APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016;
Baltimore, Maryland
Session H7: Dopants and Defects in Semiconductors: Spin Related Transport
2:30 PM–5:30 PM,
Tuesday, March 15, 2016
Room: 303
Sponsoring
Units:
DMP FIAP
Chair: Lourdes Salamanca-Riba, University of Maryland
Abstract ID: BAPS.2016.MAR.H7.1
Abstract: H7.00001 : Anomalous organic magnetoresistance from competing carrier-spin-dependent interactions with localized electronic and nuclear spins
2:30 PM–3:06 PM
Preview Abstract
Abstract
Author:
Michael E. Flatté
(University of Iowa)
Transport of carriers through disordered electronic energy landscapes occurs via hopping
or tunneling through various sites, and can enhance the effects of carrier spin dynamics
on the transport. When incoherent hopping preserves the spin orientation of carriers, the
magnetic-field-dependent correlations between pairs of spins influence the charge
conductivity of the material. Examples of these phenomena have been identified in
hopping transport in organic semiconductors and colloidal quantum dots, as well as
tunneling through oxide barriers in complex oxide devices, among other materials. The
resulting room-temperature magnetic field effects on the conductivity or
electroluminescence require external fields of only a few milliTesla. These magnetic field
effects can be dramatically modified by changes in the local spin environment. Recent
theoretical and experimental work has identified a regime for low-field
magnetoresistance in organic semiconductors in which the spin-relaxing effects of
localized nuclear spins and electronic spins interfere1. The regime is studied
experimentally by the controlled addition of localized electronic spins, through the
addition of a stable free radical (galvinoxyl) to a material (MEH-PPV) that exhibits
substantial room-temperature magnetoresistance (~ 20%). The magnetoresistance is
initially suppressed by the doping, as the localized electronic spin mixes one of the two
spins whose correlation controls the transport. At intermediate doping, when one spin is
fully decohered but the other is not, there is a regime where the magnetoresistance is
insensitive to the doping level. For much greater doping concentrations the
magnetoresistance is fully suppressed as both spins that control the charge conductivity
of the material are mixed. The behavior is described within a theoretical model describing
the effect of carrier spin dynamics on the current. Generalizations to amorphous and
other disordered crystalline semiconductors will also be described. This work was
supported by DOE and an ARO MURI and was done in collaboration with N. J. Harmon,
K. Sahin-Tiras, Y. Wang and M. Wohlgenannt.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.MAR.H7.1