Synchronizing Atomic-scale Spin and Charge Excitations to Ultrafast Currents

Scanning tunneling microscopy with high frequency signals gives access to ultrafast dynamics in real space on the atomic scale [1, 2]. In order to detect these dynamics, the fast signals must be down converted to low frequencies which inherently requires phase synchronization of the atomic-scale dynamics to the external driving. Here, I will introduce how this synchronization can induce oscillatory modes in the otherwise highly dissipative systems of individual magnetic atoms on conducting surfaces and charge-density waves pinned to atomic defects.
For magnetic atoms we find that a small harmonic modulation of the tunnel current can synchronize the evolution of the atom’s spin. By tuning the excitation frequency to match the surface-induced spin relaxation, we can observe quantum stochastic resonance on individual atoms and thereby gain unprecedented access to the time domain behavior of atomic spins.
On charge-density wave (CDW) materials we employ broadband excitation by THz-pulses to induce ultrafast alternating electric fields under the STM tip. We find that these electric fields excite an oscillatory modulation of the CDW that locally excites collective modes of the CDW near atomic pinning sites.
These experiments access the microscopic dynamics of the spin and charge degrees of freedom of atomic-scale structures and highlight pathways control quantum properties of matter at the single atom level.

References:
[1] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329, 1628 (2010).
[2] T. L. Cocker et al., Nature Photon. 7 620 (2013).