Laser Driven Magnetism in Organic Semiconductors

Carbon based pi-conjugated molecules have delocalized electrons which are responsible for their applications as semiconductors. This delocalized electron cloud can be driven externally, for example by using electric or magnetic fields. In ring- and spherical-shaped molecules, such as coronene and fullerenes, the electrons can be driven into a ring current by illuminating with circularly polarized laser light. We will study the new type of magnetism that can be generated and controlled by laser light.

In a recent preliminary study aiming to grow crystals of the pi-conjugated molecule coronene we have observed an unexpected and new phenomenon. Coronene grown in a magnetic field exhibits a previously unknown crystalline structure when compared to the known structures prepared in the absence of field (arXiv:1509.04120). Coronene and other aromatic molecules such fullerenes are known to develop ring currents if in magnetic fields.

Ring currents are a unique phenomenon which attracted the interests of many chemists and physicists trying to understand the structure of organic aromatic compounds. One of the most spectacular manifestations of ring currents are the shielding of nuclear proton spins in NMR spectroscopy. Recently, a theoretical proposal about inducing ring currents with circularly polarized laser pulses triggered a large interest (JACS 128, 7043). This is because short laser pulses can generate ring currents orders of magnitude higher than those achieved with the most common laboratory magnetic fields.

In this PhD thesis we will induce ring currents with femtosecond laser pulses in order to induce transient magnetism in molecular solids made of coronene and fullerenes. This will open up possibilities for new ways of assembling molecules in crystals and observe new undiscovered properties. In addition, this exciting project aims to demonstrate the control of transient magnetism by using laser light.

Relevant collaborations are with Dr. Simon Crampin in Bath, Dr. Simon Hall (Bristol), Prof. von Hauff (Amsterdam) and Prof. Aldo Brillante (Bologna).

There will be the possibility for the student to attend some of the lectures from the Condensed Matter Physics CDT funded by EPSRC and interact with students enrolled in that programme.

Applicants should have a background in the physical sciences and have or expect to gain a First or Upper Second Class UK Honours degree, or the equivalent from an overseas University.

Contact Dr Enrico Da Como ([Email Address Removed]) for further information on the project. http://people.bath.ac.uk/edc25/