Download Topological Insulators

Topological Insulators
Nature,online Aug 2009, P Roushan et al
Brandon Johnson
Outline
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Motivation
Theory/Background
2D Quantum/Spin Hall Insulator
Edge States – Non localized
Topological number Z2
3D Topological Insulators
Pioneering Experiments
Motivation
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New Class of Quantum Matter
Magnetic Monopole
Majorana Fermion - Quantum computing
Model Exotic Particles
High Temperature Spintronics
New Phenomenon - ?
Integer Quantum Hall Insulator
2D Cyclotron motion
Phys. Rev. Lett. 45, 494 (1980): Klitzing et al
Integer Quantum Hall Insulator
Topology Explains Edge States
V map – 2 state system
Skipping Orbits
Quantum Spin Hall Insulator
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No applied B
Picture
Spin Orbit Coupling
IQH
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Effective
Edge states ? TI
Edge States Stable?
Protected by TR Symetry
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Kramer’s Theorem E
2 states at
Dirac nodes and TRIMs
No Localization
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Elastic Scattering
Backscattering
No Backscattering without a spin flip
Protection from non-magnetic impurities
An Insulators Metallic Side J. Moore (27 Aug 2009) Nature 460 (08308) 1090
2D Topological insulators Z2
2D Topological insulators Z2
Characteristics of TIs
Edge States
Odd # Dirac nodes
Odd # Fermi Crossings
Characteristics of 3D TI
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Protected SS
Odd number of Dirac points in the
Brillouin zone
Fermi Arc encloses and odd number of
TRIMs
Experimental Realization of a Three-Dimensional Topological Insulator, Bi2Te3
Y. L. Chen et al. (10 July 2009) Science 325 (5937), 178.
ARPES
Angle Resolve Photoemission Spectroscopy
~20eV
Photon momentum is negligible
momentum is conserved in the plane
(D. Hsieh)
Example for Bi1-xSbx
(D. Hsieh)
X=0.09
Spin Resolved ARPES
Observation of Unconventional Quantum Spin Textures in Topological Ins ulators
D. Hsieh, et al. (13 February 2009) Science 323 (5916), 919.
Quantum Oscillations
de Haas van Alphen – Bi
Oscillation in magnetic susceptibility - B
A is max and min Larmor/Cyclotron orbits
Fermi Surface
Confirm 2D surface states - TI
Quantum Oscillations
Quantum Oscillations in a Topological Insulator Bi1-xSbx A.A. Taskin, arXiv (7 July 2009)
Scattering in Bi1-x Sbx
FT-STS Modulation wavelength
Amplitude – Probability of QP scattering and
QPI between
Topological Surface States Protected from Backscattering by Chiral Spin Texture
Pedram Roushan et. Al (27 Aug 2009) Nature 460 (08308) 1106
Scattering
Quasi Particle Interference
Spin-Dependant Scattering Probability
Scattering
Topological Surface States Protected from Backscattering by Chiral Spin Texture
Scattering
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Topological Surface States Protected from Backscattering by Chiral Spin Texture
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Pedram Roushan et. Al (27 Aug 2009) Nature 460 (08308) 1106
Topological Insulators
Nature,online Aug 2009, P Roushan et al
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