The theory of transport in helical spin-structure crystals

TL;DR

This paper develops a theoretical model for electronic transport in helical spin-structure crystals, revealing nonlinear conductivity behaviors and matching experimental data for MnP, with predictions for resistivity changes during phase transitions.

Contribution

It introduces a continuum model for helical spin crystals that explains nonlinear electroconductivity and spin-dependent interband transitions, aligning with experimental observations.

Findings

Nonlinear dependence of conductivity on chemical potential.

Excellent agreement with experimental resistivity data in MnP.

Prediction of zero perpendicular resistivity in the ferromagnetic phase.

Abstract

We study helical structures in spin-spiral single crystals. In the continuum approach for the helicity potential energy the simple electronic band splits into two non-parabolic bands. For the Fermi energy greater than the splitting between the bands, the lower band is described by a surface with a saddle shape in the direction of the helicity axis. Using the Boltzmann equation with the relaxation due to acoustic phonons, we discover the dependence of the current on the angle between the electric field and helicity axis leading to the both parallel and perpendicular to the electric field components in the electroconductivity. In addition, we find that the transition rates depend on an electron spin allowing the transition between the bands. The electric conductivities exhibit nonlinear behaviors with respect to chemical potential. We explain this effect as the interference of the band anisotropy, spin conservation, and interband transitions. The proposed theory with the spherical model in the effective mass approximation for conduction electrons can elucidate nonlinear dependencies that can be identified in experiments. There is the excellent agreement between the theoretical and experimental data for parallel resistivity depending on temperature at the phase transition from helical to ferromagnetic state in a MnP single crystal. In addition, we predict that the perpendicular resistivity abruptly drops to zero in the ferromagnetic phase.