Microsecond dark-exciton valley polarization memory in two-dimensional heterostructures

Jiang, Chongyun; Xu, Weigao; Rasmita, Abdullah; Huang, Zhilian; Li, Ké; Xiong, Qihua; Gao, Weibo

doi:10.1038/s41467-018-03174-3

Cited by 118 publications

(143 citation statements)

References 50 publications

(80 reference statements)

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“…The polarization degree of 0V-2 is much larger than that of 0V-1 and 0V-3. This observation further supports the presence of dark exciton 7,39 , because it has a long lifetime that suppresses valley depolarization 40,41 , as illustrated in Fig.4c and 4d. Due to long-range electron-hole exchange 40 , electrons in the K valley are scattered from the conduction band to the valence band, whereas electrons in the K' valley are scattered from the valence band to the conduction band.…”

Section: Introductionsupporting

confidence: 81%

“…This process can also be regarded as virtual recombination of an exciton in the K valley and generation of another exciton in the K' valley, or vice versa. The long-range electron-hole exchange typically takes a few picoseconds 41 , and the lifetime of the bright and dark IX is about several nanoseconds and microseconds 39 , respectively. Therefore, the valley depolarization is strong for bright IX (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Interlayer-Exciton Based Nonvolatile Valleytronic Memory

Ye¹,

Shen²,

Ren³

et al. 2020

Preprint

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Analogous to conventional charge-based electronics, valleytronics aims at encoding data via valley degree of freedom, enabling new routes for information processing. Long-lived interlayer excitons (IXs) in van der Waals heterostructures (HSs) stacked by transition metal dichalcogenides (TMDs) carry valley-polarized information and thus would find promising applications in valleytronic devices. Although great progress of IX based valleytronic devices has been achieved, nonvolatile valleytronic memories are still challenging. Here, we demonstrate IX based nonvolatile valleytronic memory in a WS2/WSe2 HS. The emission characteristics of IX exhibit a large excitonic/valleytronic hysteresis upon cyclic-voltage sweeping. Importantly, IX emission can be electrically switched between a bright state and a dark state with large light-intensity and helicity contrast of about 1.7 and 1.8, respectively, which can be ascribed to the chemical-doping of O2/H2O redox couple between TMDs and substrate. Taking advantage of the large hysteresis, IX can be utilized for manipulating and nonvolatile storing valley information and IX based nonvolatile valleytronic memory has been successfully demonstrated. These findings open up an avenue for nonvolatile valleytronic memory and would motivate more investigations on valleytronic devices.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Interlayer-Exciton Based Nonvolatile Valleytronic Memory

Ye¹,

Shen²,

Ren³

et al. 2020

Preprint

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“…The average linewidth of the observed peaks is about 100 μeV, which is comparable to the quantum emitters reported in monolayers of WSe2 (ref. [22][23][24][25] and hexagonal boron nitride 26 , and two orders of magnitude narrower than previous reports of interlayer exciton PL 10,[12][13][14][15][16][17]27,28 . Narrow PL peaks and power broadening were also observed in the 57° and 20° sample (Extended Data Fig.…”

Section: Main Textmentioning

confidence: 68%

Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers

Seyler

Rivera

et al. 2019

Nature

987

1,025

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The creation of moiré patterns in crystalline solids is a powerful approach to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional (2D) materials, a moiré pattern with a superlattice potential can form by vertically stacking two layered materials with a twist and/or finite lattice constant difference. This unique approach has led to emergent electronic phenomena, including the fractal quantum Hall effect 1-3 , tunable Mott insulators 4,5 , and unconventional superconductivity 6 . Furthermore, theory predicts intriguing effects on optical excitations by a moiré potential in 2D valley semiconductors 7-9 , but these signatures have yet to be experimentally detected. Here, we report experimental evidence of interlayer valley excitons trapped in a moiré potential in MoSe2/WSe2 heterobilayers. At low temperatures, we observe photoluminescence near the free interlayer exciton energy but with over 100 times narrower linewidths (~100 μeV). The emitter g-factors are homogeneous across the same sample and only take two values, -15.9 and 6.7, in samples with twisting angles near 60° and 0°, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley pairing configurations. At a twist angle near 20°, the emitters become two orders of magnitude dimmer, but remarkably, they possess the same g-factor as the heterobilayer near 60°. This is consistent with the Umklapp recombination of interlayer excitons near the commensurate 21.8° twist angle 7 . The emitters exhibit strong circular polarization, which implies the preservation of three-fold rotation symmetry by the trapping potential. Together with the power and excitation energy dependence, all evidence unambiguously points to their origin as interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. Our results open opportunities for 2D moiré optics with twist angle as a unique control knob.

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“…Even after the recombination of exciton, which takes place after a few nanoseconds [19,20,22], one expects the spin-valley of single, localized hole to be preserved for a much longer time. In fact from the valley lifetime of free holes [14,16,17], we expect a single spin-valley lifetime on the order of microseconds, if not longer. On longer timescales, valley relaxation could be mediated by hyperfine interaction with nuclear spins, which is expected to be quite small in TMDs [24,36].…”

Section: Energy (Mev)mentioning

confidence: 95%

“…However, as recombination lifetimes of photogenerated excitations in TMDs is on the order of a few picoseconds, optically generated valley lifetime is limited to a similar timescale. On the other hand, valley polarization of free charge carriers, as opposed to photogenerated excitations, shows promising prospect with lifetimes on the order of microseconds reported for holes [14][15][16][17][18]. A natural question for quantum information science and quantum metrology applications is whether a single spin-valley can be optically addressed and manipulated.…”

mentioning

confidence: 99%

Optical initialization of a single spin-valley in charged WSe2 quantum dots

Chen

Dubey

et al. 2019

Nat. Nanotechnol.

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Control and manipulation of single charges and their internal degrees of freedom, such as spins, is a fundamental goal of nanoscience with promising technological applications. Recently, atomically thin semiconductors such as WSe 2 have emerged as a platform for valleytronics, offering rich possibilities for optical, magnetic and electrical control of the valley index [1, 2]. While progress has been made in controlling valley index of ensemble of charge carriers [3-5], valley control of individual charges, crucial for valleytronics, remains unexplored. Here, we provide unambiguous evidence for localized holes with net spin in optically active WSe 2 quantum dots (QDs) and control their spin-valley state with the helicity of the excitation laser under small magnetic field. We estimate a lower bound on the valley lifetime of a single charge in QD from recombination time to be ∼ nanoseconds. Remarkably, neutral QDs do not exhibit such a control, demonstrating the role of excess charge in prolonging the valley lifetime. Our work extends the field of 2D valleytronics to the level of single spin-valley, relevant for quantum information and sensing applications.Localized single spins in solid-state have been widely studied for quantum information technology, spintronics and quantum sensing [6,7], in addition to serving as a versatile playground for exploring many-body physics [8]. With the rise of semiconducting van der Waals (vdW) materials having direct band gap such as group VI-B transition metal dichalcogenides (TMDs), a arXiv:1810.01887v1 [cond-mat.mes-hall]

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Microsecond dark-exciton valley polarization memory in two-dimensional heterostructures

Cited by 118 publications

References 50 publications

Interlayer-Exciton Based Nonvolatile Valleytronic Memory

Interlayer-Exciton Based Nonvolatile Valleytronic Memory

Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers

Optical initialization of a single spin-valley in charged WSe2 quantum dots

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