Anomalous Metal Phase Emergent on the Verge of an Exciton Mott Transition

Sekiguchi, Fumiya; Mochizuki, Takayasu; Kim, Changsu; Akiyama, Hidefumi; Pfeiffer, L. N.; West, K. W.; Shimano, Ryo

doi:10.1103/physrevlett.118.067401

Cited by 19 publications

(17 citation statements)

References 45 publications

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“…3(b). Such a peculiar temporal behavior accompanied by the incubation time is consistent with the recent observation on the dynamics of EMT in GaAs, 38) indicating that EMT becomes a first-order phase transition at low temperatures. The emergence of incubation time has been observed in a variety of photoinduced phase transition phenomena, e.g.…”

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“…In particular, our recent study on the ultrafast dynamics of EMT in GaAs under the resonant excitation of excitons has indicated the signature of first-order phase transition. 38) In this letter, we first show that ionization ratio of excitons exhibits a bistability as a function of total e-h pair density at low temperatures, based on a simple thermodynamic model described by the Saha equation with taking into account the empirical expression for the band-gap renormalization effect caused by the unbound e-h pairs. Furthermore, we discuss the ionization dynamics of excitons after their impulsive photoexcitation by using a rate equation analysis, and show that a peculiar incubation behavior appears on the verge of the bistable region.…”

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Rate Equation Analysis of the Dynamics of First-order Exciton Mott Transition

Sekiguchi

Shimano

2017

J. Phys. Soc. Jpn.

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We performed a rate equation analysis on the dynamics of exciton Mott transition (EMT) with assuming a detailed balance between excitons and unbound electron-hole (e-h) pairs. Based on the Saha equation with taking into account the empirical expression for the band-gap renormalization effect caused by the unbound e-h pairs, we show that the ionization ratio of excitons exhibits a bistability as a function of total e-h pair density at low temperatures. We demonstrate that an incubation time emerges in the dynamics of EMT from oversaturated exciton gas phase on the verge of the bistable region. The incubation time shows a slowing down behavior when the pair density approaches toward the saddle-node bifurcation of the hysteresis curve of the exciton ionization ratio.Photocontrol of condensed matter systems has gained continuing interests over decades, [1][2][3] e.g. in semiconductors, 4,5) Mott insulators, 3,6-9) spin crossover complexes, [10][11][12] and superconductors. 13,14) Among diverse material systems, photoexcited electron-hole (e-h) systems in semiconductors offer a unique arena to study the rich variety of phases emergent in many particle systems, and their non-equilibrium dynamics. 4,15) One of the intriguing aspects of e-h systems is that the strength of inter-particle Coulomb interaction can be effectively controlled by changing the density of photoexcited carriers through the screening effect, by simply changing the excitation light intensity. The change of the Coulomb interaction causes a phase transition, or crossover, from the insulating exciton gas phase in the low density regime to the metallic e-h plasma in the high density regime, referred to as exciton Mott transition (EMT). There is a long-standing argument whether EMT is a crossover or a first-order phase transition accompanied by a bistability at sufficiently low temperatures. [16][17][18][19][20][21][22] In general, bistability appears in diverse systems such as electronic circuits, optoelectronic systems, magnetic systems, molecular and biological systems, etc. Figure

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Rate Equation Analysis of the Dynamics of First-order Exciton Mott Transition

Sekiguchi

Shimano

2017

J. Phys. Soc. Jpn.

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“…It is an interesting direction to study dynamical aspects of ordered phases in the quasiperiodic systems, where one can expect anomalous properties of collective modes such as the phase mode and the amplitude (Higgs) mode in the SC phase [49][50][51][52][53] and the EI phase 54,55 . It is also instructive to consider whether or not the exciton-Mott transitions 56 occurs in the quasiperiodic system. These are now under consideration.…”

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Excitonic Condensation Reflecting Electronic States in Two-Band Penrose–Hubbard Model

2020

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We study the excitonic insulating (EI) phase in the two-band Hubbard models on the Penrose tiling. Performing the real-space mean-field calculations systematically, we obtain the ground state phase diagrams for the vertex and center models. We find that, in some regimes, the stable EI phase is induced by small interband interactions. We argue that this originates from the electronhole pairing for the completely or nearly degenerate states, which are characteristic of the Penrose tiling. We also study spatial distribution of the order parameter, mapping it to the perpendicular space.

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“…Eventually, the subtle interplay between these effects can also lead the correlated e-h system to exhibit a rich variety of collective phenomena, typically at low temperature. Notable examples include the emergence of correlated metallicity 13 , the instability towards nonequilibrium excitonic insulator phases (involving the Bose condensation of photoexcited e-h Cooper pairs) 3,14 , and the nucleation of e-h droplets 15,16 .…”

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Mahan excitons in room-temperature methylammonium lead bromide perovskites

et al. 2020

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In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temperature. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calculations to reveal that organic-inorganic lead-bromide perovskites host Mahan excitons at room temperature. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are observed at all achievable photoexcitation densities, well above the Mott density. This is supported by the solution of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissociation is otherwise expected, and offer promising perspectives in fundamental physics and in room-temperature applications involving high densities of charge carriers.

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Anomalous Metal Phase Emergent on the Verge of an Exciton Mott Transition

Cited by 19 publications

References 45 publications

Rate Equation Analysis of the Dynamics of First-order Exciton Mott Transition

Rate Equation Analysis of the Dynamics of First-order Exciton Mott Transition

Excitonic Condensation Reflecting Electronic States in Two-Band Penrose–Hubbard Model

Mahan excitons in room-temperature methylammonium lead bromide perovskites

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