Understanding and controlling optical excitations in individual hybrid nanostructures
Final Report Abstract
The main aim of the project is to explore the fundamental microscopic mechanisms governing the optical excitations of two specific hybrid material systems, namely (1) quantum-dot/quantum-well semiconductor based hybrid nanostructures coupled via tunneling and (2) metal/semiconductor hybrid nanostructures coupled via their exciton and plasmon resonances. In both systems, we wanted to obtain an improved understanding of the microscopic coupling mechanisms and – most importantly – to study the quantum dynamics of the coupling processes in the time domain with femtosecond resolution. This research was performed in close collaboration between the group of Prof. Greg Salamo from the University of Arkansas, a leading expert in nanofabrication and optical spectroscopy of semiconductor nanostructures, and the Ultrafast Nano-Optics group in Oldenburg. In the first part of the project, we performed a comprehensive study of the tunnel coupling in a hybrid nanostructure consisting of an InGaAs quantum well separated by a thin barrier from an InAs quantum dot layer. The tunnel coupling of electrons from the conduction band of the QW to quantized electronic states in the QD layer has been studied in a wide range of experimental conditions, varying the tunnel barrier, excitation intensity and sample temperature. Both in stationary photoluminescence excitation spectroscopy and time-resolved pump-probe experiments we found signatures of very rapid tunnel coupling dynamics on a time scale of down to 2 ps for samples with 2 nm tunneling barrier. Some of our observations went beyond the well-established weak coupling regime and entered the intermediate coupling regime. An optical Bloch equation model has been developed to successfully describe tunneling in this regime. In samples with extremely thin barriers of less than 2 nm, even faster dynamics have been found and some signatures of strong coupling could be observed in PLE spectroscopy. The experimental results provide detailed new insight into the coupling dynamics in such systems. In the second part we studied the coherent energy exchange between excitons and surface plasmon polariton excitations. We have designed a model system for exciton-plasmon coupling by depositing a metal nanoslit grating on a thin GaAs quantum well. Here, both stationary and timeresolved optical spectroscopy provided clear evidence for such coupling. An intermediate coupling regime has been reached and the effect of the exciton-plasmon coupling on long-lived Raman coherences in the quantum well has been studied for the first time. To reach the most interesting strong-coupling regime of exciton-plasmon interactions, we have designed a prototyptical model system, consisting of a metal nanoslit grating covered with a thin layer of J-aggregated dye film. In this system, hybrid exciton-plasmon excitations are formed by coupling excitonic dipole moments to locally enhanced vacuum fluctuations of the plasmon field. Rabi coupling energies of up to 200 meV have been observed which allowed us to reach strong coupling at room temperature and to study the microscopic mechanisms that govern this coupling in considerable detail. In particular, we could report the first-time-domain analysis of ultrafast Rabi oscillations with 30-fs period between an ensemble of excitons and surface plasmon polariton fields. In addition, we could demonstrate, in a series of publications, transient and reversible reductions of the Rabi splitting due to exciton state filling, ultrafast switching of hybrid exciton-plasmon excitations on a time scale of few tens of femtoseconds, sub- and superradiant damping of strongly coupled hybrid exciton-plasmon excitations and optical Stark effects in such strongly coupled hybrid systems. A fully quantummechanical model for the strong coupling in hybrid exciton-surface plasmon polariton systems, based on time dependent density matrix formalism, has been developed and successfully compared to the experimental results. These results are of fundamental interest for applications, in particular in active nanophotonics, because they show that the coating of a nanostructured metallic layer with a thin dye film essentially transforms the metal into an ultrafast and reversibly switchable metallic mirror with a switching time of only few tens of femtoseconds. This functionality may be of key relevance for future all-optical nanophotonic transistor designs. An editorial in Nature Photonics was partly dedicated to our experimental achievements (R. Won, “Transcending Limitations”, Nat. Photon. 4, 81, 2013).
Publications
- Measurement of coherent tunneling between InGaAs quantum wells and InAs quantum dots using photoluminescence spectroscopy, Physical Review B, 82, 155413 (2010)
Y. I. Mazur, V. G. Dorogan, D. Guzun, E. Marega, Jr., G. J. Salamo, G. G. Tarasov, A. O. Govorov, P. Vasa, and C. Lienau
- Tunneling-barrier controlled excitation transfer in hybrid quantum dot-quantum well nanostructures, Journal of Applied Physics, 108, 074316 (2010)
Y. I. Mazur, V. G. Dorogan, E. Marega, Jr., Z. Y. Zhuchenko, M. E. Ware, M. Benamara, G. G. Tarasov, P. Vasa, C. Lienau, and G. J. Salamo
- Excited state coherent resonant electronic tunneling in quantum well-quantum dot hybrid structures, Applied Physics Letters, 98, 083118 (2011)
Y. I. Mazur, V. G. Dorogan, E. Marega, Jr., M. Benamara, Z. Y. Zhuchenko, G. G. Tarasov, C. Lienau, and G. J. Salamo
- State filling dependent luminescence in hybrid tunnel coupled dot-well structures, Nanoscale, 4, 7509-7516 (2012)
Y. I. Mazur, V. G. Dorogan, M. E. Ware, E. Marega, Jr., M. Benamara, Z. Y. Zhuchenko, G. G. Tarasov, C. Lienau, and G. J. Salamo
(See online at https://doi.org/10.1039/c2nr32477f) - Dynamic configurational resonances caused by optical nonlinearities in ultra-fast near-field microscopy, Journal of Optics, 15, 035204 (2013)
V. Lozovski, V. Vasilenko, G. G. Tarasov, C. Lienau, Y. I. Mazur, and G. J. Salamo
(See online at https://doi.org/10.1088/2040-8978/15/3/035204) - Effect of resonant tunneling on exciton dynamics in coupled dot-well nanostructures, Journal of Applied Physics, 113, 154304 (2013)
D. Guzun, Y. I. Mazur, V. G. Dorogan, M. E. Ware, E. Marega, Jr., G. G. Tarasov, C. Lienau, and G. J. Salamo
(See online at https://doi.org/10.1063/1.4801891) - Effect of tunneling transfer on thermal redistribution of carriers in hybrid dot-well nanostructures, Journal of Applied Physics, 113, 034309 (2013)
Y. I. Mazur, V. G. Dorogan, E. Marega, Jr., D. Guzun, M. E. Ware, Z. Y. Zhuchenko, G. G. Tarasov, C. Lienau, and G. J. Salamo
(See online at https://doi.org/10.1063/1.4779686) - Real-time observation of ultrafast Rabi oscillations between excitons and plasmons in metal nanostructures with J-aggregates, Nature Photonics, 7, 128-132 (2013)
P. Vasa, W. Wang, R. Pomraenke, M. Lammers, M. Maiuri, C. Manzoni, G. Cerullo, and C. Lienau
(See online at https://doi.org/10.1038/NPHOTON.2012.340) - Quantum beats in hybrid metal-semiconductor nanostructures, ACS Photonics, 2015, 2 (9), pp 1341–1347
C. K. Dass, T. Jarvis, V. P. Kunets, Y. I. Mazur, G. G. Salamo, C. Lienau, P. Vasa, and X. Li
(See online at https://doi.org/10.1021/acsphotonics.5b00328)
