Efficient charge to spin conversion is important for low-power spin logic devices. Spin and charge interconversion is commonly performed using heavy metals and topological insulators, while the field of oxides is not yet fully explored. Strontium iridate thin films were grown, where the different crystal structures form a perfect playground to understand the key factors in obtaining high charge to spin conversion efficiency (i.e., large spin Hall angle). It was found that the semiconducting Sr2IrO4 has a spin Hall angle of ∼0.1 (depending on measurement technique), which is promising for a spin-orbit coupled electronic system and comparable to Pt. In contrast, the perovskite SrIrO3, reported to have a Dirac cone near the Fermi level, has a larger spin Hall angle of 0.3-0.4 degrees. The largest difference between the two materials is a large degree of spin-momentum locking in SrIrO3, comparable to known topological insulators. A simple semiclassical relationship is found where the spin Hall angle increases for higher degrees of spin-momentum locking and it also increases for lower Fermi wave vectors. This relationship is then able to explain the decreased spin Hall angle below 10 nm film thickness in SrIrO3, by relating it to the correspondingly higher carrier concentration (related to the higher Fermi wave vector). Breaking the commonly believed anticorrelation between resistivity and carrier concentration paves a pathway to lower power losses due to resistance while keeping large spin Hall angles.
Bibliographical noteFunding Information:
A.S.E., Y.T., and R.R. acknowledge support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 within the Quantum Materials program (KC2202). Portions of the devices were fabricated in the UC Berkeley Marvell Nanofabrication Laboratory. M.DC, X.H., S.S., S.D., J.-P.W., and R.R. were supported in part by ASCENT one of six centers in JUMP, a Semiconductor Research Corporation (SRC) program sponsored by DARPA. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure Network (NNCI) under Award No. ECCS-1542202.
© 2019 American Physical Society.