Invited Paper SA-TuA7
Unraveling Topological Properties of Spintronic Materials Using Coherent X-rays

Tuesday, November 11, 2014, 4:20 pm, Room 312

Understanding new topological states in condensed matter systems is a current research topic of tremendous interest due to both the unique physics and their potential in device applications. The topological magnetic phases have exotic spin texture, and in some cases can be moved coherently over macroscopic distances with very low currents. Recently discovered skyrmions is an example of such a topological phase that manifest in magnetic systems as a hexagonal lattice of spin vortices. In this talk we will discuss our observation of the skyrmions using resonant soft x-ray scattering in Cu₂SeO₃ and demonstrate the unexpected existence of two distinct skyrmion sub-lattices that arise from inequivalent Cu sites with chemically identical coordination numbers and valency. The skyrmion sublattices are rotated with respect to each other implying a long wavelength modulation of the lattice. The coupled response of these sub-lattices to external magnetic field suggests a secondary interaction term that has not been predicted. We will also describe an artificial spin ice system whose origin lies in geometrical frustration that comes from the topology of a well-ordered structure rather than from disorder. We observed that under certain applied magnetic field the spin ice exhibits a magnetic structure that can impart orbital angular momentum into the photon beam thereby creating a vortex beam. Further, the vortex beam can be manipulated by an applied magnetic field. Creating an x-ray vortex beams may enable new x-ray based techniques such as coherent control of excitations in quantum material, trapping and rotation of quasiparticles or biomolecules with free electron laser x-ray sources.

Work is funded by U.S. DOE.