Solomon Group − Charge and Heat Transport Theory

About the project

Over the last ten years, there has been a growing interest in quantum interference effects observed in molecules. Remarkably, given their fragility in mesoscopic physics, molecular quantum interference effects can be readily observed at room temperature in solution. This robustness comes from the extremely small size of the molecular components (1-2nm) and thereby the small dimensions over which phase coherence is required.

The aim of this project is to challenge the limits of molecular quantum interference effects delivering clear predictions of how to realise these effects in three challenge areas:

1. Beyond single molecules: intermolecular interference effects.
   This work package will investigate interference effects between molecules and in monolayers to find systems where intermolecular interference effects emerge with a long-term view to materials.
2. Beyond classical electronics: Quantum gates
   Given that interference effects are an indication of phase coherence being maintained across the molecule, we should be able to exploit the quantum nature of the system for more than simply suppressing current. Proposals exist in the literature for realising a quantum computer through scattering, so this work package will investigate use the interference effects in molecules to suggest candidate systems for this type of quantum computer.
3. Beyond electron transport: Controlling vibrational energy redistribution
   This work package will focus on how to use interference effects to control vibrational energy redistribution within single molecules with an aim of using this to modulate product ratios in organic reactions.

This project takes ideas that have come out of molecular electronics and tests the scope of their application in three neighbouring areas: supramolecular chemistry, quantum computing and organic chemistry. This project takes a first step in these directions, and success in any work package has the possibility to open a whole new field of research.

Participants

Principal Investigator

Gemma Solomon, Department of Chemistry

PhD Students

• William Bro-Jørgensen
• Tomislav Rozic
• Louise Hyllested.

Postdocs

• Joseph M. Hamill

Masters Students

• Søren Langkilde
• Xupeng Song.

Bachelor Students

• Amalie Paulsen
• Andreas Juul Bay-Smidt
• Philip Kofoed-Djursner
• Laura Nøhr Holmegård Jensen
• Sophia Mikkelsen

About the project

One of the most fundamental challenges for the further miniaturization of electronic devices is controlling the leakage current that flows through the gate dielectric in transistors.

Essentially quantum tunnelling has to be suppressed. Recently, (Nature 2018, 558 (7710), 415-419) we showed that molecules exist with functional groups that are more insulating than a vacuum gap of the same dimensions, a remarkable suppression of electron tunnelling.

In this project, we take this insight and use it to design new dielectric materials, tackling the challenge of maintaining the insulating properties of the molecule whilst enhancing the dielectric constant.

We will use a combination of high-throughput screening and atomistic studies of quantum transport through molecules, monolayers and multilayers. The project will fund one PhD student.

Principal Investigator

Gemma Solomon, Department of Chemistry

Central challenges for the project

The central aim of this project is to develop and apply a method for simulating single-molecule pulling experiments, thereby gaining new insight into the structure-function relationships that operate in these novel environments. An example of the type of system is shown in the image, we imagine a molecule bound between a metallic tip and substrate and a force can be applied to the molecule while the current through the system is measured.

The objectives can be summarised with three main goals:

1. To develop methods for modelling the dynamics of the system, both the leads (generally metallic) and the molecule.
2. To extend methods for analysing the local properties of systems and extracting the relevant information from sets of thousands of calculations.
3. To integrate methods for calculating conductance, force, IETS and SERS with the methods developed for the dynamics and apply this to experimentally relevant systems.

We hope that we can embrace the full complexity of these experiments in our calculations and see what we can learn by really doing statistical sampling over many geometries.

People

PhD Students

• Alessandro Pirrotta
• Kasper Lauritzen
• Anders Jensen
• Anders Borges
• Marc Hamilton Garner