1 / 20

How do spins interact with their surroundings?

How do spins interact with their surroundings?. Zeeman effect: Flip spins along magnetic field (Origin of Stern-Gerlach). B. H = - m .B = -g m B BS z. m B =qħ/2m = 9.27 x 10 -24 J/T ≈ 60 m eV/T. ‘g’ factor ~ 2 for electrons. Magnetic field splits the energy levels.

richardcook
Download Presentation

How do spins interact with their surroundings?

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

Presentation Transcript

  1. How do spins interact with their surroundings?

  2. Zeeman effect: Flip spins along magnetic field (Origin of Stern-Gerlach) B H = - m.B = -gmBBSz mB =qħ/2m = 9.27 x 10-24 J/T ≈ 60 meV/T ‘g’ factor ~ 2 for electrons

  3. Magnetic field splits the energy levels H = -gmBBSz = -gmBBħ/2 1 0 B = 0 B ≠ 0 0 -1

  4. Ferromagnet: Internal B field can split levels E E H = - JS1.S2 J is the exchange parameter EF EF k k Internal field B ~ J<S> D

  5. Can we transition between the spins? H = -gmBBSz = -gmBBħ/2 1 0 Need (i) an off-diagonal term coupling the states for transitions  E.g., a field along the x-axis (ii) a resonant AC field to provide the transition energy 0 -1

  6. ElectronSpin Resonance (ESR) H = -gmBBSz = -gmBBħ/2 B H1 = -gmBB1(t)Sx = -(gmBB1ħcoswt)/2 B1coswt 1 0 0 1 0 -1 1 0

  7. Electron Spin Resonance (ESR) B B1coswt iħ/t = [H + H1(t)] Solve analytically using some approximations or numerically y y y y

  8. Electron Spin Resonance (ESR) B B1coswt P(t) So we can transition between spins with a suitable field

  9. What about internal fields? Exchange fields in metallic magnets Spin-orbit fields in semiconductors

  10. Spin-Orbit coupling + Electron orbiting in electric field of nucleus

  11. What the electron sees + B ~ v x E Nucleus orbiting, creating a net current and thus  DRUMROLL…. a magnetic field !!

  12. What the electron sees + The Zeeman coupling of the electron spin to this motional field is the Spin-Orbit effect (within a factor of 2) H ~ -S.B ~ S.(p x E) ~ S.(p x r)dU/dr H ~ -S.L(dU/dr)

  13. S-O coupling: Various manifestations Atom: Gives rise to Hund’s Rule Solid: Split-off states in valence band Gated transistor: Rashba coupling H ~ S.(p x r)E ~ r.(S x p)E ~ (sxky-sykx)Ez

  14. Spintronic Devices

  15. Read: GMR, TMR, spin valves (Memory, Sensors)

  16. Write: MRAMs Rotate with field http://thefutureofthings.com/upload/image/articles/2006/mram/mram-write.jpg Write: STTRAMs Rotate with current Also  Rotate with strain (multiferroics)

  17. Computing: Datta-Das “FET” Use Rashba field to rotate spins in a modulator with a gate (sxky-sykx)Ez H = aR http://www.material.tohoku.ac.jp/~kotaib/jpg/spinFET.jpg

  18. Computing with 104 spins NkTln(pon/poff) for N charges ~kTln(pon/poff) for N spins !!

  19. Using spin for computing All spin Logic Memristors MQCA

  20. Summary: Spin is a new variable. It can be used for energy-efficient Computing Q Transport to calculate Spin current

More Related