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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

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UMD Microwave Microscopy Group

Faculty:Steven AnlageMichael Fuhrer

Graduate StudentTamin Tai

Undergraduate StudentsJohn Abrahams

Post-DocBehnood Ghamsari

Collaborators:Alexander Zhuravel, Kharkov, UkraineAlexey Ustinov, Karlsruhe Inst. Tech.Dragos Mircea, Western DigitalVladimir Talanov, NeoceraLance Cooley, FermiLabGigi Ciovatti, Jefferson Lab

Funding: ONR AppEl and DOE

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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

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Motivations

The development of new materials with new functionalities dependson establishing structure / property relationships

New forms of microscopy help to accelerate the development ofthese 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 / propertyrelations 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

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Localized Defects on Nb SRF CavitiesThese 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?

500 x 200 m pit

40%

56.6� about [19 -21 4]

36.1� about [-8 16 15]

GrainBoundaries

T. BielerMich. State Univ.

welds, oxidation,hydrogen poisoning

http://www.helmholtz-berlin.de/events/srf2009/programs/tutorials_de.html

welds, oxidation,hydrogen poisoning

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APPROACH

GOAL: To establish links between microscopic defects andthe ultimate RF performance of Nb at cryogenic temperatures

APPROACH: Near-Field Microwave Microscopy*

1) Stimulate Nb with a concentrated and intense RF magnetic field

2) Drive the material into nonlinearity (nonlinear Meissner effect)Why the NLME? It is very sensitive to defects…

3) Measure the characteristic field scale for nonlinearity: JNL

2

22

)(1)0,(),(

TJ

JTJT

NL

RFRF

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 215-253.

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),(

)(4

242

3 xTJ

TP

NLf

Total

S

I

dydxK

4

3peakK

Induce high 0K ~ 200 mT (Hc of Nb)

K(x,y) sharply peaked in space► Better spatial resolution

Current distributiongeometry factor

Nonlinear Near-Field Microscopy of Superconductors

2

22

)(1)0,(),(

TJ

JTJT

NL

RFRF

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

Pinput

Superconductor sample surface

loop

coaxial probe

P3f : NLME Nonlinearities

K(x,y)

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JNL(x)

P3f(x)

Positionx

),(4

242

3 xTJP

NLf

Defect 1 Defect 2

What do We Learn About the Superconductor?

Measured at T=60 K (below Tc of YBCO)

200m loop probe

500Å YBCO

STO

30� misorientation Bi-crystal grain boundary

GBNon-GB

on YBCO

Phys. Rev. B 72, 024527 (2005)

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BRF ~ 1 Tesla (in gap)

Lateral size ~ 100 nm x few-100 nm

How to Generate Strong RF Magnetic Fields?

Magnetic Write Head

Permalloy shields

~2m

Cu coils

Read Sensor

Write Pole

RF Magnetic Fields Air bearing surface

2 m

Magnetic recording heads providestrong and localized BRF

SEM picture of the magnetic write head gap

Side View

Bottom View

Permalloy

Gap

Reference: IEEE Trans Magn. Vol . 37, No. 2 pp.613-618 2001

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Experimental Setup

Goals: BRF ~ 200 mTLateral size ~ 100 nm

f

f, 2f, 3f,…

f

MW source

Low pass filter

Directional coupler

High pass filter

sample

Cryogenic environment

2f, 3f,…

Spectrum Analyzer

Amp

RF Coilon slider

Superconductor

Head Gimbal Assembly (HGA)

We need higher BRF and strongly localized field distributions

Probe

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Measurements on SuperconductorsAt a fixed location on MgB2 film

MgB2 Film (25nm)/SiC

Samples come from Prof. Xiao-Xing Xi Temple University, Philadelphia, PA

37.5 38.0 38.5 39.0 39.5 40.0 40.5-150

-145

-140

-135

-130

-125

-120

Pow

er, P

3f (

dB

m)

Temperature (K)

MgB2 (25 nm)

on Al2O3 substrate

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.

Noise floor

36 37 38 39 40 41-150

-145

-140

-135

-130

-125

-120

-115

Pow

er, P

3f(d

Bm

)Temperature (K)

MgB2(25nm) on

SiC substrate

Excited power: 12 dBm; Excited frequency: 3.75GHz

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75 80 85 90 95 100 105 110-150

-145

-140

-135

-130

-125

Pow

er, P

3f (

dB

m)

Temperature (K)

TL-SC sample

Noise floor

Vortex or defects/ grain boundary contribution

Excited power: 6 dBmExcited frequency: 3.75 GHz

Measurements on Tl2Ba2CaCu2O8 FilmAt a fixed location

Tc

),(

)(4

242

3 xTJ

TP

NLf

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Challenges for Measurements on Nb bulk materials

1. Probes may cause localized heating of Nb samples.

2. Temperature of cold plate reaches 4.2K but Nb surface remains warmer. (Next step: thermal grounding of probe and positioner)

3. Magnetic write head probe is still too far away from the superconductor surface. (Next step: nm-level positioning control)

Top surface of bulk Nb (thickness: 0.1 inch)

Head Gimbal Assembly (HGA)

Pit on Nb

Copper cold plate

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Current Work---Micro Loop Design

Micro loop design can enhance the current geometry factor and increase our spatial resolution.

Photolithography Result (thanks to Dr. Cihan Kurter)

Simulation Data from HFSS (Gregory Ruchti )

),(

)(4

242

3 xTJ

TP

NLf

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Laser Scanning Microscopy:

Principle of the measurement

Pout

ff0

|S21(f0)|2

|S21(f0)|2laser OFF

laser ON

co-planar resonator f0 ~ 5.2 GHz

Pin

modulatedlaser

resonator transmission

Local heating produces a change in transmission coefficient proportionalto the local value of JRF

2

J. C. Culbertson, et al. J.Appl.Phys. 84, 2768 (1998) @ NRL

A. P. Zhuravel, et al., Appl.Phys.Lett. 81, 4979 (2002)

|S12|2 ~ [ JRF(x,y)]2 A

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Typical Spatial Profile of RF PhotoresponseAlong a Lateral Cross Section of the Resonator Strip

T = 79 KP = - 10 dBmf = 5.285 GHzfmod = 99.9 kHz

YBCO/LaAlO3

CPW Resonator

1 x 8 mm scan

Wstrip = 500 m

P1 = in-plane rotated grainP2 = crack in YBCO filmP3 = LAO twin domain blocks

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Imaging of a YBa2Cu3O7 / LaAlO3 ResonatorOptical reflectivity DC Photoresponse

Room Temp. Thermoelectric PR Low-T RF PR“PR” = Photo-response

A. Zhuravel, et al., J. Appl. Phys. 108, 033920 (2010)

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Corner “A2” Detail of YBCO / LAO Resonator

m

Optical Reflectivity RF PR

A. Zhuravel, et al., J. Appl. Phys. 108, 033920 (2010)

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Laser Scanning Microscope @ UMD

LSM in Karlsruhe, Germany

UMD Microscope: configured for bulk superconductors, closed cycle refrigeratorJLab Microscope: built inside a Nb SRF cavity

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Current and Future Work

Complete the UMD Laser Scanning MicroscopeClosed cycle refrigerator for week-long runsUkraine collaborator (Zhuravel) visits to commission the microscope

Pb

Nb

reflectivity

inductive resistive

F = 3.5 GHz

T = 4.3 K

PIN = -15 dBm

Plaser = 1 mW 1

mm

1 mm

inductive resistive

At another location, there is a different kind of defect:

RF Defect Imaging in bulk Nb

Copper finger

Sapphire rod

Sapphire disc

RFIN

RFOUT

Pb ground50 m thick

Nb strip160 m thick

Scanned area

Preliminary results from Karlsruhe collaboration

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Collaborative Work onNb Cavity Laser Scanning Microscope at Jefferson Lab

Built by G. Ciovatti and P. Kneisel @ JLab

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Nano Materials

Growth of aligned carbon nanotubes

Wiring of carbon nanotubes

CNT Schottky diodesE. Cobas, Appl. Phys. Lett. 93, 043120 (2008)

Diodes rectify for frequencies up to 40 GHzEstimates: fcutoff ~ 100’s of GHz in some devices

Enrique Cobas, M. Fuhrer

3 CNTs

Pt

Cr

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D ire c tio n a lc o u p le r

D e c o u p le r

f0 = 7 - 1 1 G H zM ic ro w a v eS o u rc e

f0

D io d ed e te c to r

Q s ig n a l

F re q u e n c y s h if t s ig n a l

F e e d b a c k c irc u it (M W )

Tra

nsm

issi

on li

ne r

eson

ator

P ro b e

S a m p le

2

nL

B ia s T e e

X Y Z p ie z o

S T M fe e d b a c k

S T M tip

D ire c tio n a lc o u p le r

D e c o u p le r

f0 = 7 - 1 1 G H zM ic ro w a v eS o u rc e

f0

D io d ed e te c to r

Q s ig n a l

F re q u e n c y s h if t s ig n a l

Q s ig n a l

F re q u e n c y s h if t s ig n a l

F e e d b a c k c irc u it (M W )

Tra

nsm

issi

on li

ne r

eson

ator

P ro b e

S a m p le

2

nL

B ia s T e e

X Y Z p ie z o

S T M fe e d b a c k

S T M tip

STM Topography

High Resolution Microwave Microscopy

Scanning Tunneling Microscope(STM)- Assisted

Microwave Microscopy

Cx

Rx

Simple circuit model ofprobe-sample interaction

(constant current)

Atif Imtiaz, et al., Appl. Phys. Lett. 90, 143106 (2007)Atif Imtiaz, et al., J. Appl. Phys. 97, 044302  (2005)

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Experiments

40 m widetrench

Chip 1

Chip 2CNTs

Suspended CNTs

Fe catalyst particlesand CNTs

40 m widetrench

Chip 1

Chip 2CNTs

Suspended CNTs

Fe catalyst particlesand CNTs

a)

Prepare nanotubessuspended

over a trench

b)

A100 m-longCNT should resonateat 10 GHz

Excite resonance withmicrowave microscopeor in a CPW geometry

Luttinger liquid physics

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Intrinsic Inhomogeneity in Correlated-Electron Materials

Chuang, Science (2010)

Electron nematic phase in Co-Fe-As

Electron-Hole Puddlesin GrapheneScanning SET microscopy2 m x 3 m, 0.3 KJ. Martin, Nature Physics (2008)

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Conclusions

Near-Field Microwave Microscopy

A magnetic write head, which can generate strong RF fields on sub-m 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 ~ m length scalesPreliminary 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, 264102 (2006)