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PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-2877
DTSTART:20130328T150000Z
DURATION:PT1H0M0S
DTSTAMP:20240319T102919Z
LAST-MODIFIED:20130326T130407Z
LOCATION:5310 Chamberlin
SUMMARY:Control and possible applications of valley degree of freedom:
Valleytronics?\, R. G. Herb Condensed Matter Seminar\, Belita Koiller
\, Federal University of Rio de Janeiro
DESCRIPTION:The conduction electrons in Si are not in a well-defined s
ingle Bloch state. Instead\, the Si conduction band is six-fold degene
rate\, with minima (valleys) along the x\, y and z crystallographic di
rections. This imposes limitations to the spin manipulation and cohere
nce. It was recently proposed to encode quantum information directly i
nto the valley degree of freedom\, converting the spurious valley Hilb
ert subspace into a useful ingredient for a quantum computer. In this
talk\, valley degrees of freedom in Si are addressed in 3 different c
ontexts.
\n
\n1) Based on an atomistic pseudopotential theory\
, we demonstrate that ordered Ge-Si layered barriers confining a Si sl
ab can be optimized to enhance the VS in the active Si region by up to
one order of magnitude compared to the random alloy barriers adopted
so far. We identify Ge/Si layer sequences leading to a VS as large as
~9 meV. The splitting is "protected" even if some mixing occurs at the
interfaces.
\n
\n2) Interface states form spontaneously at so
me semiconductor-barrier interfaces and they may improve or hinder the
electron control and coherence for semiconductor-based qubits. From
a simple 1D Tight-binding model\, new insights emerge regarding the in
terface state's energy\, as well as the exponential longer (shorter) l
ocalization lengths into the Si (barrier) material. The interface stat
e may be probed experimentally by an external electric field\, which m
odulates the capacitance of the system and the lowest level spacing (v
alley splitting).
\n
\n3) We analyze the valley composition of
one electron bound to a shallow donor close to a Si/barrier interface
. A full six-valley effective mass model Hamiltonian is adopted. For l
ow fields\, the electron ground state is essentially confined at the d
onor. At high fields the ground state is such that the electron is dra
wn to the interface\, leaving the donor practically ionized. Valley sp
litting at the interface occurs due to the valley-orbit coupling\, tak
en here as a complex parameter. A sequence of two anti-crossings takes
place and the complex phase affects the symmetries of the eigenstates
and level anti-crossing gaps.
\n
\nReferences:
\n1) L. Zh
ang\, J-Wi Luo\, A. L. Saraiva\, B. Koiller\, A. Zunger\, arXiv:1303.4
932.
\n2) A. L. Saraiva\, B.Koiller\, M. Friesen\, Phys. Rev. B 82
\, 245314 (2010).
\n3) A. Baena\, A. L. Saraiva\, B.Koiller\, M. J
. Calderón Phys. Rev. B 86\, 035317 (2012).
URL:https://www.physics.wisc.edu/events/?id=2877
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