Nonreciprocal charge transport in polar Dirac metals with tunable spin-valley coupling

TL;DR

This paper demonstrates large, tunable nonreciprocal charge transport in polar Dirac metals BaMnX2, where spin-valley coupling and Fermi energy control the magnitude of resistance asymmetry, advancing rectifying device design.

Contribution

It reports the discovery of tunable nonreciprocal resistivity in layered polar metals with spin-polarized Dirac dispersion, controlled by chemical substitution and spin-valley coupling.

Findings

Nonreciprocal resistivity varies with temperature and material composition.

Chemical substitution tunes spin-valley coupling and nonreciprocal effects.

Theoretical models link nonreciprocal resistivity to Fermi energy and Dirac dispersion.

Abstract

Nonreciprocal charge transport in solids, where resistance is different between rightward and leftward currents, is a key function of rectifying devices in the modern electronics, as exemplified by $p$-$n$ semiconductor junctions. Recently, this was also demonstrated in noncentrosymmetric materials in magnetic fields, since their band structure exhibits spin polarization coupled to the position of momentum space due to the antisymmetric spin-orbit coupling. To enhance the magnitude of nonreciprocal effect, it is essential to tune such spin-momentum coupling, which has been hampered in the conventional materials owing to the difficulty in controlling the broken inversion symmetry built into the lattice and interfacial structures. Here we report large nonreciprocal resistivity in layered polar metal BaMn$X_2$ ($X$=Sb, Bi), where the spin-polarized Dirac dispersion depends on the in-plane polarization tunable by chemical substitution of the $X$ site. For $X$=Sb with a pair of single-type valleys, the nonreciprocal resistivity increases monotonically with decreasing temperature, while for $X$=Bi with multiple types of valleys it is reduced by about an order of magnitude and exhibits a peak at a low temperature. Theoretical calculations indicate that the nonreciprocal resistivity is sensitive not only to the spin-momentum (spin-valley) coupling, but also to the Fermi energy and the Dirac dispersion. The observed significant variation of nonreciprocal transport in the same series of materials might be of great use in the design of junction-free rectifying devices and circuits.