Revealing the Exciton Fine Structure in PbSe Nanocrystal Quantum Dots

Details Revealing the Exciton Fine Structure in PbSe Nanocrystal Quantum Dots Revealing the Exciton Fine Structure in PbSe Nanocrystal Quantum Dots

2010-06-29

arxiv.org/abs/1006.5673v1

Physical Review Letters 105, 067403 (2010)

Physics

Condensed Matter

Mesoscale and Nanoscale Physics

To appear in Physical Review Letters

Scientific paper

10.1103/PhysRevLett.105.067403

We measure the photoluminescence (PL) lifetime, $\tau$, of excitons in colloidal PbSe nanocrystals (NCs) at low temperatures to 270~mK and in high magnetic fields to 15~T. For all NCs (1.3-2.3~nm radii), $\tau$ increases sharply below 10~K but saturates by 500~mK. In contrast to the usual picture of well-separated ``bright" and ``dark" exciton states (found, e.g., in CdSe NCs), these dynamics fit remarkably well to a system having two exciton states with comparable - but small - oscillator strengths that are separated by only 300-900 $\mu$eV. Importantly, magnetic fields reduce $\tau$ below 10~K, consistent with field-induced mixing between the two states. Magnetic circular dichroism studies reveal exciton g-factors from 2-5, and magneto-PL shows $>$10\% circularly polarized emission.

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