Dr. Max Mustermann Referat Kommunikation & Marketing Verwaltung Daniel Steininger AG Strunk / Institut für Exp. und Angewandte Physik FAKULTÄT FÜR PHYSIK Shot noise of excited states in a CNT quantum dot

5µm Pd Re QDQD SD Gate Double Quantum Dot Layout: source, drain, SC central contact, 2 sidegates Operated as single quantum dot (QD) Transport dominated by Coulomb Blockade: Sample setup: -e-beam lithography -Metallization: Sputter (Re) Thermal (Pd)

Coulomb peaks when state is aligned within the bias window Without excited states: Excited states included: „Coulomb Diamond“ pattern Additional steps in Current Coulomb Blockade:

Noise: Noise gives additional information which is discarded in standard DC measurements a)b)

Sources of Noise: Thermal Noise Shot Noise

Sub-/Super Poissonian Noise: Super-poissonian (F > 1): -Electron bunching due to cotunneling and/or blocking states (see later…)

Measurement Circuit: Low frequencies (lock-in) High frequencies (noise) Gain: 1.09 high-frequencies low-frequencies

System calibration (in situ): Differences in peak amplitude visible down to T=20mK

Two different slopes of the Coulomb diamonds – Two CNTs? Sample Characterization: Stability diagram:

90 meV 80 meV 10 meV 20 meV Two sets of Coulomb diamonds: S D Possible configuration: 2 CNTs in parallel APL 78, 3693 (2001) 5µm

Current: dI/dV: Stability Diagram:

Excited states What kind of excitations? Electronic or Vibronic? Yar et al. PRB 84, (2011) Pro vibronic: - excitations are equidistant - alternating pattern: pos./neg. dI/dV

Comparison Franck-Condon model From experiment:

20mK 4.2K 300K Spectrum Analyzer 66uH 150 Ω 2.0nF 1K Ω 2.2 nF 10nF 50 Ω 22nF MITEQ – AU 1447 coax. DC1 100Ω 1kΩ 100kΩ 1K Ω 10K Ω LI 1 DMM1 ~ 10M Ω 100kΩ 1.1nF I-V π-filter ATF x1100 Sample Noise Measurements: 1Ω Low frequencies (lock-in) High frequencies (noise) RLC-Circuit Cryo-Amp f-Splitter 66uH 2.0nF coax.

> Remove distortions by cutting > Do Lorentzian fit > Complete spectrum for every data point (pixel) Data Processing: Current Averaging time: t=10s Current noise

Fano-Map: - Pattern of different Fano factors -Super Poissonian noise on excited states -Enhanced Fano factors on NDC-areas Modelling/Simulations required to explain this pattern and distinguish different mechanisms (vibronic or electronic)

t Origin of Super Poissonian Noise (F>1): … …

DC Current: dI/dV: Current Noise (S I ): Different gate regime:

Steps in Fano Factor: Bias Voltage

F=0.5 F=1 F=10 S I vs Current: F=0.5 F=1 F= Current F=0.5 F=1 F=10

Summary: Outlook: Modelling our experimental results Repeat measurements with higher quality QDs (suspendended CNTs) Use two amplifier chains to increase resolution (cross-correlations)  2 amps already implemented, waiting for samples! Spectrum Analyzer Thank you for your attention! Thank you for your attention!

20mK 4.2K 300K Spectrum Analyzer DC1 1Ω 100Ω 1kΩ 100kΩ LI 1 DMM1 ~ 100kΩ I-V π-filter 66uH 2.0nF coax. 10M Ω ~130 pF 150 Ω 1K Ω 10nF 50 Ω 22nF AU K Ω 10K Ω π-filter ATF x1100 Sample DC2 1Ω 100Ω 1kΩ LI 2 ~ 150 Ω 1K Ω 10nF 50 Ω 22nF AU K Ω 10K Ω 1.1nF π-filter ATF x kΩ π-filter 66uH 2.0nF coax. 10M Ω ~130 pF 1.1nF