JSPS Research Fellow (DC2)
D3
134
3793
ogata.shiki.86c_at_st.kyoto-u.ac.jp
2025
Matsumura, H; Kitagawa, S; Ogata, S; Matsubayashi, R; Fujibayashi, H; Kinjo, K; Ishida, K; Tokunaga, Y; Sakai, H; Kambe, S; Nakamura, A; Shimizu, Y; Homma, Y; Li, D; Honda, F; Miyake, A; Aoki, D
Intrinsic low-temperature magnetic properties on ultraclean UTe2 with Tc = 2.1 K revealed by 125Te NMR Journal Article
In: Physical Review B, vol. 111, pp. 094507, 2025.
@article{H.Matsumura_PRB_2025-1,
title = {Intrinsic low-temperature magnetic properties on ultraclean UTe2 with Tc = 2.1 K revealed by 125Te NMR},
author = {H Matsumura and S Kitagawa and S Ogata and R Matsubayashi and H Fujibayashi and K Kinjo 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 A Miyake and D Aoki},
url = {https://doi.org/10.1103/PhysRevB.111.094507
https://arxiv.org/abs/2503.09109},
doi = {10.1103/PhysRevB.111.094507},
year = {2025},
date = {2025-03-10},
urldate = {2025-03-10},
journal = {Physical Review B},
volume = {111},
pages = {094507},
abstract = {To investigate the intrinsic magnetic properties of UTe2, we performed 125Te-NMR measurements on the ultraclean single-crystalline UTe2 with superconducting transition temperature 𝑇c=2.1 K and compared the results with those of the 𝑇c=1.6 K sample. The broadening of the linewidth of the NMR spectrum in the 𝑎-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6 K sample are suppressed in the ultraclean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe2 are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the 𝑎 axis as the magnetic easy axis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
To investigate the intrinsic magnetic properties of UTe2, we performed 125Te-NMR measurements on the ultraclean single-crystalline UTe2 with superconducting transition temperature 𝑇c=2.1 K and compared the results with those of the 𝑇c=1.6 K sample. The broadening of the linewidth of the NMR spectrum in the 𝑎-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6 K sample are suppressed in the ultraclean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe2 are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the 𝑎 axis as the magnetic easy axis.
2024
Ogata, S; Kitagawa, S; Kinjo, K; Ishida, K; Brando, M; Hassinger, E; Geibel, C; Khim, S
Appearance of 𝑐-axis magnetic moment in odd-parity antiferromagnetic state in CeRh2As2 revealed by 75As -NMR Journal Article
In: Physical Review B, vol. 110, pp. 214509, 2024.
@article{S.Ogata_PRB_2024,
title = {Appearance of 𝑐-axis magnetic moment in odd-parity antiferromagnetic state in CeRh2As2 revealed by 75As -NMR},
author = {S Ogata and S Kitagawa and K Kinjo and K Ishida and M Brando and E Hassinger and C Geibel and S Khim},
url = {https://arxiv.org/abs/2412.10148},
doi = {10.1103/PhysRevB.110.214509},
year = {2024},
date = {2024-12-12},
urldate = {2024-12-12},
journal = {Physical Review B},
volume = {110},
pages = {214509},
abstract = {CeRh2As2 shows the superconducting (SC) multiphase under the 𝑐-axis magnetic field, which is considered to originate from local inversion symmetry breaking at the Ce site. We reported that the antiferromagnetic (AFM) order is inside the SC phase and that the AFM state disappears at the transition field to the high-field SC phase. However, the magnetic structure in the AFM state has not been clarified yet. In this paper, we performed 75 As -NMR measurements in the SC phase in 𝐻∥[110] to identify the magnetic structure. Comparing the NMR linewidth with 𝐻∥𝑐, we found that the internal magnetic field is oriented to the 𝑐 axis. This suggests a 𝒒=0 𝐴-type AFM with the moments parallel to the 𝑐 axis. We also observed the reduction of the spin susceptibility, which indicates spin-singlet superconductivity in the low-field SC phase. This study provides an important clue to clarify the correlation between the SC multiphase, magnetism, and local inversion symmetry breaking.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
CeRh2As2 shows the superconducting (SC) multiphase under the 𝑐-axis magnetic field, which is considered to originate from local inversion symmetry breaking at the Ce site. We reported that the antiferromagnetic (AFM) order is inside the SC phase and that the AFM state disappears at the transition field to the high-field SC phase. However, the magnetic structure in the AFM state has not been clarified yet. In this paper, we performed 75 As -NMR measurements in the SC phase in 𝐻∥[110] to identify the magnetic structure. Comparing the NMR linewidth with 𝐻∥𝑐, we found that the internal magnetic field is oriented to the 𝑐 axis. This suggests a 𝒒=0 𝐴-type AFM with the moments parallel to the 𝑐 axis. We also observed the reduction of the spin susceptibility, which indicates spin-singlet superconductivity in the low-field SC phase. This study provides an important clue to clarify the correlation between the SC multiphase, magnetism, and local inversion symmetry breaking.
2023
Ogata, S; Kitagawa, S; Kibune, M; Ishida, K; Kinjo, K; Brando, M; Geibel, C; Khim, S; Hassinger, E
Investigation of the Hyperfine Coupling Constant of Locally Noncentrosymmetric Heavy-fermion Superconductor CeRh2As2 Proceedings Article
In: New Phys.: Sae Mulli, pp. 1115, 2023.
@inproceedings{S.Ogata_SCES_2023,
title = {Investigation of the Hyperfine Coupling Constant of Locally Noncentrosymmetric Heavy-fermion Superconductor CeRh2As2},
author = {S Ogata and S Kitagawa and M Kibune and K Ishida and K Kinjo and M Brando and C Geibel and S Khim and E Hassinger},
url = {https://arxiv.org/abs/2401.13291},
doi = {10.3938/NPSM.73.1115},
year = {2023},
date = {2023-12-31},
urldate = {2023-12-31},
booktitle = {New Phys.: Sae Mulli},
volume = {73},
pages = {1115},
abstract = {We performed 75As-NMR measurements in H ǁ ab to investigate the normal-state magnetic properties of CeRh2As2, a recently-discovered heavy-fermion superconductor. We compared the NMR Knight shift K with the magnetic susceptibility χab, and estimated the hyperfine coupling constant Ahf from the slope of the K − χ plot. We observed that the magnitude of Ahf,ab at the As(1) site changes at around 20 K owing to emerging the heavy-fermion state, which was also observed in Ahf at the As(2) site and in H ǁ c. The sign of Ahf,ab at the As(1) site is negative in low temperature. These are important for the analysis of the NMR results of CeRh2As2 in the superconducting state.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We performed 75As-NMR measurements in H ǁ ab to investigate the normal-state magnetic properties of CeRh2As2, a recently-discovered heavy-fermion superconductor. We compared the NMR Knight shift K with the magnetic susceptibility χab, and estimated the hyperfine coupling constant Ahf from the slope of the K − χ plot. We observed that the magnitude of Ahf,ab at the As(1) site changes at around 20 K owing to emerging the heavy-fermion state, which was also observed in Ahf at the As(2) site and in H ǁ c. The sign of Ahf,ab at the As(1) site is negative in low temperature. These are important for the analysis of the NMR results of CeRh2As2 in the superconducting state.
Ogata, S; Kitagawa, S; Kinjo, K; Ishida, K; Brando, M; Hassinger, E; Geibel, C; Khim, S
Parity transition of spin-singlet superconductivity using sub-lattice degrees of freedom Journal Article
In: Physical Review Letters, vol. 130, pp. 166001 , 2023.
@article{S.Ogata_PRL_2023,
title = {Parity transition of spin-singlet superconductivity using sub-lattice degrees of freedom},
author = {S Ogata and S Kitagawa and K Kinjo and K Ishida and M Brando and E Hassinger and C Geibel and S Khim},
url = {https://arxiv.org/abs/2304.10032},
doi = {10.1103/PhysRevLett.130.166001},
year = {2023},
date = {2023-04-19},
urldate = {2023-04-19},
journal = {Physical Review Letters},
volume = {130},
pages = {166001 },
abstract = {Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh2As2, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sub-lattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh2As2 is considered as the first example of multiple SC phases owing to this sub-lattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present work reveals unique SC properties originating from the locally noncentrosymmetric characteristics. },
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh2As2, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sub-lattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh2As2 is considered as the first example of multiple SC phases owing to this sub-lattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present work reveals unique SC properties originating from the locally noncentrosymmetric characteristics.
2022
Kibune, M; Kitagawa, S; Kinjo, K; Ogata, S; Manago, M; Taniguchi, T; Ishida, K; Brando, M; Hassinger, E; Rosner, H; Geibel, C; Khim, S
Observation of Antiferromagnetic Order as Odd-Parity Multipoles inside the Superconducting Phase in CeRh2As2 Journal Article
In: Physical Review Letters, vol. 128, no. 05, pp. 057002, 2022.
@article{S.Kitagawa_PRL_2022,
title = {Observation of Antiferromagnetic Order as Odd-Parity Multipoles inside the Superconducting Phase in CeRh2As2},
author = {M Kibune and S Kitagawa and K Kinjo and S Ogata and M Manago and T Taniguchi and K Ishida and M Brando and E Hassinger and H Rosner and C Geibel and S Khim},
url = {https://arxiv.org/abs/2112.07081},
doi = {10.1103/PhysRevLett.128.057002},
year = {2022},
date = {2022-02-03},
urldate = {2022-02-03},
journal = {Physical Review Letters},
volume = {128},
number = {05},
pages = {057002},
abstract = {Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we present evidence for antiferromagnetic (AFM) order in CeRh2As2 (SC transition temperature TSC ∼ 0.37 K ), wherein the Ce site breaks the local inversion symmetry. The evidence is based on the observation of different extents of broadening of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites. This AFM ordering breaks the inversion symmetry of this system, resulting in the activation of an odd-parity magnetic multipole. Moreover, the onset of antiferromagnetism TN within an SC phase, with TN < TSC , is quite unusual in systems wherein superconductivity coexists or competes with magnetism. Our observations show that CeRh2As2 is a promising system to study how the absence of local inversion symmetry induces or influences unconventional magnetic and SC states, as well as their interaction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we present evidence for antiferromagnetic (AFM) order in CeRh2As2 (SC transition temperature TSC ∼ 0.37 K ), wherein the Ce site breaks the local inversion symmetry. The evidence is based on the observation of different extents of broadening of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites. This AFM ordering breaks the inversion symmetry of this system, resulting in the activation of an odd-parity magnetic multipole. Moreover, the onset of antiferromagnetism TN within an SC phase, with TN < TSC , is quite unusual in systems wherein superconductivity coexists or competes with magnetism. Our observations show that CeRh2As2 is a promising system to study how the absence of local inversion symmetry induces or influences unconventional magnetic and SC states, as well as their interaction.