Speaker
Description
1T-TaS$_2$ is a strongly correlated material characterized by a rich phase diagram
hosting a commensurate charge density wave (C-CDW) phase at low temperatures
accompanied by the opening of an insulating gap. These properties arise from the
interaction between electronic and lattice degrees of freedom, making 1T-TaS$_2$ a
prototype material for studying the complex quantum systems.
Time-resolved techniques, particularly pump-probe experiments, have revealed
intricate dynamics within 1T-TaS$_2$. However, the spatial-averaging nature of these
techniques limits the exploration of atomic-scale inhomogenities. For instance, it is
known that a photoinduced hidden state exists in 1T-TaS$_2$ and is characterized by
nanometer-sized domains each hosting a C-CDW. Therefore, an experimental
approach combining angstrom-spatial and femtosecond-temporal resolution is highly
desirable.
Terahertz-induced scanning tunneling microscopy (THz-STM) achieves this by
coupling broadband single-cycle THz-pulses to an STM junction and measuring the
resulting THz-induced rectified current (I$_{\rm{THz}}$). In this work, we demonstrate that THz-
STM can locally probe the amplitude mode (AM) phonon in 1T-TaS$_2$. The AM appears
as a global 3% periodic modulation of I$_{\rm{THz}}$ at a frequency of 2.45 THz. We demonstrate
that this modulation is a consequence of a symmetric gap oscillation induced by the
phonon. Our results mark an important step towards the application of THz-STM to
study the non-equilibrium dynamics of quantum materials at the atomic scale.
