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
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