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Polariton Condensates in a Trap and Photon Lasing in Two-Dimensional Semiconductor Microcavities

Nelsen, Bryan (2012) Polariton Condensates in a Trap and Photon Lasing in Two-Dimensional Semiconductor Microcavities. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Recent experiments in microcavity polaritons have shown many effects that can be associated with the phase transition known as Bose-Einstein condensation; these effects include a dramatic increase in both the population of the zero-momentum state and lowest-lying energy state, the formation of first- and second-order coherence in both space and time, and the spontaneous polarization of the polariton ensemble. However, these same results can also be a consequence of lasing. The primary focus of this dissertation is to examine these effects and determine to what degree the effects of lasing can be distinguished from those of Bose-Einstein condensation. Bose-Einstein condensation in a two-dimensional weakly-interacting gas, such as polaritons, is predicted to not occur without the aid of spatial confinement, i.e., a trap. Polaritons were subjected to various methods of confinement, including stress traps and exciton-reservoir traps, and the signatures of condensation in these traps are shown to be dramatically different than those of lasing in a system without confinement. It is also shown that, when driving the polariton condensate to very high density, the polaritons dissociate and the lasing transition succeeds Bose-Einstein condensation. The geometry of the trapping potential was also exploited to indicate that the symmetry of the condensate momentum-space distribution followed that of the ground state of the trap.

At reasonable densities, the lifetime of polaritons is of the same order as the polariton-polariton interaction time, hence the previously shown effects are an incomplete Bose-Einstein condensation since thermodynamic equilibrium is not reached. A second part of this work has been to extend the lifetime of polaritons to achieve a more thermalized ensemble. We do this by increasing the Q factor of the microcavity through improving the reflectivity of the mirrors. These samples exhibit many interesting phenomenon since the polariton lifetime becomes long enough to traverse significant distances. Here, Bose-Einstein condensation occurs at a point spatially separated from the excitation source, ruling out the possibility of nonlinear amplification of the pump laser. Also, a superfluid-like transition is observed, giving rise to possible signatures of vortices.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairSnoke, Davidsnoke@pitt.eduSNOKE
Committee MemberDutt, M.V. Gurudevgdutt@pitt.eduGDUTT
Committee MemberJasnow, Davidjasnow@pitt.eduJASNOW
Committee MemberMueller, Jamesmueller@pitt.eduMUELLER
Committee MemberFalk, Joelfalk@pitt.eduFALK
Date: 29 June 2012
Date Type: Publication
Defense Date: 11 April 2012
Approval Date: 29 June 2012
Submission Date: 26 April 2012
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 135
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Polariton, Bose-Einstein Condensation, Lasing, Microcavity, Quantum Well, Exciton, Stress Trap, Electron-Hole Exchange, Valence-Band Mixing
Date Deposited: 29 Jun 2012 19:13
Last Modified: 15 Nov 2016 13:57


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