title: Photocarrier relaxation pathway in two-dimensional semiconducting transition metal dichalcogenides.
abstract: Two-dimensional crystals of semiconducting transition metal dichalcogenides absorb a large fraction of incident photons in the visible frequencies despite being atomically thin. It has been suggested that the strong absorption is due to the parallel band or 'band nesting' effect and corresponding divergence in the joint density of states. Here, we use photoluminescence excitation spectroscopy to show that the band nesting in mono- and bilayer MX2 (M=Mo, W and X=S, Se) results in excitation-dependent characteristic relaxation pathways of the photoexcited carriers. Our experimental and simulation results reveal that photoexcited electron-hole pairs in the nesting region spontaneously separate in k-space, relaxing towards immediate band extrema with opposite momentum. These effects imply that the loss of photocarriers due to direct exciton recombination is temporarily suppressed for excitation in resonance with band nesting. Our findings highlight the potential for efficient hot carrier collection using these materials as the absorbers in optoelectronic devices.
authors: Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors: Daichi
authors: D
authors: Kozawa
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Rajeev
authors: R
authors: Kumar
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Alexandra
authors: A
authors: Carvalho
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors: Kiran
authors: K
authors: Kumar Amara
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Weijie
authors: W
authors: Zhao
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Shunfeng
authors: S
authors: Wang
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Minglin
authors: M
authors: Toh
authors: 1] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore [2] Center of Physics, Department of Physics, University of Minho, Braga PT-4710-057, Portugal.
authors: Ricardo M
authors: RM
authors: Ribeiro
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
authors: A H
authors: AH
authors: Castro Neto
authors: Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors: Kazunari
authors: K
authors: Matsuda
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore [2] Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore [3] Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors: Goki
authors: G
authors: Eda