Observation of subkelvin superconductivity in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ thin films

We report an experimental observation of superconductivity in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ thin films without application of external pressure. The films under study were synthesized by magnetron sputtering. Surface studies suggest that the observed transport characteristics are related to the polycrystalline continuous part of the investigated films with a homogeneous distribution of elements and the Cd-to-As ratio close to stoichiometric ${\mathrm{Cd}}_3{\mathrm{As}}_2$. The latter is also supported by Raman spectra of the studied films where two pronounced peaks inherent to ${\mathrm{Cd}}_3{\mathrm{As}}_2$ were observed. The obtained x-ray diffraction patterns for studied films also correspond to the ${\mathrm{Cd}}_3{\mathrm{As}}_2$ lattice. The formation of a superconducting phase in the films under study is confirmed by the characteristic behavior of the temperature and the magnetic field dependence of the sample resistivity, as well as by the presence of pronounced zero-resistance plateaus in the $dV/dI$ characteristics. The corresponding $H_c\text{−}{T}_c$ plots reveal a clearly pronounced linear behavior within the intermediate temperature range, similar to that observed for bulk ${\mathrm{Cd}}_3{\mathrm{As}}_2$ and ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ films under pressure, suggesting the possibility of a nontrivial pairing in the films under investigation. We discuss a possible role of the sample inhomogeneities and crystal strains in the observed phenomena.

Figure 1

(a) SEM image of the sample C surface. Light regions correspond to large grains at the surface of continuous films. (b) EDX scan: Distribution of the Cd- and As-related peak amplitudes within a one-dimensional (1D) scan across a surface grain as illustrated above. The corresponding amplitudes decrease in the surface grain area due to the “shadowing” effect related to the 3D shape of a surface grain. The Cd-to-As ratio within the whole scanning area is close to stoichiometric ${\mathrm{Cd}}_3{\mathrm{As}}_2$. (c) Raman spectra for sample C (I) and reference ${\mathrm{Cd}}_3{\mathrm{As}}_2$ single crystal (II). (d) 3D visualization of the AFM image of the surface of sample C. (e) XRD pattern for sample A (magenta line, smoothed data). The obtained pattern corresponds to $\alpha$ and ${\alpha }^{\prime }$ modifications of the ${\mathrm{Cd}}_3{\mathrm{As}}_2$ lattice (see text).

Figure 2

(a) Temperature dependence of resistivity for sample A at various transverse magnetic fields. (b) Corresponding $H_c\text{−}{T}_c$ diagrams for the SC transition estimated as a resistance drop to $50\%$ (midpoint) and $90\%$ of the normal value. Fitting of experimental data by Eq. (1) is shown by the dashed line.

Figure 3

(a) Temperature dependence of resistivity for sample B at various longitudinal magnetic fields. (b) Corresponding $H_c\text{−}{T}_c$ diagrams for the SC transition (midpoint). Fitting of experimental data by Eq. (1) is shown by the dashed line.

Figure 4

(a) Differential resistance for sample C at various temperatures. (b) Corresponding temperature dependence of critical current $I_c$.

Figure 5

Low-field magnetoresistivity of sample C at various temperatures at (a) transverse and (b) longitudinal magnetic fields. (c) Corresponding $H_c\text{−}{T}_c$ diagrams for the SC transition.