Polarization analysis of excitons in monolayer and bilayer transition-metal dichalcogenides

Dery, Hanan; Song, Yang

doi:10.1103/physrevb.92.125431

Cited by 160 publications

(222 citation statements)

References 61 publications

Supporting

Mentioning

211

Contrasting

Order By: Relevance

“…First prototype device applications, such as transistors [17][18][19] and light emitters [20][21][22], have shown the promise of this atomically thin material for electronics and optoelectronics. Another motivation for research into MoS 2 is the high natural abundance of the naturally occurring mineral molybdenite [23].…”

Section: Introductionmentioning

confidence: 99%

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

et al. 2017

View full text Add to dashboard Cite

The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS 2 an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the bettercharacterized ML materials MoSe 2 and WSe 2 . In this work, we show that encapsulation of ML MoS 2 in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T ¼ 4 K. Narrow optical transition linewidths are also observed in encapsulated WS 2 , WSe 2 , and MoSe 2 MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.

show abstract

Section: Introductionmentioning

confidence: 99%

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

et al. 2017

View full text Add to dashboard Cite

show abstract

“…An excitonic valley polarization can be read out optically via the circular polarization degree of the emitted photoluminescence (PL), and initial studies using continuous-wave excitation revealed a large steadystate polarization 4,5 , which was shown to be stable against depolarization in large in-plane magnetic fields 6 . While many early studies of valley physics focused on the naturally abundant MoS 2 , synthetic TMDC crystals quickly garnered scientific attention due to their spectrally narrow PL emission 7 , and the large tuning range of conduction-and valence-band spin splitting [8][9][10] afforded by the different combinations (or alloys 11,12 ) of the constituent elements Mo, W, S, Se, and Te. Time-resolved studies of exciton recombination and valley dynamics showed that ultrafast radiative recombination 13-17 is partially responsible for the large valley polarization observed in experiments, as the exciton lifetime limits the time window for valley dephasing.…”

mentioning

confidence: 99%

Long-lived spin polarization in n-doped MoSe2 monolayers

Schwemmer

Nagler

Hanninger

et al. 2017

Applied Physics Letters

View full text Add to dashboard Cite

Transition metal dichalcogenide monolayers are highly interesting for potential valleytronic applications due to the coupling of spin and valley degrees of freedom and valley-selective excitonic transitions. However, ultrafast recombination of excitons in these materials poses a natural limit for applications, so that a transfer of polarization to resident carriers is highly advantageous. Here, we study the low-temperature spin-valley dynamics in nominally undoped and n-doped MoSe 2 monolayers using time-resolved Kerr rotation. In the ndoped MoSe 2 , we find a long-lived component of the Kerr signal which we attribute to the spin polarization of resident carriers. This component is absent in the nominally undoped MoSe 2 . The long-lived spin polarization is stable under applied in-plane magnetic fields. Spatially resolved measurements allow us to determine an upper boundary for the electron spin diffusion constant in MoSe 2 .Transition metal dichalcogenide (TMDC) monolayers have a peculiar band structure 1,2 , in which spin and valley degrees of freedom are coupled, and the optical selection rules allow for valley-selective generation of excitons 3 . An excitonic valley polarization can be read out optically via the circular polarization degree of the emitted photoluminescence (PL), and initial studies using continuous-wave excitation revealed a large steadystate polarization 4,5 , which was shown to be stable against depolarization in large in-plane magnetic fields 6 . While many early studies of valley physics focused on the naturally abundant MoS 2 , synthetic TMDC crystals quickly garnered scientific attention due to their spectrally narrow PL emission 7 , and the large tuning range of conduction-and valence-band spin splitting 8-10 afforded by the different combinations (or alloys 11,12 ) of the constituent elements Mo, W, S, Se, and Te. Time-resolved studies of exciton recombination and valley dynamics showed that ultrafast radiative recombination 13-17 is partially responsible for the large valley polarization observed in experiments, as the exciton lifetime limits the time window for valley dephasing. However, the ultrafast excitonic recombination also severely limits potential applications of the valley degree of freedom in novel devices, so that a transfer of valley polarization to resident carriers, which was observed in several TMDCs 18,19 , is highly advantageous. Among the TMDC family, MoSe 2 is characterized by a comparatively low optically induced valley polarization degree, which is only observable at all under near-resonant excitation conditions 20-22 and can be increased by modifying the recombination dynamics using coupling to photonic cavities 23 . To investigate the anomalously low valley polarization in MoSe 2 , timeresolved studies of valley dynamics are needed.Here, we directly compare the low-temperature spinvalley dynamics in nominally undoped and n-doped MoSe 2 monolayers using time-resolved Kerr rotation (TRKR). We find a long-lived component of the Kerr a) Electronic mail: tobias.ko...

show abstract

“…1 and 2, whereas in ML WSe 2 , the discrete emitters can overlap with broad peaks linked to localized 2D excitons and/or their phonon replica. 30 (ii) The 2D neutral exciton states in ML MoSe 2 are optically bright, whereas the lowest energy transition in ML WSe 2 is optically dark, [30][31][32][33][34][35] which will impact carrier relaxation and recombination dynamics. The MoSe 2 ML flakes are obtained by micro-mechanical cleavage of a bulk crystal using viscoelastic stamping.…”

mentioning

confidence: 99%

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

Branny

Wang

Kumar

et al. 2016

Applied Physics Letters

118

110

View full text Add to dashboard Cite

Transition metal dichalcogenide monolayers such as MoSe2,MoS2 and WSe2 are direct bandgap semiconductors with original optoelectronic and spin-valley properties. Here we report spectrally sharp, spatially localized emission in monolayer MoSe2. We find this quantum dot like emission in samples exfoliated onto gold substrates and also suspended flakes. Spatial mapping shows a correlation between the location of emitters and the existence of wrinkles (strained regions) in the flake. We tune the emission properties in magnetic and electric fields applied perpendicular to the monolayer plane. We extract an exciton g-factor of the discrete emitters close to -4, as for 2D excitons in this material. In a charge tunable sample we record discrete jumps on the meV scale as charges are added to the emitter when changing the applied voltage.

show abstract

Polarization analysis of excitons in monolayer and bilayer transition-metal dichalcogenides

Cited by 160 publications

References 61 publications

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

Long-lived spin polarization in n-doped MoSe2 monolayers

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

Contact Info

Product

Resources

About