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SUMMARY:Improved single-electron pumping with surface acoustic waves in Zn
 O/GaAs systems  - Mr Hangtian Hou ( University of Cambridge)
DTSTART:20160420T131500Z
DTEND:20160420T141500Z
UID:TALK64320@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:For a piezoelectric substrate\, a surface acoustic wave (SAW) 
 is a combined mechanical and potential wave propagating along the surface.
  In a GaAs/AlGaAs heterostructure\, SAWs are able to pump single electron 
 from a high-mobility two-dimensional electron gas (2DEG)  [1].  The GaAs s
 ubstrate\, as a weak piezoelectric material (piezoelectric coupling coeffi
 cine K2≃0.06%)\, requires a high power to of an RF signal generate a str
 ong SAW. However\, a high power cause a electromagnetic wave crosstalk dis
 turbing the result. We use a thin layer ZnO to improve the SAW amplitude a
 nd suppress the crosstalk\, \n\nWe have developed a room-temperature techn
 ique for sputtering ZnO on to the GaAs surface [2] . However\, we found th
 at the sputtering process strongly depletes high mobility 2D electron or h
 ole gases in a GaAs/AlGaAs heterostructure at liquid helium temperatures\,
  presumably through implantation of ions. We find that depositing a 25 nm-
 thick aluminium oxide layer by ALD before sputtering the ZnO is sufficient
  to protect the 2DEG. With the help of the good piezoelectric coupling coe
 fficient of ZnO (K2≃1%)\, the SAW resonance on the ZnO/GaAs substrate (s
 cattering parameter ∆S11 =10 dB) is much stronger than the pure GaAs sub
 strate (∆S11=2 dB). In the ZnO-coated devices\, The SAW-delayed pinch-of
 f voltage from 100mV in GaAs increase to 350mV in ZnO/GaAs system.  The mi
 nimum RF power required for SAW pumping was reduced from 7 dBm to ˗4 dBm 
 and the minimum RF power to observe SAW single-electron pumping decreased 
 from 10 dBm to 3 dBm. These results show the great enhancement of the SAW 
 amplitude. Furthermore\, the ZnO enhancement of the amplitude is so great 
 that SAWs can propagate even under the surface of liquid helium\, where ma
 ss-loading normally damps it out very strongly. When the device is dipped 
 into liquid helium\, the SAW pumping current oscillates with time\, which 
 we explain by the heat dissipation from the SAW that generates a thin heli
 um gas buffer layer on the interface between the ZnO and liquid helium. In
  future\, we will use the ZnO sputtering technique to further investigate 
 SAW pumping spectroscopically. A comprehensive explanation of the SAW sing
 le-electron pumping process\, and improvement of SAW strength\, will benef
 it the development of SAW quantum technology\, such as the manipulation of
  SAW flying qubits [3] in quantum computation [4].\n\n[1] V. I. Talyanskii
 \, J. M. Shilton\, M. Pepper\, C. G. Smith\, C. J. B. Ford\, E. H. Linfiel
 d\, D. A. Ritchie and G. A. C. Jones\, Phys. Rev. B 56\, 15180 (1997).\n[2
 ] J. Pedros\, L. Garcia-Gancedo\, C. J. B. Ford\, C. H. W. Barnes\, J. P. 
 Griffiths\, G. A. C. Jones and\nA. Flewitt\,  J. Appl. Phys. 110\, 103501 
 (2011).\n[3] R. P. G. McNeil\, M. Kataoka\, C. J. B. Ford\, C. H. W. Barne
 s\, D. Anderson\, G. A. C. Jones\, I. Farrer and D. A. Ritchie\, Nature 47
 7\, 439 (2011)\; Hermelin\, S. et al. ibid\, p.435. \n[4] C. H. W. Barnes\
 , J. M. Shilton\, and A. M. Robinson\, Phys. Rev. B 62\, 8410 (2000).
LOCATION:Mott Seminar Room (Mott Building Room 531)\, Cavendish Laboratory
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