Quantum materials science meets spintronics

Within the realm of materials science, one-dimensional spin liquids and one of their quasiparticles known as spinons, are rare. Although they’ve both been established theoretically and experimentally, detailed investigations of their properties remain difficult. So far, only thermal conductivity measurements have provided direct insight to their transport properties; conventional transport techniques rely on the fact that spinons can convey entropy.

In the Journal of Applied Physics, researchers report using an experimental technique called the spin-Seebeck effect measurement, which is based on spinons being spin excitations that can serve as spin current carriers. Spin-Seebeck effects refer to the generation of spin currents due to temperature gradients in magnetically ordered materials.

With the technique they predicted some materials that may serve as spin current conductors. “Our study’s significance is the combination of spintronics and quantum materials science,” said co-author Daichi Hirobe.

They generated spin currents via spin-Seebeck effects using the spin chain compound Sr₂CuO₃ as a model material of a one-dimensional spin liquid. Different spin systems have different spin excitations, so these spin excitations produce a variety of spin current effects, which cannot be produced by conventional spin waves.

“Thermally excited spinons first convey spin currents in a temperature gradient,” said Hirobe. “The spin current then reaches the interface of Sr₂CuO₃ to Pt and forms a spin accumulation there.” The accumulated spins finally diffuse into Pt where strong spin-orbit coupling converts the spin currents into charge currents, which allows electrical detection of the spin currents originating in Sr₂CuO₃.

The researchers also highlight that this work demonstrates that quantum spin chains in Sr₂CuO₃ can propagate spin currents thanks to the one-dimensional spin liquid state — a novel finding since spin currents previously observed in experiments flowed simply in 3-D magnets. “Our finding suggests a possible application of one-dimensional spin systems as atomic wiring for spin currents,” Hirobe said.

Source: “Generation of spin currents from one-dimensional quantum spin liquid,” by Daichi Hirobe, Takayuki Kawamata, Koichi Oyanagi, Yoji Koike, and Eiji Saitoh, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5021022 .