High-mobility carriers induced by chemical doping in the candidate nodal-line semimetal CaAgP

We report the electronic properties of single crystals of the candidate nodal-line semimetal CaAgP. The transport properties of CaAgP are understood within the framework of a hole-doped nodal-line semimetal. In contrast, Pd-doped CaAgP shows a drastic increase of magnetoresistance at low magnetic fields and a strong decrease of electrical resistivity at low temperatures probably due to weak antilocalization. Hall conductivity data indicated that the Pd-doped CaAgP has not only hole carriers induced by the Pd doping, but also high-mobility electron carriers in the proximity of the Dirac point. Electrical resistivity of Pd-doped CaAgP also showed a superconducting transition with onset temperature of $1.7-1.8\mathrm{K}$.

Figure 1

Electrical resistivity of single crystals of undoped and Pd-doped CaAgP and CaAgAs. (a) Temperature dependence of electrical resistivity. The inset shows the single crystals of the undoped (upper) and Pd-doped (lower) CaAgP. (b)−(e) Magnetic-field dependence of electrical resistivity for the undoped (b),(c) and Pd-doped (d),(e) CaAgP measured at various temperatures. Transverse and longitudinal magnetoresistances are shown in (b),(d) and (c),(e), respectively. (f) Magnetic-field orientation dependence of magnetoresistance for the Pd-doped CaAgP at 5 K. Angles of 0° and 90° correspond to the perpendicular and parallel directions relative to the electric current, respectively. In (b)−(f), the differences between electrical resistivity and zero-field resistivity are shown. (g) Temperature dependence of electrical resistivity for the Pd-doped CaAgP measured at various magnetic fields. The magnetic fields were applied perpendicular to the electric current. (h) Schematic pictures showing the directions of electric current and magnetic field. The left panel shows the cases of (b), (d), (g), and 0° in (f) and the right panel shows those of (c), (e), and 90° in (f).

Figure 2

(a),(b) Hall resistivity of undoped and Pd-doped CaAgP single crystals measured at various temperatures. In (a), the data taken at 10−200 K have been shifted upward for clarity. (c),(d) Carrier density and mobility of the undoped and Pd-doped CaAgP single crystals. The data of the undoped CaAgP were obtained by a linear fit of the Hall resistivity data, while those for Pd-doped one were obtained by fitting the Hall conductivity data shown in (e). (e) Hall conductivity of the Pd-doped CaAgP. The solid curves are the fitting results described in the main text. (f) Schematic pictures of the electronic states near $E_F$ in undoped and Pd-doped CaAgP.

Figure 3

Temperature dependences of electrical resistivity (a) and heat capacity (b) of the single crystals of Pd-doped CaAgP measured at various magnetic fields.