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Ultrafast nanoscopy of charge carrier dynamics and correlations in 2D systems

Date: 2022-10-20
Time: 15:00
Venue: Zoom
Speaker: Markus A. Huber

(University of Regensburg) 

Zoom: 897 5032 2416(Passcode: 363647)

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 [2], 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.

Dr. Markus A. Huber has studied physics at the University of Regensburg (Germany) and University of Colorado at Boulder (USA). In his studies, he focused on ultrafast near-field microscopy to study atomic and electron dynamics on the nanometer length scale. After his Ph.D., Dr. Huber joined Tony Heinz’s group at Stanford university to learn more about atomically thin materials. Recently, Dr. Huber has obtained a staff scientist position in Regensburg, continuing his work on nanoscopy, especially on 2D systems, as a team leader.


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