit.