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Seminarium "Coherence-Correlations-Complexity" (KFT, PWr)

13:15 środa, 02-03-16
Sala 320a bud. A-1, Politechnika Wrocławska

Long-lived photoluminescence polarization of liquid exfoliated monolayer tungsten disulphide

dr Łukasz Kłopotowski

Instytut Fizyki Polskiej Akademii Nauk w Warszawie

Transition metal dichalcogenides (TMDs) have recently emerged as an exciting playground where novel electronic degrees of freedom can be studied. The particular band structure of monolayer TMDs exhibits two inequivalent minima (valleys) at +K and -K corners of a hexagonal Brillouin zone. The K valleys constitute a binary index (pseudospin), which can be addressed with optical transitions in circular polarizations, opening a way to applications in quantum information processing. Moreover, the direct energy gap of monolayer TMDs provide an easy spectroscopic access to valley dynamics via monitoring the photoluminescence (PL) circular polarization. In this talk, I will present our results on low temperature PL of monolayer tungsten disulphide. The nanosheets of this material can be easily obtained by liquid exfoliation, a method which provides large quantities of the material, so no microscopic techniques are required for PL studies. I will demonstrate that the PL at low temperature is dominated by localized states, which behave as quasi-zero dimensional centers. I will show that the PL retains up to 60% of the polarization from the excitation laser and that this polarization decays on a timescale significantly exceeding the PL lifetime. Finally, employing a rate equation model, I will propose a relaxation mechanism responsible for the observed dynamics.

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