【直播】【超快物质科学论坛】Dr. Markus A. Huber 学术报告

Advancements in electronics, quantum technology and nanoscience require a nanoscopic understanding of the internal processes in custom-tailored quantum materials. Since the elementary building blocks of condensed matter are in constant motion, still images are not enough.

In this talk, I will show how femtosecond terahertz nanoscopy unravels the dynamics of photoexcited charge carriers in custom-tailored van der Waals (vdW) heterostructures. I will introduce a novel polarization nanoscopy technique to trace charge carrier dynamics in conducting and non-conducting materials [1]. We demonstrate ~40 nm spatial and sub-cycle temporal resolution and non-invasively probe the interlayer tunneling across an atomically sharp WSe2/WS2 interface. We see pronounced variations in the formation and annihilation of optically bright and dark excited states as a result of nanoscale strain and changes in atomic registry. Our results demonstrate that ultrafast nanoscopy is an indispensable tool to study intrinsically disordered materials like vdW heterostructures.

On a WSe₂ homobilayer, we precisely tune the density of excitons by photodoping and observe the transition of a gas of strongly bound excitons into an electron-hole plasma. By revealing this excitonic Mott transition on the nanoscale, we circumvent averaging over nanoscale inhomogeneities and extract the true nature of the process. We find a continuous transition with spatial variations not correlated with topography. Our results indicate that the exciton binding energy can be modulated on length scales inaccessible to other ultrafast non-contact probes. We foresee that the technique could resolve the interplay between excitons and a broad variety of quantum phases in real space.

As an outlook, I will shortly discuss recent breakthroughs in lightwave scanning tunneling microscopy and how ultrafast multi-messenger scanning probe microscopy could be achieved. This novel approach could soon allow us to tailor (bio)chemical reactions or ultrafast phase transitions, on their intrinsic atomic-scale spatial and fs-temporal scales.

编辑：黄琦