aspects of intrinsic josephson...

Microelectronics and Nanoscience, Chalmers University of Technology and Göteborg UniversityS-412 96 Göteborg, Sweden, e-mail: [email protected]

GOTHENBURG UNIVERSITY

Aspects ofIntrinsic Josephson Tunneling

Aspects ofIntrinsic Josephson Tunneling

D. Winkler,1,2 A. Yurgens,1 V.M. Krasnov,1 Y.S. Sudershan,1 T.Claeson,1 E. J. Tarte,3 M.G. Blamire3

• Chalmers University of Technology and Göteborg UniversityDepartment of Microelectronics and Nanoscience,SE-412 96 Göteborg, Sweden

2) Imego InstituteAschebergsg 46, Building 11, SE-411 33 Göteborg, Sweden

3) IRC in Superconductivity, University of CambridgeMadingley Rd, Cambridge, CB3 0HE, UK


Giacomo Rotoli

Giacomo Rotoli

This publication is based (partly) on the presentations made at the European Research Conference (EURESCO) on "Future Perspectives of Superconducting Josephson Devices: Euroconference on Physics and Application of Multi-Junction Superconducting Josephson Devices, Acquafredda di Maratea, Italy, 1-6 July 2000, organised by the European Science Foundation and supported by the European Commission, Research DG, Human Potential Programme, High-Level Scientific Conferences, Contract HPCFCT-1999-00135. This information is the sole responsibility of the author(s) and does not reflect the ESF or Community's opinion. The ESF and the Community are not responsible for any use that might be made of data appearing in this publication."

Giacomo Rotoli

1)



Contents

• Background and the system• Ways of making small junctions• The experimental ”toolbox”• Recent work and some understanding• The pseudogap

vs. superconducting gap and T, H, HgBr2

• Interlayer coupling and pressure• Bi2212 films• Conclusions



KLEINER AND MÜLLER



INTRINSIC JOSEPHSON JUNCTIONS

q

Josephson effectintrinsic CuO

Ca

SrOBiOBiOSrOCuO

CuO

CuOCa

intrinsic junctions

I V

I

AB

Bi2212 single crystal 'large'

mesa

stacks

S

S

S

S'S'

S'

S'S'

a) b)

-300 -200 -100 0 100 200 300

VOLTAGE (mV)

CU

RR

ENT

(mA

)

4

6

2

0

-2

-4

-6


GOTHENBURG UNIVERSITYMESA STRUCTURES- using photolithography

height ~ 15 - 300 Å(in situ controlled)

Advantages:•specifiednumber ofjunctions•smallvolume•less defects•less heating

area ~ 200-600 µm^2

Ar ion etching orChemical etching (EDTA) Appl. Phys. Lett. 70, 1760 (1997)



CROSS-BARPHOTOLITHOGRAPHY

photoresist

gold

CaF2

CaF2

CaF2

gold

photoresist

photoresistgold

Bi2212

Bi2212

Bi2212

FIB track


GOTHENBURG UNIVERSITYGOTHENBURG UNIVERSITY

FABRICATION OF MESAS OF Bi2212 INTRINSICJOSEPHSON JUNCTIONS USING A FOCUSSED ION BEAM


GOTHENBURG UNIVERSITYFABRICATION OF MESAS OF Bi2212 INTRINSIC JOSEPHSONJUNCTIONS USING A FOCUSSED ION BEAM



The experimental ”toolbox”

! Charge transport, current-voltage! Temperature! Magnetic field! Pressure! Intercalation! Irradiation with heavy ions! Light and microwaves! Number of Cu-O planes



RECENT WORK ON Bi2212 INTRINSIC JUNCTIONS

! Pseudogap in the c-axis tunneling! Interlayer coupling theory and intrinsic Josephson

effects! A pressure-induced increase of 2 – 3 times in Ic of both Bi2212

and Bi2201- single crystals in contrast to 2-6% increase of Tc

! Vortex dynamics related work! The c-axis magnetoresistance peak effect in Bi2212 determined

by the zero-field sub-gap current-voltage characteristics. 60-foldincrease at 6 T.

! Mapping the vortex magnetic phase diagram from I-V! The influence of 5 GeV Pb+ ion radiation was studied. Ic has a

peak at 1/3 of the matching field Bφφφφ

! Multiple valued critical current! Zero-voltage-state lifetime measurements! Critical current switching distribution! Phase-locking between junctions in a stack! Comparison to numerical simulations




PSEUDOGAP versus theSUPERCONDUCTING GAP – two scenarios...

(From J.L. Tallon and J.W. Loram)


GOTHENBURG UNIVERSITYPSEUDOGAP

(Krasnov et al. PRL84, 5860 (2000))


GOTHENBURG UNIVERSITYdI/dV PSEUDOGAP



PSEUDOGAP

(Winkler et al., Supercond. Sci. Technol. 12, 1013-1015 (1999))



Tord Claeson

about one week at 230-240 C

Jin-Ho Choy, Seong-Ju Hwang, and Nam-Gyu Park

J. Am. Chem. Soc. 119, 1624 (1997)

HgBr2 intercalation

less heating

Decrease ofthe c-axis

criticalcurrent



PSEUDOGAP

(Krasnov et al. PRL84, 5860 (2000))



Tord Claeson

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-1600 -800 0 800 1600

I(m

V)

V(mV)

(HgBr2) Bi-2212T = 4.2 K

-0.1

0

0.1

-300 -200 -100 0 100 200 300

I(m

A)

V(mV)

2

468

10

I (m

A)

The intercalation does not changethe quality of I-V's

10 intrinsic Josephson junctions

10 intrinsic Josephson junctions



Tord Claeson

0

5

10

15

20

25

-300 -200 -100 0 100 200 3000

10

20

30

40

50

60

V/10 (mV)

4.2 K

38 K

50 K

92 K

174 K

dI/d

V (m

S)Tc = 66 K

dI/d

V (p

S)

0

5

10

15

20

25

30

-60 -40 -20 0 20 40 60

dI/d

V (m

S)

V (mV)

dI/dV(kΩ-1) = 1.068e-3 V(mV) 2.5 + 0.426

3% of data presented

0 50 100 150 200 250 300

RES

ISTA

NC

ETEMPERATURE (K)

Tc = 66K



Tord Claeson

0

5

10

15

20

25

-50 0 50 100 150 200

dI/d

V (m

S)

V(mV)

Tc = 66 K29 K

50 K

56 K

65 K81 K

0

1

2

3

-200 0 200 400 600 800 1000 1200

0 50 100 150

dI/d

V (m

S)

V(mV)

110 K78 K

66 K

60 K

50 KTc = 65-68 K

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40 50 60 70 80

∆(Τ)

/∆(4

.2)

∆(Τ)

/∆(4

.2)

∆(Τ)

/∆(4

.2)

∆(Τ)

/∆(4

.2)

TEMPERATURE (K)

HgBr2-Bi2212;

∆(4.2) = 31 meV

pristine Bi2212;∆

1(4,2) = 12.5 meV

∆2(4,2) = 18.5 meV

BCS

Superconducting &pseudogap structures

Two intercalated samples



Magnetic field dependence H || I || c for Bi2212

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.60

10

20

30

40Bi2212 (S875b) H=0T H=14T

T=80K

T=72K

T=60K

T=40K

V (Volt)

dI/d

V (m

S)

Superconducting gap

and

pseudogap

(Krasnov et al. cond-mat/0006479, 29 June 2000)



Intercalated HgBr2- Bi2212 mesa at 4.2 K

0.2 0.4 0.6 0.80

2

4

6

8

10

HgBr2-Bi2212

H=0TH=2TH=4TH=6TH=10TH=14T

dI/d

V (m

S)

V (Volt)

640

660 a)

T=4.2KV s (m

V)

H (T)

0 2 4 6 8 10 12 140

10

20

30

40

b)

I=0

σ(H

)- σ(0

) (µS

)

H (T)



H || I || c – pure Bi2212

0.1 0.2 0.3 0.4 0.5 0.6

5

10

H=0TH=1TH=2TH=4TH=7TH=10TH=12TH=14T

a) T =72K S875b

dI/d

V (m

S)

0.1 0.2 0.3 0.4 0.5 0.6

5

10H=0TH=1TH=2TH=4TH=6TH=10TH=14T

b) T =80K Bi2212

dI/d

V (m

S)V (Volt)



INTERLAYER COUPLING AND PRESSURE



PENETRATION DEPTH

cc Js

c2

0

8πλ Φ=



PRESSURE

1-

1-

GPa%6.0

GPa%2.0

=

==

cc

bb

aa

δ

δδ



HIGH PRESSURE CELL

Opt i on #1 #2 #3Pr e s s ur e r a nge , GPa 1. 0 2. 0 3. 0Out e r di a me t e r , mm 30 40 60I nne r di a me t e r , mm 8 6 6Wor ki ng vol ume a tma x pr e s s ur e , c c m

1 0. 35 0. 35

We i ght , k g 1. 0 1. 7 2. 7

I ns t i t ut e f or Hi gh Pr e s s ur e Phys i c s Te l . ( 7- 095) 3340582142092 TROI TSK Mos c ow Re g. RUSSI A Fa x. ( 7- 095) 3340012

10/25/00 27Microelectronics and Nanoscience, Chalmers University of Technology and Göteborg UniversityS-412 96 Göteborg, Sweden, e-mail: [email protected]


Tord Claeson

-12

-8

-4

0

4

8

12CU

RREN

T (m

A)

VOLTAGE

T = 30 K

50 mV

P = 0

P = 0.8 GPa

(a)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

VOLTAGE

2 mV

0.85 GPa

0.04 GPa

T = 4.2 K

(b)

No change in shape of I-V´s

Bi-2201Bi-2212

TWO OR ONE PLANE



INTERLAYER COUPLING AND PRESSURE



PRESSURE EFFECTS

0.0

0.1

0.2

4 5 6 7 8

0.04 GPa

0.85 GPa

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1

(1-T

c/Tc0

) (%

)

PRESSURE (GPa)

Bi-2201

Bi-2212

(b)

0

1

2

3

4

5

6

7

8

0 20 40 60 80

Ic (m

A)

TEMPERATURE (K)

0.80.60.40.10.0

P(GPa)

The pressure affects the c-axis transport but not the superconducting transition

Bi-2201Bi-2212



INTERLAYERCOUPLING

ANDPRESSURE

Bi2212

Ic goes up with pressure,but Tc remains about thesame



CONCLUSIONS

! Fabrication – several methods

! Pseudogap and the superconducting gap seem tocoexist – T, H, HgBr2, pressure,...

! No evidence for the interlayer coupling theory forHTS from experiments on Bi2212 and Bi2201

! Intrinsic Josephson effect and vortex matter

! Multiple valued critical current



REFERENCES AND FURTHER READING

• Yurgens, ”Intrinsic Josephson Junctions - Recent Developments” Supercond. Sci. Technol. 13, R85-100 (2000).

• D. Winkler, Niklas Mros, August Yurgens, and Vladimir M. Krasnov, Edward J. Tarte, David T. Foord,Wilfred E. Booij, and Mark G. Blamire “Intrinsic Josephson effects in submicrometer Bi2212 mesasfabricated by using focussed ion beam etching”, Supercond. Sci. and Technol. 12, 1013-1015 (1999).

• A. Yurgens, D. Winkler, T. Claeson, T. Murayama, and Y. Ando, “Interlayer coupling andsuperconducting critical temperature of Bi2Sr1.5La0.5CuO6+δ and Bi2Sr2CaCu2O8+δ: Incommensurateeffects of pressure” scheduled for Phys. Rev. Lett. 82, 3148-3151(1999).

• V.M.Krasnov, A.Yurgens, D.Winkler, P.Delsing and T.Claeson, "Evidence for Coexistence of theSuperconducting Gap and the Pseudogap in Bi-2212 from Intrinsic Tunneling Spectroscopy”,Phys.Rev.Lett. 84, 5860 (2000)

• V.M.Krasnov, A.E.Kovalev, A.Yurgens, D.Winkler, "Discrimination between the superconducting gapand the pseudo-gap in Bi2212 from intrinsic tunneling spectroscopy in magnetic field" cond-mat/0006479 (subm. to PRL, title "Magnetic field dependence of the superconducting gap and thepseudogap in Bi2212 studied by intrinsic tunneling spectroscopy")

• http://fy.chalmers.se/~winkler/

• http://fy.chalmers.se/~yurgens/ijj.html

• http://fy.chalmers.se/~krasnov/

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