Origin of the large magnetoresistance in the candidate chiral superconductor $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$

The intriguing electronic phase diagram involving charge density wave (CDW) transitions in the $\mathrm{Ta}{\mathrm{S}}_2$ system has been widely investigated over the past decade, especially for the $1T$ and $2H$ phases. $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$, regarded as the natural heterostructure that combines the characteristics of $1T$ and $2H\text{−}\mathrm{Ta}{\mathrm{S}}_2$, has also been the focus recently, due to the prospects for fundamental research and device applications. Here, we have systematically investigated the electrical transport properties of $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$ single crystals combined with the band structure calculations and found that the low-temperature phase of candidate chiral superconductor $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$ ($T_c\sim 3.5$ K) at normal state is not the simple CDW but exhibits a strong magnetic field dependence. The most significant result is the emergence of the large magnetoresistance (MR), which may originate from the high mobility of holes and partial compensation. In addition, the symmetry of MR under the low magnetic field has also changed significantly in $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$, which is closely related to the CDW structures formed in the $H$ layers at 22 K. The results are conducive to the understanding of the mechanism of MR appearing in layered CDW compounds, and the presence of MR in $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$ suggests the potential applications for functional devices in the future.

Figure 1

The crystal structures of (a) $1T$, (b) $2H$, and (c) $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$. The band structures of (d) $1T$, (e) $2H$, and (f) $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$. The colored lines refer to the bands passing through the Fermi surface. Fermi surfaces of (g) $1T$, (h) $2H$, and (i) $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$.

Figure 2

(a) The single crystal XRD pattern of $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$. The inset (left) presents the picture of the studied crystal, and the right inset shows the single crystal XRD patterns of $1T$ and $2H\text{−}\mathrm{Ta}{\mathrm{S}}_2$ and the corresponding pictures. (b) The powder XRD pattern of the crushed $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$ crystals measured at room temperature. (c) The temperature dependence of in-plane resistivity (${\rho }_{ab}$) of $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$, inset presents the enlargement of superconducting transition at the low temperature region. (d) ZFC and FC magnetic susceptibility of $4H_b\text{−}\mathrm{Ta}{\mathrm{S}}_2$ measured at $H=10$ Oe, perpendicular to the $ab$ plane. The inset shows the magnetic hysteresis loop at $T=2$ K.

Figure 3

The temperature dependence of (a) ${\rho }_{ab}$ /(c) ${\rho }_c$ at 0 T and 8 T, and the corresponding MR is displayed in (b)/(d). (e), (f) The field dependence of MR at different temperatures. (g) The angular dependent MR data under $H=0.1$ T at different temperatures around 22 K. (h) AMR with various magnetic fields at 22 K.

Figure 4

The field dependence of Hall resistivity ${\rho }_{yx}(H$) at (a) 320–100 K and (b) 50–10 K, respectively. (c) The temperature-dependent Hall coefficient $R_H$. The temperature dependence of (d) measured MR and (e) calculated MR based on the two-band model. The temperature-dependent (f) density of electrons/holes $n_e$/$n_h$, and (g) carrier mobility ${\mu }_e$/${\mu }_h$ (extracted from the multiband fitting of ${\sigma }_{xy}$ in Fig. S6).