C.F. Hirjibehedin
MIT Lincoln Laboratory,
United States
Keywords: scanning tunneling microscopy (STM), atomic force microscopy (AFM), 2D materials, ferroelectric, multiferroic
Summary:
Controlling electric and magnetic dipoles at the atomic scale is a major challenge in the development of novel materials and devices. We demonstrate that non-zero electric polarization can be induced and reversed in a hysteretic manner in bilayers made of ultrathin insulators whose electric polarization cannot be switched individually [1]. Using scanning tunneling microscopy and atomic force microscopy, we explore the interface between ionic rock salt alkali halides such as NaCl or KBr and polar insulating Cu2N terminating bulk copper. The strong compositional asymmetry between the polar Cu2N and the vacuum gap breaks inversion symmetry in the alkali halide layer, inducing out of plane dipoles that are stabilized in one orientation (self-poling). The dipole orientation can be reversed by a critical electric field applied from the tip of a scanning tunneling microscope, producing sharp switching of the tunnel current passing through the junction. Furthermore, when a Co atom is near a vacancy on the NaCl surface, spin-sensitive inelastic electron tunneling spectroscopy measurements can reveal changes in magnetic anisotropy experienced by the Co for the two different surface polarization states. Demonstrating atomic-scale control of electronic and magnetic properties using an electric field opens new possibilities for probing the origins of magnetoelectric coupling and will stimulate the development of model artificial multiferroic systems. * This work was done in collaboration with Jose Martinez-Castro, Marten Piantek, Sonja Schubert, Mats Persson, and David Serrate. [1] J. Martinez-Castro et al., Nature Nanotechnology 13, 19 (2018)