Faculty
Assistant professor
Room 140
+81 (0)75 753 3744
kitagHelloUglyBot!awa.shuHelloUglyBot!nsaku.8HelloUglyBot!u@kyoto-u.ac.jp
my publications in the group follow:
2010
5.
Y Nakai, T Iye, S Kitagawa, K Ishida, S Kasahara, T Shibauchi, Y Matsuda, T Terashima
P 31 and A 75 s NMR evidence for a residual density of states at zero energy in superconducting BaFe2( As0.67P 0.33)2 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 81, no. 2, 2010.
@article{Nakai2010d,
title = {P 31 and A 75 s NMR evidence for a residual density of states at zero energy in superconducting BaFe2( As0.67P 0.33)2},
author = {Y Nakai and T Iye and S Kitagawa and K Ishida and S Kasahara and T Shibauchi and Y Matsuda and T Terashima},
doi = {10.1103/PhysRevB.81.020503},
year = {2010},
date = {2010-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {81},
number = {2},
abstract = {P 31 and A 75 s NMR measurements were performed in superconducting BaFe2( As0.67P0.33)2 with Tc =30 K. The nuclear-spin-lattice relaxation rate T 1 -1 and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T 1 -1 in the superconducting (SC) state decreases without a coherence peak just below Tc, as observed in (Ba1-x Kx) Fe2 As 2. In contrast to other iron arsenide superconductors, the T 1 -1 T behavior is observed below 4 K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe2 (As1-x Px)2despite a comparable Tc value, an analogous phase diagram, and similar Fermi surfaces to (Ba1-x Kx) Fe2 As2. © 2010 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
P 31 and A 75 s NMR measurements were performed in superconducting BaFe2( As0.67P0.33)2 with Tc =30 K. The nuclear-spin-lattice relaxation rate T 1 -1 and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T 1 -1 in the superconducting (SC) state decreases without a coherence peak just below Tc, as observed in (Ba1-x Kx) Fe2 As 2. In contrast to other iron arsenide superconductors, the T 1 -1 T behavior is observed below 4 K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe2 (As1-x Px)2despite a comparable Tc value, an analogous phase diagram, and similar Fermi surfaces to (Ba1-x Kx) Fe2 As2. © 2010 The American Physical Society.
2009
4.
K Ishida, Y Nakai, S Kitagawa, Y Kamihara, M Hirano, H Hosono
75As and 139La NMR studies on LaFeAs (O1 - x Fx) Journal Article
In: Physica B: Condensed Matter, vol. 404, no. 19, pp. 3089-3094, 2009.
@article{Ishida20093089,
title = {75As and 139La NMR studies on LaFeAs (O1 - x Fx)},
author = {K Ishida and Y Nakai and S Kitagawa and Y Kamihara and M Hirano and H Hosono},
doi = {10.1016/j.physb.2009.07.078},
year = {2009},
date = {2009-01-01},
journal = {Physica B: Condensed Matter},
volume = {404},
number = {19},
pages = {3089-3094},
abstract = {We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs (O1 - x Fx) (x = 0.0, 0.04, 0.07 and 0.11) where superconductivity occurs in x greater than 0.04. In the undoped LaFeAsO, 1 / T1 of 139La exhibits a distinct peak at TN ~ 142 K below which the La NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1 / T1 T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the x = 0.11 sample, in contrast, pseudogap behavior is observed in 1 / T1 T at the 75As site with a gap value of ΔPG ~ 175 K. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure by the electron-doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, 1 / T1 of 75As in all compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results seemingly suggests that unconventional superconductivity with zero gap along lines, whereas the lack of the residual density of states at the low temperatures is incompatible with the presence of the line-nodes. We discuss similarity and difference between LaFeAs (O1 - x Fx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F-doping dependence of Tc and 1 / T1. Crown Copyright © 2009.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs (O1 - x Fx) (x = 0.0, 0.04, 0.07 and 0.11) where superconductivity occurs in x greater than 0.04. In the undoped LaFeAsO, 1 / T1 of 139La exhibits a distinct peak at TN ~ 142 K below which the La NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1 / T1 T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the x = 0.11 sample, in contrast, pseudogap behavior is observed in 1 / T1 T at the 75As site with a gap value of ΔPG ~ 175 K. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure by the electron-doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, 1 / T1 of 75As in all compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results seemingly suggests that unconventional superconductivity with zero gap along lines, whereas the lack of the residual density of states at the low temperatures is incompatible with the presence of the line-nodes. We discuss similarity and difference between LaFeAs (O1 - x Fx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F-doping dependence of Tc and 1 / T1. Crown Copyright © 2009.
3.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
Systematic A 75 s NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAsO1-x Fx Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 21, 2009.
@article{Nakai2009,
title = {Systematic A 75 s NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAsO1-x Fx},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1103/PhysRevB.79.212506},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {79},
number = {21},
abstract = {We report A 75 s NMR studies on LaFeAs (O1-x Fx) (0≤x≤0.14). At x=0.04 near the phase boundary, from resistivity, spin-lattice relaxation rate 1/ T1, and NMR spectrum measurements, we found weak magnetic order at TN □30 K. Antiferromagnetic (AFM) fluctuations proved through 1/ T1 are suppressed significantly with F doping, and pseudogap behavior without pronounced AFM fluctuations is observed at x=0.11 where TC is maximum. This significant suppression of 1/ T1 T upon F doping while TC remains nearly unchanged suggests that low-energy AFM fluctuations probed with A 75 s NMR do not play a crucial role in the superconductivity. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report A 75 s NMR studies on LaFeAs (O1-x Fx) (0≤x≤0.14). At x=0.04 near the phase boundary, from resistivity, spin-lattice relaxation rate 1/ T1, and NMR spectrum measurements, we found weak magnetic order at TN □30 K. Antiferromagnetic (AFM) fluctuations proved through 1/ T1 are suppressed significantly with F doping, and pseudogap behavior without pronounced AFM fluctuations is observed at x=0.11 where TC is maximum. This significant suppression of 1/ T1 T upon F doping while TC remains nearly unchanged suggests that low-energy AFM fluctuations probed with A 75 s NMR do not play a crucial role in the superconductivity. © 2009 The American Physical Society.
2.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
An NMR study on the F-doping evolution of the iron oxypnictide LaFeAs(O1-xFx) Journal Article
In: New Journal of Physics, vol. 11, 2009.
@article{Nakai2009b,
title = {An NMR study on the F-doping evolution of the iron oxypnictide LaFeAs(O1-xFx)},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1088/1367-2630/11/4/045004},
year = {2009},
date = {2009-01-01},
journal = {New Journal of Physics},
volume = {11},
abstract = {We report the experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs(O 1−xFx) (x = 0.0, 0.04, 0.07, 0.11 and 0.14) where superconductivity occurs at x > 0.03. In the undoped LaFeAsO, 1/T 1 of 139La exhibits a distinct peak at TiN ∼ 142 K below which the La-NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1/T1T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with a decrease in temperature. At x = 0.11 and 0.14, in contrast, pseudogap behavior is observed in 1/ T1T at the 75As site with a gap value of δPG ∼ 175 and 165 K, respectively. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure because of the electron doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, the 1 / T1 of75 As in the three samples does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results may suggest unconventional superconductivity with a zero gap along the lines, but neither the field-induced extra relaxation rate nor the residual density of states at the low temperatures is incompatible with the presence of the line nodes. We discuss the similarities and differences between LaFeAs(O1−xFx) and cuprates and also discuss the relationship between spin dynamics and superconductivity on the basis of the F-doping dependence of Tc and 1/T1. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs(O 1−xFx) (x = 0.0, 0.04, 0.07, 0.11 and 0.14) where superconductivity occurs at x > 0.03. In the undoped LaFeAsO, 1/T 1 of 139La exhibits a distinct peak at TiN ∼ 142 K below which the La-NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1/T1T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with a decrease in temperature. At x = 0.11 and 0.14, in contrast, pseudogap behavior is observed in 1/ T1T at the 75As site with a gap value of δPG ∼ 175 and 165 K, respectively. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure because of the electron doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, the 1 / T1 of75 As in the three samples does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results may suggest unconventional superconductivity with a zero gap along the lines, but neither the field-induced extra relaxation rate nor the residual density of states at the low temperatures is incompatible with the presence of the line nodes. We discuss the similarities and differences between LaFeAs(O1−xFx) and cuprates and also discuss the relationship between spin dynamics and superconductivity on the basis of the F-doping dependence of Tc and 1/T1. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
1.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
75As and 139La NMR/NQR investigations of iron-based superconductor LaFeAs(O0.89F0.11) Conference
vol. 150, no. 5, 2009.
@conference{Nakai2009c,
title = {75As and 139La NMR/NQR investigations of iron-based superconductor LaFeAs(O0.89F0.11)},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1088/1742-6596/150/5/052179},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We report 75As and 139La NMR/NQR results in LaFeAs(O0.89F0.11). In the normal state, 1/T1T decreases with lowered temperature, which is reminiscent of the pseudogap behavior in the high-Tc cuprates. In the superconducting (SC) state, 1/T1 decreases suddenly below Tc without a Hebel-Slichter coherence peak, followed by a T3 dependence, which is characteristics of unconventional superconductors with lines of nodes. However, the residual density of states in the low temperatures, which is usually observed in unconventional superconductors with crystal imperfections and/or impurity phases, was not observed. Knight shift measurements show that spin susceptibility decreases in the SC state. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We report 75As and 139La NMR/NQR results in LaFeAs(O0.89F0.11). In the normal state, 1/T1T decreases with lowered temperature, which is reminiscent of the pseudogap behavior in the high-Tc cuprates. In the superconducting (SC) state, 1/T1 decreases suddenly below Tc without a Hebel-Slichter coherence peak, followed by a T3 dependence, which is characteristics of unconventional superconductors with lines of nodes. However, the residual density of states in the low temperatures, which is usually observed in unconventional superconductors with crystal imperfections and/or impurity phases, was not observed. Knight shift measurements show that spin susceptibility decreases in the SC state. © 2009 IOP Publishing Ltd.
