Daniel Ralph

F.R. Newman Professor of Physics

538 Clark Hall
dcr14@cornell.edu
607/255-9644

Education

B.S., 1986, Physics and Mathematics, Vanderbilt University. Ph.D., 1993, Physics, Cornell University. Postdoctoral Research Associate, Harvard University, 1993-96. Assistant Professor, Physics, Cornell University, 1996-2000. Associate Professor, Physics, Cornell University, 2000-2004. Professor, Physics, Cornell University, 2004-2013. F.R. Newman Professor of Physics, Cornell University, 2013-present. Lester B. Knight Director, Cornell NanoScale Science Technology Facility (CNF) 2010-present. Alfred P. Sloan Fellow, 1996-99. David and Lucile Packard Foundation Fellow, 1997-2002. William L. McMillan Award, 1997. Research Corporation Research Innovation Award, 1997. ONR Young Investigators Award, 1997-2000. Member, Kavli Institute at Cornell.

Departments and programs

Physics

Academic interests

Experimental Atomic and Condensed Matter Physics

Overview

New nanofabrication techniques; spin transport and high-speed dynamics in magnetic devices; electron and spin states in magnets, superconductors, and 2D layered materials

Research Focus

Our group's research focuses on the electronic and magnetic properties of nm-scale samples. The work in the group consists of making nanometer-size devices using equipment at the Cornell NanoScale Science Technology Facility (CNF), and then performing electrical, magnetic, and optical measurements in Clark Hall. Students and postdocs in the group are pursuing a wide variety of projects.

In collaboration with the groups of Greg Fuchs, Katja Nowack, Farhan Rana, and several groups outside Cornell, we are investigating the “spin-transfer torque effect.” This is a phenomenon by which the magnetic orientation of a small magnet can be manipulated by transferring angular momentum from a current of spin-polarized electrons, rather than by using magnetic fields. We are using the spin torque as a tool for studying the fundamental physics of ferromagnetic and antiferromagnetic dynamics. This project is also progressing quickly toward applications for magnetic memory devices and high-speed signal processing.

Some of the most recent discoveries made by the group involve new and more efficient techniques for generating spin currents that can be used to exert spin transfer torques. These include the spin Hall effect in certain heavy metals and the Rashba-Edelstein effect generated by topological insulators. Several current experiments are aimed at better understanding and optimizing these phenomena.

The group is also in the process of starting new projects, including studies of spin and optical effects in devices containing graphene and other 2-dimensional atomic-layer materials.

Graduate Students
Thow Min Cham, Vishakha Gupta, Rakshit Jain, Saba Karimeddiny, Ruofan Li, Joseph Mittelstaedt, Maciej Olszewski, Yongjian Tang, Bozo Vareskic

Postdocs

Kelly Yunqiu Luo, Lijun Zhu.

Publications

Valley degeneracy breaking by magnetic field in monolayer MoSe2, D. MacNeill, C. Heikes, K. F. Mak, Z. Anderson, A. Kormányos, Viktor Zólyomi, J. Park, and D. C. Ralph, Phys. Rev. Lett. 114, 037401 (2015).
Spin-transfer torque generated by a topological insulator, A. R. Mellnik, J. S. Lee, A. Richardella, J. L. Grab, P. J. Mintun, M. H. Fischer, A. Vaezi, A. Manchon, E.-A. Kim, N. Samarth, and D. C. Ralph, Nature 511, 449-451 (2014).
Deterministic switching of ferromagnetism at room temperature using an electric field, J. T. Heron, J. L. Bosse, Q. He, Y. Gao, M. Trassin, J. D. Clarkson, C. Wang, J. Liu, S. Salahuddin, D. C. Ralph, D. G. Schlom, J. Íñiguez, B. D. Huey, and R. Ramesh, Nature 516, 370-373 (2014).
Spin torque switching with the giant spin Hall effect of tantalum, Luqiao Liu, Chi-Feng Pai, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman, Science 336, 555-558 (2012).
Spin Torque Ferromagnetic Resonance Induced by the Spin Hall Effect, Luqiao Liu, Takahiro Moriyama, D. C. Ralph, and R. A. Buhrman, Phys. Rev. Lett. 106, 036601 (2011).
Mechanical Control of Spin States in Spin-1 Molecules and the Underscreened Kondo Effect, J. J. Parks, A. R. Champagne, T. A. Costi, W. W. Shum, A. N. Pasupathy, E. Neuscamman, S. Flores-Torres, P. S. Cornaglia, A. A. Aligia, C. A. Balseiro, G. K.-L. Chan, H. D. Abruña, and D. C. Ralph, Science 328, 1370-1373 (2010).
Coupling of Spin and Orbital Motion of Electrons in Carbon Nanotubes, F. Kuemmeth, S. Ilani, D. C. Ralph, and P. L. McEuen, Nature 452, 448-452 (2008).
Measurement of the Spin-Transfer-Torque Vector in Magnetic Tunnel Junctions, J. C. Sankey, Y.-T. Cui, J. Z. Sun, J. C. Slonczewski, R. A. Buhrman, and D. C. Ralph, Nature Physics 4, 67-71 (2008).
Magnetic vortex oscillator driven by dc spin-polarized current, V. S. Pribiag, I. N. Krivorotov, G. D. Fuchs, P. M. Braganca, O. Ozatay, J. C. Sankey, D. C. Ralph, and R. A. Buhrman, Nature Physics 3, 498-503 (2007).
Time-Domain Measurements of Nanomagnet Dynamics Driven by Spin-Transfer Torques, I. N. Krivorotov, N. C. Emley, J. C. Sankey, S. I. Kiselev, D. C. Ralph, and R. A. Buhrman, Science 307, 228-231 (2005).
The Kondo effect in the presence of ferromagnetism, A. N. Pasupathy, R. C. Bialczak, J. Martinek, J. E. Grose, L. A. K. Donev, P. L. McEuen, and D. C. Ralph, Science 306, 86-89 (2004).
Microwave oscillations of a nanomagnet driven by a spin-polarized current, S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, N. C. Emley, R. J. Schoelkopf, R. A. Buhrman, and D. C. Ralph, Nature 425, 380-383 (2003).
Coulomb Blockade and the Kondo Effect in Single Atom Transistors, Jiwoong Park, A. N. Pasupathy, J. I. Goldsmith, C. Chang, Y. Yaish, J. R. Petta, M. Rinkoski, J. P. Sethna, H. D. Abruña, P. M. McEuen, and D. C. Ralph, Nature 417, 722-725 (2002).
Current-Driven Magnetization Reversal and Spin Wave Excitations in Co/Cu/Co Pillars, J. A. Katine, F. J. Albert, R. A. Buhrman, E. B. Myers, and D. C. Ralph, Phys. Rev. Lett. 84, 3149-3152 (2000).
Current-Induced Switching of Domains in Magnetic Multilayer Devices, E. B. Myers, D. C. Ralph, J. A. Katine, R. N. Louie, and R. A. Buhrman, Science 285, 867-870 (1999).