1. 75As NQR Studies on LaFeAsO1-y and NdFeAsO0.6
LT25 , Rump session on Fe-Oxipnictide Superconductors
Amsterdam, Aug 8, 2008
75As NQR Studies on LaFeAsO1-y and NdFeAsO0.6
H. Mukuda1, N. Terasaki1, H. Kinouchi1, M. Yashima1, Y. Kitaoka1, S. Suzuki1,
S. Miyasaka1, S. Tajima1, K. Miyazawa2, P. M. Shirage2, H. Kito2, H. Eisaki2, A. Iyo2
1Osaka Univ., 2AIST
75As-NQR spectra
LaFeAsO
LaFeAsO0.75
LaFeAsO0.6
NdFeAsO0.6
TN~145K
Tc=20K
Tc=28K
Tc=53K
H. M. et al. arXiv
( To be published in JPSJ, No.9 (2008))

2. 1/T1 in LaFeAsO0.6 with Tc=28 K 75As-NQR (H=0) 1/T1 ∝ T3
No Korringa’s relation in normal state
75As-NQR (H=0)
No coherence peak just below Tc
1/T1 ∝ T3
Consistent with other NMR results
 Line-node gap?
2Δ0 /kBTc~5,
Tc=28K
It is inconsistent with full gap state
evidenced by other experiments + -
Parish et al. / arXiv:
Full gap s± -wave scenario ?
Parker et al./ arXiv:
Interband effect suppresses coherence peak
Refs.)
Two full gaps for hole FS & electron FS

3. Experimental relationship between Tc & 75νQ
75As-NQR spectra
Close relationship between Tc & 75νQ
[New!] PrFeAsO0.6

4. Vzz(EFG) is dominated by two contributions
NQR frequency (75νQ)
Vzz : electric field gradient (EFG) at As nuclear site
Vzz(EFG) is dominated by two contributions
① Charge distribution around As atoms
(Fe, La,,,,) Fe As
LaFeAsO1-y
Charge distribution
at As(4p) orbitals
Hybridization between
Fe(3d) and As(4p) orbitals
EFG
C. H. Lee et al., JPSJ (2008)
Close to regular tetrahedron Fe As
NdFeAsO1-y
Local configuration of Fe & As
is very important
for enhancing Tc

5. Summary
◇ 75As-NQR 1/T1 measurements revealed that LaFeAsO0.6 with Tc = 28K is the unconventional superconductor
 extended s±　wave  suppress the coherence peak ?
◇ We found an intimate relationship
between the nuclear quadrupole
frequency 75νQ and Tc.
◇ Local configuration of Fe and As
is very important for superconductivity.
H. M. et al. arXiv
( To be published in JPSJ, No.9 (2008))

6. 1/T1T (Normal state) in LaFeAsO0.6
cf. ) Normal metals,
(Korringa’s relation)
75As-NQR (H=0)
Tc = 28K
・ Pseudo gap-like behavior ?
ΔPG / kB ~ 196K
・ Decrease of DOS at EF?
Decrease of 1/T1T or
Fitting by assuming

7. Variation in the distance between Fe- & As-plane
C. H. Lee et al. to be published in JPSJ,77(2008)
(Neutron diffraction)
LaFeAsO
LaFeAsO0.6
NdFeAsO0.6
Tc increases when distance between Fe-As plane becomes long.
 Close to Regular tetrahedron !!
C. H. Lee et al. Fe As
C. H. Lee et al.

8. 1/T1 in various superconductors
Conventional SC (BCS)
Unconventional SC
NS(E)
NS(E)
Line nodes N0
s-wave N0 EF
EF +Δ0 EF
EF +Δ0
d-wave
Coherence peak
p-wave
T1T = const.-like behavior

9. Local configuration of Fe and As
The enhancement of nQ
Local configuration of Fe and As
Fe atom
closer each other
farther from the Fe plane
As atom
closer to REO1-d layer As
Increasing of Tc
LaFeAsO
NdFeAsO0.6 As
Decreasing of volume c Fe a Fe Fe Fe Fe Fe a Fe Fe
 Close to Regular tetrahedron !!
Hybridization between As-4p orbitals and Fe-3d orbitals

10. Vzz(EFG) is given by two contributions
NQR frequency (75νQ)
LaFeAsO
LaFeAsO0.6
NdFeAsO0.6
C. H. Lee et al.,
JPSJ (2008)
Close to regular
tetrahedron
Vzz : electric field gradient (EFG) along c-axis
Vzz(EFG) is given by two contributions
① Point charges (Fe, La,) around As Fe As
② Charge distribution at As(4p) orbitals
 Hybridization between Fe(3d) and As(4p) orbitals As Fe Fe
Local configuration of Fe & As
is very important
for enhancing Tc Fe Fe
LaFeAsO1-y NdFeAsO1-y

11. Point charge model
Contribution from Fe atoms is large.

12. Phase diagram