1 / 26

280 likes | 554 Vues

Spin relaxation rates in quantum dots. 學生 : 廖英彥 指導教授 : 褚德三 交通大學電子物理所. Outline. Introduction Experiment Model Results Conclusion. Qubit vs Spin relaxation. Proposal: A qubit based on the electron spin of quantum dot Relaxation: Phonon induced spin flip

Télécharger la présentation
## Spin relaxation rates in quantum dots

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Spin relaxation rates in quantum dots**學生: 廖英彥 指導教授: 褚德三 交通大學電子物理所**Outline**• Introduction • Experiment • Model • Results • Conclusion**Qubit vs Spin relaxation**• Proposal: A qubit based on the electron spin of quantum dot • Relaxation: Phonon induced spin flip • Spin flip source: Spin-orbit interaction • Requirement: Long relaxation time**A GaAs QD defined in**a 2DEG Spin relaxation time is 50 µs at an in-plane field 7.5 T**Studies on spin relaxation**Theory A. V. Khaetskii and Y. V. Nazarov, PRB 61,12639 (2000) A. V. Khaetskii and Y. V. Nazarov, PRB 64,125316 (2001) Structure: A QD in bulk material (all) Phonon: Bulk phonon (3D phonon wavevector) Our goal: (a) Different type of phonon vs spin relaxation (b) Free-standing structure (2D phonon wavevector)**Long(4 µm), wide(950 nm), thick(130 nm)**QD (40 nm below the surface)**Wide(600 nm), thick(130 nm)**• QD (40 nm below the surface)**Model**Total Hamiltonian Electron term +spin orbit coupling Phonon term + electron-phonon coupling**Single electron in a QD**Electron Hamiltonian Fock-Darwin states**Spin orbit coupling (1)**Zinc-blende crystal : GaAs Dresselhauls vs Rashba term Origin: bulk inversion asymmetry Dependence: (a) parameter of material (b) z-direction confinement width**Spin orbit coupling (2)**Rashba term Origin: Structure inversion asymmetry Dependence: (a) parameter of material (b) perpendicular confinement field Comparison: Electric field : V/cm Ratio : 0.1 ~ 0.7**Perturbative approach vs Exact diagonalization**Perturbative approach Spin-orbit coupling is viewed as a small perturbation Exact diagonalization Large spin-orbit coupling Small electron levels**Phonon (1)**Acoustic phonon in a free-standing structure Confined phonon modes: Shear waves, Dilatational waves, Flexural waves do not interact with electrons**Phonon (2)**Dilatational waves Symmetric waves Dispersion relation**Phonon (3)**Flexural waves Antisymmetric waves Dispersion relation**Electron-phonon interaction**Deformation potential interaction Dilatational and flexural**Spin relaxation rate**Fermi golden rule Parameters: (1) GaAs quantum dot (2) A QD is located at z=0**A van Hove singularity occurs**This is due to zero phonon group velocity**Spin relaxation rate completely vanishes at the magnetic**field A vanishing divergence of the displacement field**phonon number**• This enhances the electron-phonon scattering**Phonon number**• Rate**Two huge rates and suppressed rates display**• Interplay between SO coupling and Zeeman levels**Two singular rates clearly occur for small width case**• They disappear as the width is large (bulk-like system)**Conclusion**A huge rate is due to a van Hove singularity A suppressed rate is due to a vanishing divergence of the displacement field We hope that these results are useful in understanding spin relaxation in a suspended quantum dot nanostructure

More Related