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Chapter 3. Differential Resistance Through a Quantum Dot
Chapter 3. Differential Resistance Through a Quantum Dot:
Signature of Kondo Correlation
Academic and Research Staff
Professor Patrick A. Lee
Graduate Students
Jari M. Kinaret, Dmitri B. Chklovskii
Technical and Support Staff
Imadiel Ariel
3.1 Project Description
Sponsor
Joint Services Electronics Program
Contract DAAL03-92-C-0001
The behavior of an atomic impurity coupled to conduction electrons has become one of the paradigms
of condensed matter physics. Competition between
on-site Coulomb interaction and band hybridization
produces the Kondo effect: a crossover from weak
to strong coupling between the localized and band
electrons below the Kondo temperature, TK. The
study of the Kondo effect has been limited,
however, by the nature of the impurity system.
Since it is a daunting task to drive the host metal
out of equilibrium, it is the equilibrium properties of
Kondo impurities that have been explored.
In the study of transport through a quantum dot, we
have
a
new
Kondo
system
in
which
non-equilibrium--a semiconductor quantum dot
weakly coupled to its leads-is routinely achieved.
Anderson's model for a Kondo impurity-discrete,
interacting levels coupled to a band-also describes
quantum dots. The discrete spectrum of a single
dot has been probed experimentally by transport
and capacitance spectroscopy, and the strong
on-site Coulomb interaction is observed in
Coulomb-blockade
conductance
oscillations.'
Anderson's model has provided an excellent theoretical description of these experiments.2 However, it
is only the high temperature regime that has been
explored experimentally, while it is below TK that
the Kondo effect emerges.
We have previously shown that below TK, the
Kondo resonance leads to perfect transparency of
the quantum dot at the Fermi energy. This leads to
dramatic effects on the lineshape of the conductance peaks as a function of gate voltage.3 We
recently realized that a striking signature on the
Kondo correlation appears in nonequilibrium properties, such as the differential conductance, even at a
temperature higher than TK. 4 The requirement is
that the temperature must be less than F, the
intrinsic line width of the resonant transmission
peak. This latter condition is much easier to realize
experimentally. We have shown that if the gate
voltage is set so that we are on the shoulder of a
conductance peak and the source drain voltage VsD
is increased, the differential conductance would
exhibit a peak around VSD=O.
Furthermore, if a
magnetic field B is applied, the differential conductance peak will split into two peaks centered at the
Zeeman energy ± giB1B. We believe that the observation of this conductance peak is a clean signature
of the Kondo correlation in the quantum dot system.
1 U. Meirav, M. Kastner, and S.J. Wind, "Single-Electron Charging and Periodic Resonances in GaAs Nanostructures," Phys. Rev.
Lett. 65: 771 (1990).
2 Y. Meir, N. Wingreen, and P.A. Lee, "Transport Through a Strongly Interacting Electron System," Phys. Rev. Lett. 66: 3048 (1991).
3
T.K. Ng and P.A. Lee, "On-site Coulomb Repulsion and Resonant Tunnelling," Phys. Rev. Lett. 61: 1768 (1988).
4 Y. Meir, N. Wingreen, and P.A. Lee, "Low Temperature Transport Through a Quantum Dot: The Anderson Model Out of Equilibrium,"
submitted to Phys. Rev. Lett.
Chapter 3. Differential Resistance Through a Quantum Dot
3.2 Publications
Lee, P.A. "Few Electron Nanostructures: A New
Laboratory for Studying Strongly Correlated
Proceedings of NATO Workshop,
Systems."
Nordwig, Netherlands, 1992.
Meir, Y., N. Wingreen, and P.A. Lee. "Low Temperature Transport Through a Quantum Dot: The
Anderson Model Out of Equilibrium." Submitted
to Phys. Rev. Lett.
46
RLE Progress Report Number 135