One-way roads for spin currents
A group of scientists based in Singapore, Italy and Brazil have shown that systems with strong interactions can rectify extremely well the flow of spins. This discovery could unlock new applications of spintronics.
The spin is a type of angular momentum which is intrinsic to particles, grossomodo as if they were spinning on themselves. Particles can exchange their spin, and in this way spin currents can be formed in a material. With years of work, scientists have learned how to control such spin currents in an analogous way in which they control the flow of electrons, a field of physics known as spintronics.

The interaction between electrons, when strong, can completely alter the properties of materials. For example, one of the first discovery in this direction showed that material which are expected to be conductors if we consider the interaction between the electrons to be weak, are in effect insulators because of the actual strong interactions present in the system (these materials are known as Mott-insulators). If it was possible to tune the electron interactions, we would observe a drastic change of the material properties, i.e. a phase transition, from a conducting phase to an insulating one.
Since then, more quantum phases of matter have been discovered in materials with strongly interacting electrons, such as high-temperature superconductivity, and in analogous systems built with atoms trapped with lasers and magnetic fields near absolute zero.

In a recent work appeared on Physical Review Letters, V. Balachandran and co-authors showed a completely now approach to control spin currents based on spin-spin interactions, which results in diodes for spin current with a giant rectification. In this work they demonstrated, both analytically and using advanced numerical simulations that, if the interactions are stronger than a certain amount, the system can drastically change and becomes an insulator and no current can flow. Interestingly, this drastic change to insulating behavior occurs only for a particular direction of the flow of the spin current, while the flow remains possible in the opposite direction. This is how a highly performing spin current diode can be realized.

These predictions, once tested in experiments with atoms near absolute zero temperature or with structures made of a few atoms deposited carefully on surfaces, can open the way to substantial progress in material science and to build new devices based on this principle

REF: V. Balachandran, G. Benenti, E. Pereira. G. Casati and D. Poletti, Perfect diode in quantum spin chains, Phys. Rev. Lett. 120, 200603 (2018).

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