We study the van der Waals force at equilibrium between two Weyl semimetal particles. The dielectric response of the Weyl semimetal is nonreciprocal, giving rise to a repulsive force that depends on the relative alignment of the Weyl nodes of the particles. However, the aforementioned response is accompanied by a metalliclike contribution that precludes the controllability of the force sign. We show that a dielectric medium other than vacuum can yield an interparticle separation range for which the force sign can be changed by simply switching the alignment direction of the Weyl nodes of the particles. We analyze general conditions for van der Waals force repulsion between anisotropic particles and show that controlling the sign of the force requires a background medium with a large dielectric function at frequencies close to those associated with the Fermi energies of the Weyl semimetal particles. As temperature rises, the regime of force-sign controllability gradually deteriorates and eventually disappears. We discuss possible experimental implementation of our setup: background medium dispersion and force measurement. Despite current challenges in liquid materials and force detection, this should become feasible with upcoming advances. Our work might have implications on the dynamics of the motion of nanoscale devices.

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• Casimir effect
• Fluctuation mediated interactions
• van der Waals interaction
• Weyl semimetal