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UID:UW-Physics-Event-2877
DTSTART:20130328T150000Z
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DTSTAMP:20260412T041557Z
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.<br>
\n<br>
\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.<br>
\n<br>
\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).<br>
\n<br>
\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.<br>
\n<br>
\nReferences:<br>
\n1) L. Zh
 ang\, J-Wi Luo\, A. L. Saraiva\, B. Koiller\, A. Zunger\, arXiv:1303.4
 932.<br>
\n2) A. L. Saraiva\, B.Koiller\, M. Friesen\, Phys. Rev. B 82
 \, 245314 (2010).<br>
\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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