FMMMarch 22, 2013

Dario MaradanZumbühl Group

Design of a scanning gate microscope

in a cryogen-free dilution refrigerator

M. Pelliccione, A. Sciambi, J. Bartel, A. Keller, and D. Goldhaber-Gordon

arXiv:1211.6546v1, 28 Nov 2012

Intro: Pulsed Tube Cooler

cooling power is generated by locally separated expansion and contraction of gas

the Pulsed Tube (PT) cooler originated from the Gifford-McMahon cooler

CryoMechJ. Bert, Stanford University, 2007

Two-stage Pulsed Tubes

series arrangement of two pulsed tubes

parallel arrangement of two pulsed tubes

(regenerators in series)

J. Bert, Stanford University, 2007

Remote Motor

motor drive (similar to the one supplied by Cryomech)

linear motor drive

→ EMI: pickup of 10 mV on coaxial cables in 10 kHz to 1 MHz!!!

→ no measurable difference in the noise, vib @ 140 Hz factor 10 smaller

→FFT

→FFT

How to Measure Vibrations

• geophone: magnet hanging from a spring inside a solenoid→ induction of voltage → Fourier transform signal

• AFM tip: piezoresistive cantilever, glued on a tuning fork,electrical excitation and read-out

www.geophone.comGomez et al., Ultramicroscopy 111, 186-190 (2011)

Spring Stage

Cooling Power

less vibrations → lower cooling power

heat applied to scanner stage

• scanner: 11 µW @ 100 mK, while MC is 31 mK

• cooling power of MC @ 120 mK: 615 µW

ε = 0

MC: Tbase = 14.5 mK

scanner: Tbase = 15.4 mK

apply 1 µW:

Tscanner = 35 mK, TMC = 16.4 mK

Vibration Measurements (Geophone)

PT on, RTon MC flange, RT

1.9 µm @ MC, 0.58 µm @ spring stage

Vibration Measurements (AFM)

scanner stage, 15 mK: integrated RMS vibration is 2.1 nm (BW 1 kHz)

0.8 nm @ 3.3 K with DR not running

Conclusion

• effective damping of vibrations generated by PT using

• linear motor drive

• spring stage

• vibrations of 0.8 nm w/o dilution refrigerator and 2.1 nm @ 15 mK (integrated RMS within a 1 kHz bandwidth measurement)

• difference explained by mixture flowing in the dilution circuit (?!)

What do we learn from this?

• replacing the motor drive with a linear one might be a huge improvement

• putting a spring stage is a nice idea, but could be hard to implement in our setup (trade-off in cooling power)