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Events on Thursday, September 4th, 2014

R. G. Herb Condensed Matter Seminar
Multiplexing of Nanostructure Devices
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Dr. Luke Smith, University of Cambridge
Abstract: It is highly desirable to increase the number of nanostructure devices on a single low temperature semiconductor chip for high through-put testing, and for creation of integrated quantum devices. We have developed an on-chip multiplexing technique which significantly increases the number of devices that can be measured during a single cooldown in a cryostat. This was used to address an array of 256 split gates on a GaAs/AlGaAs heterostructure; the largest number of such devices on an individual chip to date.

A rich variety of physical phenomena can be investigated using the split gate, despite the simple device geometry. Electron-electron interaction effects manifest in the formation of an anomalous conductance feature known as the ‘0.7 structure’, the specific origin of which is currently debated. We have performed a detailed statistical analysis of this structure using arrays of identical devices, as well as arrays in which the geometry of the split gates vary. Our results link this structure to small variations in the specific confining potential within individual devices.

Aside from exploring fundamental physics, the multiplexer can also be used to perform important tests of the suitability of nanostructure devices as elements for nanoelectronic or quantum computing architectures. We have performed yield studies, and investigated the reproducibility of device characteristics on repeated cooldowns. Additionally we have presented a technique which can be used to assess the homogeneity of the semiconducting substrate itself.

The multiplexing scheme is versatile and recently a charge-locking technique has been developed to sequentially bias a large number of gates, in order to form complex device structures. Initial studies have shown that this can be used to contact an array of quantum dots. Multiplexing is a powerful tool which both increases the efficiency of research and presents a new approach to measurements in this field.
Host: Mark Eriksson
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