Magnetoresistance of Nanoscale Molecular Devices

Abstract

Affecting the current through a molecular or nanoscale junction is usually done by a combination of bias and gate voltages. Magnetic fields are less studied because nanodevices can capture only low values of the magnetic flux. We review recent work done with the aim of finding the conditions for magnetic fields to significantly affect the conductance of such junctions. The basic idea is to create narrow tunneling resonances through a molecular ring-like structure that are highly sensitive to the magnetic field. We describe a computational method that allows us to examine atomistic models of such systems and discuss several specific examples of plausible systems, such as the quantum corral, carbon nanotubes, and polycyclic aromatic hydrocarbon molecules. A unique property of the magnetic field, namely, its ability to split degenerate levels on the ring, is shown to allow prototypes of interesting new nanoscale devices, such as the three-terminal parallel logic gate.

Real-space method for highly parallelizable electronic transport calculations

“…ABCs have been previously used in combination with a variety of approaches for electron transport and for effectively mimicking self-energies in non-equilibrium Green's function approaches. [24][25][26][27][28][29][30][31][32][33] In this approach, H op is represented by…”

“…In this paper, we present a real-space, highly parallel method for first-principles Landauer electronic transport calculations, using absorbing boundary conditions [24][25][26][27][28] (ABCs, also known as complex absorbing potentials, or CAPs) to mimic the proper outgoing-wave boundary conditions. We base our implementation, which we call TRANSEC, on the PARSEC (Pseudopotential Algorithm for Real-Space Electronic Calculations) realspace DFT code.…”

Controlling the transmission line shape of molecular t-stubs and potential thermoelectric applications

“…[21][22][23][24] More recently, research in QI has been extended to aromatic molecules of increasing size [25][26][27][28] as well as incoherent transport in the Coulomb blockade regime 29,30 and also led to proposals for the usage of molecular interferometers in spintronics. 31,32 Thermoelectric materials, on the other hand, can convert thermal gradients to electric fields for power generation or vice versa for cooling or heating which makes them useful as Peltier elements. The efficiency of a thermoelectric material is measured by a dimensionless number, the figure of merit ZT = S 2 TG/κ, which includes the thermopower S, the average temperature T, the electronic conductance G, and the total thermal conductance κ, which has contributions from electrons (κ el ) as well as from phonons (κ ph ).…”

Avoiding self-repulsion in density functional description of biased molecular junctions

“…The problem might be especially acute for theoretical estimates of conductance of molecular junctions, for which many methods relying on DFT have been developed [14,[23][24][25][26][27][28][29][30][31]. In molecular electronics, as the bias changes so does the charge distribution on the bridge and contacts; a correct description of this charge distribution is important for understanding the response (in terms of electric current) to the bias.…”