Delocalization-localization Transition of Plasmons in Random GaAs/AlGaAs Superlattices Y.A.Pusep Institute of Physics of São Carlos, University of São Paulo Collaborators: Experiment – A.D.Rodrigues, UFSCar. Theory - S.S.Sokolov, B.Verkin Institute for Low-Temperature Physics and Engineering, National Academy of Sciences of Ukraine. Samples – H.Arakaki, C.A. de Souza, IFSC/USP.
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Y.A.Pusep Institute of Physics of São Carlos, University of São Paulo Collaborators: Experiment – A.D.Rodrigues, UFSCar. Theory - S.S.Sokolov, B.Verkin.
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Delocalization-localization Transition of Plasmons in Random GaAs/AlGaAs
Superlattices
Y.A.Pusep
Institute of Physics of São Carlos, University of São Paulo
Collaborators:
Experiment – A.D.Rodrigues, UFSCar.Theory - S.S.Sokolov, B.Verkin Institute for Low-Temperature Physics and Engineering, National Academy of Sciences of Ukraine.Samples – H.Arakaki, C.A. de Souza, IFSC/USP.
MotivationWhy plasmons ?
Advantages of optical and electrical circuits:Fast data transfer by transmitting optical signals through minuscule nanoscale structures .
Optical fibers versus electrical circuits. Diffraction limit.
Manipulation of plasmons (localization and propagation).
Electrons and Plasmons1. Electrons: single-particle excitations
2. Plasmons: collective excitations
Outline
1. Random superlattices
2. Raman scattering by collective excitations
3. Plasmon localization: theory and experiment
4. Conclusions
Artificially disordered superlattices
DSL
Nwell
E
0
= /W
(GaAs)n(Al
0.3Ga
0.7As)
m
W
Z E(kz)
kz /D
SL
Criterion of Localization
Electrons
( = 0, w T = 0) 0, /T < 0
( = 0, w T = 0) = 0, /T > 0
metal (kFl>1):
insulator (kFl<1):
Obs: l is the electron free path length, kF = 2π/λe, λe is the electron wavelength.
Criterion of Plasmonlocalization - ?
Theory of plasmon localization
Plasmon wave function:
with0.2 0.4 0.6 0.8 1.0 1.2
0
10
20
30
Lc R
0
p,
cm-1
2R0/L
c
Lc R
0
R0= 7 nm
U0= 12 cm-1
Results of calculations
Neutral impurity scattering potential:
Localized plasmon: Lc < R0
Delocalized plasmon: Lc > R0
2. Relation between Lc and R0 determine propagation of
Delocalized plasmon: Lc > Ro – the increasing disorder results in increasing plasmon linewidth;
Localized Plasmon: Lc < Ro – no influence of the disorder on plasmon linewidth;
The independence of the plasmon linewidth on disorder is the manifestation of plasmon localization.
The increasing temperature enhances the localization of the weakly localized plasmons, while it causes the delocalization of the strongly localized plasmons.