Giant Magnetoresistance in Ultrasmall Graphene Based Devices

Abstract

By computing spin-polarized electronic transport across a finite zigzag graphene ribbon bridging two metallic graphene electrodes, we demonstrate, as a proof of principle, that devices featuring 100% magnetoresistance can be built entirely out of carbon. In the ground state a short zigzag ribbon is an antiferromagnetic insulator which, when connecting two metallic electrodes, acts as a tunnel barrier that suppresses the conductance. The application of a magnetic field makes the ribbon ferromagnetic and conductive, increasing dramatically the current between electrodes. We predict large magnetoresistance in this system at liquid nitrogen temperature and 10 T or at liquid helium temperature and 300 G.

Edge states in graphene-like systems

“…Graphene ribbons are interesting by their own sake, and there has been enormous progress in the fabrication of ribbons with smooth edges [53][54][55][56][57] , so that inter-edge coupling is also an interesting topic [30][31][32]35,37,38,40,42,51,57,58 .…”

“…In most of papers 29,30,33,35,37,38,40,51,52 an additional approximation has been used, that assumes a collinear magnetization so that the Fock term vanishes. However, instances in which this is not the case are very interesting and also reviewed here 43 .…”

“…More importantly, there is quite strong experimental evidence that the QSH phase has been observed both in HgTe quantum wells 25 and inverted InAs/GaSb quantum wells 26 , both theoretically predicted to be QSH insulators 27,28 The role of Coulomb interactions can also affect dramatically the properties of some of these edge states, in particular, whenever edge states produce a large density of states at the Fermi energy, that makes them prone to Stoner instabilities. This is the case of zigzag edge states for which ferromagnetic order is expected [29][30][31][32][33][34][35][36][37][38] . The interplay between this magnetism, spin-orbit interactions [39][40][41][42] and the Quantum Hall phases 43 is a very fascinating area of research that we also review here.…”

Interplay between sublattice and spin symmetry breaking in graphene

“…[17][18][19][20][21][22]25,27,49 The most prominent feature of their electronic structure is given by the flat bands associated to edge states. At = U = 0, these bands are located at the Fermi energy, giving rise to a large density of states at the Fermi energy.…”

“…17 Density functional calculations confirmed the scenario, 18,19 showing that the long-range Coulomb interactions and the other atomic orbitals, absent in the Hubbard model, do not play a major role in this system. Both the mean field Hubbard model 17,[20][21][22][23][24][25][26][27] and DFT calculations show that the magnetic phase with zero total spin has a gap, which opens due to interedge correlations. 22 The fabrication of graphene ribbons with ultrasmooth edges is now possible by unzipping carbon nanotubes.…”