We use nonlinear pump-probe spectroscopy to study optical excitations in a charge-tunable MoSe$_2$\WS$_2$ moiré heterostructure. An intense red-detuned laser pulse creates a photonic dressing of the material by introducing a large virtual population of excitons or exciton polarons in a deep moiré potential. By measuring the resulting ac Stark effect with a weak resonant laser pulse, we gain access to the nature and mutual interactions of the elementary optical excitations. At charge neutrality, our measurements reveal that different exciton resonances, associated with confinement of their center-of-mass motion in the moiré potential, have a significant spatial overlap. The resulting short-range interactions manifest themselves as a density-dependent blueshift for same-valley excitons and bound biexciton states for opposite-valley excitons. The attractive polaron resonance that appears upon injection of electrons into the heterostructure shows a contrasting behavior: Here, we observe an electron-density-independent light shift and a clear pump-power-dependent saturation. These features are equivalent to that of an ensemble of independent two-level emitters and indicate a breakdown of the Fermi-polaron picture for optical excitations of electrons subject to a strong moiré potential. Our work establishes an experimental approach to elucidate the elementary optical excitations of semiconductor moiré heterostructures, providing a solid ground for the spectroscopy of correlated electronic and excitonic states in such materials.
Purely electronic model for exciton-polaron formation in moiré heterostructures
Technical University of Munich（慕尼黑工业大学）；Munich Center for Quantum Science and Technology (MCQST)（慕尼黑量子科学与技术中心）；Joint Quantum Institute, University of Maryland（马里兰大学联合量子研究所）
Columbia University（哥伦比亚大学）；University of Washington（华盛顿大学）；Istituto CNR di Scienze e Tecnologie Chimiche (CNR-SCITEC)（意大利国家研究委员会化学科学与技术研究所）；University of Perugia（佩鲁贾大学）；National Institute for Materials Science（国立材料研究所）；Prince Mohammad Bin Fahd University（穆罕默德·本·法赫德国王大学）；Sungkyunkwan University（成均馆大学）
Interaction-driven spin polaron in itinerant flat-band ferromagnetism
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University（南京大学固态微结构国家重点实验室和物理学院）；School of Physics, Nanjing University of Science and Technology（南京理工大学物理学院）；Jiangsu Physical Science Research Center（江苏省物理科学研究中心）；Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Jiangsu Key Laboratory of Quantum Information Science and Technology, Nanjing University（南京大学江苏省量子信息科学与技术重点实验室）
Two Dimensional Polarons with Linearly Dispersing Self Energy and Other Novel Features in the Study of Bi/Single Layer Graphene, and Semi-Dirac Semi-metals on Polar Substrates
Probing Quantum Anomalous Hall States in Twisted Bilayer WSe2 via Attractive Polaron Spectroscopy
Joint Quantum Institute (JQI), University of Maryland（马里兰大学联合量子研究所）；Electrical Engineering Department, University of Maryland（马里兰大学电气工程系）；Center for Functional Nanomaterials, Brookhaven National Laboratory（布鲁克海文国家实验室功能纳米材料中心）
Moiré superlattice in a MoSe$_2$/hBN/MoSe$_2$ heterostructure: from coherent coupling of inter- and intra-layer excitons to correlated Mott-like states of electrons
