1. 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

2. 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)

3. 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:

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

5. Sources of Noise: Thermal Noise Shot Noise

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

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

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

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

10. 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

11. Current: dI/dV: Stability Diagram:

12. Excited states What kind of excitations? Electronic or Vibronic? Yar et al. PRB 84, 115432 (2011) Pro vibronic: - excitations are equidistant - alternating pattern: pos./neg. dI/dV

13. Comparison Franck-Condon model From experiment:

14. 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 - 34143 x1100 Sample Noise Measurements: 1Ω Low frequencies (lock-in) High frequencies (noise) RLC-Circuit Cryo-Amp f-Splitter 66uH 2.0nF coax.

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

16. 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)

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

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

19. Steps in Fano Factor: 1 2 3 3 2 1 Bias Voltage

20. F=0.5 F=1 F=10 S I vs Current: 1 2 3 3 F=0.5 F=1 F=10 2 1 Current F=0.5 F=1 F=10

21. 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 1. 2. Thank you for your attention! Thank you for your attention!

22. 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 1447 1K Ω 10K Ω π-filter ATF - 34143 x1100 Sample DC2 1Ω 100Ω 1kΩ LI 2 ~ 150 Ω 1K Ω 10nF 50 Ω 22nF AU 1447 1K Ω 10K Ω 1.1nF π-filter ATF - 34143 x1100 100kΩ π-filter 66uH 2.0nF coax. 10M Ω ~130 pF 1.1nF