Quantum interference in single-molecule devices

Quantum interference offers a rich resource which could be exploited in molecular devices. If there are multiple pathways for energy transport through a molecule, or if electrical transport is subject to resonances within a molecule, then these effects could be exploited for practical technologies. For example, it may be possible to make transistors with much lower power consumption than current silicon CMOS, and it may be possible to develop improvement of thermovoltaic materials for scavenging heat that would otherwise be wasted. Understanding such phenomena may also shed light on postulated quantum coherent processes in biology, ranging from photosynthesis to bird navigation.

The project requires nanofabrication of carbon-based devices into which individual molecules can be inserted. The current through the molecules will be measured with a view to discovering mechanisms of quantum interference. A major challenge will be to devise and fabricate geometries with additional gates to control the quantum interference. The project will involve nanofabrication, chemical attachment of the molecules, and electrical measurements over a range of temperatures and frequencies, with especial regard to discovering the conditions under which quantum coherence can be found. A successful outcome will be to find regimes in which quantum coherence gives enhanced device performance.

The objectives of the project are:

- Design and synthesise molecular structures that are engineered to have specific quantum interference properties, so that we generate a catalogue of modular design features including, for example, anchor groups and Fano-active cores.
- Develop a platform for reproducibly contacting and measuring a wide range of molecules, so that different molecular designs can be analysed in a quantitative matter.
- Implement a systematic measurement strategy to inform molecular design decisions and to investigate fundamental transport properties of individual molecules.
- Provide a theoretical framework to analyse experimental results and to develop the foundation underpinning the vision.

National and international reports highlight challenges addressed by this project. DSTL's 2014 analysis, UK Quantum Technology Landscape, observes (p. 55) that 'Recent research has demonstrated the possibility of assembling, at the molecular level, highly efficient devices that will be able to deliver electrical power from waste heat. ... There is a UK gap in experimental capability, which will need multi-discipline collaboration'. ITRS (the International Technology Roadmap for Semi- conductors) calls for 'further fundamental work' on the 'knowledge base for molecular electronics'.

This work on novel molecular logic systems will directly address the 'Non-CMOS device technology' research area, where EPSRC's strategy is to maintain investment in light of a strong UK manufacturing base and the potential to secure a leading position on novel nano- or micro-electronics. Novel uses of graphene for logic and electronic devices will contribute to EPSRC's 'Graphene and carbon nanotechnology' research area. The project will also contribute, at a higher level, to EPSRC Grand Challenges in 'Quantum Physics for New Quantum Technologies' (electronic nanodevices that use quantum phenomena to decrease consumption and process information) and 'Nanoscale Design of Functional Materials' (new synthetic tools for the creation of molecular nanoelectronic devices which can be produced cheaply and in large quantities).

This project is aligned with the EPSRC Programme Grant 'Quantum Effects in Electrinic Nanodevices' and is in collaboration with Prof Harry Anderson at the Department of Chemistry (Oxford) and Prof Colin Lambert (Lancaster).

The Themes are:
Physical sciences
Quantum technologies