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Fermi-Edge Singularitäten im resonanten Transport durch II-VI Quantenpunkte

Fermi-Edge Singularitäten im resonanten Transport durch II-VI Quantenpunkte. Universität Würzburg Am Hubland, D-97074 Michael Rüth, Anatoliy Slobodskyy, Charles Gould, Georg Schmidt, Laurens W. Molenkamp Physikalisches Institut (EP3) Spintronics. Outline. Project and status

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Fermi-Edge Singularitäten im resonanten Transport durch II-VI Quantenpunkte

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  1. Fermi-Edge Singularitäten im resonanten Transport durch II-VI Quantenpunkte Universität Würzburg Am Hubland, D-97074 Michael Rüth, Anatoliy Slobodskyy, Charles Gould, Georg Schmidt, Laurens W. Molenkamp Physikalisches Institut (EP3) Spintronics

  2. Outline • Project and status • Magnetic structures • FES in non-magnetic structures • Conclusion and outlook

  3. Project and status • Goal • Investigation of tunneling transport through self assembled II-VI quantum dots in semimagnetic barriersmagnetic tunneling barriers • Setback • Several consecutive breakdowns in the MBE interrupted by calibration periods • Status • MBE up and running again • New III-V chamber running (18 months after installation) • Working RTDs fabricated • All presented experiments performed on samples from the beginning of the project

  4. layer structure and transport mechanism • II-VI double barrierheterostructure • (10x10) μm² pillars • approximately 104quantumdots • transportdominatedby a fewdotsatlowbiasvoltages

  5. magnetic (Zn,Be,Mn)Se tunnel barriers 10x10 μm² 100x100 μm² • Further samples show clear zero field spin splitting (left)Þmediated ferromagnetic interaction with Mn ions in barriers • Slight variation in layer thickness and smaller mesa lead to higher PVR (not sharper resonance) without zero field splitting (right)Þ Transistion 0D -> 2D is observed

  6. nonmagnetic (Zn,Be,Mn)Se tunnel barrierszerofieldmeasurements – FES signal • resonance has shape of a Fermi-Edge-Singulariy enhanced tunneling current • RTD with self assembled InAs dots showing FES enhancement –Frahm et al. Phys. Rev. B 72, 5375 (2006)

  7. Fermi Edge Singularity in resonant tunneling • interaction between tunneling electrons and the Fermi sea in the contacts • two competing effects: • attraction of contact electrons to the emtpy state in the localized level • Fermi sea shake-up (appearance of hole potential in localized level modifies many particle wave function – suppression of tunneling rate) • Description with one body scattering potential with two phase shifts Geim et al. `93 – tunneling between a localized level and a 2DEG

  8. nonmagnetic (Zn,Be,Mn)Se tunnel barrierstemperaturedependenceandtheory • tunneling enhancement reduces with increasing temperature • resonance still visible at 45 K with a PVR of nearly 2 • theory (Frahm et al. 2006) reproduces data up to 45K • rescaling collapses data from varioustemperatures on one curve accordingto theory

  9. nonmagnetic (Zn,Be,Mn)Se tunnel barrierszerofieldmeasurements – FES signal Marcus & Zumbuhl: resonant tunneling in an open qdot • superimposed FES peaks + finestructure at low temperatures • finestructure not included at low temperatures

  10. nonmagnetic (Zn,Be,Mn)Se tunnel barriersmagneticfieldmeasurements (perpendiculartolayerstack @~100mK) Parallel setup @1.6K • complex structure in perpendicular field • Resonances run to lower voltages with increased field • no field dependence in parallel setup

  11. nonmagnetic (Zn,Be,Mn)Se tunnel barriersemitter Landau fan fit • main features can be fitted with an emitter landau fan • Additional features cannot be explained with only one landau fan or by adding Darwin-Fock like behavior of the conducting dot level • only one visible resonance at B=0T  no other conducting dot levels • disordered 2D-like emitter states produce multiple landau fan like structures (intersecting levels on magnetic field – energy – plane)

  12. summary • magnetic tunneling barriers • Zero field spin splitting could be reproduced for 0D and vanishes in 2D • nonmagnetic tunneling barriers • resonant tunneling through self assembled CdSe quantum dots in a II-VI device • Current enhancement by a fermi edge singularity • Isolated signla of a conducting quantum dot level • FES theory reproduces data for all temperatures • Disordered 2D-like emitter with visible landau level structure in perpendicular magnetic field

  13. outlook • Grow new samples and follow up on project program • Coupled dots • Magnetic/Non-magnetic barriers • ...

  14. I/V measurements in magneticfieldinfluenceofappliedfields

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