51
|
Richard M, Kasprzak J, Romestain R, André R, Dang LS. Spontaneous coherent phase transition of polaritons in CdTe microcavities. PHYSICAL REVIEW LETTERS 2005; 94:187401. [PMID: 15904409 DOI: 10.1103/physrevlett.94.187401] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Revised: 08/27/2004] [Indexed: 05/02/2023]
Abstract
We report on evidence for polariton condensation out of a reservoir of incoherent polaritons. Polariton population and first-order coherence are investigated by spectroscopic imaging of the far-field emission of a CdTe-based microcavity under nonresonant pumping. With increasing pumping power, stimulated emission with thresholdlike behavior and spectral narrowing is observed in the strong exciton-photon coupling regime. We show that it comes from a narrow ring in k space, exhibiting enhanced spatial and angular coherence at the stimulation onset.
Collapse
Affiliation(s)
- Maxime Richard
- CEA-CNRS-UJF group Nanophysique et semiconducteurs, Laboratoire de Spectrométrie Physique (CNRS UMR5588), Université J. Fourier-Grenoble, BP87, 38402 St Martin d'Hères, France
| | | | | | | | | |
Collapse
|
52
|
Levitov LS, Simons BD, Butov LV. Pattern formation as a signature of quantum degeneracy in a cold exciton system. PHYSICAL REVIEW LETTERS 2005; 94:176404. [PMID: 15904321 DOI: 10.1103/physrevlett.94.176404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Revised: 01/14/2005] [Indexed: 05/02/2023]
Abstract
The development of a Turing instability to a spatially modulated state in a photoexcited electron-hole system is proposed as a novel signature of exciton Bose statistics. We show that such an instability, driven by kinetics of exciton formation, can result from stimulated processes that build up near quantum degeneracy. The stability of an electron-hole interface which describes recently observed exciton rings is analyzed. Interface instability occurs below a critical temperature, with a periodic 1D pattern developing via a continuous (type II) transition, in a qualitative agreement with observations.
Collapse
Affiliation(s)
- L S Levitov
- Department of Physics, Center for Materials Sciences & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
| | | | | |
Collapse
|
53
|
Balatsky AV, Joglekar YN, Littlewood PB. Dipolar superfluidity in electron-hole bilayer systems. PHYSICAL REVIEW LETTERS 2004; 93:266801. [PMID: 15698002 DOI: 10.1103/physrevlett.93.266801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Indexed: 05/24/2023]
Abstract
Bilayer electron-hole systems, where the electrons and holes are created via doping and are confined to separate layers, undergo excitonic condensation when the distance between the layers is smaller than the typical distance between the particles within the layer. We argue that the excitonic condensate is a novel dipolar superfluid in which the phase of the condensate couples to the gradient of the vector potential. We predict the existence of a dipolar supercurrent which can be tuned by an in-plane magnetic field. Thus the dipolar superfluid offers an example of excitonic condensate in which the composite nature of its constituent excitons is manifest in the macroscopic superfluid state. We also discuss various properties of this superfluid including the role of vortices.
Collapse
Affiliation(s)
- Alexander V Balatsky
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
| | | | | |
Collapse
|
54
|
Yu. GOLINEY I, LEV SB, SUGAKOV VI, VERTSIMAKHA GV. GIANT INCREASE OF THE EXCITON LIFETIME IN SEMIMAGNETIC SEMICONDUCTORS WITH DOUBLE QUANTUM WELLS IN MAGNETIC FIELD. INTERNATIONAL JOURNAL OF NANOSCIENCE 2004. [DOI: 10.1142/s0219581x04002358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Magnetic field dependence of the excitonic spectrum and the intensity of the optical transitions for excitons in the double quantum well heterostructures based on semimagnetic semiconductors of various compositions are studied. The calculations carried out for (Zn, Mn)Se -based double quantum well structures showed that in the weak magnetic fields, the lowest energy states are the single-well states (direct excitons) for which both the electron and the hole are predominantly localized in the same well. At some values of magnetic field, the crossing of the direct exciton with indirect exciton formed by an electron and a hole, situated predominantly in the different wells, occurs. In the magnetic field exceeding some critical value, the lowest energy level belongs to the indirect exciton. According to the estimates, the lifetime of the indirect exciton is by several orders of magnitude larger than that of a single-well exciton. The exciton lifetime depends significantly on the width and the material of the barrier between the wells.
Collapse
Affiliation(s)
- I. Yu. GOLINEY
- Department of Materials Science, National University of Singapore, S1A, #02-10 Science Drive 4, Singapore 117543, Singapore
| | - S. B. LEV
- Institute for Nuclear Research, Prospect Nauki 47, 03680 Kiev, Ukraine
| | - V. I. SUGAKOV
- Institute for Nuclear Research, Prospect Nauki 47, 03680 Kiev, Ukraine
| | - G. V. VERTSIMAKHA
- Institute for Nuclear Research, Prospect Nauki 47, 03680 Kiev, Ukraine
| |
Collapse
|
55
|
Keeling J, Levitov LS, Littlewood PB. Angular distribution of photoluminescence as a probe of bose condensation of trapped excitons. PHYSICAL REVIEW LETTERS 2004; 92:176402. [PMID: 15169175 DOI: 10.1103/physrevlett.92.176402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Indexed: 05/24/2023]
Abstract
Recent experiments on two-dimensional exciton systems have shown that excitons collect in shallow in-plane traps. We find that Bose condensation in a trap results in a dramatic change of the exciton photoluminescence (PL) angular distribution. The long-range coherence of the condensed state gives rise to a sharply focused peak of radiation in the direction normal to the plane. By comparing the PL profile with and without Bose condensation, we provide a simple diagnostic for the existence of a Bose condensate. The PL peak has strong temperature dependence due to the thermal order parameter phase fluctuations across the system. The angular PL distribution can also be used for imaging vortices in the trapped condensate. Vortex phase spatial variation leads to destructive interference of PL radiation in certain directions, creating nodes in the PL distribution that imprint the vortex configuration.
Collapse
Affiliation(s)
- Jonathan Keeling
- Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, United Kingdom
| | | | | |
Collapse
|
56
|
Butov LV, Levitov LS, Mintsev AV, Simons BD, Gossard AC, Chemla DS. Formation mechanism and low-temperature instability of exciton rings. PHYSICAL REVIEW LETTERS 2004; 92:117404. [PMID: 15089167 DOI: 10.1103/physrevlett.92.117404] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Indexed: 05/24/2023]
Abstract
The macroscopic rings observed in the photoluminescence patterns of excitons in coupled quantum wells are explained by a mechanism of carrier imbalance, transport, and recombination. The rings originate from the spatial separation of p and n carriers, and occur at the interface of the p and n domains, where excitons are generated. We explore the states of excitons in the ring over a range of temperatures down to 380 mK and report a transition of the ring into a periodic array of aggregates, a new low-temperature ordered exciton state.
Collapse
Affiliation(s)
- L V Butov
- Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | | | | | | | | | | |
Collapse
|
57
|
Rapaport R, Chen G, Snoke D, Simon SH, Pfeiffer L, West K, Liu Y, Denev S. Charge separation of dense two-dimensional electron-hole gases: mechanism for exciton ring pattern formation. PHYSICAL REVIEW LETTERS 2004; 92:117405. [PMID: 15089168 DOI: 10.1103/physrevlett.92.117405] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2003] [Indexed: 05/24/2023]
Abstract
We report on new experiments and theory that unambiguously resolve the recent puzzling observation of large diameter exciton emission halos around a laser excitation spot in two dimensional systems. We find a novel separation of plasmas of opposite charge with emission from the sharp circular boundary between these two regions. This charge separation allows for cooling of initially hot optically generated carriers as they dwell in the charge reservoirs for very long times.
Collapse
Affiliation(s)
- R Rapaport
- Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
| | | | | | | | | | | | | | | |
Collapse
|
58
|
Abstract
Degenerate exciton systems have been produced in quasi-two-dimensional confined areas in semiconductor coupled quantum well structures. We observed contractions of clouds containing tens of thousands of excitons within areas as small as (10 micron)2 near 10 kelvin. The spatial and energy distributions of optically active excitons were determined by measuring photoluminescence as a function of temperature and laser excitation and were used as thermodynamic quantities to construct the phase diagram of the exciton system, which demonstrates the existence of distinct phases. Understanding the formation mechanisms of these degenerate exciton systems can open new opportunities for the realization of Bose-Einstein condensation in the solid state.
Collapse
Affiliation(s)
- C W Lai
- Applied Science and Technology, University of California at Berkeley, Berkeley, CA 94720, USA.
| | | | | | | |
Collapse
|
59
|
La Rocca G. Wannier–Mott Excitons in Semiconductors. ELECTRONIC EXCITATIONS IN ORGANIC NANOSTRUCTURES 2003. [DOI: 10.1016/s1079-4050(03)31002-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
|
60
|
Mani RG, Smet JH, von Klitzing K, Narayanamurti V, Johnson WB, Umansky V. Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures. Nature 2002; 420:646-50. [PMID: 12478287 DOI: 10.1038/nature01277] [Citation(s) in RCA: 600] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2002] [Accepted: 11/04/2002] [Indexed: 11/09/2022]
Abstract
The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature T(c) (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs). In quantum Hall systems and superconductors, zero-resistance states often coincide with the appearance of a gap in the energy spectrum. Here we report the observation of zero-resistance states and energy gaps in a surprising setting: ultrahigh-mobility GaAs/AlGaAs heterostructures that contain a 2DES exhibit vanishing diagonal resistance without Hall resistance quantization at low temperatures and low magnetic fields when the specimen is subjected to electromagnetic wave excitation. Zero-resistance-states occur about magnetic fields B = 4/5 Bf and B = 4/9 Bf, where Bf = 2pifm*/e,m* is the electron mass, e is the electron charge, and f is the electromagnetic-wave frequency. Activated transport measurements on the resistance minima also indicate an energy gap at the Fermi level. The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.
Collapse
Affiliation(s)
- Ramesh G Mani
- Gordon McKay Laboratory of Applied Science, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138, USA.
| | | | | | | | | | | |
Collapse
|
61
|
Abstract
In the past decade, there has been an increasing number of experiments on spontaneous Bose coherence of excitons and polaritons. Four major areas of research are reviewed here: three-dimensional excitons in the bulk semiconductor Cu2O, two-dimensional excitons in coupled quantum wells, Coulomb drag experiments in coupled two-dimensional electron gases, and polaritons in semiconductor microcavities. The unifying theory of all these experiments is the effect of spontaneous symmetry breaking in the Bose-Einstein condensation phase transition.
Collapse
Affiliation(s)
- David Snoke
- Department of Physics, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
| |
Collapse
|