Tunable spin and transport in porphyrin-graphene nanoribbon hybrids

TL;DR

This paper uses first principles calculations to explore spin-dependent transport in porphyrin-graphene nanoribbon hybrids, revealing tunable spin states and transport properties relevant for spintronics and sensing applications.

Contribution

It introduces a theoretical study of Fe-porphyrin GNR hybrids showing spin-crossover effects and transport sensitivity, advancing understanding of carbon-based spintronic materials.

Findings

Fe embedding induces spin polarization with S=1

Fano anti-resonance affects spin transport near Fermi level

Mechanical strain or chemical adsorption switch spin states

Abstract

Recently, porphyrin units have been attached to graphene nanoribbons (Por-GNR) enabling a multitude of possible structures. Here we report first principles calculations of two prototypical, experimentally feasible, Por-GNR hybrids, one of which displays a small band gap relevant for its use as electrode in a device. Embedding a Fe atom in the porphyrin causes spin polarization with a spin ground state $S=1$. We employ density functional theory and nonequilibrium Green's function transport calculations to examine a 2-terminal setup involving one Fe-Por-GNR between two metal-free, small band gap, Por-GNR electrodes. The coupling between the Fe-$d$ and GNR band states results in a Fano anti-resonance feature in the spin transport close to the Fermi energy. This feature makes transport highly sensitive to the Fe spin state. We demonstrate how mechanical strain or chemical adsorption on the Fe give rise to a spin-crossover to $S=1$ and $S=0$, respectively, directly reflected in a change in transport. Our theoretical results provide a clue for the on-surface synthesis of Por-GNRs hybrids, which can open a new avenue for carbon-based spintronics and chemical sensing.