TheMo 





Presentation
Studies of nanoscale objects require the development of dedicated theoretical tools : as the size decreases,
rapid variations of chemical composition and strain play an increasing role in determining the structural
and electronic properties. Continuum models (classical elasticity, envelope function theory of electronic
states) become innacurate and miss qualitative features associated with local, « atomistic » symmetries.
The use of computational approaches, modeling nanostructures at the atomistic level, becomes essential
not only for quantitative accuracy, but also for qualitative understanding of experiments. Conversely,
problematics arising from experimental activity in nanosciences sometimes question accepted ideas and
can give a strong impulse to purely theoretical work. From a theoretical point of view, nanoscience
is a new, pluridisciplinary playground where first principle methods, empirical parameter atomistic
modeling and continuum approaches closely interact.
The Theory/Modeling activity of LPNGOSS is focused on the extendedbasis spds* tightbinding model
which is particularly well suited to our objectives : this method allows to reproduce all the different
energy scales of the electronic structure (from spin splittings to fullband integrated properties like
the dielectric funtion), using universal and transferable parameters. Our work is based on a strong
interaction within a virtual team including Mikhail Nestoklon (Ioffe Institut RAS, St Petersburg),
J.M. Jancu (FOTON, INSA Rennes) and P. Voisin (LPNCNRS). We are developing a highly versatile
tightbinding code that can handle 3dimensional supercells up to several hundred thousand atoms.
Topics of current interest include the modeling of STM images of subsurface acceptor states, the
electronic properties of dilute alloys (dilue nitrides, GaMnAs..) as well as methodological issues
such as the local wavefunction in the tightbinding approach.

Figure: Tightbinding calculation of exchange interaction for the neutral
acceptor state associated with a Mn dopant in GaAs.
The crosssection of impurity wavefunction in the (110) plane
containing the impurity is shown as a function of Mn spin orientation,
from [001] (left) to [110] (right) (M. Nestoklon et al. 2011)

Members
Contacts
PublicationsPublication in journals
 Tightbinding calculations of imagecharge effects in colloidal nanoscale platelets of CdSe
, R. Ben Chamekh, N. A. Gippius, J. Even, M. Nestoklon, J.M. Jancu, S. Ithurria, B. Dubertret, Al. L. Efros, P. Voisin, Phys. Rev. B 89, 35307 (2014)
 Nuclear spin physics in quantum dots: An optical investigation
, B. Urbaszek, X. Marie, T. Amand, O. Krebs, P. Voisin, P. Maletinsky, A. Hoegele, A. Imamoglu, Rev. Mod. Phys. 85, 79 (2013)
 Spin splitting of electron states in (110) quantum wells: Symmetry analysis and k.p theory versus microscopic calculations , M. Nestoklon, S.A. Tarasenko, J.M. Jancu, P. Voisin, Phys. Rev. B 85, 205307 (2012)
 Type II heterostructures formed by zincblende inclusions in InP and GaAs wurtzite nanowires
, J.M. Jancu, K. Gauthron, L. Largeau, G. Patriarche, J.C. Harmand, P. Voisin, Appl. Phys. Lett. 97, 41910 (2010)
 Electric field effect on electron spin splitting in SiGe/Si quantum wells
, E. L. Ivchenko, J.M. Jancu, P. Voisin, Phys. Rev. B 77, 155328 (2008)
 STM Images of Subsurface Mn Atoms in GaAs: Evidence of Hybridization of Surface and Impurity States
, J.M. Jancu, J.C. Girard, A. Lemaître, F. Glas, Z.Z. Wang, P. Voisin, Phys. Rev. Lett. 101, 196801 (2008)
 Large intrinsic birefringence in zincblendebased artificial semiconductors
, J.M. Jancu, J.C. Harmand, G. Patriarche, A. Talneau, K. Gauthron, F. Glas, P. Voisin, C.R. Phys. 8, 1174 (2007)
 Diamagnetic contribution to the effect of inplane magnetic field on a quantumdot exciton fine structure
, M.M. Glazov, E. L. Ivchenko, O. Krebs, K. Kowalik, P. Voisin, Phys. Rev. B 76, 193313 (2007)
 Tetragonal and trigonal deformations in zincblende semiconductors: a tight binding point of view
, J.M. Jancu, P. Voisin, Phys. Rev. B 76, 115202 (2007)
 Valence band spin splitting in GaAs/AlGaAs quantum wells
, Q.T. Nguyen, J.M. Jancu, P. Voisin, Physica E 34, 352 (2006)
 Comment on "Spininduced forbidden evanescent states in IIIV semiconductors"
, Q.T. Nguyen, J.M. Jancu, P. Voisin, Phys. Rev. Lett. 97, 109701 (2006)
 Atomistic spinorbit coupling and kp parameters in IIIV semiconductors
, J.M. Jancu, R. Scholz, E.A. De Andrada e Silva, G.C. La Rocca, Phys. Rev. B 72, 193201 (2005)
 Giant birefringence in zincblende based artificial semiconductors
, J.M. Jancu, R. Magri, A. Vasanelli, P. Voisin, Phys. Rev. B 69, 241303(R) (2004)
 Giant spin splittings in GaSbAlSb Lvalley quantum wells
, J.M. Jancu, R. Scholz, G.C. La Rocca, E.A. Andreada e Silva, P. Voisin, Phys. Rev. B 70, 121306(R) (2004)
Past and current Internship TrainingPhDs
 Local wavefunction in the tightbinding theory
R. Ben Chamekh(20081201 / 20111130)
Contact : D. Mailly
, P. Voisin
Group : Optic of Semiconductor nanoStructures Group (GOSS)
More
The extended basis spds* tight binding model is undoubtedly the best representation of single particle states in bulk and nanostructured semiconductors but from a theoretical point of view, it suffers from the lack of knowledge of the spatial properties of the basis function, which hampers the calculation of interactions between quasiparticles. In this thesis, we attempt to solve this methodological issue. In his thesis, Ramzi Benchamekh starts from a set of Slater orbitals that depend on arbitrary « screening coefficients ». He orthogonalizes them and optimizes the screening coefficients in order to reproduce the optical matrix elements between various bands, at various points in the Brillouin zone. The obtained Bloch functions are compared and yield excellent agreement with ab initio calculations.
