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.
“Spin transfer due to quantum fluctuations of magnetization” A. Zholud, R. Freeman, R. Cao, A. Srivastava, S. Urazhdin, PRL (in press, 2017) arxiv:1703.09335 (2017) We expeirmentally demonstrate 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 be described by the spin current-dependent chemical potential and 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.
“ Excitation of coherent propagating spin waves by pure spin currents ” Nature Communications (2016) In collaboration with the group of Sergej Demokritov at U.Muenster, we demonstrate a novel nanostructure based on the concepts of nonlocal spin injection and dipolar waveguides. Nonlocal spin injection is an approach to generating pure spin currents not accompanied by electrical currents, which is very useful for spintronic devices utilizing insulating materials. Dipolar waveguides developed by us in the last year enable efficient guiding of spin waves in profiled continuous magnetic films. In this paper, we demonstrated current-induced excitation of coherent spin waves directionally propagating in a dipolar waveguide. This advancement can enable the development of electronically operated magnonic nano-circuits that can store, transmit and process information, all on the same chip.
“ Spin-current nano-oscillator based on nonlocal spin injection ” Scientific Reports (2015) In collaboration with the group of Sergej Demokritov at U.Muenster, we demonstrate the possibility to induce local oscillations in a magnetic film, by using a pure spin current injected in this film through a nonlocal point contact. Pure spin currents are flows of spin that are not directly tied to the electrical current. Pure spin currents do not require a concurrent path for the electrical current, provide unprecedented opportunities for the development of new, previously impossible, architectures of active spintronic devices. Using pure spin currents can also make spintronic devices more efficient, and minimize the effects of Joule heating and electromigration.