Quasi-ballistic transport of excitons in quantum wells

Kalt, H.; Zhao, Hui; Don, B. Dal; Schwartz, Gregor; Bradford, C.; Prior, K. A.

doi:10.1016/j.jlumin.2004.09.012

Cited by 9 publications

(8 citation statements)

References 13 publications

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“…in Cu 2 O39 and II-VI40 . Therefore, the unconventionally high speed makes condensed excitons in direct-bandgap monolayer MoS 2 the fastest excitation in electronic matter observed in a solid-state system.…”

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confidence: 94%

Exciton Condensation in an Atomically-thin MoS2 Semiconductor

Xiong

Águila²,

Wong

et al. 2021

Preprint

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Condensation of a dilute Bose gas of excitons (coupled electron-hole pairs) in a direct bandgap semiconductor was first theoretically predicted in 19681. This exotic state of matter is expected to exhibit spectacular non-linear properties, such as superradiance and superfluidity. However, direct experimental observation of condensation of optically active excitons in conventional semiconductors has been hindered by their short lifetimes and weak collective excitonic interactions. Here, we have experimentally realized the condensation of short-lived excitons in a direct-bandgap, atomically-thin MoS2 semiconductor. The signature is the anomalous transport of the fast-expanding exciton density, originating from a thermalized dilute gas generated under the laser spot. Below the critical temperature Tc~150 K, the exciton liquid propagates over ultra-long distances (at least 60 micrometers) with record speed in a solid-state system of 1.8*10^7 m/s (~6% the speed of light), fuelled by the unconventionally strong repulsions among excitons. The condensation is controlled by many-body interactions in the gas mixture of excitons (bosons) and free-carriers (fermions) via an electrical backgate. Our results demonstrate electrostatic doping as a simple approach for the investigation of correlated states of matter at high-temperatures, excitonic circuitry and spin-valley Hall devices mediated by exciton superfluids in semiconducting monolayers.

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confidence: 94%

Exciton Condensation in an Atomically-thin MoS2 Semiconductor

Xiong

Águila²,

Wong

et al. 2021

Preprint

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“…21,22 Among them are colloidal CdSe nanosheets (NSs) with atomically precise thicknesses of only a few CdSe layers. [23][24][25][26][27][28] In addition to strong quantum connement in the thickness direction, these nanosheets have large absorption cross sections, 29 high photoluminescence (PL) quantum yields, 25,30 and fast in-plane carrier transport, [30][31][32] making them promising light-absorbing materials for photocatalysis. However, in semiconductor-metal heterostructures such as CdSe NS-Pt (Fig.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast exciton quenching by energy and electron transfer in colloidal CdSe nanosheet–Pt heterostructures

et al. 2015

Chem. Sci.

164

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“…The observation of hot exciton transport in CdSe/CdTe and CdSe/CdS NPLs differs from exciton transport mechanisms in more extensively studied multiple-quantum-well (MQW) materials grown by molecular beam epitaxy that consist of an active layer a few nanometers thick sandwiched by barrier layers. − In these MQW materials, exciton transport at room temperature can be described by diffusion of thermalized excitons (i.e., classical transport), and nonclassical transport (ballistic transport and hot exciton diffusion) becomes notable only at low temperatures. The difference may be attributed to the very different lateral dimension studied in these materials.…”

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confidence: 99%

Efficient Diffusive Transport of Hot and Cold Excitons in Colloidal Type II CdSe/CdTe Core/Crown Nanoplatelet Heterostructures

Zhou

McBride

et al. 2016

ACS Energy Lett.

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Cadmium chalcogenide colloidal quantum wells or nanoplatelets (NPLs), a class of new materials with atomically precise thickness and quantum confinement energy, have shown great potential in optoelectronic applications. Short exciton lifetimes in two-dimensional (2D) NPLs can be improved by the formation of type II heterostructures, whose properties depend critically on the mechanism of exciton transport. Herein, we report a study of room-temperature exciton in-plane transport mechanisms in type-II CdSe/CdTe core/crown (CC) colloidal NPL heterostructures with the same CdSe core and different CdTe crown sizes. Photoluminescence excitation measurements show unity quantum efficiency for transporting excitons created at the crown to the CdSe/CdTe interface (to form lower-energy chargetransfer excitons). At near band edge excitation, the crown-to-core transport time increases with crown size (from 2.7 to 5.6 ps), and this size-dependent transport can be modeled well by 2D diffusion of thermalized excitons in the crown with a diffusion constant of 2.5 ± 0.3 cm 2 /s (about a factor of 1.6 times smaller than the bulk value). With excitation energy above the band edge, there is an increased contribution of hot exciton transport (up to 7% of the total excitons at 400 nm excitation with diffusion constant that is over twice that of cold excitons). The percentage of hot exciton transport decreases with increasing NPL sizes and decreasing excess excitation photon energy. The observed ultrafast and efficient hot and cold exciton crown-to-core transport suggests their potential applications as light-harvesting and light-emitting materials.

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Quasi-ballistic transport of excitons in quantum wells

Cited by 9 publications

References 13 publications

Exciton Condensation in an Atomically-thin MoS2 Semiconductor

Exciton Condensation in an Atomically-thin MoS2 Semiconductor

Ultrafast exciton quenching by energy and electron transfer in colloidal CdSe nanosheet–Pt heterostructures

Efficient Diffusive Transport of Hot and Cold Excitons in Colloidal Type II CdSe/CdTe Core/Crown Nanoplatelet Heterostructures

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