title: Stability of High-Density Two-Dimensional Excitons against a Mott Transition in High Magnetic Fields Probed by Coherent Terahertz Spectroscopy.
abstract: We have performed time-resolved terahertz absorption measurements on photoexcited electron-hole pairs in undoped GaAs quantum wells in magnetic fields. We probed both unbound- and bound-carrier responses via cyclotron resonance and intraexciton resonance, respectively. The stability of excitons, monitored as the pair density was systematically increased, was found to dramatically increase with increasing magnetic field. Specifically, the 1s-2p_{-} intraexciton transition at 9 T persisted up to the highest density, whereas the 1s-2p feature at 0 T was quickly replaced by a free-carrier Drude response. Interestingly, at 9 T, the 1s-2p_{-} peak was replaced by free-hole cyclotron resonance at high temperatures, indicating that 2D magnetoexcitons do dissociate under thermal excitation, even though they are stable against a density-driven Mott transition.
authors.affiliation: Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Yongrui
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Weilu
authors.initials: W
authors.lastname: Gao
authors.affiliation: Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Zhongqu
authors.initials: Z
authors.lastname: Long
authors.affiliation: Department of Physics and Astronomy, Station Q Purdue, and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: Watson
authors.affiliation: Department of Physics and Astronomy, Station Q Purdue, and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.|School of Materials Engineering and School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Manfra
authors.affiliation: Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Alexey
authors.initials: A
authors.lastname: Belyanin
authors.affiliation: Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.|Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.|Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Junichiro
authors.initials: J
authors.lastname: Kono