1. Nanoscale Electrodynamics Measurements with Radical New Forms of Microwave Microscopy
Steven Anlage, Michael Fuhrer
ONR AppEl Review
26 August, 2010
Work funded by ONR and DOE

2. UMD Microwave Microscopy Group
Faculty:
Steven Anlage
Michael Fuhrer
Graduate Student
Tamin Tai
Undergraduate Students
John Abrahams
Post-Doc
Behnood Ghamsari
Collaborators:
Alexander Zhuravel, Kharkov, Ukraine
Alexey Ustinov, Karlsruhe Inst. Tech.
Dragos Mircea, Western Digital
Vladimir Talanov, Neocera
Lance Cooley, FermiLab
Gigi Ciovatti, Jefferson Lab
Funding: ONR AppEl and DOE

3. All-electric and munitions-free ships require new materials technologies
Superconducting RF cavities for free-electron lasers
Superconducting tapes and wires for compact, efficient motors
‘Quantum’ materials with novel properties

4. the materials will be utilized
Motivations
The development of new materials with new functionalities depends
on establishing structure / property relationships
New forms of microscopy help to accelerate the development of
these novel materials
Development of new Nano-Electromagnetic devices requires
understanding of electrodynamics at the nano-scale
We are developing two new types of microscopy to establish structure / property
relations at high frequency and low temperatures, under conditions where
the materials will be utilized
Near-Field Microwave Microscopy of Nb for SRF applications
Laser Scanning Microscopy of superconductors and novel electronic materials

5. Localized Defects on Nb SRF Cavities
These defects can lead to hot spots on accelerator cavity within operating frequency region (1-2 GHz)
However, many defects are benign. How to distinguish the ‘good’ ones from the ‘bad’ ones?
Grain
Boundaries
welds, oxidation,hydrogen poisoning
welds, oxidation,hydrogen poisoning
500 x 200 mm pit
T. Bieler
Mich. State Univ.

6. APPROACH GOAL: To establish links between microscopic defects and
the ultimate RF performance of Nb at cryogenic temperatures
Near-Field Microwave Microscopy*
APPROACH:
1) Stimulate Nb with a concentrated and intense RF magnetic field
Drive the material into nonlinearity (nonlinear Meissner effect)
Why the NLME? It is very sensitive to defects…
Measure the characteristic field scale for nonlinearity: JNL
4) Map out JNL(x,y) → relate to previously-characterized defects
*S. M. Anlage, V. Talanov, A. Schwartz, "Principles of Near-Field Microwave Microscopy," in Scanning Probe Microscopy: Vol. 1,
edited by S. V. Kalinin and A. Gruverman (Springer-Verlag, New York, 2007), pages

7. Nonlinear Near-Field Microscopy of Superconductors
P3f : NLME Nonlinearities
Pinput
sample surface
coaxial probe
K(x,y)
loop
Superconductor
Current distribution
geometry factor
Induce high m0K ~ 200 mT (Hc of Nb)
K(x,y) sharply peaked in space
► Better spatial resolution
D. Mircea, S. Anlage, Phys. Rev. B 80, (2009) + references therein

8. What do We Learn About the Superconductor?
P3f(x)
JNL(x)
Position x
Defect 1
Defect 2
on YBCO
Measured at T=60 K (below Tc of YBCO)
Phys. Rev. B 72, (2005)

9. Magnetic recording heads provide strong and localized BRF
How to Generate Strong RF Magnetic Fields?
Magnetic Write Head
Magnetic recording heads provide
strong and localized BRF
Permalloy shields ~2 m
Cu coils
Read Sensor
Write Pole
RF Magnetic Fields
Air bearing surface
2 mm
Side View
SEM picture of the magnetic write head gap
Permalloy
Bottom View
BRF ~ 1 Tesla (in gap)
Gap
Lateral size ~ 100 nm x few-100 nm
Reference: IEEE Trans Magn. Vol . 37, No. 2 pp

10. Experimental Setup
We need higher BRF and strongly localized field distributions
Goals: BRF ~ 200 mT
Lateral size ~ 100 nm
RF Coil
on slider
Superconductor
Probe
Head Gimbal Assembly (HGA)

11. Measurements on Superconductors At a fixed location on MgB2 film
Excited power: 12 dBm; Excited frequency: 3.75GHz
Noise floor
MgB2 Film (25nm)/SiC
A peak in P3f(T) near the Tc of MgB2 is found.
No other P3f peak is found below Tc. It implies there is no defect near this measurement point.
Samples come from Prof. Xiao-Xing Xi Temple University, Philadelphia, PA

12. Measurements on Tl2Ba2CaCu2O8 Film
At a fixed location
Excited power: dBm
Excited frequency: 3.75 GHz Tc
Vortex or defects/ grain boundary contribution
Noise floor

13. Challenges for Measurements on Nb bulk materials
Top surface of bulk Nb (thickness: 0.1 inch)
Head Gimbal Assembly (HGA)
Pit on Nb
Copper cold plate
Probes may cause localized heating of Nb samples.
Temperature of cold plate reaches 4.2K but Nb surface remains warmer. (Next step: thermal grounding of probe and positioner)
Magnetic write head probe is still too far away from the superconductor surface. (Next step: nm-level positioning control)

14. Photolithography Result (thanks to Dr. Cihan Kurter)
Current Work---Micro Loop Design
Simulation Data from HFSS (Gregory Ruchti )
Photolithography Result (thanks to Dr. Cihan Kurter)
Micro loop design can enhance the current geometry factor G and increase our spatial resolution.

15. Laser Scanning Microscopy: Principle of the measurement
resonator transmission
modulated
laser
laser OFF
|S21(f0)|2
Pout
laser ON
Pin
|S21(f0)|2 f f0
co-planar resonator f0 ~ 5.2 GHz
D|S12|2 ~ [l JRF(x,y)]2 A dl
Local heating produces a change in
transmission coefficient proportional
to the local value of JRF2
J. C. Culbertson, et al. J.Appl.Phys. 84, 2768 NRL
A. P. Zhuravel, et al., Appl.Phys.Lett. 81, 4979 (2002)

16. Typical Spatial Profile of RF Photoresponse
Along a Lateral Cross Section of the Resonator Strip
YBCO/LaAlO3
CPW Resonator
1 x 8 mm scan
T = 79 K
P = - 10 dBm
f = GHz
fmod = 99.9 kHz
P1 = in-plane rotated grain
P2 = crack in YBCO film
P3 = LAO twin domain blocks
Wstrip = 500 mm

17. Imaging of a YBa2Cu3O7 / LaAlO3 Resonator Room Temp. Thermoelectric PR
Optical reflectivity
DC Photoresponse
“PR” = Photo-response
Room Temp. Thermoelectric PR
Low-T RF PR
A. Zhuravel, et al., J. Appl. Phys. 108, (2010)

18. Corner “A2” Detail of YBCO / LAO Resonator
Optical Reflectivity
RF PR
A. Zhuravel, et al., J. Appl. Phys. 108, (2010)
25 mm

19. JLab Microscope: built inside a Nb SRF cavity
Laser Scanning UMD
LSM in Karlsruhe, Germany
UMD Microscope: configured for bulk superconductors, closed cycle refrigerator
JLab Microscope: built inside a Nb SRF cavity

20. RF Defect Imaging in bulk Nb
Current and Future Work
Complete the UMD Laser Scanning Microscope
Closed cycle refrigerator for week-long runs
Ukraine collaborator (Zhuravel) visits to commission the microscope
Preliminary results from Karlsruhe collaboration
RF Defect Imaging in bulk Nb

21. Nb Cavity Laser Scanning Microscope at Jefferson Lab
Collaborative Work on
Nb Cavity Laser Scanning Microscope at Jefferson Lab
Built by G. Ciovatti and P. JLab

22. Nano Materials Diodes rectify for frequencies up to 40 GHz
Growth of aligned carbon nanotubes
Wiring of carbon nanotubes Pt
3 CNTs
Enrique Cobas, M. Fuhrer Cr
CNT Schottky diodes
E. Cobas, Appl. Phys. Lett. 93, (2008)
Diodes rectify for frequencies up to 40 GHz
Estimates: fcutoff ~ 100’s of GHz in some devices

23. High Resolution Microwave Microscopy
Scanning Tunneling Microscope
(STM)- Assisted
Microwave Microscopy
Atif Imtiaz, et al., Appl. Phys. Lett. 90, (2007)
Atif Imtiaz, et al., J. Appl. Phys. 97,   (2005)
STM Topography
(constant current) Cx Rx
Simple circuit model of
probe-sample interaction

24. Experiments Prepare nanotubes suspended over a trench A100 mm-long
CNT should resonate
at 10 GHz
Excite resonance with
microwave microscope
or in a CPW geometry
Luttinger liquid physics

25. Electron-Hole Puddles in Graphene 2 mm x 3 mm, 0.3 K
Intrinsic Inhomogeneity in Correlated-Electron Materials
Electron-Hole Puddles
in Graphene
Scanning SET microscopy
2 mm x 3 mm, 0.3 K
J. Martin, Nature Physics (2008)
Electron nematic phase in Co-Fe-As
Chuang, Science (2010)

26. Conclusions Near-Field Microwave Microscopy
A magnetic write head, which can generate strong RF fields on sub-mm length
scales, is successfully integrated into the near field microwave microscope
operating at cryogenic temperatures.
A clear reproducible nonlinear response signal from TBCCO and MgB2 are
obtain by this magnetic write head probe.
Further improvements will enable SRF defect microscopy on bulk Nb surfaces.
Laser Scanning Microscopy
The LSM gives unique insights into structure / property relations at ~ mm length scales
Preliminary data on bulk Nb resonators is encouraging
Microscopy-related ongoing research efforts:
Purely evanescent probe: Time-reversed microscopy to eliminate far-field radiation,
S. M. Anlage, et al., Acta Physica Polonica A 112, 569 (2007)
Use of Metamaterials to enhance evanescent waves and resolution,
M. Ricci, et al., Appl. Phys. Lett. 88, (2006)