Recent Advances

in iron-based Superconductors

: Actors are ready

Hideo HOSONO Frontier Research Center

Tokyo Institute of Technology, Yokohama, JAPAN

ASC 2012@ Portland, US (Oct 10, 2012)

Acknowledgements

1. Collaborators

(TIT) S.Matsuishi, T.Hanna, Y.Muraba, S.Iimura,

H.Hiramatsu, T.Kamiya, T.Katase, H.Sato

(ISTEC)

K.Tanabe, Y. Ishimaru, A.Tsukamoto

(Los Alamos)

B. Maiorov

2. Sponsor JSPS FIRST Program

OUTLINES

1. Background

2. Parent Compounds

3. Generic Phase Diagram and Mechanism

4. Thin Films and Grain Boundary Nature

5. Wire & Tape Applications

6. Summary

Year

Met

C Cuprates

Metals

Organics

Iron pnictides

Year

Cri

tical

Tem

p.

77K (boiling point of N2)

100 Years of Superconductivity

Superconductivity & Magnetism

• Cooper Pair

Coherent length

Magnetic Ordering

Ferro/Anti-Ferromagnetism

Transition metal

Pnicogen

Iron was believed to

the worst element for superconductivity

Compete

Fe As

e-

O F

LaFePnO (Pn=P,As)

JACS(2006) JACS (2008)

dCo-Co : 2.54 Å

No B-B bonding

La

131°

3.45Å

3.04Å 1.99Å

B

Co

Co

B

La

0 - 5 - 10 5 Energy (eV)

Total

Covalent Co-B bonding

LaCo2B2 :122 type

H (104 Oe)

2 3 4 5 6 7 8

ZFC

FC

(

em

u/m

ol-C

o)

T (K)

-10

-5

0

5

T=2K

M (

em

u/m

ol-

Co

)

0

-0.1

-0.2

-0.3

0 0.5 1.0

2 4 6 8 10 120

10

20

0.20

0.30

0.150.10

x=0.00

(1

0

cm

)

La(Co1-x

Fex)

2B

2

T (K)

Mizoguchi et al.Phys.Rev.Lett. (2011)

Fe-substituted

FeCh (Ch =Se, Te)

AFe2Pn2 (A = Ca,

Sr, Ba, K,

Eu)

LiFeAs, NaFeAs

Ae2MFePnO3 (M =Sc, Ti, V, Cr

Ae = Ca, Sr

Pn = P, As)

LnFePnO

AeFePnF

(Ln = La,

Ce,..,

Ae = Ca, Sr

Pn = P, As)

1111 122

11

111

Ch

Fe

A

Fe

As

Li, Na

Tc ~ 55 K

Tc ~ 38 K

Ln

Fe

Pn

O

Sr3Sc2Fe2As2O5

O

Sr

Sc

Ae

O

M

Fe

As

21113 32225

Tc ~ 37 K

Tc ~ 20 K

Parent Materials

Fe

(a)

Jahrendt G

Chu et al. Jin et al

Wu et al Shimoyama G, Wen G Tc~15K

AFeCh

Guo (2010)

New Parent Phase: 245

Chemical Composition

A0.8Fe1.6Se2.0

(A= K,Rb,Cs,Tl )・・・・)

High Neel Tem. : ~500K Large magnetic moment : ~3.3mB/Fe

Band Gap: = ~0.35eV

Fe vacancy : 25% & ordered

Mott Insulator (?)

1111-type 122-type

Te

mp

era

ture

Te

mp

era

ture

Doping level Doping level

AFM

(Ortho.)

PM

(Tetra.)

SC

(Tetra.)

AFM

(Ortho.) SC

(Tetra.)

PM

(Tetra.)

SC

(Ortho.?)

QPC

Electronic Phase Diagram

Ln

Fe

Pn

O AeFe2Pn2 LnFePnO

hPn low hPn high

g disappear appear

Mazin et al. PRL(2008),

Kuroki et al.PRL(2008) Spin Fluctuation (FS nesting)Model

Kuroki et al PRB(2009)

Sm-1111 La-1111, LaFeOP

Tc vs. pnictgen height from iron plane

T

c (

K)

hPn (nm)

1111(Oxide)

1111(Fluoride)

122

111

11

21113

Sm1111

Gd1111

Pr1111

Nd1111

Tb1111

SrCr21113

SrV21113

Sr2ScFePO3

FeSe FeSe0.125Te0.875

FeSe0.25Te0.75

FeSe0.5Te0.5

Ce1111

La1111

Ca1111

Sr1111 K122

Na111

Li111

BaNi2P2

LiFeP

BaNi2As2

LaFePO LaNiAsO

SmFePO

LaRu2P2

Sr122

Ba122

Eu122

Hosono et al. Bull Phys.Soc.Jpn (2010)

Mizuguchi et al. SuST(2011)

Does nesting scenario work well ?

K0.8Fe2Se2 Tc=30K (Guo et al.PRB 2010)

Feng et al Nature Phys.(2011)

Hole pocket @Gdisappears

Cf. heavily e-doped BaFe2As2:Co

hole pocket X , Tc X

（Ding et al.EPL(2008),Zhang et al.PRL 2010)

KFe2As2 electron pocket X

(Sato et al PRL2009)

Tc=3K, d-wave

(Zhang et al.ArXiv2010)

FS

FS nesting is not a primary ingredient

Complete Tc Dome in 1111 • Hydrogen Substitution to 1111 type iron-arsenides

– Extension of 1111 type group

– Alternative technique for electron doping to FeAs-layer

– Overcoming the substitution limit of fluorine

Improvement of Tc ?

information on over-doped region

REFeAsO1-xHx (0 < x ≤ 0.5)

0.1

Sm

New e-doping method

O2-= F- +e O2- =H- +e-

x

5 10 15 20

0

2

4

0.0 0.2 0.4

0.0

0.2

0.4

0.6

CeFeAsO0.7

D0.3

(RT)

wRp = 3.26%

Rp = 2.92%

S = 1.36

Inte

nsity (

arb

.units)

Q (Å-1) xnominal

Analy

zed x

xEPMA

xNPD

Space group:P4/mmm,

Ce: 2c (1/4, 1/4, zCe) Fe: 2a (3/4, 1/4, 0) As: 2b (1/4, 1/4, zAs) O/D: 2c (3/4, 1/4, 1/2 )

xnominal [O] gD a (Å) c (Å) zCe zAs wRp (%) Rp (%) S

0 0 0 4.00033(3) 8.65926(10) 0.63990(16) 0.15476(12) 3.94 3.21 1.57

0.1 0.854 0.132(5) 3.99812(4) 8.63525(12) 0.64124(16) 0.15589(12) 3.29 2.70 1.38

0.3 0.721 0.238(4) 3.97749(3) 8.60913(11) 0.64639(16) 0.15869(13) 3.26 2.92 1.36

0.4 0.574 0.368(5) 3.95386(4) 8.59259(12) 0.65145(20) 0.16340(16) 3.93 3.30 1.48

Matsuishi et al. PRB(2012)

0

10

0

10

0

5

0

5

-8 -6 -4 -2 0 20

5

-8 -6 -4 -2 0 20

1

-8 -6 -4 -2 0 2

(a) CeFeAsO

Total

(b)

up

dn

CeD

ensity o

f S

tate

s (

eV

–1,

f. u

.)

Fe

As

O

Energy (eV)

2p

CeFeAsO0.75

H0.25

Total 0.3 eV0.3 eV

Ce

Fe

As

O

Energy (eV)

2p

F

CeFeAsO0.75

F0.25

Total

Ce

Fe

As

O

1s2H

Energy (eV)

Calculated DOS of H

XRD data at 20K

EF

0.0 0.1 0.2 0.3 0.4 0.5

0.5

0.6

0.7

0.8

0.9

1.0

Xm

ol%

/Fe

mol%

Nominal X

X= Ce

X= Fe

X= As

X= O

O

As

EPMA ( O content)

0.0 0.1 0.2 0.3 0.4 0.50.0

0.2

0.4

0.6

0.8

1.0

me

asu

red

co

nte

nt

of

H a

nd

O

Nominal X

CeFeAsO1-y

Hx

O

H

O+H

EPMA and TG-Mass

CeFeAsO1-xHx

Tc(max)=46K

Data on F-doped samples were cited from X.H.Cheng Nature (2008)

Matsuishi et al.PRB(2012)

SmFeAsO1-xHx: Phase diagram

Y. Kamihara et al, NJP 12 (2010) 033005.

0 100 2000

2

Tc

(

mc

m)

T (K)

Tanorm

x = 0.03

0.0 0.1 0.2 0.3 0.4 0.50

50

100

150

Tanorm

Tc

AFM

(orth.)

PM(tet.)

SmFeAsO1-x

Fx

Tanorm

Tc

Measured x

T (

K)

SmFeAsO1-x

Hx

SC

Optimal Tc = 56 K (onset)

Very wide SC range

Optimal X : 0.2-0.3

Coexistence of Tanorm and Tc at x = 0.03

Hanna et al. PRB (2011)

Two Dome Structures

H

F

Iimura et al.Nat Comm(2012)

High pressure effects

CeFeAsO1-xHx

Da/a of ~1% of La-1111 corresponds to Ce-1111

LaFeAsO1-xHx

3GPa

-0.5

0.0

0.5

0 3 6 0 3 6 0 3 6 0.1 0.2 0.3 0.4

0.00

0.25

0.50

0.1 0.2 0.3 0.4

110

112

114

0 3 6

- 0

x = 0.08

Totald

xy

dyz,zx

dxy

+dyz,zx

x = 0.21

Density of States (eV-1 f.u.

-1)

x = 0.36

E (

eV

)

G

x

G

Gdyz,zx

Gdxy

Ganti-dxy

x

E (

eV

)

-2

x = 0.21 x = 0.36

Gdxy

Ganti-dxy

Gdyz,zx

0

1.0

-1

0

1

2

0.5

x = 0.08

E (

eV

)

x = 0.40

G

00.2

00.2

G

00.2 0.2

0

G

G

NMLK

J

IHGF

EDDCB

GGG

k k

- 0

ky

kx

- 0

x = 0.08

dxy

dyz,zx

A

dxy

dyz,zx

- 0

x = 0.21 x = 0.40

x = 0.36

-

G

E (

eV

)

Ð A

s-F

e-A

s (

de

g.)

109.47

0

1.30

1.32

1.34

1.36

hA

s (

Å)

x = 0.40

.

DFT calculation with virtual crystal approximation

Hydrogen behaves as fluorine

Nuclear charge of O site: Z = 8+x

Experimental Lattice parameters & atomic position

Wien2k LAPW+lo

Dome First Second

x 0.05 < x < 0.2 0.2 < x < 0.5

Exponent n 2.0 < n < 2.3 0.7 < n < 2.0

Tcmax 29 K 36 K

Tc-sensitivity to x High Low

Under high pressure Unified

FS nesting Strong Weak

DOS (EF) No shoulder Shoulder

Characteristic of two domes

La

Ce

Sm

● La 1st Opt.

● La 2nd Opt.

● Ce Opt.

● Sm Opt.

0 100 200 300 0.0

0.5

1.0

300K

T (K)

Phase diagram : RE-dependence

Single Unit-Cell FeSe Films on SrTiO3

１U.C. 2U.C

Sc gap=20meV

(Tl0.58Rb0.42)Fe1.72Se2 Single layer FeSe

(Ba1.6K0.4)Fe2As2 b-FeSe (cald.) Nat.Commun.(2012) D.Liu et al.

Fermi Surface

Jc of iron pnictide epitaxial films

Lee, Nat. Mater. (2010). Katase, APEX (2010).

Rall, PRB (2011).

Kidszun, PRL (2011). Hiramatsu, APEX (2008).

Maiorov, SuST (2009).

Eisterer, SuST (2011).

Mele, SuST (2010).

Choi, APL (2009).

Ueda, APL (2012).

Superconducting films on IBAD-MgO tape

Fe(Se,Te) film

Jc = 0.31 MA/cm2 at 4.2 K

(W. Si et al., APL 2011.)

Ba(Fe,Co)2As2 film

Jc = 13 MA/cm2 at 2 K

(T. Katase et al., APL 2011.)

Ba(Fe,Co)2As2 film

Jc = 0.1 MA/cm2 at 8 K

(K. Iida et al., APEX 2011.)

Superconducting tapes

Anomalous mixed-state Hall effect

in high-Jc Ba122:Co film

Paper No. 3MB-05 11:45– in A107-109, H. Sato et al.

T sweep (5→25 K) H sweep (0→9 T)

Origin： Wide vortex liquid phase due to disorders and high-density pinning centers

H

J = 5 kA/cm2

ρxx

ρxy

T sweep (5 → 25 K) H sweep (0 → 9 T)

Fixed H / T 1 → 9 T 13 → 16 K

b value 1.7–1.8 (const.) 1.8→2.0 (Increase)

Different !

Superconductor devices GB Josephson

junction SQUID

Katase et al., APL 2010.

PbIn / Au / BaFe2As2:Co film

Hybrid SNS junction

Schmidt et al., APL 2010. Katase et al., SuST 2010.

BaFe2As2:Co film

Fabrication of SC Wires and Josephson Junction

Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 Tc = 33 K, mechanical strong

Ca10(Pt4As8)(Fe1.8Pt0.2As2)5

Diameter ＜ 1 μm Length ～ 2 mm

SIS Josephson Junction

(diameter～2mm), clear hysteresis in J-V curve

１ｍｍ

NIMS Muromachi G. JACS (2012)

Intrinsic JJ

C-axis

Experimental

Ba122:Co epitaxial films

on [001]tilt-bicrystal substrates

（LSAT, MgO : qGB=3 – 45o)

8mm-wide micro-bridges

Grain Boundary Nature

JcBGB(qGB) = Jc0exp(–qGB/q0)

q0=~9o (Ba122:Co) q0=~4

o (YBCO)

※ H. Hilgenkamp et al., Rev. Mod. Phys. (2002).

YBCO at 4 K

YBCO at 77 K

JcB

GB (

A/c

m2)

YBCO at 4 K

qc=8–9o

JcB

GB / J

cG

rain

qGB (deg.)

qGB (deg.)

qGB dependence of JcBGB

Ba122:Co/MgO at 4K

Ba122:Co/LSAT at 4K

Ba122:Co/MgO at 12K

Ba122:Co/LSAT at 12K

Transition to weak link occurs at qc = 8– 9o.

Higher q0: Gentler decay of JcBGB

Decay in the weak link region :

qc=5o(YBCO)

5%

Nat.Commun.(2011)

# Coherent length (Ba122:Co)

xab = 2.6 nm at 4K.

qc=8–9o : D=2.5–2.8 nm.

xab D : Weak link

Strong current channels still remain between dislocations (qGB qc)

BGB

YBCO at 4 K

JcB

GB / J

cG

rain

qGB (deg.)

qc and TEM Obs.

qc=8–9o

[Ref] Putti et al., SuST (2010).

Nature Commun.Aug 2 isuue

High Jc PIT Wire : (Ba0.6K0.4)Fe2As2

4cm long, 1.3 mm dia.

Ball milling CIPed at 275MPa HIPed under 192MPa at 600C

Weiss et al .Nat.Mat.(2012)

Tc=38K

200nm sized grain PIT

Comparison with other Fe-based sc.

Practical level

Mixed powders (10% excess K) by balling milling/(900℃, 35 h)

Cold rolled into tapes with a large processing rate

Tapes with 0.5 mm in thickness

New texturing process of PIT (Sr,K)122 tapes

XRD, SEM, R(H), PPMS, V-I

HT Sintering (1100℃, 1-5 min)

Photograph of the final

122 tapes

Fe tube used sheath material

Wire of 2.0 mm in diameter

Pb or Sn added

Gao, et al., APL 99, 242506 (2011) L. Wang, et al., Physica C 471, 1689 (2011).

SEM Photo and Jc

Cross-section

By optimizing the texturing process and Sn addition

At 4.2 K, the Jc values reached high values of over 104 A/cm2 at 14 T,

which approach the Jc level desired for practical applications.

Rapid Improvement of Jc

in 122 Wires and Tables

Fe-pnictides MgB2 Cuprates Parent

Material (bad) metal

(TN~150K) metal Mott Insulator

(TN~400K)

Fermi

Level 3d 5-bands 2-bands 3d single band

Max Tc 56K 40K ~140K

SC gap

symmetry extended

s-wave (+- or ++) s-wave d-wave

Hc2(0) 100-200T> ~40T ~100T

Critical GB angle 8-9(Ba 122)

Impurity robust sensitive sensitive

g 2-4 (122) ~3.5 5-7 (YBCO)

50-90(Bi system)

Comparison

~5°（YBCO)

Very robust to magnetic field & strong grain boundary

Summary: Actors are ready

1.The major ingredient member of glue

for pairing have been ready.

Spin (Magnetism), Orbitals (Lattice) , Charge (Mott insulators)

2. Maximum Jc at high magnetic field is

approaching to the practical level.

Conventional FS nesting is NOT dominant mechanism

Anisotropy (122) ~2, High Hc2

Critical grain boundary angle ~twice of YBCO

PIT & bulk (122) Jc >~104 A/cm2 @ 10T, 4.2K

LaO T M

P ( T M

= Fe, Ni)

Cu - based oxides

Non - magnetic metals

TM oxypnictides

REFeAs(O,F )

1986 Cuprates

LaO T M

P ( T M

= Fe, Ni)

Cu - based oxides

Non - magnetic metals

TM oxypnictides

REFeAs(O,F )

LaO T M

P ( T M

= Fe, Ni)

REFeAs(O,F)

1986 Cuprates 77K

Strike while the iron is hot

Cu oxides Non-mag. metals

Fe pnicides

First book on Iron-based Superconductors

Nan Ling Wang

Hideo Hosono

Pencheng Dai

Pan Stanford

(2012)

520 Pages