Experimental Data Confirm Carrier-Cascade Model for Solid-State Conductance across Proteins

TL;DR

This study confirms a carrier-cascade model explaining the nearly temperature-independent conductance in protein films, supported by experimental data and DFT calculations showing consistent activation energies across different proteins.

Contribution

The paper introduces and validates a generalized Landauer-based model for protein conductance, highlighting the role of specific energy differences over the HOMO-LUMO gap.

Findings

Experimental conductance remains nearly constant from room temperature to a few Kelvin.

Activation energies derived from experiments match DFT calculations.

The model accurately predicts an Arrhenius-like dependence at low temperatures.

Abstract

The finding that electronic conductance across ultra-thin protein films between metallic electrodes remains nearly constant from room temperature to just a few degrees Kelvin has posed a challenge. We show that a model based on a generalized Landauer formula explains the nearly constant conductance and predicts an Arrhenius-like dependence for low temperatures. A critical aspect of the model is that the relevant activation energy for conductance is either the difference between the HOMO and HOMO-1 or the LUMO+1 and LUMO energies instead of the HOMO-LUMO gap of the proteins. Analysis of experimental data confirm the Arrhenius-like law and allows us to extract the activation energies. We then calculate the energy differences with advanced DFT methods for proteins used in the experiments. Our main result is that the experimental and theoretical activation energies for these three different proteins and three differently prepared solid-state junctions match nearly perfectly, implying the mechanism's validity.