Transcript The Specific Heat of Co

The Low-Temperature
Specific Heat of Chalcogenbased FeSe
J.-Y. Lin,1 Y. S. Hsieh,1 D. Chareev,2
A. N. Vasiliev,3 Y. Parsons,4 and H. D.
Yang4
1
Institute of Physics/National Chiao Tung University, Hsinchu 30010,
Taiwan
2Institute of Experimental Mineralogy, Cherngolovka, Moscow Region
142432, Russia
3Department of Low temperature Physics, Moscow State University,
Moscow 119991, Russia
4Department of Physics, University of California, Santa Babara, CA 93106,
USA
4Department of Physics, National Sun Yat-sen University, Kaohsiung 804,
Taiwan
Contents
• Introduction to Fe-based superconductors
• Specific heat as a probe of the
superconducting order parameter
• Experiments and results
• Conclusions
A brief introduction to iron-based
superconductors
Structure
The Race to Beat Cuprates?
Hg - cuprate
150
？
TI - cuprate
100
Tc(K)
YBCO
Fe-based
superconductors
Cuprates
MgB2
LSCO
50
e-doped SmOFeAs
Nb3Ge
e-doped LaOFeAs
Metallic alloys
e-doped LaOFeP
0
70
80
90
100
110
Year of discovery
The crusade of Room Temperature superconductors?
Motivation
•The
order
parameter
in
Fe-based
superconductors remains elusive. To get
insight into the pairing mechanism, it is crucial
to determine the gap structure in the
superconductors like FeSe or pnictides.
•Though with lower Tc, FeSe has the simplest
structure, and this very simplicity could
provide the most appropriate venue of
understanding both the order parameter and
the superconducting mechanism of Fe-base
superconductors.
Johnston, 2010
(Subedi
et al., 2008)
Specific heat as the probe
• Revealing the superconducting order
parameter from the specific heat
• Information from k-space integration.
Non phase-sensitive.
• Surprisingly selective if well excuted
FeSe single crystals
FeSe single crystal
1500
C (mJ/mol K)
FeSe
H=0
1000
500
(a)
0
0
5
10
T (K)
15
FeSe single crystal
100
FeSe
2
C/T (mJ/mol K )
80
60
40
20
(a)
0
0
5
10
T (K)
15
60
H=0
H=0.5 T
H=1 T
H=2 T
H=3 T
H=5 T
H=7 T
H=9 T
2
C/T (mJ/mol K )
50
40
30
FeSe
H//c
20
10
0
0
20
40
60
2
2
T (K )
80
100
60
H=0
H=0.5 T
H=1 T
H=2 T
H=3 T
H=5 T
H=7 T
H=9 T
2
C/T (mJ/mol K )
50
40
30
FeSe
20
10
Cn=5.73T+0.4208T
3
0
0
20
40
60
2
2
T (K )
80
100
n=5.73 mJ/mol K2
=210 K
nearly identical to the results of polycrystals from T.
M. McQueen et al. (2009)
60
H=0
H=0.5 T
H=1 T
H=2 T
H=3 T
H=5 T
H=7 T
H=9 T
2
C/T (mJ/mol K )
50
40
30
FeSe
20
Cn=5.73T+0.4208T
3
10
(b)
0
0
20
40
60
2
2
T (K )
80
100
Weak limit BCS isotropic s-wave: C/nTc=1.43
6
4
0
S (mJ/mol K2)
8
2
C(=C-Cn)/T (mJ/mol K )
10
-5
-10
-15
2
0
2
4
6
8
10
T (K)
0
C/nTc=1.65
-2
-4
-6
0
2
4
6
T (K)
8
10
C. P. Sun et al. (2004)
12
8
(a)
1
0
-1
-2
0.0
0.2
0.4
0.6
6
12
10
-1
-2
0.0
0.2
0.4
0.6
8
2
(c)
1
0
-1
-2
0.0
0.2
0.4
0.6
0.8
2
1
(d)
0
-1
-2
0.0
T/Tc
6
0.2
0.4
0.6
0.8
T/Tc
4
s-wave 2L/kTc=4.43 71%
2
s-wave 2S/kTc=1.28 29%
s-wave 20/kTc=3.82
0.5
1.0
33%
E. s-wave 2e/kTc=3.22 67%
 =0.78
0
0.0
0.8
extended s-wave
2e/kTc=3.59  =0.64
d-wave 20/kTc=5.51
2
14
0
T/Tc
4
0
16
0.8
(b)
1
T/Tc
DF (mJ/mol K2)
Ces/T (mJ/mol K2)
10
2
2
DF (mJ/mol K2)
14
=e(1+cos2)
DF (mJ/mol K2)
16
DF (mJ/mol K2)
=0cos2
0.0
T/Tc
0.5
1.0
Nicholson et al. (2011)
2.0
FeSe
2
Ces/T (mJ/mol K )
1.5
1.0
0.5
0.0
0.00
d-wave
s-wave + extended s-wave
s-wave + s-wave
0.05
0.10
0.15
T/Tc
0.20
0.25
Quasi-linear (H) in high H was also observed in 122. (J. S. Kim et al. 2010)
2
 (H) (mJ/mol K )
6
n
H//c
FeSe
H//ab
2
3
C=T+T +T
4
2
0
0
2
4
6
8
H (T)
Hc2=13.1 T?
/n=0~0.69
10
2
C/T (mJ/mol K )
H=0
H=0.5 T
H=1 T
H=2 T
H=3 T
H=5 T
H=7 T
H=9 T
5
FeSe H//c
0
0
1
T (K)
2
2
 (H) (mJ/mol K )
6
n
H//c
H//ab
FeSe
4
2
(a)
0
0
2
4
6
H (T)
8
10
ӨD C/nTc
(mJ/mo (K)
l K2)
n
5.73
210
1.65

1.55
Hc2,H//c Hc2,Hc
(T)
(T)
13.1
27.9
Bang, 2010
Anisotropic Hc2
10
20
15
H (T)
FeSe
10
5
H (T)
0
0
2
5
4
6
8
T (K)
H//c
H//ab
0
6.6
6.8
7.0
(b)
7.2
7.4
7.6
T (K)
7.8
8.0
8.2
8.4
STM on FeSe
C. L. Song et al., 2011
Comparison between FeSe and Fe(Se,Te)
Fe(Se,Te)
Hanaguri et al., 2010
FeSe
Song et al., 2011
The fitting parameters
Conclusions for FeSe
• Existence of low-energy excitations more
than in an isotropic s-wave.
• Gap anisotropy. S + exntended s. Probably
No accidental nodes.
• Existence of an isotropic s-wave.
• Hc2,H//c13.1 T and Hc2,Hc27.9 T. The
anisotropy in Hc2 is about 2.1.
6
n
2
 (H) (mJ/mol K )
0.55±0.03
H//c H
0.60±0.05
H//ab H
2
3
C=T+T +T
4
2
FeSe
0
0
2
4
6
H (T)
8
10
0
-20
30
-40
S
-60
20
-80
-100
-120
-140
-180
10
0
2
4
6
2
Ce/T (mJ/mol K )
-160
8 10 12 14 16 18 20 22 24 26 28
T (K)
0
(C (x=0.08)- nT - fs*Clat ) /T
-10
n=27.02
C/nTc=1.13
-20
fs=1.0345
-30
0
5
10
15
20
T (K)
25
30
35
Fig. 4 The specific heat of MgB2. The dashed lines are determined by
the conservation of entropy around the anomaly and used to
estimate ΔC/Tc. Inset: Entropy difference ΔS by integration of ΔC/T.
60
50
40
2
Ce/T (mJ/mol K )
30
20
10
0
-10
d-wave 2S/kBTc=2.70 55%
-20
s-wave 2L/kBTc=4.18 45%
-30
0.0
0.5
1.0
T/Tc
1.5
-5
5.0x10
magnetic moment (emu)
0.0
-5
-5.0x10
-4
-1.0x10
H =20 Oe
ZFC
FC
-4
-1.5x10
-4
-2.0x10
-4
-2.5x10
-4
-3.0x10
0
2
4
6
8
10
Temperature (K)
12
14
16