1. (As required by the Governor of the State of California)
Quantum Hall Effect
Jesse Noffsinger
Group Meeting Talk
(As required by the Governor of the State of California)
April 17, 2007

2. Classical Hall Effect B +++++++++++++++++++ Ex, jx VH Ey
Experimental Values* B
Metal RH
(-1/nec) Li
0.8 Na
1.2 Rb
1.0 Ag
1.3 Be
-0.2
Ex, jx VH Ey
*Ashcroft and Mermin

3. Integer QHE Discovered in 1980,
Nobel Prize awarded to von Klitzing in 1985 aa
SEM image of a Hall bar*
*Georgia Tech physics website

4. Quantum Mechanical Description
Landau Gauge:

5. Degeneracy of Landau Levels
Each wavefunction is centered at
Energy
DOS:
Increasing B

6. Only extended states carry current! Impurity Effects
Isolated fn potential localizes one extended state
Only extended
states carry current!
Extended States E
Localized States
DOS

7. The Laughlin Argument for the Integer Hall effect
Form a closed loop w/ Hall bar
Change the flux through the loop by one quanta:
No change can take place in the bulk –
move one electron to the other edge
p must be an integer

8. Fractional QHE Cannot be explained in terms of free electrons
Filling factor is a rational fraction
Cannot be explained in
terms of free electrons

9. Composite Fermion Picture
Electrons IQHE
Composite Fermions FQHE
Fractional Hall effect encompasses states with filling factors:
Composite fermions can be viewed as electrons with attached flux quanta
is screened to

10. Lowest Landau level splitting for composite fermions
Energy
v=1 lowest Landau Level splits into levels separated by
The fractional filling of electrons is really the integral filling of composite fermions

11. Conclusion Integral Quantum Hall effect can be accurately modeled as
a non-interacting electron gas in a magnetic field
The Fractional Quantum Hall effect involves composite fermion
quasi-particles which are electrons with attached flux quanta