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SUMMARY:Thermometry and Refrigeration using Quantum Dots - Miss Aquila Mav
 alankar\, Semiconductor Physics Group\, University of Cambridge
DTSTART:20131209T141500Z
DTEND:20131209T151500Z
UID:TALK48256@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:The two-dimensional electron gas in GaAs/AlGaAs heterostructur
 es has diverse applications at cryogenic temperatures\, but is heated by n
 oise in the measurement set up. Our work involves the fabrication of a qua
 ntum dot refrigerator which can cool the electron gas to below the ambient
  lattice temperature[1]. \n \nLithographically defined Ti/Au gates pattern
 ed on the surface of a GaAs/AlGaAs heterostructure define three quantum do
 ts (left\, right\, and top) of radius 150 nm\, tunnel-coupled to an enclos
 ed\, macroscopic\, two-dimensional reservoir of electrons 100μm2 in area.
  The QDR uses the discrete energy levels of two quantum dots to cool the c
 entral electron reservoir. The third quantum dot (the 'thermometer') probe
 s the temperature of the two dimensional reservoir being cooled. \n \nOur 
 temperature measurement scheme consists of monitoring the charge distribut
 ion of the thermometer dot. This dot is open only to the enclosed reservoi
 r whose temperature we want to extract. Changing the energy level of the d
 ot through the Fermi-Dirac energy distribution of the enclosed reservoir r
 esults in the occupation probability of the dot being described by the sam
 e distribution. This is reflected in the current flowing through an adjoin
 ing quantum point contact. Fitting a Fermi-Dirac distribution to the measu
 red current thus yields the temperature of the two-dimensional reservoir. 
 Electronic temperatures between 120 and 951 mK are measured with an accura
 cy of better than 1 mK in the best case\, and agree with the lattice tempe
 rature measured by a resistance thermometer. The thermometer is non-invasi
 ve and does not pass a current through the electron system being measured.
  The tuning is independent of temperature\, and the device is robust in a 
 magnetic field up to 5.6T[3]. Using this scheme\, we have also investigate
 d the variation in the electron temperature as a function of the voltages 
 on the top and right plunger gates. This variation is produced because the
  changing voltages on the plunger gates move the energy level of the entra
 nce dot down through the Fermi level of the source while moving the level 
 of the exit dot up through the Fermi level at the drain\, thus changing th
 e energy extracted from the reservoir. Our results agree qualitatively wit
 h the model of electron cooling developed by Edwards[2].\n\nReferences	\n[
 1] J. R. Prance\, C. G. Smith\, J. P. Griffiths\, S. J. Chorley\, D. Ander
 son\, G. A. C. Jones\, I. Farrer\, and D. A. Ritchie 2009 Phys. Rev. Lett.
  102 146602 \n[2] H. L. Edwards\, Q. Niu\, G. A. Georgakis\, and A. L. de 
 Lozanne 1995 Phys. Rev. B 52 5714\n[3] A. Mavalankar\,a) S. J. Chorley\, J
 . Griffiths\, G. A. C. Jones\, I. Farrer\, D. A. Ritchie\, and C. G. Smith
  2013 Appl. Phys. Lett. 103\, 133116\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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