design of a scanning gate microscope in a cryogen-free dilution … · 2017-09-25 · fmm march 22,...
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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
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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
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Two-stage Pulsed Tubes
series arrangement of two pulsed tubes
parallel arrangement of two pulsed tubes
(regenerators in series)
J. Bert, Stanford University, 2007
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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
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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)
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Spring Stage
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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
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Vibration Measurements (Geophone)
PT on, RTon MC flange, RT
1.9 µm @ MC, 0.58 µm @ spring stage
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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
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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)