Spin filter for arbitrary spins by substrate engineering

TL;DR

This paper proposes a method to design spin filters for particles with arbitrary spin using a one-dimensional magnetic atom chain, enabling selective spin transmission and spin flipping, with potential applications in ultracold gases.

Contribution

It introduces an analytical approach to engineer spectral gaps for arbitrary spins via substrate design, and demonstrates robust spin filtering and flipping effects.

Findings

The chain acts as a spin-selective transmission device.

The system can flip spins using a spin spiral configuration.

The scheme is applicable to ultracold quantum gases.

Abstract

We design spin filters for particles with potentially arbitrary spin S (= 1/2, 1, 3/2,....) using a one-dimensional periodic chain of magnetic atoms as a quantum device. Describing the system within a tight-binding formalism we present an analytical method to unravel the analogy between a one-dimensional magnetic chain and a multi-strand ladder network. This analogy is crucial, and is subsequently exploited to engineer gaps in the energy spectrum by an appropriate choice of the magnetic substrate. We obtain an exact correlation between the magnitude of the spin of the incoming beam of particles and the magnetic moment of the substrate atoms in the chain desired for opening up of a spectral gap. Results of spin polarized transport, calculated within a transfer matrix formalism, are presented for particles having half-integer as well as higher spin states. We find that the chain can be made to act as a quantum device which opens a transmission window only for selected spin components over certain ranges of the Fermi energy, blocking them in the remaining part of the spectrum. The results appear to be robust even when the choice of the substrate atoms deviates substantially from the ideal situation, as verified by extending the ideas to the case of a spin spiral. Interestingly, the spin spiral geometry, apart from exhibiting the filtering effect, is also seen to act as a device flipping spins - an effect that can be monitored by an interplay of the system size and the period of the spiral. Our scheme is applicable to ultracold quantum gases, and might inspire future experiments in this direction.