Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 35: Ultrafast Phenomena I

O 35.3: Talk

Tuesday, March 8, 2016, 10:00–10:15, H10

Ultrafast carrier dynamics in bulk MoS₂ studied by transient absorption spectroscopy — •Tim Völzer, Matthias Lütgens, Franziska Fennel, and Stefan Lochbrunner — Institut für Physik, Universität Rostock, Albert-Einstein-Str. 23, 18059 Rostock

Transistion metal dichalcogenides feature unique electronic and optical properties. In addition, they are characterised by a layered structure, allowing the preparation of atomically thin crystals. As a representative of those materials, molybdenum disulfide is suggested as a promising candidate for optoelectronic and photocatalytic applications. To characterise the optical excitation and its dynamics we performed both static transmission and time-resolved pump-probe spectroscopy.

Two absorption bands, labelled A and B, are observed in the static absorption spectrum which are attributed to direct transitions at the K point of the Brillouin zone. The lower electronic transition is excited within the femtosecond absorption measurements and the dynamics is followed by a white light continuum covering the whole visible range. A decrease of absorption for the A and B transition is observed whereas an increase of absorption is present for lower energies. This signature is indicative for a band renormalization induced by the population in the first excited band. The subsequent signal decay shows two distinct time dependencies, an exponential sub picosecond contribution caused by carrier-carrier and carrier-phonon scattering and a strongly non-exponential component for longer times. The latter is attributed to electron-hole recombination via defect states and shows an acceleration with increasing excitation density.