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Tamin Tai, Steven M. Anlage Department of Physics Center for Nanophysics and Advanced Materials University of Maryland 19 February, 2010. PROGRESS IN NEAR-FIELD MICROWAVE MICROSCOPY OF SUPERCONDUCTING MATERIALS. Funding from Department of Energy NSF Division of Materials Research

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Progress in near field microwave microscopy of superconducting materials

Tamin Tai, Steven M. Anlage

Department of Physics

Center for Nanophysics and Advanced Materials

University of Maryland

19 February, 2010

PROGRESS IN NEAR-FIELD MICROWAVE MICROSCOPY

OF SUPERCONDUCTING MATERIALS

Funding from

Department of Energy

NSF Division of Materials Research

Maryland Center for Nanophysics and Advanced Materials

6th SRF Materials Workshop

NHMFL, Tallahassee, Florida


Progress in near field microwave microscopy of superconducting materials

APPROACH

GOAL: To establish links between microscopic defects and

the ultimate RF performance of Nb at cryogenic temperatures

APPROACH: Work with the SRF community to develop well-

characterized defects and subject them to 2 forms of

microscopy:

Near-Field Microwave Microscopy

Laser Scanning Microscopy


Progress in near field microwave microscopy of superconducting materials

NEAR-FIELD MICROWAVE MICROSCOPY

The Idea

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)

5) Relate JNL(x,y) maps to candidate defects

Leads to

Harmonic

Generation

f → 3f, etc.

Meissner-state properties now

depend on current J → Nonlinearities

in inductance and loss

l(T, JRF)

JRF


Progress in near field microwave microscopy of superconducting materials

How to Generate Strong RF Magnetic Fields?

Magnetic recording heads provide

strong and localized BRF

BRF ~ 1 Tesla

Lateral size ~ 100 nm


Progress in near field microwave microscopy of superconducting materials

Magnetic Recording Head Slider

Cross-section (next slide)

Au bond pads to reader and writer

Read/Write

Head

Air bearing

surface

Thickness

(~1.2 mm)

Suspension


Progress in near field microwave microscopy of superconducting materials

Magnetic Recording Head Cross Section

Cu coils

Permalloy shields

m

~2

m

Write Pole

Read Sensor

2 mm

RF Magnetic Fields

Air bearing surface


Progress in near field microwave microscopy of superconducting materials

Measured Input Impedance of Write Head

Impedance Matched to 50 W

Seagate Longitudinal Head

Pole width ~ 200 nm

Pole gap ~ 100 nm

Pole thickness ~ 1 mm

Coil turns 6 ~ 8


Progress in near field microwave microscopy of superconducting materials

Next Generation Experiment

We need higher BRF and strongly localized field distributions

RF Coil

on slider

Superconductor

D. Mircea, Phys. Rev. B 80, 144505 (2009)

Goals: BRF ~ 200 mT

Lateral size ~ 100 nm


Progress in near field microwave microscopy of superconducting materials

What do We Learn About the Superconductor?

Simulated current distribution beneath probe

Induce high m0K ~ 200 mT

K(x,y) sharply peaked in space

► Better spatial resolution

Current distribution

geometry factor

D. Mircea, SMA, Phys. Rev. B 80, 144505 (2009) + references therein


Progress in near field microwave microscopy of superconducting materials

What do We Learn About the Superconductor?

P3f(x)

JNL(x)

Position

x

Defect 1

Defect 2

P3f


Progress in near field microwave microscopy of superconducting materials

NEAR-FIELD MICROWAVE MICROSCOPY

Expected Outcome

Locally (< 1 mm) stimulate Nb surface with large (BRF ~ 200 mT)

RF field and induce nonlinear response

Map JNL(x,y) and relate to known defects

Catalog of Defects and their Superconducting RF Properties


Progress in near field microwave microscopy of superconducting materials

Measurements on Tl2Ba2CaCu2O8 Film

At a fixed location

~40 dB higher

response expected

Vortex Nonlinearity?

Tc

Noise floor


Progress in near field microwave microscopy of superconducting materials

Accomplishments

Suppressed background nonlinearity (3f) from write head

Proven that heads are impedance matched

Seeing clear, reproducible signal from superconducting sample

Receiving technical assistance from the magnetic recording industry

Dragos Mircea, Sining Mao (Western Digital)

Tom Clinton (Seagate → Nth Degree)

Unresolved Issues

Not achieving the P3f response levels expected

Gap may be too far from sample: Dirt, roughness

Gap may be too close to sample: Gap+SC creates large reluctance

Stray fields from slider inducing vortices?


Progress in near field microwave microscopy of superconducting materials

Next Steps

Slider gap - sample distance control

Micro-Loops

G = 1.3 x 106 A3/m2

Original loop probes had G ~ 103 A3/m2

Greg Ruchti, Senior Thesis, UMD


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

Experiments in collaboration with Alexey Ustinov and

Alexander Zhuravel at Uni. Karlsruhe, Germany

New round of experiments in March+April on bulk Nb + films


Progress in near field microwave microscopy of superconducting materials

Conclusions

Near-field microwave microscopy and Laser Scanning Microscopy are quantitative measurement techniques capable of addressing important materials issues in Nb

The microscopes are flexible, simple, broadband, and have frequency-independent spatial resolution

Looking for materials collaborators with well-characterized local defects

Objectives:

Develop Bsurf ~ 200 mT, mm-scale probes for RF Critical Field imaging

Develop compact resonators with Nb coupon samples

Relate local cryogenic RF properties to microstructure

http://www.cnam.umd.edu/anlage/AnlageHome.htm


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

The Idea

1) Create a compact resonant structure involving a Nb coupon

2) While exciting on resonance, scan a focused laser spot on sample

  • Image the Photo-Thermal effects:

JRF(x, y) - RF current density in A/cm2

Thermo-Electric imaging

JNL(x,y) – Nonlinearity current scale in A/cm2

RF vortex breakdown, flow, critical state

4) Relate these images to candidate defects


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

Preliminary Results


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

Preliminary Results on YBa2Cu3O7 Patterned Film

DC Critical

State Image

(T < Tc, I > Ic)

Reflectivity

Image

Thermo-Electric

Image

(room temperature)

JRF(x,y) Image

(5.5 GHz, T < Tc)


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

Preliminary Results

RF Defect Imaging in bulk Nb


Progress in near field microwave microscopy of superconducting materials

LASER SCANNING MICROSCOPY

Expected Outcome

Candidate

Resonant

Structures

Bulk Nb “Short Sample” structures to measure RF breakdown fields and relate to defects

and surface processing

Measure RF breakdown fields in SC / Ins / SC / Ins … multilayer samples

Gurevich, Appl. Phys. Lett. (2006)

Image variations in the thermal healing length to better understand the role of heat

dissipation in RF performance


Progress in near field microwave microscopy of superconducting materials

PLANS FOR THE FUTURE

Laser Scanning Microscope Collaborators:

Dr. Alexander Zhuravel, B. I. Verkin Inst. of Low Temperature Physics

Kharkiv, Ukraine

Prof. Dr. Alexey Ustinov, University of Karlsruhe, Germany

We seek representative samples containing well-characterized

defects and/or surface treatments


Progress in near field microwave microscopy of superconducting materials

Acknowledgements

Collaborators

Post-Docs

F. C. Wellstood

R. Ramesh

J. Melngailis

Johan FeenstraAndrew Schwartz C. CanedyA. Stanishevsky Alexander Tselev

Graduate Students

NSF REU Students

David Steinhauer

Atif Imtiaz

Sheng-Chiang Lee

Wensheng Hu

Ashfaq Thanawalla

Sangjin Hyun (Seoul Nat. Univ.)

Dragos Mircea

Young-noh Yoon

Yi Qi

Nadia Fomin (Georgetown)

Eric Wang (UC Berkeley)

Tom Hartman (Princeton)

Industrial Collaborators

Undergraduate Students

Hans Christen (Neocera)

Vladimir Talanov (Neocera  SSM)

Robert Hammond (STI)

Andrew Schwartz (Neocera)

Steve Remillard (Agile Devices)

C. P. Vlahacos

Sudeep Dutta

Jonah Kanner

Greg Ruchti

Akshat Prasad


Progress in near field microwave microscopy of superconducting materials

Single-tone sinusoidal microwave signal with single frequency input, f

Microwave current induced on the sample

NEAR-FIELD MICROWAVE MICROSCOPY

Preliminary Results

3f : NLME Nonlinearities

2f : Vortex Nonlinearities

Superconductor

Kmax ~ 50 A/m

Bmax ~ 60 mT

Create a sample with well-characterized defects and probe

them with localized RF currents in the superconducting state


Progress in near field microwave microscopy of superconducting materials

Bi

Bi

Bi

Bi

Bi

Bi

-

-

-

-

-

-

crystal grain boundary

crystal grain boundary

crystal grain boundary

crystal grain boundary

crystal grain boundary

crystal grain boundary

0

0

0

0

0

0

2

2

2

2

2

2

4

4

4

4

4

4

6

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6

Y (microns)

Y (microns)

Y (microns)

Y (microns)

Y (microns)

Y (microns)

8

8

8

8

8

8

10

10

10

10

10

10

0

0

0

0

0

0

2

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X (microns)

X (microns)

X (microns)

X (microns)

X (microns)

X (microns)

STM image of

Bi-Crystal Grain

Boundary in YBa2Cu3O7

Nonlinear Response Image of Known Defect

Bi-Crystal Grain Boundary in YBa2Cu3O7-d

y (mm)

x (mm)

T = 60 K

f = 6.5 GHz

S.-C. Lee, et al., Phys. Rev. B 72 , 024527 (2005)


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