Anisotropic transport for $\nu=2/5$ FQH state at intermediate magnetic field

TL;DR

This paper investigates anisotropic transport phenomena at the $ u=2/5$ fractional quantum Hall state using composite fermion theory, revealing a lower-energy unidirectional density wave state and its dependence on magnetic field tilt and filling factors.

Contribution

It introduces a theoretical framework explaining anisotropic transport at intermediate magnetic fields in the $ u=2/5$ FQH state, emphasizing the role of composite fermion Landau level mixing.

Findings

Unidirectional charge/spin density wave state is energetically favored over Wigner crystal.

Transport anisotropy occurs when the magnetic field is in an appropriate range.

Easy transport direction is perpendicular to the in-plane magnetic field.

Abstract

The $\nu=2/5$ state is spin-unpolarized at weak magnetic field and fully polarized at strong field. At intermediate field, a plateau of half the maximal polarization is observed. We study this phenomenon in the frame of composite fermion theory. Due to the mixing of the composite fermion Landau levels, the unidirectional charge/spin density wave state of composite fermions is lower in energy than the Wigner crystal. It means that transport anisotropy, similar to those for electrons in higher Landau levels at half fillings, may take place at this fractional quantum Hall state when the external magnetic field is in an appropriate range. When the magnetic field is tilted an angle, the easy transport direction is perpendicular to the direction of the in-plane field. Varying the partial filling factor of composite fermion Landau level from 0 to 1, we find that the energy minimum occurs in the vicinity of one-half.