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Biexciton in one-dimensional Mott insulators
Communications Physics ( IF 5.4 ) Pub Date : 2019-10-31 , DOI: 10.1038/s42005-019-0223-8
T. Miyamoto , T. Kakizaki , T. Terashige , D. Hata , H. Yamakawa , T. Morimoto , N. Takamura , H. Yada , Y. Takahashi , T. Hasegawa , H. Matsuzaki , T. Tohyama , H. Okamoto

Mott insulators sometimes show dramatic changes in their electronic states after photoirradiation, as indicated by photoinduced Mott-insulator-to-metal transition. In the photoexcited states of Mott insulators, electron wave functions are more delocalized than in the ground state, and long-range Coulomb interactions play important roles in charge dynamics. However, their effects are difficult to discriminate experimentally. Here, we show that in a one-dimensional Mott insulator, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane (ET-F2TCNQ), long-range Coulomb interactions stabilize not only excitons, doublon-holon bound states, but also biexcitons. By measuring terahertz-electric-field-induced reflectivity changes, we demonstrate that odd- and even-parity excitons are split off from a doublon-holon continuum. Further, spectral changes of reflectivity induced by a resonant excitation of the odd-parity exciton reveals that an exciton-biexciton transition appears just below the exciton-transition peak. Theoretical simulations show that long-range Coulomb interactions over four sites are necessary to stabilize the biexciton. Such information is indispensable for understanding the non-equilibrium dynamics of photoexcited Mott insulators.



中文翻译:

一维莫特绝缘子中的双激子

莫特绝缘子有时在光辐照后会显示出电子状态的巨大变化,如光诱导莫特-绝缘体到金属的转变所表明的那样。在Mott绝缘子的光激发态下,电子波函数比在基态下更离域,并且长距离库仑相互作用在电荷动力学中起重要作用。但是,它们的作用很难通过实验加以区分。在这里,我们表明在一维Mott绝缘体中,双(亚乙基二硫代)四硫富瓦烯-二氟四氰基喹二甲烷(ET-F 2TCNQ),长距离库仑相互作用不仅可以稳定激子,杜布隆-霍隆结合态,而且还可以稳定双激子。通过测量太赫兹电场引起的反射率变化,我们证明了奇偶校验和激子是从杜宾-霍隆连续体中分离出来的。此外,由奇偶校验激子的共振激发引起的反射率的光谱变化表明,激子-比西克顿跃迁出现在激子跃迁峰的正下方。理论模拟表明,要稳定双激子,必须在四个位点进行长距离库仑相互作用。这样的信息对于理解光激发的Mott绝缘子的非平衡动力学是必不可少的。

更新日期:2019-11-01
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