Most advanced spintronic devices [CHAP2011] are today based on the manipulation of spin currents that do not carry electrical charges but can be described as equal and opposite flows of electrons with opposite spins. The main operations in spintronics are the creation of spin currents from charge currents (electrical currents) and the detection of these spin currents by conversion into charge currents. Classical spintronics generally uses magnetic materials for these inter-conversions, but it now appears that they can also be obtained by harnessing the spin-orbit coupling (SOC) interaction, the relativistic correction to the equation of quantum physics that can be significantly strong in materials containing heavy atoms. Typical examples of SOC effects are the spin Hall effect (SHE) occurring in the bulk of heavy metals by which a charge current can be converted into a transverse spin current and the inverse effect (ISHE) to convert spin into charge [VALE2006]. An example of an application based on SHE is the so-called spin-orbit torque random access memory [CUBU2014].
During the last decade, topological insulators (TIs) have been widely studied for their peculiar fermions properties leading to the discovery of quantum Anomalous Hall effect [CHAN2013]. The much studied prototypical materials [WRAY2011–BIAN2010] are Bi2Se3 or Bi2(TexSe1-x)3 where a surface state with linear dispersion has been clearly observed using angle resolved photoelectron spectroscopy (ARPES). In Fig. 2, we illustrate the case of -Sn studied by partners from the SPiCY consortium where surface states can be observed by ARPES [ROJA2016]. Nevertheless, magneto-transport experiments revealed the complexity to master these materials as a bulk contribution makes it hard to isolate that of the surface states.
Recent investigations of new 2D or topological materials have demonstrated new opportunities for their implementation as “ideal” sources of spin current in future spintronic applications. In particular, large spin to charge current interconversion can be expected offering new perspectives in information technologies [MELL2014, KOND2016, HAN2017, SHI2019, ROJA2016]. Although reports in the literature have revealed the potential benefit for spintronics, it has also been emphasized that material control and interfacial properties (i.e. doping level, chemical reaction, bend bending…) are critical issues for success. It is an asset of the SPiCY project to involve partners with expertise including MBE growth, TEM characterization combined with ARPES and magneto-transport focusing on the very same hybrid systems [BARB2018].
Handbook of Spin Transport, and Magnetism
edited by I. Žutic and E. Y. Tsymbal
[VALE2006] S.O. Valenzuela and M. Tinkham
Direct electronic measurement of the spin Hall effect
Nature 442, 176 (2006)
[CHAN2013] C.Z. Chang et al.
Experimental observation of the quantum anomalous Hall effect in a magnetic topological insulator
Science 340, 167 (2013)
[WRAY2011] L. Andrew Wray et al.
A topological insulator surface under strong Coulomb, magnetic and disorder perturbations
Nat. Phys. 7, 32 (2011)
[BIAN2010] M. Bianchi et al.
Coexistence of the topological state and a two-dimensional electron gas on the surface of Bi2Se3
Nature Communications 1, 128 (2010)
[MELL2014] A.R. Mellnik et al.
Spin-transfer torque generated by a topological insulator
Nature 511, 449 (2014)
[KOND2016] K. Kondou et al.
Fermi-level-dependent charge-to-spin current conversion by Dirac surface states of topological insulators
Nature Physics 12, 1027 (2016)
[HAN2017] J. Han et al.
Room-temperature spin-orbit torque switching induced by a topological insulator
Phys. Rev. Lett. 119, 077702 (2017)
[SHI2019] S. Shi et al.
All-electric magnetization switching and Dzyaloshinskii–Moriya interaction in WTe2/ferromagnet heterostructures
Nature Nanotechnology 19 0525 (2019)
[ROJA2016] J.-C. Rojas-Sanchez et al.
Spin to charge conversion at room temperature by spin pumping into a new type of topological insulator: α-Sn Films
Phys. Rev. Lett. 116, 096602 (2016)
[BARB2018] Q. Barbedienne et al.
Angular-resolved photoemission electron spectroscopy and transport studies of the elemental topological insulator α-Sn
Phys. Rev. B 98, 195445 (2018)