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The Hall Effects

The Hall Effects. Richard Beck 141A 2013. Hall Effect. Discovery The physics behind it Applications Personal experiments. Discovery. Observed in 1879 Edwin Herbert Hall Discovered 18 years before the electron. Via Wikimedia Commons (public domain). Principles.

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The Hall Effects

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  1. The Hall Effects Richard Beck 141A 2013

  2. Hall Effect • Discovery • The physics behind it • Applications • Personal experiments Richard Beck - Physics 141A, 2013

  3. Discovery • Observed in 1879 • Edwin Herbert Hall • Discovered 18 years before the electron Via Wikimedia Commons (public domain) Richard Beck - Physics 141A, 2013

  4. Principles • Mobile charges pressed to one side from Lorentz force, immobile charges unaltered • Creates internal electric potential, known as Hall voltage. • For simple metals, is V =   Note: t refers to the thickness of the metal along the direction of the B-field Richard Beck - Physics 141A, 2013

  5. A Visual Representation From Non-Destructive Testing (NDT) Resource Center Richard Beck - Physics 141A, 2013

  6. Hall Coefficient • Magnitude parameter: • In metals: • In semiconductors: Richard Beck - Physics 141A, 2013

  7. Triumphs • Classical Picture: only electrons moving in same average direction in both hole (p-type) and electron (n-type) conductivity • Opposite sign indicates that electrons in valence bands move in opposite direction than previously thought Richard Beck - Physics 141A, 2013

  8. Applications • Measurement can tell about charge carrier mobility, concentration • Conversely, knowing the above allows for sensitive measurement of an external B-field • Resistant to outside contaminants unlike optical, electromechanical testing Richard Beck - Physics 141A, 2013

  9. Hall Probes Via LessEMF.com Via the NDT Resource Center Richard Beck - Physics 141A, 2013

  10. Rotation Sensing • Hall Effect sensors capable of switching very fast, does not distort like capacitative or inductive sensors • Contactless sensing Richard Beck - Physics 141A, 2013

  11. In Cars • Used expansively in rotating systems • Anti-lock brakes, motor feedback, ignition Via Draper, 2005 Via Power Systems Design, Ltd. Richard Beck - Physics 141A, 2013

  12. In Space • Hall Effect thruster • Trap electrons in a magnetic field, electrons ionize propellant, creates thrust Richard Beck - Physics 141A, 2013

  13. New Discoveries • QuantumHall Effect • Spin Hall Effect • Anomalous Hall Effect Richard Beck - Physics 141A, 2013

  14. Quantum Hall Effect • Quantization of normal Hall Effect • Seen at low temperature, high magnetic field • Very precise, magnitude determined by Landau levels and electron interaction Richard Beck - Physics 141A, 2013

  15. Spin Hall Effect • Separation of electron spins in current-carrying object, no magnetic field needed • Predicted in 1971, observed in 2004 via emission of circularly polarized light • Universal, present in metals and semiconductors at high and low temperature Richard Beck - Physics 141A, 2013

  16. Anamolous Hall Effect • Ferromagnetic materials have internal magnetic field • Much larger than normal Hall Effect, but not well understood ; Possible Berry-phase effect Via Toyosaki et al. 2004 Richard Beck - Physics 141A, 2013

  17. Personal Experiments • Aluminum-doped Germanium 1 sq cm chip • Van Der Pauw configuration Richard Beck - Physics 141A, 2013

  18. Hall Coefficients Richard Beck - Physics 141A, 2013

  19. Extrapolated Carrier Mobility Clear temperature dependence! Has to do with electron energy Richard Beck - Physics 141A, 2013

  20. Summary • Physics of the Hall Effect • Popular Applications • Future Potential Richard Beck - Physics 141A, 2013

  21. References • Kittel, Charles, Introduction to Solid State Physics, John Wiley & Sons, Inc.. 2005 • Kasap, Safa. Hall Effect in Semiconductors, University of Saskatchewan, 2001 • Non Destructive Testing Resource Center, http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/Measuring.htm , 2004 • Power Systems Design, http://www.powersystemsdesign.com/hall-effect-sensors-deliver-higher-efficiency-in-brushless-dc-motors?a=1&c=1399#, 2004 • Ando, Tsuneya; Matsumoto, Yukio; Uemura, Yasutada (1975). Theory of Hall Effect in a Two-Dimensional Electron System. J. Phys. Soc. Jpn. 39 (2): 279–288. • Spin effect M.I. Dyakonov (2007). Magnetoresistance due to edge spin accumulation. Phys. Rev. Lett. 99 (12): 126601 • N. A. Sinitsyn (2008). Semiclassical Theories of the Anomalous Hall Effect. Journal of Physics: Condensed Matter 20 (2): 023201. Richard Beck - Physics 141A, 2013

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