Quantum spin mixing in Dirac materials

The spin of the electron is nowadays replacing the charge as basic carrier of information not only in spintronics applications, but also in the emerging field of quantum information. Topological quantum materials, where spin-momentum locking is believed to lead to particularly long spin lifetimes, are regarded as a promising platform for such applications. However, spin-orbit coupling, that is essential to all topological matter, at the same time gives rise to spin mixing and decoherence as a major obstacle for quantum computing. Here, we give experimental evidence that hot-spots of spin-mixing and spin-conserving contributions of the spin-orbit operator coexist in an archetypal topological Dirac metal, and that these hot spots can have a strongly anisotropic distribution of their respective wave vectors with respect to the spin quantization direction. Our results can be understood within a theory that takes into account the decomposition of the spin-orbit Hamiltonian into spin-conserving and spin-flip terms, contributing to a better understanding of quantum decoherence in topological materials, in general. Spintronic devices, where the spin of the electron becomes the main carrier of information, offer a promising avenue to develop quantum devices. The authors experimentally and theoretically investigate spin-polarization and spin-orbit mixing in a W(110) surface, and provide a mean to fine tune the quantum (de)coherence of materials by changing the spin polarization of a conduction electron in a spintronic device