1. 25th International Conference on Low Temperature Physics
High-pressure studies on superconducting iron-based compound LaFeAsO1-xFx
Title
25th International Conference on
Low Temperature Physics
August 8, 2008

2. Authors H.Takahashi, H.Okada, K.Igawa, K.Arii, Y.Takahashi
Nihon University
(High pressure studies; DAC, Piston-cylinder)
Y.Kamihara, S.Matsuishi, M.Hirano, H.Hosono
JST, Tokyo Institute of Technology
(Sample preparations)
K.Matsubayashi, Y.Uwatoko
ISSP, The University of Tokyo
(High-pressure studies; cubic anvil press)
High pressure work was done by our group. cubic anvil press are uesed at Uwatoko Group at ISSP, Univ of Tokyo.
Samples we measured are prepared by Hosono’s group.

3. LaFeAsO1-xFx (x=0,0.05,0.11,0.14) e- Fe As La La-O layer Fe-As O F
x=0 : undoped
x=0.05: under-doped
x=0.11: optimum-doped
x=0.14: over-doped Fe As La e-
La-O
layer
Fe-As O F
:This study
: Previous study
Firstly I report the F doped LaFeAsO
We measured the pressure effect for these 3 compound.
Undope and So-called under-doped and optimally doped
Schematic crystal structure
of LaFeAsO1-xFx
Tc(x) in LaFeAsO1-xFx
Y.Kamihara et al., J.Am.Chem.Soc. 130 (2008)

4. Optimum doped x=0.11 ・Maximum Tc = 43 K ・Tc decreases above 4 GPa
・Initial increase of Tc is very steep
・Maximum Tc = 43 K
・Tc decreases above 4 GPa
LaFeAsO1-xFx
Fig. 2d summarizes the onset TC values in the P–T phase diagram of La(O0.89F0.11)FeAs. Note that TC increases steeply from 1 to 2 GPa, where dln TC/dP is more than 20%/GPa and then decreases sharply with a further increase in P above ~4 GPa: the maximum TC of 43 K is observed at ~4 GPa. It is noteworthy that the small resistance loss caused by superconductivity was observed at around 50 K in 4 GPa data
Pressure dependence of Tc for x=0.11
(Run1: Piston cylinder, Run2: Diamond anvil cell )
H.Takahashi et al., Nature 453 (2008)

5. Pressure dependence of TC
Under-doped x = 0.05
LaFeAsO1-xFx
Pressure dependence of TC
for x=0.11 and x=0.05
R(T) curve for x=0.05(under-doped)
at several pressures up to 20 GPa
The initial increase in optimally doped one is much steeper compared with those of high-TC superconductors, for which the dln TC/dP values are less than 10% / GPa.
Under-doped LaFeAsO1-xFx (x=0.05) shows
similar behavior to x=0.11, but pressure
dependence of Tc is small.
Maximum Tc is also smaller.

6. Pressure dependence of Tc
Over-doped x=0.14
Pressure dependence of Tc
for all samples
R(T) curve for x=0.14
using piston cylinder device
・Initial increase of Tc is very steep for over-doped x=0.14
・Maximum Tc = 43 K for over-deped x=0.14 , same as x=0.11
・Tc decreases above 6 GPa for over-doped x=0.14
・Pressure-induced superconductivity was observed for undoped LaFeAsO(x=0)

7. Undoped LaFeAsO Cubic anvil press ( up to 12 GPa)
Pressure transmitting medium: Fluorinert
Gasket: MgO
Zero resistivity

8. Pressure dependence of electrical resistivity for SrFe2As2
Maximum Tc～35K
enlarge
Zero resistivity
Cubic anvil press ( up to 8 GPa)
　　Medium: Fluorinert
　　Gasket: Pyrophylite

9. Summary
Pressure dependence of TC in LaFeAsO1-xFx (x=0.0, 0.05, 0.11,0.14) are obtained. TC’s initially increase with applying pressure.
Tc (P=0)
dTc/dP
(K/GPa-1)
Tc max
undoped - 3 22
under-doped 25 2 29
optimum-doped 28 8 43
over-doped 19 12
・Pressure-induced superconductivity is observed in undoped LaFeAsO and undoped SrFe2As2