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Unusual magnetoresistance in Ge-Au alloys for low temperature thermometry

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It would be useful to be able to produce thermometers which can be easily fabricated on devices and which work over a wide range of temperatures, especially at low temperatures. Such thermometers could be used in thermoelectric measurements on a variety of materials, possibly including the surface states of topological insulators. Ge-Au alloys have been investigated for this purpose. The composition of the alloy and the annealing conditions have both been varied to investigate how to produce the best thermometers.

The resistance has been observed to vary logarithmically with temperature. This could be explained by the material being composed of conducting grains embedded in an insulating matrix. SEM /TEM images seem to support this explanation. The logarithmic variation of resistance should mean that the material could be useful as a thermometer over a wide range of temperatures as desired.

The magnetoresistance of the Ge-Au alloys exhibits unusual hysteresis. The shape of the magnetoresistance curve depends on the direction in which B is being ramped. There are several possible explanations for this, although as of yet no definite conclusions have been reached.

This talk is part of the Semiconductor Physics Group Seminars series.

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