Prof Jan Mol

Jan Mol

Professor of Physics

School of Physical and Chemical Sciences
Queen Mary University of London
www.qmul.ac.uk/spcs/staff/academics/profiles/jmolqmulacuk.html
Centre for Experimental and Applied Physics
Centre for Chemical Research
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Research

quantum materials and devices, nanoscale thermodynamics, molecular electronics, solid-state nanopores, quantum sensing, atomically precise engineering

Interests

Summary:
The overarching theme of my research is to engineer materials at the atomic and molecular level with the aim of harnessing their properties for emerging quantum and nanotechnologies. Throughout my career I have worked at the cutting edge of physics, materials science, and chemistry, with a view towards translating fundamental science into real-world technology.

Research Interests:
The overarching theme of my research is to engineer quantum effects in atomic- and molecular-scale devices. During my PhD I developed novel scanning tunnelling microscopy and spectroscopy techniques to investigate the properties of individual dopant atoms in silicon that hold a significant promise for quantum computation. In particular, I mapped out the quantum mechanical wavefunction of atoms that where placed with atomic precision in the silicon substrate. Following my PhD, I started to apply his expertise in quantum transport to molecular-scale devices as an independent researcher. My research now covers a broad range of research topics from fundamental studies of electron transfer in individual molecules, and nanoscale thermodynamics, to applications including solid-state nanopores for DNA sequencing and molecular data storage, and single-molecule biosensors for rapid pathogen detection.

Research highlights from my independent career include the observation of nuclear tunnelling in a graphene-based single-molecule transistor and direct entropy measurement in a nanoscale quantum system. Most recently, I have begun developing atomically precise materials for energy harvesting applications. The scope and impact of my work is reflected by the patents that I have filed on devices for quantum computing, DNA sequencing, neuromorphic computing, and nanoscale manufacturing.

A summary of the work conducted under my supervision is given below.
Quantum interference: Dirac considered the superposition principle by which every quantum state can be represented as a sum of two or more other distinct states to be the most fundamental principle in quantum mechanics. I study the quantum superposition – and the resulting quantum interference – of electrons in low-dimensional nanostructures, including nanowires that are only about silicon 30 atoms in diameter and atomically-thin graphene nanoconstrictions. A telling illustration of the quantum, wave-like, nature of electrons on the atomic and molecular scale is the observation of Fano resonances. First observed by Majorana in atomic excitation spectra, a Fano resonance is wave phenomenon that results from the inference between a continuum of states and a discrete state. Quantum inference in nanometre wide graphene constrictions leads to asymmetric electrical conductance peaks that have a characteristic Fano lineshape and have no classical counterpart. The ability to harness quantum interference in atomic- and molecular-scale systems make them into attractive components in designing functional circuits. Of particular interest in this respect is the question of how much ‘quantumness’ these systems should have for optimal performance. My research shows that electrical conductance in molecular systems is most efficient when it is at the boundary between wave-like quantum transport and particle-like classical transport.

Single-molecule devices: Electron transfer is a ubiquitous chemical process, playing a role in everything from battery technology to our sense of smell. My research on charge transport in single-molecule transistors established the connection between the well-known Marcus theory for electron transfer in chemistry and the orthodox theory of sequential electron tunnelling in physics. Building on my previous work on fabricating and characterising graphene-based single-molecule transistors, and studying the interaction between electronic and mechanical degrees of freedom in these systems, I was able to pinpoint the contribution of nuclear tunnelling (the motion of nuclei through a classically forbidden region) upon reduction or oxidation of an individual molecule. The experimental verification of the theoretical framework to describe charge transport in the presence of electron-vibrational interactions has made a significant contribution in the field of single-molecule electronics. However, the success in contacting individual molecules using graphene nanoelectrodes has not only enabled new science, but also lead to a patent on their use for single-molecule DNA sequencing which is currently licensed to a world-leading biotechnology company based in the UK.

Nanoscale thermodynamics: Heat engines are one of the central tenets of thermodynamics. In cyclical heat engines, a working gas moves through a reversible cycle to transfer heat between a hot and a cold reservoir and perform useful work. The steam engine and the internal combustion engine are two well-known examples of cyclical heat engines. Particle-exchange heat engines also convert thermal energy into useful work, however heat is transferred from a hot to a cold reservoir via the exchange of particles, for example electrons, in a finite energy range. I have created single-electron heat engines where a molecule or quantum dot is placed between a hot and a cold reservoir and the useful work is done by electrons moving against the applied electric field to generate power. Using these single-electron heat engines I was not only able to demonstrate the fundamental limits of the Seebeck coefficient that relates the net charge flow to the temperature difference, but also the effect of level-degeneracy and electron-vibrational interactions.Interestingly, the heat-to-electricity conversion efficiency in these spin-degenerate systems is direct measure for the entropy difference ∆S = kBln2 between one and two micro-states.