Our group investigates new physical phenomena the emerge in nanoscale systems, at surfaces and interfaces of different materials. Our overarching goal is to develop fundamental understanding of the effects of confinement, interfaces, the resulting emerging interactions, and strongly nonequilibrium physical states that become possible to achieve only at nanoscale, and use this knowledge to develop nanoscale devices with new functionalities. Our laboratory is located in rooms W104, W106, and E108 of the Math and Science Building on the beautiful campus of Emory University.
“ Excitation and Amplification of Spin Waves by Spin-Orbit Torque ”, Advanced Materials, 2018. In collaboration with the group of Sergej Demokritov at U.Muenster, we demonstrate the possibility to locally generate coherent spin waves, and to simulataneously enhance their propagation. The developed nanostructure is based on a Permalloy/Pt nanowire, with a narrow notch. Magnetization oscillation is produced in the nano-notch regoin by the spin Hall effect in Pt, resulting in emission of coherent spin waves into the nanowire. The propagation of spin waves in the nanowire is enhanced by the same spin Hall mechanism, resulting in the reduction of effective dynamical damping. Surprisingly, the emission of spin waves is strongly asymmetric, opening the possibility to nonreciprocal spin wave-based magnonic and neuromorphic circuits
“Evidence for Dyakonov-Perel-like spin relaxation in Pt”, Phys. Rev. Lett., 2018. Spin-orbit interaction (SOI) plays a prominent role in modern spintronics, by providing the ability to control the spin and the orbital electronic degrees of freedom. Materials with strong SOI, such as Pt, can efficiently generate spin currents, due to the spin Hall effect (SHE). It is believed that SHE in Pt is determined mostly be the band structure - the intrinsic SHE. However, until now it was believed that the spin relaxation in Pt, also determined by SOI, was caused entirely by the electron scattering - the extrinsic mechanism. In this work, we experimentally demonstrate a significant, previously unrecognized intrinsic spin relaxation mechanism complementary to the intrinsic SHE.
“Spin transfer due to quantum fluctuations of magnetization”, Phys. Rev. Lett., 2017, featured in the PRL Viewpoint . We expeirmentally demonstrate that the interaction between electron spins in electrical current and magnetization of ferromagnets can enhance not only thermal magnetization fluctuations, but also its quantum fluctuations. This process can be driven not only by directional flows of spin-polarized current, but also by unpolarized currents and by thermal motion of conduction electrons. Surprisingly, the observed quantum effect remains significant even at room temperature. It also entails a significant and ubiquitous contribution to spin-polarizing properties of ferromagnets. These findings open a new chapter in our understanding of interaction between magnetic and electronic degrees of freedom, and in applications utilizing control of dynamical magnetization states by electrical current.
“Chemical potential of quasi-equilibrium magnon gas driven by pure spin current ” Nature Communications, 2017. In collaboration with the group of Sergej Demokritov at U.Muenster, we demonstrated that a nanoscale magnetic system subjected to spin current remains in a quasi-equilibrium state, well described by spin current-dependent thermodynamic parameters - the chemical potential and the effective temperature. Appropriate spin-polarization can lower the effective temperature to 225 K (-48 C). The opposite spin-polarization increases the chemical potential until it closely approaches the lowest-energy dynamical state, demonstrating the possibility of spin current-induced room-temperature Bose-Einstein condensation of magnons – a macroscopic quantum-coherent state of the magnetization.