band-edge divergence and fermi-edge singularity in an n-type doped quantum wire. toshiyuki ihara...
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Band-edge divergence and Fermi-edge singularityBand-edge divergence and Fermi-edge singularity
in an n-type doped quantum wire.in an n-type doped quantum wire.
Toshiyuki IharaToshiyuki Ihara Ph.D student of Akiyama groupPh.D student of Akiyama group
in Institute for Solid State Physics, University of Tokyo and CREST, JST, Chiba in Institute for Solid State Physics, University of Tokyo and CREST, JST, Chiba 2778581, Japan2778581, Japan
’’06 08/02 @ EPFL Switzerland06 08/02 @ EPFL Switzerland
Members in Akiyama Members in Akiyama LaboratoryLaboratory
秋山 英文Hidefumi AKIYAMA
吉田 正裕Masahiro YOSHITA
劉 舒曼 Liu Shu-man
安東 頼子Yoriko ANDO
伊藤 弘毅Hirotake ITOH
井原 章之Toshiyuki IHARA
稲田 智志Satoshi INADA
岡田 高幸Takayuki OKADA
岡野 真人Makoto OKANO
宗像 孝光Takamitsu MUNAKATA
Recent research topicsRecent research topics
1D many-body systems
Firefly (Lightning bug)
T-wire Laser
Quantum wire laser action by electro- and optical-excitation Optical response of low-dimensional many-body systems
Bioluminescence quantum-efficiency measurement
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What is T-shaped quantum wire ?What is T-shaped quantum wire ?
BenefitSize controllability
High quality
Weak point Small confinement Difficult fabrication
T-shaped quantum wireis made of two quantum wells
(Arm well & Stem well)grown by
molecular beam epitaxy
Our experiments on Our experiments on quantum wiresquantum wires
Micro-PL and resonant PLE measurements
Waveguide transmission measurements
Lasing by electro- and optical-excitation
Single / Multi T-wire with optical waveguide
n-type doped single T-wire with FET structure
sample
measurement
Our experiments on Our experiments on quantum wiresquantum wires
Micro-PL and resonant PLE measurements
Waveguide transmission measurements
Lasing by electro- and optical-excitation
Single / Multi T-wire with optical waveguide
n-type doped single T-wire with FET structure
sample
measurement
Band edge and Fermi edge in the optical spectraBand edge and Fermi edge in the optical spectra
“Band-edge peak” and/or “Fermi-edge peak” appears in the spectra !?
Without many-body effects With Fermi-edge singularity effect
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G. D. Mahan, Phys. Rev. 153, 882 (1967).
5.0
Both experimental and theoretical investigations have reported since early 90’s.
Sample structure of n-type doped T-wireSample structure of n-type doped T-wire< fabrication >
MBE with cleaved edge overgrowth method
< size of wire >
14 x 6nm x 4mm(single)
< doping >
①Si modulation doping②FET gate structure→tunable electron density
< measurement >
Temperature-elevated micro-PL spectra & resonant PLE spectra
Result at high electron Result at high electron densitydensityHigh electron density : 6x105 cm-1
Cryostat temperature : 5K(Estimated temperature : 10K)
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’04 T. Ihara et. al.
We observed the Fermi-edge absorption onset with small FES enhancement
Comparison with Oberli’s experimentsComparison with Oberli’s experimentsD. Y. Oberli et al, Physica E 11, 224 (2001).
What if we change temperature and electron What if we change temperature and electron density ?density ?
Higher temperature
Lower temperatureBand-edge absorption ?
Band gap renormalization ?Metal-Insulator crossover ?
Bound states ?1D screening ?
Low density
Band-edge absorption ?
Fermi edge singularity ?
Band edge & Fermi edgeinduced by 1D DOS and
Pauli Blocking
Results : PL and PLE spectra at various Results : PL and PLE spectra at various temperaturetemperature
- Same energy with PL peak. - Good agreements with calculations.- Characteristic of 1D electron systems
Tem
pera
ture
high
low
A sharp absorptionpeak (BE) appears.
Fermi-edge absorption onset (FE) appears.
Sharp absorption peak at 50K
Band-edge absorption peak induced by 1D DOS divergence !!
T=50K (kBT/Ef ~ 1)non-degenerate 1DEG
T=5K (kBT/Ef ~ 0.1)degenerate 1DEG
※ Electron density : 6x105 cm-1
Results : PL and PLE spectra at various electron density at Results : PL and PLE spectra at various electron density at T=5KT=5K
Sharp band-edge absorption appears at ne = 1.5x105cm-1 ~ 3x105cm-1
Discrete symmetrical peaks appear only at low densities (ne < 1.5x105cm-1 )
Ele
ctro
n de
nsity
high
low
ne=6x105cm-1 ~ 3x105cm-1
degenerate 1DEG (kBT/Ef < 0.5)
-Fermi edge absorption onset-Band edge emission-Band gap renormalization
ne=3x105cm-1 ~ 1.5x105cm-1
non-degenerate 1DEG (kBT/Ef > 0.5)
Sharp band-edge absorption
ne < 1.5x105cm-1
Discrete peaks of bound states
SummarySummary
Low-temperature PL and PLE spectra are studied in an n-type modulation-doped T-shaped single quantum wire with a gate to tune electron densities.
With non-degenerate 1D electron gas, band-edge absorption exhibits a sharp band-edge-divergence of 1D density of states.
When the dense 1D electron gas is degenerate at a low temperature, we observe a band-edge emission peak and a Fermi-edge absorption onset with small FES effect.
Further investigations
- Trion / Band-edge problem- PL and PLE measurement at lower temperature ( ~ 1K) - Contrast with 2D electron systems.
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