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:
2022
55.
Y Sato, S Suetsugu, T Tominaga, Y Kasahara, S Kasahara, T Kobayashi, S Kitagawa, K Ishida, R Peters, T Shibauchi, A H Nevidomskyy, L Qian, J M Moya, E Morosan, Y Matsuda
Charge neutral fermions and magnetic field driven instability in insulating YbIr3Si7 Journal Article
In: Nature Communications, vol. 13, pp. 394, 2022.
@article{Y.Sato_NComm_2022,
title = {Charge neutral fermions and magnetic field driven instability in insulating YbIr3Si7},
author = {Y Sato and S Suetsugu and T Tominaga and Y Kasahara and S Kasahara and T Kobayashi and S Kitagawa and K Ishida and R Peters and T Shibauchi and A H Nevidomskyy and L Qian and J M Moya and E Morosan and Y Matsuda},
url = {https://arxiv.org/abs/2103.13718},
doi = {10.1038/s41467-021-27541-9},
year = {2022},
date = {2022-01-19},
urldate = {2022-01-19},
journal = {Nature Communications},
volume = {13},
pages = {394},
abstract = {Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.
2021
54.
K Ishida, S Matsuzaki, M Manago, T Hattori, S Kitagawa, M Hirata, T Sasaki, D Aoki
Pairing interaction in superconducting UCoGe tunable by magnetic field Journal Article
In: Physical Review B, vol. 104, no. 14, pp. 144505, 2021.
@article{K.Ishida_PRB_2021,
title = {Pairing interaction in superconducting UCoGe tunable by magnetic field},
author = {K Ishida and S Matsuzaki and M Manago and T Hattori and S Kitagawa and M Hirata and T Sasaki and D Aoki},
url = {https://arxiv.org/abs/2109.14426},
doi = {10.1103/PhysRevB.104.144505},
year = {2021},
date = {2021-10-18},
journal = {Physical Review B},
volume = {104},
number = {14},
pages = {144505},
abstract = {The mechanism of unconventional superconductivity, such as high-temperature-cuprate, Fe-based, and heavy-fermion superconductors, has been studied as a central issue in condensed-matter physics. Spin fluctuations, instead of phonons, are considered to be responsible for the formation of Cooper pairs, and many efforts have been made to confirm this mechanism experimentally. Although a qualitative consensus seems to have been obtained, experimental confirmation has not yet been achieved. This is owing to a lack of the quantitative comparison between theory and experiments. Here, we show a semiquantitative comparison between the superconducting-transition temperature ( T SC ) and spin fluctuations derived from the NMR experiment on the ferromagnetic (FM) superconductor UCoGe in which the FM fluctuations and superconductivity are tunable by external fields. The enhancement and abrupt suppression of T SC by applied fields, as well as the pressure variation of T SC around the FM criticality are well understood by the change in the FM fluctuations on the basis of the single-band spin-triplet theoretical formalism. The present comparisons strongly support the theoretical formalism of spin-fluctuation-mediated superconductivity, particularly in UCoGe.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The mechanism of unconventional superconductivity, such as high-temperature-cuprate, Fe-based, and heavy-fermion superconductors, has been studied as a central issue in condensed-matter physics. Spin fluctuations, instead of phonons, are considered to be responsible for the formation of Cooper pairs, and many efforts have been made to confirm this mechanism experimentally. Although a qualitative consensus seems to have been obtained, experimental confirmation has not yet been achieved. This is owing to a lack of the quantitative comparison between theory and experiments. Here, we show a semiquantitative comparison between the superconducting-transition temperature ( T SC ) and spin fluctuations derived from the NMR experiment on the ferromagnetic (FM) superconductor UCoGe in which the FM fluctuations and superconductivity are tunable by external fields. The enhancement and abrupt suppression of T SC by applied fields, as well as the pressure variation of T SC around the FM criticality are well understood by the change in the FM fluctuations on the basis of the single-band spin-triplet theoretical formalism. The present comparisons strongly support the theoretical formalism of spin-fluctuation-mediated superconductivity, particularly in UCoGe.
53.
S Kitagawa, K Ishida, A Ikeda, M Kawaguchi, S Yonezawa, Y Maeno
Peak in the superconducting transition temperature of the nonmagnetic topological line-nodal material CaSb2 under pressure Journal Article
In: Physical Review B, vol. 104, no. 6, pp. L060504, 2021.
@article{S.Kitagawa_PRB_2021,
title = {Peak in the superconducting transition temperature of the nonmagnetic topological line-nodal material CaSb_{2} under pressure},
author = {S Kitagawa and K Ishida and A Ikeda and M Kawaguchi and S Yonezawa and Y Maeno},
url = {https://arxiv.org/abs/2108.08992},
doi = {10.1103/PhysRevB.104.L060504},
year = {2021},
date = {2021-08-17},
journal = {Physical Review B},
volume = {104},
number = {6},
pages = {L060504},
abstract = {Investigating the pressure dependence of the superconducting (SC) transition temperature Tc is crucial for understanding the SC mechanism.
Herein, we report on the pressure dependence of Tc in the nonmagnetic topological line-nodal material CaSb2 based on measurements of electric resistance and alternating current magnetic susceptibility.
Tc initially increases with increasing pressure and peaks at ~ 3.1 GPa. With a further increase in pressure, Tc decreases and finally becomes undetectable at 5.9 GPa.
Because no signs of phase transition or Lifshitz transition are observed in the normal state, the peculiar peak structure of Tc suggests that CaSb2 has an unconventional SC character.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Investigating the pressure dependence of the superconducting (SC) transition temperature Tc is crucial for understanding the SC mechanism.
Herein, we report on the pressure dependence of Tc in the nonmagnetic topological line-nodal material CaSb2 based on measurements of electric resistance and alternating current magnetic susceptibility.
Tc initially increases with increasing pressure and peaks at ~ 3.1 GPa. With a further increase in pressure, Tc decreases and finally becomes undetectable at 5.9 GPa.
Because no signs of phase transition or Lifshitz transition are observed in the normal state, the peculiar peak structure of Tc suggests that CaSb2 has an unconventional SC character.
Herein, we report on the pressure dependence of Tc in the nonmagnetic topological line-nodal material CaSb2 based on measurements of electric resistance and alternating current magnetic susceptibility.
Tc initially increases with increasing pressure and peaks at ~ 3.1 GPa. With a further increase in pressure, Tc decreases and finally becomes undetectable at 5.9 GPa.
Because no signs of phase transition or Lifshitz transition are observed in the normal state, the peculiar peak structure of Tc suggests that CaSb2 has an unconventional SC character.
52.
H Takahashi, S Kitagawa, K Ishida, M Kawaguchi, A Ikeda, S Yonezawa, Y Maeno
S-Wave Superconductivity in the Dirac Line-Nodal Material CaSb2 Journal Article
In: Journal of the Physical Society of Japan, vol. 90, pp. 073702, 2021.
@article{H.Takahashi_JPSJ_2021,
title = {S-Wave Superconductivity in the Dirac Line-Nodal Material CaSb2},
author = {H Takahashi and S Kitagawa and K Ishida and M Kawaguchi and A Ikeda and S Yonezawa and Y Maeno},
url = {https://arxiv.org/abs/2105.13614},
doi = {10.7566/JPSJ.90.073702},
year = {2021},
date = {2021-06-11},
urldate = {2021-06-11},
journal = {Journal of the Physical Society of Japan},
volume = {90},
pages = {073702},
abstract = {We performed 121/123Sb-nuclear quadrupole resonance (NQR) measurements on the superconducting (SC) line-nodal material CaSb2 in order to investigate electronic properties in the normal and SC states from a microscopic point of view. In the normal state, the nuclear spin–lattice relaxation rate 1/T1 for the Sb(1) site, which is responsible for the line-nodal parts, is approximately proportional to temperature, indicating the conventional Fermi liquid state. From comparison with band structure calculations, it is considered that the NQR properties related to the line-nodal character are hidden because the conventional behavior originating from Fermi-surface parts away from the nodes is dominant. In the SC state, a clear coherence peak just below the transition temperature and an exponential decrease at lower temperatures were observed in 1/T1. These results strongly suggest that conventional s-wave superconductivity with a full gap is realized in CaSb2.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We performed 121/123Sb-nuclear quadrupole resonance (NQR) measurements on the superconducting (SC) line-nodal material CaSb2 in order to investigate electronic properties in the normal and SC states from a microscopic point of view. In the normal state, the nuclear spin–lattice relaxation rate 1/T1 for the Sb(1) site, which is responsible for the line-nodal parts, is approximately proportional to temperature, indicating the conventional Fermi liquid state. From comparison with band structure calculations, it is considered that the NQR properties related to the line-nodal character are hidden because the conventional behavior originating from Fermi-surface parts away from the nodes is dominant. In the SC state, a clear coherence peak just below the transition temperature and an exponential decrease at lower temperatures were observed in 1/T1. These results strongly suggest that conventional s-wave superconductivity with a full gap is realized in CaSb2.
51.
G Nakamine, K Kinjo, S Kitagawa, K Ishida, Y Tokunaga, H Sakai, S Kambe, A Nakamura, Y Shimizu, Y Homma, D Li, F Honda, D Aoki
Inhomogeneous Superconducting State Probed by 125Te NMR on UTe2 Journal Article
In: Journal of the Physical Society of Japan, vol. 90, no. 064709, pp. 7, 2021.
@article{G.Nakamine_JPSJ_2021,
title = {Inhomogeneous Superconducting State Probed by 125Te NMR on UTe2},
author = {G Nakamine and K Kinjo and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},
url = {https://arxiv.org/abs/2105.11823},
doi = {10.7566/JPSJ.90.064709},
year = {2021},
date = {2021-05-25},
journal = {Journal of the Physical Society of Japan},
volume = {90},
number = {064709},
pages = {7},
abstract = {UTe2 is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe2, we have performed 125Te-NMR measurements, which are sensitive to the local spin susceptibility at a nuclear site. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature Tc in H || b, and a slight decrease in the Knight shift along the b and c axes (Kb and Kc, respectively) below Tc at a low magnetic field H. Although the decrease in Kc vanished above 5.5 T, the decrease in Kb was independent of H up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in Kb, we compared the 125Te-NMR spectra obtained when H || b and H || c and measured the 125Te-NMR spectra for H || b up to 14.5 T. The intensity of the shoulder signal observed for H || b has a maximum at ∼6 T and vanishes above 10 T, although the superconductivity is confirmed by the χAC measurements, which can survive up to 14.5 T (maximum H in the present measurement). Moreover, the decrease in Kb in the SC state starts to be small around 7 T and almost zero at 12.5 T. This indicates that the SC spin state gradually changes with the application of H. Meanwhile, in H || c, an unexpected broadening without the shoulder signals was observed below Tc at 1 T, and this broadening was quickly suppressed with increasing H. We construct the H–T phase diagram for H || b and H || c based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
UTe2 is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe2, we have performed 125Te-NMR measurements, which are sensitive to the local spin susceptibility at a nuclear site. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature Tc in H || b, and a slight decrease in the Knight shift along the b and c axes (Kb and Kc, respectively) below Tc at a low magnetic field H. Although the decrease in Kc vanished above 5.5 T, the decrease in Kb was independent of H up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in Kb, we compared the 125Te-NMR spectra obtained when H || b and H || c and measured the 125Te-NMR spectra for H || b up to 14.5 T. The intensity of the shoulder signal observed for H || b has a maximum at ∼6 T and vanishes above 10 T, although the superconductivity is confirmed by the χAC measurements, which can survive up to 14.5 T (maximum H in the present measurement). Moreover, the decrease in Kb in the SC state starts to be small around 7 T and almost zero at 12.5 T. This indicates that the SC spin state gradually changes with the application of H. Meanwhile, in H || c, an unexpected broadening without the shoulder signals was observed below Tc at 1 T, and this broadening was quickly suppressed with increasing H. We construct the H–T phase diagram for H || b and H || c based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom.
50.
G Nakamine, K Kinjo, S Kitagawa, K Ishida, Y Tokunaga, H Sakai, S Kambe, A Nakamura, Y Shimizu, Y Homma, D Li, F Honda, D Aoki
Anisotropic response of spin susceptibility in the superconducting state of UTe2 probed with 125Te − NMR measurement Journal Article
In: Physical Review B, vol. 103, no. 10, pp. L100503, 2021.
@article{G.Nakamine_PRB_2021,
title = {Anisotropic response of spin susceptibility in the superconducting state of UTe2 probed with 125Te − NMR measurement},
author = {G Nakamine and K Kinjo and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},
url = {https://arxiv.org/abs/2103.02876},
doi = {10.1103/PhysRevB.103.L100503},
year = {2021},
date = {2021-03-17},
journal = {Physical Review B},
volume = {103},
number = {10},
pages = {L100503},
abstract = {To investigate spin susceptibility in a superconducting (SC) state, we measured the 125 Te -NMR Knight shifts at magnetic fields ( H ) up to 6.5 T along the b and c axes of single-crystal UTe 2 , a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the b and c axes ( K b and K c , respectively) decreased slightly, and the decrease in K b was almost constant up to 6.5 T. The reduction in K c decreased with increasing H , and K c was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the b and c axes slightly decrease in the SC state in low H , and the H response of SC spin susceptibility is anisotropic on the b c plane. We discuss the possible d -vector state within the spin-triplet scenario and suggest that the dominant d -vector component for the case of H ∥ b changes above 13 T, where T c increases with increasing H .},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
To investigate spin susceptibility in a superconducting (SC) state, we measured the 125 Te -NMR Knight shifts at magnetic fields ( H ) up to 6.5 T along the b and c axes of single-crystal UTe 2 , a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the b and c axes ( K b and K c , respectively) decreased slightly, and the decrease in K b was almost constant up to 6.5 T. The reduction in K c decreased with increasing H , and K c was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the b and c axes slightly decrease in the SC state in low H , and the H response of SC spin susceptibility is anisotropic on the b c plane. We discuss the possible d -vector state within the spin-triplet scenario and suggest that the dominant d -vector component for the case of H ∥ b changes above 13 T, where T c increases with increasing H .
2020
49.
T Yamamoto, A Chikamatsu, S Kitagawa, N Izumo, S Yamashita, H Takatsu, M Ochi, T Maruyama, M Namba, W Sun, T Nakashima, F Takeiri, K Fujii, M Yashima, Y Sugisawa, M Sano, Y Hirose, D Sekiba, C M Brown, T Honda, K Ikeda, T Otomo, K Kuroki, K Ishida, T Mori, K Kimoto, T Hasegawa, H Kageyama
Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides Journal Article
In: Nature Communications, vol. 11, pp. 5923, 2020.
@article{Yamamoto_NC_2020,
title = {Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides},
author = {T Yamamoto and A Chikamatsu and S Kitagawa and N Izumo and S Yamashita and H Takatsu and M Ochi and T Maruyama and M Namba and W Sun and T Nakashima and F Takeiri and K Fujii and M Yashima and Y Sugisawa and M Sano and Y Hirose and D Sekiba and C M Brown and T Honda and K Ikeda and T Otomo and K Kuroki and K Ishida and T Mori and K Kimoto and T Hasegawa and H Kageyama},
doi = {10.1038/s41467-020-19217-7},
year = {2020},
date = {2020-11-23},
journal = {Nature Communications},
volume = {11},
pages = {5923},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
48.
T Okuno, Y Kinoshita, S Matsuzaki, S Kitagawa, K Ishida, M Hirata, T Sasaki, K Kusada, H Kitagawa
Magnetic-Field Dependence of Novel Gap Behavior Related to the Quantum-Size Effect Journal Article
In: Journal of the Physical Society of Japan, vol. 89, no. 9, pp. 095002, 2020.
@article{Okuno_JPSJ_2020,
title = {Magnetic-Field Dependence of Novel Gap Behavior Related to the Quantum-Size Effect},
author = {T Okuno and Y Kinoshita and S Matsuzaki and S Kitagawa and K Ishida and M Hirata and T Sasaki and K Kusada and H Kitagawa},
url = {https://arxiv.org/abs/2007.07688},
doi = {10.7566/JPSJ.89.095002},
year = {2020},
date = {2020-08-03},
journal = {Journal of the Physical Society of Japan},
volume = {89},
number = {9},
pages = {095002},
abstract = {195Pt-NMR measurements of Pt nanoparticles with a mean diameter of 4.0 nm were performed in a high magnetic field of approximately μ0H = 23.3 T to investigate the low-temperature electronic state of the nanoparticles. The characteristic temperature T*, below which the nuclear spin-lattice relaxation rate 1/T1 deviates from the relaxation rate of the bulk, shows a magnetic-field dependence. This dependence supports the theoretical prediction of the appearance of discrete energy levels.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
195Pt-NMR measurements of Pt nanoparticles with a mean diameter of 4.0 nm were performed in a high magnetic field of approximately μ0H = 23.3 T to investigate the low-temperature electronic state of the nanoparticles. The characteristic temperature T*, below which the nuclear spin-lattice relaxation rate 1/T1 deviates from the relaxation rate of the bulk, shows a magnetic-field dependence. This dependence supports the theoretical prediction of the appearance of discrete energy levels.
47.
S Kitagawa, K Ishida, T C Kobayashi, Y Matsubayashi, D Hirai, Z Hiroi
In: Journal of the Physical Society of Japan, vol. 89, no. 5, pp. 053701, 2020.
@article{S_Kitagawa2020,
title = {Variation in Superconducting Symmetry Against Pressure on Noncentrosymmetric Superconductor Cd_{2}Re_{2}O_{7} Revealed by ^{185/187}Re Nuclear Quadrupole Resonance},
author = {S Kitagawa and K Ishida and T C Kobayashi and Y Matsubayashi and D Hirai and Z Hiroi},
url = {https://arxiv.org/abs/2004.00919},
doi = {10.7566/JPSJ.89.053701},
year = {2020},
date = {2020-04-02},
journal = {Journal of the Physical Society of Japan},
volume = {89},
number = {5},
pages = {053701},
abstract = {We performed 185/187Re nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd2Re2O7 under various crystal structures. The pressure dependence of superconducting transition temperature Tc determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [Kobayashi et al., J. Phys. Soc. Jpn. 80, 023715 (2011)]. Below 2.2 GPa, in the nuclear spin–lattice relaxation rate 1/T1, a clear coherence peak was observed just below Tc, indicating conventional s-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the p-wave dominant state against pressure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We performed 185/187Re nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd2Re2O7 under various crystal structures. The pressure dependence of superconducting transition temperature Tc determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [Kobayashi et al., J. Phys. Soc. Jpn. 80, 023715 (2011)]. Below 2.2 GPa, in the nuclear spin–lattice relaxation rate 1/T1, a clear coherence peak was observed just below Tc, indicating conventional s-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the p-wave dominant state against pressure.
46.
T Okuno, M Manago, S Kitagawa, K Ishida, K Kusada, H Kitagawa
NMR-based gap behavior related to the quantum size effect Journal Article
In: Physical Review B, vol. 101, no. 12, 2020.
@article{Okuno2020,
title = {NMR-based gap behavior related to the quantum size effect},
author = {T Okuno and M Manago and S Kitagawa and K Ishida and K Kusada and H Kitagawa},
url = {https://arxiv.org/abs/2003.07585},
doi = {10.1103/PhysRevB.101.121406},
year = {2020},
date = {2020-03-30},
journal = {Physical Review B},
volume = {101},
number = {12},
abstract = {We conducted Pt195-NMR measurements on various-diameter Pt nanoparticles coated with polyvinylpyrrolidone in order to detect the quantum size effect and the discrete energy levels in the electron density of states, both of which were predicted by Kubo more than 50 years ago. We succeeded in separating the signals arising from the surface and interior regions and found that the nuclear spin-lattice relaxation rates in both regions show the metallic behavior at high temperatures. Surprisingly, the magnetic fluctuations in both regions exhibited anomalous behavior below the same temperature T∗, which points to a clear size dependence and is well scaled with δKubo. These results suggest that a size-tunable metal-insulator transition occurs in the Pt nanoparticles as a result of the quantum size effect. © 2020 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We conducted Pt195-NMR measurements on various-diameter Pt nanoparticles coated with polyvinylpyrrolidone in order to detect the quantum size effect and the discrete energy levels in the electron density of states, both of which were predicted by Kubo more than 50 years ago. We succeeded in separating the signals arising from the surface and interior regions and found that the nuclear spin-lattice relaxation rates in both regions show the metallic behavior at high temperatures. Surprisingly, the magnetic fluctuations in both regions exhibited anomalous behavior below the same temperature T∗, which points to a clear size dependence and is well scaled with δKubo. These results suggest that a size-tunable metal-insulator transition occurs in the Pt nanoparticles as a result of the quantum size effect. © 2020 American Physical Society.
