Non-reciprocal Magnetoresistances in Chiral Tellurium

TL;DR

Chiral tellurium, a material with broken inversion symmetry and strong spin–orbit coupling, is used to explore non-reciprocal magnetoresistance arising from spin, orbital, and thermal effects. The authors perform systematic angular magnetoresistance measurements on single-crystal Te with current along the chiral axis and magnetic fields oriented in three orthogonal directions, employing ac and dc-biased excitations to separate distinct contributions. They extract three non-reciprocal coefficients, alpha_z, alpha_y, and alpha_x, by fitting a phenomenological model that includes Edelstein-, Nernst-, and orbital-magnetization–driven terms, and they confirm these mechanisms via first- and second-harmonic responses. The study shows that Edelstein non-reciprocity is chirality-dependent along the chiral axis, Nernst-related non-reciprocity along the in-plane direction is chirality-independent and thermal in origin, and orbital-magnetization–driven effects appear for out-of-plane fields with signs influenced by device orientation, highlighting a bulk-origin interplay of spin, orbital, and thermal phenomena with implications for spintronics and orbitronics.

Abstract

Materials with broken fundamental symmetries, such as chiral crystals, provide a rich playground for exploring unconventional spin-dependent transport phenomena. The interplay between a material's chirality, strong spin-orbit coupling, and charge currents can lead to complex non-reciprocal effects, where electrical resistance depends on the direction of current and magnetic fields. In this study, we systematically investigate the angular dependencies of magnetoresistance in single-crystalline chiral Tellurium (Te). We observe distinct non-reciprocal magnetoresistances for magnetic fields applied along three orthogonal directions: parallel to the current along the chiral axis (z), in the sample plane but perpendicular to the current (y), and out of the sample plane (x). Through detailed analysis of the chirality- and thickness-dependence of the signals, we successfully disentangle multiple coexisting mechanisms. We conclude that the Edelstein effect, arising from the chiral structure's radial spin texture, is responsible for the non-reciprocity along the z-axis. In contrast, the chirality-independent signal along the y-axis is attributed to the Nernst effect, and the non-reciprocity along the x-axis may originate from intrinsic orbital magnetizations. These findings elucidate the complex interplay of spin, orbital, and thermal effects in Te, providing a complete picture of its non-reciprocal transport properties.

Figures (4)

• Figure 1: (a)Diagrams showing left-handed and right-handed Te crystal structures and the corresponding spin polarizations due to Edelstein effect.(b)Microscopic image of a fabricated Te device, with current channels both along and perpendicular to the chiral axis. (c)Schematics showing the measurement setup under various field scans.
• Figure 2: (a) and (d)$\beta$ and $\phi$ scans of mangetoresistance of Te with pure ac currents. (b) and (e)$\phi$, $\beta$ scans of Te with positive(orange) and negative(purple) dc offsets at 5 $K$. (c) and (f)Angular dependencies of $\Delta V_{I^+}^\omega$ - $\Delta V_{I^-}^\omega$ to extract components with sine and cosine angular dependencies.
• Figure 3: (a)-(c)$\Delta V_B^{2\omega}$ under $B_z$, $B_y$, and$B_x$ field sweep for Te(R1) at 5 $K$. (e)-(g)$\Delta V_B^{2\omega}$ under $B_z$, $B_y$, and$B_x$ field sweep for Te(L1) at 5 $K$. (d) and (h) $\Delta V_B^{2\omega}/(I_0 B)$ vs current for Te(R1) and (L1). Red, blue, and green dots correspond to $\Delta V_B^{2\omega}/(I_0 B)$ at fields along $B_z$, $B_y$, and $B_x$ at different current densities.
• Figure 4: Ratio of absolute values of extracted $\alpha_z$, $\alpha_y$, and $\alpha_x$ and the corresponding device resistance $R_0$ as a function of $R_0$. Sqaures and triangles represent left and right handedness.