Single photon emitters in exfoliated WSe 2 structures M. Koperski, 1,2 K. Nogajewski, 1 A. Arora, 1 V. Cherkez, 3 P. Mallet, 3 J.-Y. Veuillen, 3 J. Marcus, 3 P. Kossacki, 1,2 and M. Potemski 1 1 Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, Grenoble, France 2 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 3 Institut Néel, CNRS-UGA, Grenoble, France Harmonia MOMB ICPS 2016, 1st August 2016
WSe 2 Transition Metal Dichalcogenides (TMD) layered materials Thin films can be fabricated by mechanical exfoliation (like graphene) Direct band gap for monolayers efficient emitters of light K. F. Mak, et al., Phys. Rev. Lett. 105, 136805 (2010) M. Aaron, et al., Nature Nanotechnology 8, 634 (2013) C. Chakraborty, et al., Nature Nanotechnology 10, 507 (2015) J. S. Ross, et al., Nature Nanotechnology 9, 268 (2014) G. Aivazian, et al., Nature Physics 11, 148 152 (2015) unique, unconventional band structure, huge excitonic effects valley selective polarization rules
PL intensity (a. u.) T=4.2 K Line identification: 2D WSe 2 monolayer typical photoluminescence response broad (10-20meV) emission/absorption peaks "localized, bound excitons" 1650 1700 1750 Emission energy (mev) M. Aaron, et al., Nature Nanotechnology 8, 634 (2013) "negatively charged exciton" "X - " (free) neutral exciton (free)
( Imperfections at edges? ) Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes) 1ML
Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes) ( Imperfections at edges? ) 1ML
( Imperfections at edges? ) Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes) T=4.2 K
( Imperfections at edges? ) Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes)
Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes) ( Imperfections at edges? )
( Imperfections at edges? ) Narrow line emitting centers appear at the edges of WSe 2 flakes (monolayer and thick flakes) T=4.2 K
First reports on the observation of narrow lines emitting centers (from Europe and USA) M. Koperski et al., Single photon emitters in exfoliated WSe 2 structures (France, Poland) A. Srivastava et al., Optically active quantum dots in monolayer WSe 2 (Switzerland) Y-M, He et al., Single quantum emitters in monolayer semiconductors (China, USA) C. Chakraborty et al., Voltage controlled of quantum light from an atomically thin semiconductor (USA) Nature Nanotechnology 10 (2015) What are those emitters?
PL intensity (arb. units) a) correlated line b) 1560 1580 1600 1620 1640 1660 Energy 1680 1700 (mev) g 2 ( ) 1.0 0.5 T=4.2 K g 2 ( ) 1.1 1.0 0.9 0.8 0 300 600 900 Time (ns) 0.0-30 -20-10 0 10 Time 20 (ns) 30 150 W 6 W Photon antibunching = an unambiguous attribute of single photon emitters semiconductor (single) quantum dots, nanocrystals (colloidal dots), NV centers in diamond (SiC), organic molecules interesting applications; issues: stability, room temperature operation, electrical pumping
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer PL intensity (a. u.) 1650 1700 1750 Emission energy (mev) Emission in the same energy range, similar excitation spectra
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer PL intensity (a. u.) PL intensity (a. u.) 1650 1700 1750 Emission energy (mev) 1650 1700 1750 Emission energy (mev) Emission in the same energy range, similar excitation spectra
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer PL intensity (a. u.) PL intensity (a. u.) PL PLE 1650 1700 1750 Emission energy (mev) 1650 1700 1750 Emission energy (mev) Emission in the same energy range, similar excitation spectra
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer PL intensity (a. u.) PL intensity (a. u.) PL PLE 1650 1700 1750 Emission energy (mev) PL PLE 1650 1700 1750 Emission energy (mev) Emission in the same energy range, similar excitation spectra
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer g factor = 13.5 4.3 s+ s- Similar, anomalously large "Zeeman" splitting
Optical response of narrow lines, linked to the 2D properties of a WSe 2 monolayer g factor = 13.5 4.3 s+ s- Similar, anomalously large "Zeeman" splitting
Temperature effect: PL inetnsity (arb. units) 20K 15K 10K 4.5K 1600 1650 1700 Emission energy (mev) Broadening (similar to acoustic phonon effect in semiconductor QDs)
Pronounced (sometimes) linear anisotropy: PL intensity (arb. units) A B pol 1 ( ) pol 2 ( ) 1600 1625 1650 1675 1700 1725 1750 1775 Emission energy (mev) Normalized PL inensity (arb. u.) 1.0 0.5 0.0 1.0 0.5 0.0 line A line B 0 40 80 120 160 200 240 280 320 360 Linear polarization angle (deg.) Similar to a polarized emission of a quantum wire/anisotropic quantum dot S. Schwarz, et al., 2D materials 3 (2016)
Summary Single photon emitters appear at the edge of exfoliated WSe2 structures Properties inherited from 1ML WSe 2 film Suprisingly large magnetooptical effects Single photon emitters in exfoliated WSe 2 structures = nano-flakes of monolayer at the edges of WSe 2 films?
Thank you for your attention! Harmonia MOMB ICPS 2016, 1st August 2016
What are they? Monolayer "nanoflakes" at the edges of monolayers and thicker flakes??? STM: Monolayer nanoflake at the edge of a thicker flake
What are they? Monolayer "nanoflakes" at the edges of monolayers and thicker flakes? An attempt to correlate PL and STM
Electrical pumping Also antibunching in electrically pumped emitters: C. P. Berraquero, et al., arxiv:1603.08795 (2016) PL from the STM tip? S. Schwarz, et al., 2D materials 3 (2016)
What are these emitting centers? Weakly localised excitons: localised: narrow spectral lines, spatial mapping weakly: temperature dependence, no cascaded emission but, rather not defect bound excitons: density of emitters too scarce, every spot with a unique patterns of lines Thus: small nano -flakes or strain induced localisation (?)
Other TMDs : WS 2 M.R. Molas et al., to be published
Other TMDs : MoSe 2 30T s 1 s 2 25T PL intensity (mev) 20T 15T 10T 5T 0T 1550 1600 1650 1700 Emission energy (mev)