nripen dhar p63149. outlines of presentation discovery principles importance existing measurement...

Nripen Dhar

p63149

Outlines of PresentationDiscovery

Principles

Importance

Existing measurement system

Applications

New Discoveries

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Discovery

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Edwin Herbart Hall

Principles

Due to the transverse (magnetic) force,

→ Mobile charges pressed to one side

→ immobile charges are unaltered

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Magnetic Force:

PrinciplesAccumulation of mobile charges

→ Creates internal electric potential, known as Hall voltage.

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Figure 1 : Visual presentation of Hall effect

For simple metals, is V =  

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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

VHall

Hall Coefficient

Magnitude parameter:

In metals:

In semiconductors:

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Note: μp refers to the hole mobility and μn refers to the electron mobility.

μ , NA & ρ from Hall Effect Mobility,

Carrier Concentration,

Resistivity,

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Here, n=NA

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

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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

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Existing System

Figure 3: HMS-3000 hall effect measurement system

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Important parts of the system

Figure 4: Spring clip board

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Figure 5: Magnet

Figure 6: Low temperature measurement system

HMS-3000 Software

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

I-V & I-R curve

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

Hall Probes

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Figure 9: Pictorial view of hall probe

•Transverse Probe• Axial Probe

In AutomobilesUsed expansively in rotating systemsAnti-lock brakes, motor feedback, ignition

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Figure 10: Using Hall effect in cars

In SpaceHall Effect thrusterTrap electrons in a magnetic field, electrons ionize

propellant, creates thrust

Figure 11 :Hall effect thruster in space17

New Discoveries

Quantum Hall 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 (single-particle orbital of an electron in a magnetic field) and electron interaction

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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

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Anomalous Hall EffectFerromagnetic materials have internal magnetic field

Much larger than normal Hall Effect.

Figure 12 : Anamolous Hall Effect

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Summary

Physics of the Hall Effect

Existing system

Popular Applications

New discoveries

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Thank you

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