Chirality-Induced Spin-Polarized State of a Chiral Crystal ${\mathrm{CrNb}}_3{\mathrm{S}}_6$

Chirality-induced spin transport phenomena are investigated at room temperature without magnetic fields in a monoaxial chiral dichalcogenide ${\mathrm{CrNb}}_3{\mathrm{S}}_6$. We found that spin polarization occurs in these chiral bulk crystals under a charge current flowing along the principal $c$ axis. Such phenomena are detected as an inverse spin Hall signal which is induced on the detection electrode that absorbs polarized spin from the chiral crystal. The inverse response is observed when applying the charge current into the detection electrode. The signal sign reverses in the device with the opposite chirality. Furthermore, the spin signals are found over micrometer length scales in a nonlocal configuration. Such a robust generation and protection of the spin-polarized state is discussed based on a one-dimensional model with an antisymmetric spin-orbit coupling.

Figure 1

Schematics of a crystal structure of ${\mathrm{CrNb}}_3{\mathrm{S}}_6$ (a) and device design (b),(c), together with a scanning electron micrograph (top view) of the device fabricated on a ${\mathrm{SiO}}_2/\mathrm{Si}$ substrate (d). The device is made of a ${\mathrm{CrNb}}_3{\mathrm{S}}_6$ strip with a tungsten electrode at the center and gold electrodes beside. The $c$ axis of ${\mathrm{CrNb}}_3{\mathrm{S}}_6$ is indicated by a white arrow. An enlarged image on the upper right in (d) shows the area of the tungsten electrode edge, which is partially covered by the gold electrode.

Figure 2

A dataset and experimental setup of the EMC (a), direct CISS (b), and inverse CISS (c) measurements performed in the three ${\mathrm{CrNb}}_3{\mathrm{S}}_6$ devices with the tungsten electrode. The EMC signals taken at 150 K with sweeping the magnetic field are given in the normalized unit (${\mathrm{m}}^2/\mathrm{A}$) to see the EMC coefficient $\widehat{\gamma }$ in (a). Current-voltage CISS and ICISS characteristics at 300 K at 0 T are provided in (b) and (c), respectively. The slope values of the CISS and ICISS signals are $-1.35$ and $-1.05\mathrm{\Omega }$ for device 1, $-0.77$ and $-0.76\mathrm{\Omega }$ for 2, and 0.54 and $0.49\mathrm{\Omega }$ for 3, respectively.

Figure 3

A dataset and experimental setup of the EMC (a) and nonlocal CISS (b) measurements. The chirality distribution was examined by using the EMC data in the left, center, and right areas of device 2. The data for the center area are the same ones shown in Fig. 2. The nonlocal CISS data were obtained with a configuration where the current was injected in the left and right areas of the device. The slope values of the nonlocal CISS signal are $-4.36$ and $4.24\mathrm{\Omega }$ in the linear regime at a small current, respectively.