An ultra sensitive radio frequency single electron transistor working up   to 4.2 K
  We present the fabrication and measurement of a radio frequency single electron transistor (rf-SET), that displays a very high charge sensitivity of 1.9 microlectrons/sqrt(Hz) at 4.2 K. At 40 mK, the charge sensitivity is 0.9 and 1.0 microlectrons/sqrt(Hz) in the superconducting and normal state respectively. The sensitivity was measured as a function of radio frequency amplitude at three different temperatures: 40 mK, 1.8 K and 4.2 K. 
Henrik Brenning, Sergey Kafanov, Tim Duty, Sergey Kubatkin and Per   Delsing