Speaker: Vedran Jelic, University of Alberta, Department of Physics, Ultrafast Nanotools Laboratory
Title: Exploring Ultrafast Dynamics on the Atomic Scale with Terahertz Scanning Tunneling Microscopy
Date: Thu, 22 Feb 2018, 12:00 pm – 1:00 pm
Location: 1400 BPS Bldg.
Fig. 1 — An atomically sharp tungsten tip scans a Si(111)-7×7 surface inside an ultrahigh vacuum chamber with a THz pulse focused onto the tip, driving an ultrafast tunnel current between the tip and sample.
Image artist: Walter Gordy.
Terahertz-pulse-coupled scanning tunneling microscopy (THz-STM) is a new technique for exploring dynamics at sub-picosecond timescales and sub-nanometer length scales. Ultrafast terahertz pulses are coupled to the apex of an atomically sharp scanning tunneling microscope (STM) tip (Fig. 1), enabling coherently driven terahertz-field-induced electron tunneling through single atoms at ultrafast timescales. In our work, extremely large terahertz-pulse-driven transient tunnel currents up to 107 times larger than the steady-state currents in conventional STM are used to image the Si(111)-7×7 surface with 0.3 nm spatial resolution. This large transient current burst is the result of a terahertz tunnel conductance that is fundamentally different than that of the steady-state due to ultrafast terahertz-field-induced band bending and nonequilibrium charging of surface states.