Towards nano-mri in mesoscopic transport systems

Transcription

1 Towards nano-mri in mesoscopic transport systems P. Peddibhotla, M. Montinaro, D. Weber, F. Xue, and M. Poggio Swiss Nanoscience Institute Department of Physics University of Basel Switzerland 3 rd Nano-MRI Research Conference July 2010, Domaine du Tremblay

2 New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices

3 New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator

4 arxiv:

5 New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes)

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7 Nuclear spins in QDs In a QD, a single electron spin interacts with nuclear spins Hyperfine interactions cause decoherence of the electron spin MRFM may provide a way to directly observe this small ensemble of nuclei J. M. Taylor et al., Nat. Phys. 1, 177(2005)

8 MRFM of nuclei in QDs QD

9 New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes) sensitive detection of cantilever motion

10 Mechanical Force Transducers F x F kx We have a nano-mechanical transducers of force into displacement. We require a sensor for mechanical displacement

11 Sensors for Mechanical Displacement Tunneling Optical Deflection Optical Interferometry Microwave Interferometry Magnetomotive Piezoelectric Capacitive

12 STM Detection

13 Capacitive detection m/ Hz

14 Capacitive detection m/ Hz

15 Spectral Density (Ang 2 / Hz) Spectral Density (Å 2 / Hz) Spectral Density (A 2 / Hz) Spectral Density (Amp 2 / Hz) Measurement of Cantilever Thermal Noise DC V sd drive: 2.0 mv m / (Hz) 1/2 1E E E E Frequency (khz) Frequency (Hz) E E E E

16 New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes) sensitive detection of cantilever motion

17 Basic Setup Diagram cantilever laser Device (e.g. QPC, SET, microwire)

18 Displacement Spectral Density (m 2 /Hz) 1E E T = 400 mk Q = 18,000 k = 45 mn/m 1E E E Frequency (Hz) January 2009 March

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20 UHV BeCo springs chip carrier Soft Cu braids T = 300 mk 3D positioning of sample Cantilever holder & interferometer Interferometer with m/hz socket 1/2 4 coaxial touch cables sensorsfor RF signals 20 wire-bondable contacts to sample sample/device holder 3D positioners & scanners Rf coax lines

21 Basic Setup Diagram cantilever laser Device (e.g. QPC, SET, microwire)

22 RF coax connections piezo actuator lens cantilever chip device (e.g. microwire, QPC, SET) wire-bonding pads 22

23 QPC Samples markers 200 nm

24 Coupling to a Carbon Nanotube cantilever Ti-Au leads CNT

25 Carbon Nanotube Samples 1 mm

26 Carbon Nanotube Samples

27 cantilever chip cantilever nanotube devices bonds & pads Si sample reflection of cantilever chip

28 Interferometer laser beam Ultrasensitive cantilever Resonant slice (B = 2.70 T) 1 H Nuclear spin i rf Magnetic tip Microwire generating 115 MHz magnetic field

29 Cantilevers & sample preparation A tiny CaF2 sample was glued to the end of an ultrasolf Si cantilever with the aid of a needle held by a micro-manipulator Cantilever nanotube 5 mm tip 5 mm CaF 2 needle Cantilever CaF 2 Cantilever

30 Microwires & magnetic tips for MRFM FeCo tip Au microwire Effort at making a high gradient tip

31 New microwire MRFM geometry The cantilever s axis of rotation is parrallel to the applied magnietic field B 0. B 0 points in the plane of the device surface (for mesoscopic transport measurements) This configuration avoids magnetic dissipation known to be present even in nonmagnetic cantilevers. B

32 Spectral Density (m 2 /Hz) Force (an 2 ) First MRFM Signal Microwire F CaF 2 Crystal Particle B = 2.8 T T = 600 mk H Frequency (MHz) CaF 2 Cantilever 1E-19 1E-20 1E-21 cantilever thermal noise spin noise 1E Frequency (Hz)

33 Force (an 2 ) Gradient & RF field Magnitude Nutation Experiment T = 600 mk B 1 field 4.5 mt 190 khz T = 600 mk B rf 4.5 mt RF field (190 khz) B tip 10 6 T/m lateral field gradient B tip B rf i rf µ 10.0µ 15.0µ 20.0µ Pulse width (s)

34 Topical Review Force-detected nuclear magnetic resonance: Recent advances and future challenges M. Poggio and C. L. Degen, Nanotechnology, in press; arxiv: (2010)

35 Group members PhD Students Post-doc Masters Student Phani Peddibhotla Michele Montinaro Dr. Fei Xue Benedikt Herzog Dennis Weber