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SUMMARY:Towards a Multi-Scale Theory for Charge and Spin Transport in Orga
 nic Single Crystal-based Devices - Professor Stefano Sanvito\, Trinity Col
 lege Dublin
DTSTART:20160119T143000Z
DTEND:20160119T153000Z
UID:TALK63269@talks.cam.ac.uk
CONTACT:Stuart Higgins
DESCRIPTION:Constructing a materials-specic theory of charge and spin tra
 nsport in organic single crystal-based devices\nis a complex problem\, whe
 re the computation of accurate structural and vibrational properties needs
  to be\ncoupled to ways of determining the charge mobility and the spin-di
 usion characteristics. Here I will present a\nfew steps towards a multi-s
 cale theory of charge and spin transport in organic devices\, in particula
 r focussing\non architectures where the organic channel is formed by a hig
 h-mobility organic single crystal.\n\nFirstly I will discuss the interface
  between an organic crystal and a standard inorganic metallic electrode.\n
 In this case once the interface geometry is optimised with state of the ar
 t density functional theory\, including\ndispersive forces\, the electroni
 c structure and the correct level alignment is extracted rigorously and ac
 cu-\nrately from constrained density functional theory (1). This allows on
 e to identify the necessary quasi-particle\ncorrections to apply to the sp
 ectrum. The obtained electronic structure can be then compared with availa
 ble\nUPS data (2). Intriguingly\, often the dynamics of the injection of c
 harge and spin at the interface is not simply\ndominated by the density of
  states of the constituents. In particular I will discuss a case where dyn
 amical\ninteraction between spin-carrier and molecular vibration can aect
  dramatically the spin lifetime at the\ninterface (3).\n\nThen I will move
  to discuss a scheme to calculate the charge carrier mobility of pure orga
 nic crystals\nat nite temperature\, which is material-specic\, it accoun
 ts for van der Waals interactions and it includes\nvibrational contributio
 ns from the entire phonon spectrum of the crystal. Such an approach is als
 o based on\ndensity functional theory\, which now is combined with the con
 struction of a tight-binding eective model\nvia Wannier transformation. T
 he nal Hamiltonian includes coupling of the charge carriers to the crysta
 ls\nphonons\, which are also calculated from density functional theory. Fu
 rthermore\, in the case of spin transport\nboth spin-orbit and hyperne in
 teraction complete the picture. I will apply this methodology to a range\n
 of molecular crystals\, and here I will present in detail the case of dure
 ne (4)\, a small -conjugated molecule\,\nwhich forms a high-mobility herr
 ingbone-stacked crystal. I will show that accounting correctly for dispers
 ive\nforces is fundamental for obtaining a high-quality phonon spectrum\, 
 in agreement with experiments. Then\nthe mobility as a function of tempera
 ture is calculated along dierent crystallographic directions and the\npho
 nons most responsible for the scattering are identied.\n\n\nREFERENCES\n\
 n1 A.M. Souza\, I. Rungger\, C.D. Pemmaraju\, U. Schwingenschloegl and S. 
 Sanvito\, Constrained-DFT method\nfor accurate energy-level alignment of m
 etal/molecule interfaces Phys. Rev. B 88\, 165112 (2013).\n2 A. Droghetti\
 , S.Steil\, N. Grossmann\, N. Haag\, H. Zhang\, M. Willis\, W.P. Gillin\, 
 A.J. Drew\, M. Aeschli-\nmann\, S. Sanvito and M. Cinchetti\, Electronic a
 nd magnetic properties of the interface between metal-\nquinoline molecule
 s and cobalt \, Phys. Rev. B 89\, 094412 (2014).\n3 A. Droghetti\, I. Rung
 ger\, M. Cinchetti\, and S. Sanvito\, Vibron-assisted spin relaxation at a
  metal/organic\ninterface\, Phys. Rev. B 91\, 224427 (2015).\n4 C. Motta a
 nd S. Sanvito\, Charge Transport Properties of Durene Crystals from First-
 Principles\, J. Chem.\nTheory Comput. 10\, 4624 (2014).
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
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