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Researchers within the QED group are investigating
the electrical and optical properties of nanometer scale semiconductor
devices. At these small length scales the device properties are no longer
governed by semi-classical physics, but are instead determined by quantum
mechanical effects. The group makes its own quantum semiconductor devices
here at UNSW, and uses a variety of electronic and optical probes, at
milliKelvin temperatures and in strong magnetic fields, to further the
understanding of quantum electronics.
Hole quantum wires
|Optical and electron
micrographs of high quality, high stability hole quantum
wire fabricated at UNSW.
Although there has been tremendous international
interest in the properties of semiconductor nanostructures, almost
all of this effort has concentrated on the properties of n-type
devices, in which electrons carry the current. We are interested
in devices where conduction is by holes rather than electrons, as
holes have very different quantum properties. Electrons are spin-1/2
particles, whereas holes can be spin 3/2, and have a very strong
coupling between spin and momentum. In principle this would make
it possible to control the hole spin by altering its momentum, which
can be done with applied electric fields. The ability to manipulate
the hole spin could be useful for spintronic (spin-electronic) device
applications. However nanoscale hole systems are notoriously difficult
We have developed new techniques for fabricating
extremely high quality hole nanostructures, which eliminate the
instabilities that have plagued previous experiments for over 10
quantum wire shows conductance quantization in units of
2e²/h at B=0. A magnetic field applied parallel to
the wire lifts the spin degeneracy, causing additional
plateaus. A perpendicular magnetic field does not.
We have found an extreme anisotropy in the response
of these one-dimensional hole quantum wires to an external magnetic
field. When the magnetic field is applied along the axis of the
wire, it causes a Zeeman splitting of the spin states, but when
it is applied perpendicular to the wire it has no effect! This result
is completely different to electrons in quantum wires, which show
no anisotropy, and is a direct result of the strong coupling between
spin and momentum.
feature can be seen below the first subband - the so-called
We have also performed the first studies of the
anomalous "0.7 feature" that has been the subject of intense
interest in one-dimensional systems. An anomalous platueau is seen
at 0.7x2e^2/h, which cannot be explained in standard non-interacting
theories. Explanations range from a spontaneous spin-splitting at
B=0, through to Kondo effect, and formation of a one-dimensional
Our studies show that the 0.7 feature, and the
related zero-bias anomaly, are both related to spin, and also have
an anisotropic response to an applied magnetic field. The observation
of the 0.7 feature in strongly interacting, spin 3/2 systems, opens
up new potentials for research and places important constraints
on theoretical models of this phenomena.
Future work is now focused on fully exploring the effects
of strong spin-orbit coupling in hole nanostructures. In addition to their
fundamental significance, potential applications may include all-electrical
manipulation of spin, and new spintronic devices..
OF NOTHING: a hole new quantum spin is a media release for the
popular press about our work on hole quantum wires:"Electronic devices
are always shrinking in size but its hard to imagine anything beating
what researchers at the University of New South Wales have created (read
more)". Photos are available of some of the group
members and the devices,
as well as a conceptual web
animation of how the devices work.
quantization in induced one-dimensional hole systems,
O. Klochan, W. R. Clarke, R. Danneau, A. P. Micolich, L. H. Ho, A. R.
Hamilton, K. Muraki and Y. Hirayama,
American Institute of Physics Conference Proceedings 893, 681 (2007).
Zeeman splitting in ballistic one-dimensional hole systems,
R. Danneau, O. Klochan, W. R. Clarke, L. H. Ho, A. P. Micolich, M. Y.
Simmons, A. R. Hamilton, M. Pepper, D. A. Ritchie and U. Zülicke,
American Institute of Physics Conference Proceedings 893, 699 (2007).
transport in induced one--dimensional hole systems,
O. Klochan, W.R. Clarke, R. Danneau, A.P. Micolich, L.H. Ho, A.R. Hamilton,
K. Muraki and Y. Hirayama,
Applied Physics Letters 89, 092105 (2006).
splitting in ballistic hole quantum wires
R. Danneau, O. Klochan, W. R. Clarke, L.H. Ho, A. P. Micolich,M. Y. Simmons,
A. R. Hamilton, M. Pepper, D. A. Ritchie and U. Zuelicke,
Physical Review Letters 97, 026403 (2006).
Also appeared in Virtual Journal of Nanoscale Science & Technology
quantization and the 0.7×2e2/h conductance anomaly in one-dimensional
R. Danneau, W. R. Clarke, O. Klochan, A. P. Micolich, A. R. Hamilton,
M. Y. Simmons, M. Pepper, and D. A. Ritchie,
Applied Physics Letters 88, 012107 (2006).
Also appeared in Virtual Journal of Nanoscale
Science & Technology 13(2), (2006).
of induced two-dimensional hole systems on (311)A GaAs,
W.R. Clarke, A.P. Micolich, A.R. Hamilton, M.Y. Simmons, K. Muraki and
Journal of Applied Physics 99, 023707 (2006).
separated one-dimensional wires: Coupled ballistic conduction and compressibility
"I.M Castleton, A.G. Davies, A.R. Hamilton, J.E.F.
Frost, M.Y. Simmons, D.A. Ritchie, M. Pepper",
Physica B , 249-251, 157, (1998)