the hall effects
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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. - PowerPoint PPT PresentationTRANSCRIPT
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The Hall Effects
Richard Beck141A 2013
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Hall Effect
• Discovery
• The physics behind it
• Applications
• Personal experiments
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Discovery
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Via Wikimedia Commons (public domain)
Richard Beck - Physics 141A, 2013
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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 =
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Note: t refers to the thickness of the metal along the direction of the B-field
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A Visual Representation
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From Non-Destructive Testing (NDT) Resource Center
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Hall Coefficient
• Magnitude parameter:
• In metals:
• In semiconductors:
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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
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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
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Hall Probes
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Via LessEMF.comVia the NDT Resource Center
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Rotation Sensing
• Hall Effect sensors capable of switching very fast, does not distort like capacitative or inductive sensors
• Contactless sensing
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In Cars
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• Used expansively in rotating systems
• Anti-lock brakes, motor feedback, ignition
Via Power Systems Design, Ltd. Via Draper, 2005
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In Space
• Hall Effect thruster
• Trap electrons in a magnetic field, electrons ionize propellant, creates thrust
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New Discoveries
• QuantumHall Effect
• Spin Hall Effect
• Anomalous Hall Effect
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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
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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
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Anamolous Hall Effect
• Ferromagnetic materials have internal magnetic field
• Much larger than normal Hall Effect, but not well understood ; Possible Berry-phase effect
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Via Toyosaki et al. 2004
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Personal Experiments
• Aluminum-doped Germanium 1 sq cm chip
• Van Der Pauw configuration
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Hall Coefficients
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Extrapolated Carrier Mobility
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Clear temperature dependence! Has to do with electron energy
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Summary
• Physics of the Hall Effect
• Popular Applications
• Future Potential
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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.
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