Quantum Light matter group

Yushan Young Fellow, 2021

Dr. Chaw-Keong Yong has been elected as Yushan Young Fellow by the Ministry of Education of Taiwan.

Columbus Research Grant, 2021

The Ministry of Science and Technology of Taiwan has awarded our group with the prestigious Columbus Research grant for the next 5 years to explore quantum optoelectronic properties in the atomically thin semiconductor and quantum materials. We will be building our team in the Department of Physics at National Taiwan University and developing various ultrafast nonlinear optical spectroscopy to explore the ultrafast electron dynamics, light-matter interactions, and wavefunction engineering in the atomically thin semiconductor and quantum systems. We are recruiting postdocs, graduate, undergraduate and exchange students to join our new adventure. Please contact us at chawkyong@phys.ntu.edu.tw for more information. 

Quantum engineering exciton-phonon hybridization in 2D heterostructure

In-collaboration with the groups of Prof. Ermin Malic (Philipps-Universität Marburg), we use WSe2/gypsum as model system to experimentally and theoretically demonstrate proximity control of exciton-phonon hybridization up to strong coupling limits. We show that van der Waals stacking provides an effective ways to quantum design the polaron physics at the atomic length scale, giving rise to rich eigenmodes that are not seen in the constituted layer alone. Our results open up a new pathway to design the spatial shape of the exciton wave­function at the atomic scale that allows us to precisely manipulate the electron-phonon coupling dynamics, providing a promising new strategy to engineer novel ground states of two-dimensional systems. 

The results have been published in Nature Communications

Twist-tailoring Coulomb correlation in quantum materials

In-collaboration with the groups of Prof. Ermin Malic (Philipps-Universität Marburg), Prof. John Lupton (University of Regensburg), and Prof. Janina Maultzsch (Friedrich-Alexander University Erlangen-Nürnberg), we experimentally and theoretically demonstrate the control of Coulomb correlation in quantum materials through twisting the orbital overlap in an atomically thin homostructure of WSe2. By merely modifying the stacking angle between the 2 layers, we observe drastic change of exciton binding energy, exciton recombination rate, and many-body exciton interactions. These results pave the way for tailoring novel phases of matter in a broad range of van der Waals heterostructures. 

The results have been published in Nature Communications

Berry phase-induced splitting of exciton fine-structure and valley-dependent Autler-Townes doublets in quantum materials

In-collaboration with the groups of Prof. Steven Louie (UC Berkeley), Prof. Alex Zettl (UC Berkeley), Prof. Hui Deng (UC Berkeley), Prof. Takashi Taniguchi (National Institute for Materials Science) and Prof. Sefaattin Tongay (Arizona State University) we experimentally and theoretically demonstrate the control of the Berry phase-induced splitting of the 2p exciton states in monolayer MoSe2 using the intraexciton optical Stark spectroscopy. We show that the light–matter coupling between intraexciton states is remarkably strong, leading to a prominent valley-dependent Autler–Townes doublet under resonant driving. Our study opens up pathways to coherently manipulate the quantum states and excitonic excitation with infrared radiation in two-dimensional semiconductors.

The results have been published in Nature Materials

Biexcitonic optical Stark effects in atomically thin quantum materials

In-collaboration with the groups of Prof. Sefaattin Tongay (Arizona State University) and Prof. Takashi Taniguchi (National Institute for Materials Science), we demonstrate that prominent exciton-exciton interactions break down the valley selection rule from the non-interacting exciton picture and lead to a rich set of light-driven coherent phenomena. By tuning the driving pulse frequency, we observe anticrossing behaviors at energy below 1 exciton transition when the helicity of the probe is opposite to the driving pulse and reveal the intervalley biexciton binding energy of 21 meV. Our results open up new windows to coherently control the quantum states of matters using light and can have important implications for the general study of Floquet physics in atomically thin 2D materials.

The results have been published in Nature Physics

Spin-entangled biexcitonic state in organic semiconductor

In collaboration with the groups of Prof. John Anthony (University of Kentucky), Prof. David Beljonne (University of Mons), Prof. Jenny Clark (University of Sheffield), and Prof. Laura Herz (University of Oxford), we demonstrate the generality of 1(TT) state as the immediate product of singlet exciton fission in a range of acene and heteroacene, and giving rise to photon-to-charge conversion quantum efficiencies of > 100% in a photovoltaic blends. We experimentally and theoretically quantify the binding energy of such biexciton to be ~30 meV.

This work has been published in Nature Communications