Van der Waals torque induced by external magnetic fields

TL;DR

This paper introduces a method to induce and control van der Waals torques between parallel slabs using external magnetic fields, leveraging optical anisotropy in semiconductors like InSb.

Contribution

It demonstrates how magnetic fields can generate and modulate van der Waals torques via optical anisotropy in otherwise isotropic materials, expanding control over dispersive forces.

Findings

Torque increases with magnetic field strength.

No torque without magnetic field.

Magnetic field of about 1 T produces significant torque.

Abstract

We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as $InSb$, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of $InSb$. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of $InSb$ increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magnetic fields is close to 1 T.