Nripen Dhar p63149

Outlines of Presentation Discovery Principles Importance Existing measurement system Applications New Discoveries 2

Discovery Observed in 1879 Edwin Herbert Hall Discovered 18 years before the electron 3 Edwin Herbart Hall

Principles Due to the transverse (magnetic) force, → Mobile charges pressed to one side → immobile charges are unaltered 4 Magnetic Force:

Principles Accumulation of mobile charges → Creates internal electric potential, known as Hall voltage. 5 Figure 1 : Visual presentation of Hall effect

For simple metals, is V = 6 Here, n is the no. of charge carriers and t refers to the thickness of the metal along the direction of the B-field Figure 2 : Visual presentation of Hall effect V Hall

Hall Coefficient Magnitude parameter: In metals: In semiconductors: 7 Note: μ p refers to the hole mobility and μ n refers to the electron mobility.

μ, N A & ρ from Hall Effect Mobility, Carrier Concentration, Resistivity, 8 Here, n=N A

Features 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 9

Importance Measurement of charge carrier mobility, concentration, resistivity Sensitive measurement of an external B-field No need to use electrochemical materials Ease to use (no vacuum, ambient temp, etc.) Less sensitive to switching 10

Existing System Figure 3: HMS-3000 hall effect measurement system 11

Important parts of the system Figure 4: Spring clip board 12 Figure 5: Magnet Figure 6: Low temperature measurement system

HMS-3000 Software 13 Figure 7 : Screen-shot showing HMS-3000 Software

I-V & I-R curve 14 Figure 8 : I-V & I-R curve from software

Hall Probes 15 Figure 9: Pictorial view of hall probe Transverse Probe Axial Probe

In Automobiles Used expansively in rotating systems Anti-lock brakes, motor feedback, ignition 16 Figure 10: Using Hall effect in cars

In Space Hall Effect thruster Trap electrons in a magnetic field, electrons ionize propellant, creates thrust Figure 11 :Hall effect thruster in space 17

New Discoveries Quantum Hall Effect Spin Hall Effect Anomalous Hall Effect 18

Quantum Hall Effect Quantization of normal Hall Effect Seen at low temperature, high magnetic field Very precise, magnitude determined by Landau levels ( single-particle orbital of an electron in a magnetic field ) and electron interaction 19

Spin Hall Effect Predicted in 1971 Russian physicists M.I. Dyakonov and V.I. Perel, observed in 2004 via emission of circularly polarized light Separation of electron spins in current-carrying object, no magnetic field needed Universal, present in metals and semiconductors at high and low temperature 20

Anomalous Hall Effect Ferromagnetic materials have internal magnetic field Much larger than normal Hall Effect. Figure 12 : Anamolous Hall Effect 21

Summary Physics of the Hall Effect Existing system Popular Applications New discoveries 22

Thank you 23