OSC Colloquium: Xiaoqin Elaine Li, "The Versatile World of Excited States in Semiconductor Moiré Superlattices"

March 28, 2024
Xiaoqin Elaine Li

Optical Physics

Xiaoqin Li Colloquium

Title

The Versatile World of Excited States in Semiconductor Moiré Superlattices 

Abstract

In van der Waals bilayers, the strict requirement of lattice matching at the interface is lifted. The periodic changes in atomic alignment lead to the formation of an in-plane superlattice, known as the moiré superlattice. The twist angle acts as a unique knob to control the material properties. I will discuss how different types of excited states, i.e. excitons and trions can be engineered in semiconductor moiré superlattices.  I will discuss two recent developments. One is the discovery of a charge-transfer trion resonance in twisted homobilayers. Another is to confine excitons in a semiconductor functional layer with twisted-hBN substrates.  

Bio

Prof. Li is a professor in the physics department at the University of Texas-Austin. She received her Ph.D. at the University of Michigan in 2003 and worked as a postdoctoral researcher at JILA, Colorado. Since establishing her research group at the University of Texas in 2007, she has worked in several research areas including low-dimensional semiconductors, most recently in atomically thin van der Waals materials, magnetic materials, and nanophotonics. She has received several awards including the Presidential Early Career Award for Scientists and Engineers in the U. S. and a Sloan Fellowship. She was a Humboldt research fellow at the Technical University of Berlin between 2013-2015. She is a fellow of the American Physics Society and OPTICA.  

Contact

Florian Willomitzer, Colloquium Chair & Professor: colloquium@optics.arizona.edu

Colloquium Calendar

Subscribe to Upcoming Colloquium Announcements

Cannot Attend In-Person? Attend Online!

Dec
05
Donna Strickland Colloquium
OSC Colloquium: Donna Strickland, "High Intensity Fiber lasers for Nonlinear Optics"
3:30 – 5 p.m., Dec. 5, 2024

Ti:sapphire lasers offer the largest bandwidths and therefore the shortest pulses.   The highest laser intensities have been achieved using Chirped Pulse Amplification (CPA) of large diameter solid state lasers.  CPA was needed to avoid damage from the nonlinear process of self-focusing.  The disadvantage of solid-state lasers is the limited average power.  On the other hand, diode pumped fiber laser systems offer significantly higher average power than solid state lasers. Self-focusing is eliminated in single mode fibers by guiding and so nonlinear optics can be beneficial rather than detrimental and used to broaden the gain bandwidth.  Single fiber laser amplifiers will not reach the highest intensities offered by solid state lasers, but in this talk, I will discuss developing fiber laser amplifiers for nonlinear optical interactions such as mid-infrared generation and laser acceleration of electrons that require high intensity and benefit from high average power.

Past Speakers

Hendra Nurdin
3:30 – 5 p.m., Nov. 21, 2024

OSC Colloquium: Hendra Nurdin, "Physical Learning Machines: Classical and Quantum Reservoir Computers and Beyond"

This colloquium will give a brief introduction to reservoir computing, an overview of its theoretical foundations, including the notion of a universal family of reservoir computers that is capable of approximating a certain family of nonlinear maps from input sequences to output sequences, as well as its inherent limitations. It will then motivate and touch on efforts by the speaker and his collaborators to exploit noisy near-term quantum computers as quantum reservoir computers. Finally, the colloquium will conclude with a discussion of research directions for further development of quantum reservoir computers as well as research trends in the broader recent efforts on engineered physical learning machines going beyond reservoir computers.
caleb baker colloquium
3:30 – 5 p.m., Nov. 7, 2024

OSC Colloquium: Caleb Baker, "Doing it for the 'Graph (Design, Function, and System Test Results of the Roman Coronagraph Instrument)"

As the Nancy Grace Roman Space Telescope approaches its planned launch date in 2027, the engineers of one of its two instruments have recent cause to celebrate. Roman’s Coronagraph Instrument (CGI), a technology demonstration chasing direct images of Jupiter-like exoplanets, completed its system-level thermal vacuum test in May 2024, successfully demonstrating that it performs to its threshold requirements in a flight-like environment. Please join me as we walk through the design, function, and performance demonstration of one of the most complex optical instruments NASA has ever attempted to fly.