Details of Grant 

EPSRC Reference:	EP/D500222/1
Title:	Electron dynamics and collective effects in semiconductor quantum devices
Principal Investigator:	Eaves, Professor L
Other Investigators:	Patane, Professor A Henini, Professor M Benedict, Dr KA Fromhold, Professor TM Kent, Professor A Mellor, Dr CJ
Researcher Co-Investigators:
Project Partners:	Osaka University University of North Texas University of Regensburg
Department:	Sch of Physics & Astronomy
Organisation:	University of Nottingham
Scheme:	Standard Research (Pre-FEC)
Starts:	01 September 2005	Ends:	28 February 2009	Value (£):	1,822,530
EPSRC Research Topic Classifications:	Condensed Matter Physics
EPSRC Industrial Sector Classifications:	Electronics
Related Grants:
Panel History:
Summary on Grant Application Form
The overarching theme of this proposal is the imaging and control of electrons in quantum devices in the presence of a strong magnetic field. The project requires an integrated programme of growth, experiment, theory, and computer modelling. It will develop the new knowledge and concepts required for emerging technologies in electronics and optoelectronics.(i) We will explore a new type of chaos In quantum semiconductor superlattice devices in which the wave-like character of the electrons dominates their behaviour. The evolution of a chaotic system depends critically on how we set it in motion. Chaos is usually thought to be a macroscopic phenomenon occurring in large, complex systems such as weather patterns or the solar system, and describable using Newton's Laws; however, it has a subtle but important effect on the quantum behaviour of electrons. We recently discovered that electrons moving in semiconductor superlattices can exhibit a new type of chaotic motion called non-KAM chaos, which arises from the coupling of the tunnelling motion of electrons through the quantum barriers of the superlattice, with the cyclotron motion generated by a strong tilted magnetic field. Each type of motion has a characteristic frequency, and by using a small electrical signal to switch the frequencies on or off-resonance, we can dramatically modify the shape and length of the chaotic orbits of the electrons as they move through the tunnel barriers. This makes the device an extremely sensitive and fast electrical switch, with possible applications as a source or detector of high frequency radiation.(ii) At Nottingham, we have invented and refined a technique, magnetotunnelling spectroscopy (MTS), to image the shape of the wavefunction of electrons bound in nanostructures such as quantum dots (QDs) and wires, and to measure the relation between the energy and momentum of an electron (i.e. the energy dispersion curve). We now propose to use this technique to study the properties of many electrons confined in QDs and also how adding to the QD a small number of nitrogen (N) atoms affects the electrons' behaviour; the strong electronegativity of N should strongly modify the shape of the wavefunctions in the QD. We will also use MTS to investigate the wavefunctions of charged and neutral excitons, exploiting our recent observation of new peaks in the current-voltage characteristics of photoexcited resonant tunnelling diodes at very high magnetic fields. Finally we will investigate the appearance of anomalies In the tunnelling current associated with interactions between an electron which has tunnelled onto the dot and those left behind in a 2D electron sheet.(iii) We will use our newly-developed scanning capacitance microscope (SCM) to image the distribution of electronic charge in quantum Hall effect (QHE) samples and in new devices in which we have recently observed negative differential conductivity (NDC). In the QHE, the electrons flow along equipotentials without dissipation, so that the Hall conductivity is quantised, thus providing a universal electrical resistance standard. Our recent experimental and theoretical work on the QHE breakdown has shown that the dissipationless current is destroyed above a critical flow velocity when a stream of electron-hole pairs forms in the vicinity of a charged impurity - a quantum analogue of the von Karman vortex pairs in classical fluid mechanics. We will search for evidence of the local breakdown, and its effect on the electron charge distribution in the device as well as pursuing theoretically the analogy with instabilities in fluids. We will also use the SCM to image the conducting and insulating regions of a sheet of electron fluid and to investigate the electron charge domains associated with new NDC effects that we have just discovered in GaAs samples containing a small amount of N, and in short-channel GaAs quantum well structures in which hole carriers travel ballistically.
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Organisation Website:	http://www.nottingham.ac.uk