642 citations · 3.6k across the 25 of their papers we have counts for
25 papers
Brightening interlayer excitons by electric-field-driven hole transfer in bilayer WSe2
Tianyi Ouyang, Erfu Liu, Soonyoung Cha +8
We observe the interlayer A1s^I, A2s^I, and B1s^I excitons in bilayer WSe2 under applied electric fields using reflectance contrast spectroscopy. Remarkably, these interlayer excit…
Enhancing resonant second harmonic generation in bilayer WSe2 by layer-dependent exciton-polaron effect
Soonyoung Cha, Tianyi Ouyang, Takashi Taniguchi +3
Two-dimensional (2D) materials serve as exceptional platforms for controlled second harmonic generation (SHG), an important nonlinear optical phenomenon with diverse applications.…
Thickness and twist angle dependent interlayer excitons in metal monochalcogenide heterostructures
Wenkai Zheng, Li Xiang, Felipe de Quesada +18
Interlayer excitons, or bound electron-hole pairs whose constituent quasiparticles are located in distinct stacked semiconducting layers, are being intensively studied in heterobil…
Electric-field-tunable intervalley excitons and phonon replicas in bilayer WSe
Mashael M. Altaiary, Erfu Liu, Ching-Tarng Liang +7
We report the direct observation of intervalley exciton between the Q conduction valley and valence valley in bilayer WSe by photoluminescence. The Q exciton lies at ~18…
Spin-Induced Linear Polarization of Excitonic Emission in Antiferromagnetic van der Waals Crystals
Xingzhi Wang, Jun Cao, Zhengguang Lu +8
Antiferromagnets display enormous potential in spintronics owing to its intrinsic nature, including terahertz resonance, multilevel states, and absence of stray fields. Combining w…
Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2
Erfu Liu, Jeremiah van Baren, Takashi Taniguchi +3
We observe a set of three replica luminescent peaks at ~21.4 meV below the dark exciton, negative and positive dark trions (or exciton-polarons) in monolayer WSe2. The replica reds…
Magneto-photoluminescence of exciton Rydberg states in monolayer WSe
Erfu Liu, Jeremiah van Baren, Takashi Taniguchi +3
Monolayer WSe hosts a series of exciton Rydberg states denoted by the principal quantum number n = 1, 2, 3, etc. While most research focuses on their absorption properties, the…
Gate tunable dark trions in monolayer WSe
Erfu Liu, Jeremiah van Baren, Zhengguang Lu +5
We report the observation and gate manipulation of intrinsic dark trions in monolayer WSe. By using ultraclean WSe devices encapsulated by boron nitride, we directly resolv…
Large, valley-exclusive Bloch-Siegert shift in monolayer WS2
Edbert J. Sie, Chun Hung Lui, Yi-Hsien Lee +3
Coherent light-matter interaction can be used to manipulate the energy levels of atoms, molecules and solids. When light with frequency ω is detuned away from a resonance ωo, repul…
Interlayer breathing and shear modes in NbSe2 atomic layers
Rui He, Jeremiah van Baren, Jia-An Yan +6
Atomically thin NbSe2 is a metallic layered transition metal dichalcogenide (TMD) with considerably different crystallographic structure and electronic properties from other TMDs,…
Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure
Qiong Ma, Trond I. Andersen, Nityan L. Nair +11
Ultrafast electron thermalization - the process leading to Auger recombination, carrier multiplication via impact ionization and hot carrier luminescence - occurs when optically ex…
Coupling and stacking order of ReS2 atomic layers revealed by ultralow-frequency Raman spectroscopy
Rui He, Jia-An Yan, Zongyon Yin +5
We investigate the ultralow-frequency Raman response of atomically thin ReS2, a special type of two-dimensional (2D) semiconductors with unique distorted 1T structure. Bilayer and…
Observation of interlayer phonon modes in van der Waals heterostructures
Chun Hung Lui, Zhipeng Ye, Chao Ji +9
We have investigated the vibrational properties of van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs), specifically MoS2/WSe2 and MoSe2/MoS2 hetero…
Stacking-dependent shear modes in trilayer graphene
Chun Hung Lui, Zhipeng Ye, Courtney Keiser +2
We observed distinct interlayer shear mode Raman spectra for trilayer graphene with ABA and ABC stacking order. There are two rigid-plane shear-mode phonon branches in trilayer gra…
Temperature-activated layer-breathing vibrations in few-layer graphene
Chun Hung Lui, Zhipeng Ye, Courtney Keiser +2
We investigated the low-frequency Raman spectra of freestanding few-layer graphene (FLG) at varying temperatures (400 - 900 K) controlled by laser heating. At high temperature, we…
Semiconducting-to-metallic photoconductivity crossover and temperature-dependent Drude weight in graphene
A. J. Frenzel, C. H. Lui, Y. C. Shin +2
We investigated the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrated that graphene exhi…
Spin Induced Optical Conductivity in the Spin Liquid Candidate Herbertsmithite
Daniel V. Pilon, Chun Hung Lui, Tianheng Han +5
A quantum spin liquid (QSL) is a state of matter in which magnetic spins interact strongly, but quantum fluctuations inhibit long-range magnetic order even at zero temperature. A Q…
Tunable Infrared Phonon Anomalies in Trilayer Graphene
Chun Hung Lui, Emmanuele Cappelluti, Zhiqiang Li +1
Trilayer graphene in both ABA (Bernal) and ABC (rhombohedral) stacking sequences is shown to exhibit intense infrared absorption from in-plane optical phonons. The feature, lying a…
Observation of out-of-plane vibrations in few-layer graphene
Chun Hung Lui, Leandro M. Malard, SukHyun Kim +4
We report the observation of layer breathing mode (LBM) vibrations in few-layer graphene (FLG) samples of thickness from 2 to 6 layers, exhibiting both Bernal (AB) and rhombohedral…
Water-Gated Charge Doping of Graphene Induced by Mica Substrates
Jihye Shim, Chun Hung Lui, Taeg Yeoung Ko +4
We report on the existence of water-gated charge doping of graphene deposited on atomically flat mica substrates. Molecular films of water in units of ~0.4 nm-thick bilayers were f…
Structurally Dependent Fano Resonances in the Infrared Spectra of Phonons in Few-Layer Graphene
Zhiqiang Li, Chun Hung Lui, Emmanuele Cappelluti +5
The in-plane optical phonons around 200 meV in few-layer graphene are investigated utilizing infrared absorption spectroscopy. The phonon spectra exhibit unusual asymmetric feature…
Observation of an electrically tunable band gap in trilayer graphene
Chun Hung Lui, Zhiqiang Li, Kin Fai Mak +2
A striking feature of bilayer graphene is the induction of a significant band gap in the electronic states by the application of a perpendicular electric field. Thicker graphene la…
Thermal conductance at the graphene-SiO2 interface measured by optical pump-probe spectroscopy
Kin Fai Mak, Chun Hung Lui, Tony F. Heinz
We have examined the interfacial thermal conductance σint of single and multi-layer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By usi…
Ultrafast Photoluminescence from Graphene
Chun Hung Lui, Kin Fai Mak, Jie Shan +1
Since graphene has no band gap, photoluminescence is not expected from relaxed charge carriers. We have, however, observed significant light emission from graphene under excitation…