Download - Ordered States of Adatoms in Graphene V. Cheianov, O. Syljuasen, V. Fal’ko, and B. Altshuler
Graphene
graphite graphene FET
K. S. Novoselov, A. K. Geim, S. V.Morozov, D. Jiang, Y. Zhang, S. V.Dubonos, I. V. Grigorieva, A. A. FirsovScience, Vol. 306. pp. 666 – 669 (2004)
Graphene Field Effect Transistor
Gate VoltageR
esis
tanc
e
Contacts
Si back gate
SiO
Resistance at its maximum is close to h/e2. Large on-off ratio is a challenge.
DisorderMobility is controlled by disorder scattering.
Types of disorder:
• Long-range Coulomb scatterers (charged traps in SiO2)• Lattice defects• Surface adsorbants
The latter can stick to the surface naturally or be deposited artificially
(STM images from NIST)
The main question.Gapless electron spectrum
Local perturbation of the electronsystem propagates over a large distance (e.g. as Friedel oscillations)
Long-range interactions between impurity atoms (RKKY).
Q: How will electron mediated interaction affect relative positions of mobile(non-magnetic) adatoms and what feedback will these correlations have on the electron system.
Pseudo-spin and pseudo-flavor
Sublattice mixing matrices (similarto spin).
Valley mixing matrices (similarto flavor).
Electron-adatom interaction
Small parameterThe position of theimpurity
A 4x4 matrix
is defined by the quantum chemistry of the adatom. But not entirely!
An example
K
K
K K’
K’
K’
Intervalley scattering = momentum transfer K-K'
There are 3 inequivalent positions of the adatom in the lattice.
Conclusions and open questions
• Electron-mediated interactions may lead to correlations in the positions of adatoms
• The transition to ordered states is accompanied by a gap opening in the electron spectrum
• Outstanding: competition between order and disorder contributions, glassy states, domains, quantum chemistry, experiment…