Download Observation of multiple anisotropic superconducting energy gaps in

ARPES studies of unconventional
superconductors
Hong Ding
Institute of Physics, Chinese Academy of Sciences
Heavy Fermion Physics Workshop, January 9, 2012
Phase diagrams
pnictide SC
cuprate SC
heavy fermion SC
organic SC
Fermi surface mapping of cuprates
Bi2Sr2CaCu2O8
Tight binding fitting
0.1
0.2
0.1
0.3
0.2
0.4
-š
0.3
0.4
Unoccup
ied
states
Oc cupie
d states
0
0
Large FS, area = 1-x: Luttinger’s theorem
š
Momentum
Binding energy (eV)
0
Binding energy (eV)
0
d-wave superconducting gap in cuprates
Y
M
40
Half-Integer Flux Quantum Effect
1
15
30

15
M
1
20
10
dx2-y2

+
0
0
20
40
60
FS angle
80
-
+
Pseudogap in underdoped cuprates
Temperature
Tc = 83 K, at Fermi surface along M-Y
14K
underdoped
overdoped
0.2
0.1
40K
0.0
-0.1 0.2
0.1
70K
0.0 -0.1
0.2
0.1
0.0 -0.1
100
AFM
S.C.
State
90K
0
120K
200K
Doping (e/Cu)
0.2
0.1
pseudogap
0.0
-0.1 0.2
0.1
0.0 -0.1 0.2
0.1
Binding Energy (eV)
T* = 170K
0.0
-0.1
Phase diagram of Ba122 system
Electron
doping
Hole doping
M. Neupane et al., PRB 83, 094522 (2011)
Electron-hole asymmetry?
ARPES observation of five bands and five FSs
Fermi surface evolution in “122”
Heavily OD
Slightly OD
OPT
UD
QAF
QAF
Tc = 37 K
Tc = 26 K
QAF
QAF
Tc = 3 K
Tc = 22 K
Hole doping
Parent
UD
OPT
QAF
TN = 135 K
Tc = 0 K
Tc = 11 K
Heavily OD
QAF
QAF
Tc = 25 K
Tc = 0 K
Electron doping
8
ARPES observation of superconducting gap
H. Ding et al., EPL 83, 47001 (2008)
2/Tc ~ 7
Nodeless SC gap in Ba0.6K0.4Fe2As2 (Tc = 37K)
H. Ding et al., EPL 83, 47001 (2008)
K. Nakayama et al., EPL 85, 67002 (2009)
J1 – J2 model predicts almost isotropic s± gap
local interactions
J 1- J 2
Order parameters in
momentum Space
Real space configuration
of pairing symmetry
-
+
-
+
+
-
pnictides: large J2 and FS topology favor
 = 0
cuprates: large J1 and FS topology favor  =
0
d-wave
coskxcosky, s±-wav
(coskx–cosky)/2,
K. Seo, A. B. Bernevig, J. Hu PRL 101, 206404 (2008)
Most weak-coupling theories predict anisotropic s± gap
D.H. Lee
EPL 85, 37005 (2009)
I. Mazin
PRB 79, 060502 (2009)
when
S. Graser
NJP 11, 025016 (2009)
overdoped Ba0.3K0.7Fe2As2 (Tc ~ 20K)
K. Nakayama et al., PRB 83, 020501(R) (2011)
underdoped Ba0.75K0.25Fe2As2 (Tc = 26K)
Y.-M. Xu et al.,
Nature Communications
2, 392 (2011)
Doping dependence of the SC gaps in Ba1-xKxFe2As2
K. Nakayama et al., PRB 83, 020501(R) (2011)
Electron doped BaFe1.85Co0.15As2 (Tc = 25.5K)
K. Terashima et al, PNAS 106, 7330 (2009)
kz dependence of SC gaps
single gap function
Jab = 30
Jc = 5
2/1
≈ Jc/Jab
≈ 0.17
Y.-M. Xu et al., Nature Physics 7, 198 (2011)
“111” - NaFe0.95Co0.05As (Tc = 18K)
Z.-H. Liu et al., arXiv:1008.3265, PRB
“11” - FeTe0.55Se0.45 (Tc = 13K)
J1 = -34
J2 = 22
J3 = 6.8
2/3
≈ J2/J3
≈ 0.3
H. Miao et al.,
arXiv:1107.0985
(Tl,K)Fe2-xSe2 (Tc ~ 30K)
T. Qian et al., PRL (2011)
Isotropic SC gap on electron FS
J1 < 0, FM, d-wave is not favored
X.-P. Wang et al., EPL 93, 57001 (2011)
Selection Rules of Pairing Symmetry
Self-consistent meanfield equation for t-J model
Overlap strength between pairing form factor and Fermi surface
OS =
Three classes of high-Tc superconductors
J1
J2
J2+J3
Three classes of high-Tc superconductors
J1
J2
J2+J3
Summary
1.The SC gap of all iron-based superconductors
measured by ARPES can by described approximately
by J1-J2-J3 model
1.A possible unified paradigm of high-Tc
superconductivity:
local AFM magnetic exchange
+ collaborative FS topology
J.-P. Hu and H. Ding, arXiv:1107.1334