Exciton dephasing in lead sulfide quantum dots by X-point phonons

Article English OPEN
Masia, Francesco ; Langbein, Wolfgang Werner ; Moreels, Iwan ; Hens, Zeger ; Borri, Paola (2011)
  • Publisher: American Physical Society
  • Related identifiers: doi: 10.1103/PhysRevB.83.201309
  • Subject: Q1 | QC
    arxiv: Condensed Matter::Materials Science | Condensed Matter::Mesoscopic Systems and Quantum Hall Effect

Using a sensitive transient four-wave mixing technique in heterodyne detection, we measured the ground-state excitonic dephasing in PbS colloidal quantum dots of 4–6-nm diameter in the temperature range from 5 to 100 K. We observe an ultrafast (<100 fs) initial decay followed by a component of about 300 fs at 5 K, which becomes faster with decreasing dot size and increasing temperature. This dynamics is attributed to pure dephasing of phonon-assisted transitions in the peculiar band structure of PbS, which allows coupling to phonons with wave vectors both near the Brillouin zone center and near the (100) zone edge, the X point. We estimate an upper limit of 7% for the weight of the zero-phonon line with 2.6-ps spin-flip limited dephasing.
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