L. Ya. Vinnikov , 1 I. S. Veshchunov, 1 T. M. Artemova, 1 M. R. Eskildsen 2 J. M. Densmore, 2

L. Ya. Vinnikov,1

I.S. Veshchunov,1 T. M. Artemova,1

M. R. Eskildsen2 J. M. Densmore,2

T. D. Blasius,3

C. D. Dewhurst,4

N. Ni,5 A. Kreyssig,5 S. L. Bud'ko,5 P. C. Canfield,5 and A. I. Goldman5

J.Karpinski6 , N.Zhigadlo6

A.Boris7 P. Popovich,7 D. L. Sun,7 C. T. Lin, 7

1 Institute of Solid State Physics RAS, Chernogolovka, Moscow Region, 142432, Russia2 Department of Physics, University of Notre Dame, Notre Dame, IN 46556 USA3 Physics Department, University of Michigan, Ann Arbor, MI 481094 Institut Laue-Langevin, 6 Rue Jules Horowitz, F-38042 Grenoble, France5 Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa

50011, USA6 Laboratory for Solid State Physics, ETH, Zurich, Switzerland7 Max Planck Institute for Solid State Research Stuttgart, Germany

Schegolev Memorial Conference Chernogolovka 2009

Vortex Structure in Superconducting Iron Pnictide Single Crystals

Outline*Crystal Structures of pnictides 122 1111 , single crystals

*Motivation

* Method

* Vortices in BaFe1.8Co0.2As2 single crystals

(Decoration, SANS, STM)

*Vortex structure in K doped Ba1-xKxFe2As2 single crystals

* Vortex structure in Sr1-xKxFe2As2 & SmFeAsO1-xFy single crystals

* DISCUSSION

Comparision with others single crystals

LuNi2B2C, MgB2 ,BSCCO, YBa2Cu4O8 , organic superconductor

Strong pinning

*Summary

Marianne Rotter, Michael Pangerl, Marcus Tegel and Dirk Johrendt

Cond-mat :0807.4096

<<1111>> <<112>>

MOTIVATION

*A new family of high-Tc superconductors

-iron pnictides, Y.Kamihara et al (2008)

112 - BaFe1.8Co0.2As2 , (changes in”superconducting” FeAs layers)

Ba1-xKxFe2As2 (changes in”insulating” BaK layers)

1111- SmFeAsO1-xFy

*Comparison with vortex structures others single crystals

• A high critical current for single crystal (~106 A/cm2)

• Pinning centers , ξ cogerence length

Single crystals:BaFe1.8Co0.2As2 AmesLab, USAReNi2B2C Re(Lu,Er,Ho)

SmFeAsO1-xFy , ETH, Switzerland

MgB2

Sr1-xKxFe2As2 MPI, Germany

Ba1-xKxFe2As2

Bi2Sr2Ca1Cu2O (BSCCO) ISSP, Russia


* Method





* DISCUSSION

Sketch illustrating the main idea of the decoration method (Trauble and Essmann)

PPN-2009

Size distribution of Fe decoration particles. N-number of Fe particles on the scanned area of 2µm2.He gas pressure was ~2x10-2 Torr. The high resolution of about 100 nm of Bitter decoration technique is due to the small size of the magnetic particles (the average size is less than 10 nm).


* Method





* DISCUSSION

Vortices in BaFe1.8Co0.2As2 single crystals at magnetic field H=10 Oe

NN-NN-2009


NN-NN-2009

Vortices in BaFe1.8Co0.2As2 single crystals at magnetic field H=40 Oe with Delaunay triangulation

Distorted vortex lattices in BaFe1.8Co0.2As2 single crystals at magnetic field H=80 Oe

2mkm

Vortices in BaFe1.8Co0.2As2 single crystal near the edge at magnetic field H=40 Oe

The SANS vortex diffraction patterns were obtained at 2 K and applied fields of 810 (a), 740 (b), 630 (c) and 450 mT (d),

M.R. Eskildsen et al , PRB 79 100501 (R) March 2009BaFe1.8Co0.2As2

Scanning Tunneling Spectroscopy and Vortex Imaging in theIron-Pnictide Superconductor BaFe1:8Co 02As2

Yi Yin, M. Zech, T. L. Williams, X. F. Wang, G. Wu, X. H. Chen & J. E. Hoffman

arXiv: 0810 v1[cond-mat. Supr-con] 6 Oct 2008

100 nm

В интервале 0.001 – 9 T не наблюдается упорядоченная вихревая решетка


* Method





* DISCUSSION

Vortices in Ba1-xKxFe2As2 single crystals at magnetic field H=10 Oe (G19 x=0.2)

Vortices in Ba1-xKxFe2As2 single crystals (G17,x=0.4;Sn-flux) at magnetic field H=20 Oe

Vortices in BSCCO single crystals at magnetic field H=20 Oe

Vortices in Ba1-xKxFe2As2 single crystals at magnetic field H=110 Oe (G41e ,x=0.35,selfflux) Tc =38K)

Ba1-KxFe2As2 BSCCO (2212)

Vortices in Ba1-xKxFe2As2 single crystals at magnetic field H=160 Oe (G41e ,x=0.35, Tc =38K)



* Method





* DISCUSSION

Vortices in Sr1-xKxFe2As2 single crystals (G15, x=0.08, Tc=32K) at magnetic field H=46 Oe

Vortices in SmFeAsO1-xFy single crystals at magnetic field 46 Oe


*Motivation

* Method





* DISCUSSION



Strong pinning

*Summary

LuNi2B2C

Vortices in MgB2

MgB2 at small magnetic field (He=9 Oe) near the edge of the crystal

Flux Line Lattice destruction by columnar defects in BSCCO

Vortex domain in YBa2Cu4O8 single crystals at magnetic field 41Oe

Observation flux Line Lattice in the Organic Superconductors


*Motivation

* Method





* DISCUSSION



Strong pinning

*Summary

Jc (H) BaFe1.8Co0.2As2

N.Ni et al arXiv:0811.1767

SmFeAs O1-xFy single crystals Zhigadlo et al J. Phys. Cond. Matter 20 (2008) 342 202

Summary Computing the average area associated with each vortex we

find a magnetic flux per vortex of 2.1±0.1 x10-7 G sm2 in perfect agreement with theoretical φ0= hc/2e.

Highly distorted vortex lattices were revealed in BaFe1.8Co0.2As2 single crystals at magnetic fields 10- 320 Oe by high resolution decoration method (Bitter technique) as well as in SmFeAsO1-xFy Sr1-xKxFe2As2 and Ba1-xKxFe2As2 single crystals .

We have revealed the disordered vortex structure in the single crystals of a new family of high-temperature superconductors based on layered

compounds, iron pnictides, which is independent of the crystal structure type, doping, and synthesis methods. This allows us to conclude that the intrinsic mechanism of the vortex pinning of unclear nature exists in the iron pnictide single crystals.

The question is :are there distorted vortex lattice in iron pnictides becausewe have “bad” (with many defects) single crystals (trivial pinning)?Or absence of the regular vortex lattice in single crystals are attributedto strong intrinsic pinning related to magnetic or structural features Fe-As layers ?

J.T. Park et al arXiv:0811.2224

Ba1-xKx Fe2As2

Vortices in Ba1-xKxFe2As2 single crystals at magnetic field H=46 Oe

Cond-mat :0807.4096

Marianne Rotter, Michael Pangerl, Marcus Tegel and Dirk Johrendt

Vortices in Ba1-xKxFe2As2 single crystals at magnetic field H=100 Oe

20 30 40 50 60 70 80 900

50

100

150

200

250

||(

cm

)

T (K)

G19 BKFA

Temperature dependence specific resistivity of Ba1-xKxFe2As2 (G19,x=

Tc

V. A. Gasparov

L. Ya. Vinnikov , 1 I. S. Veshchunov, 1 T. M. Artemova, 1 M. R. Eskildsen 2 J. M. Densmore, 2

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