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Journal Articles

Anomalous vortex dynamics in the spin-triplet superconductor UTe$$_2$$

Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.

Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10

https://doi.org/10.1103/PhysRevB.108.144502
 Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)

The vortex dynamics in the spin-triplet superconductor, UTe$$_2$$, are studied by measuring the DC electrical resistivity with currents along the $$a$$-axis under magnetic fields along the $$b$$-axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.

Journal Articles

Field induced multiple superconducting phases in UTe$$_2$$ along hard magnetic axis

Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori

Physical Review Letters, 130(19), p.196002_1 - 196002_6, 2023/05

https://doi.org/10.1103/PhysRevLett.130.196002
 Times Cited Count：6 Percentile：93.15(Physics, Multidisciplinary)

The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields ($$H$$) along the hard magnetic $$b$$-axis using a high-quality single crystal with $$T_{rm c}$$ = 2.1 K. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the $$H^{ast}$$ of $$sim15$$ T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near $$H^{ast}$$, indicating an intermediate SC phase characterized by small flux pinning forces.

Journal Articles

Partial breakdown of translation symmetry at a structural quantum critical point associated with a ferroelectric soft mode

Ishii, Yui*; Yamamoto, Arisa*; Sato, Naoki*; Nambu, Yusuke*; Kawamura, Seiko; Murai, Naoki; Ohara, Koji*; Kawaguchi, Shogo*; Mori, Takao*; Mori, Shigeo*

Physical Review B, 106(13), p.134111_1 - 134111_7, 2022/10

https://doi.org/10.1103/PhysRevB.106.134111
 Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)

Journal Articles

Homogeneity of (U, $$M$$)O$$_2$$ ($$M$$ = Th, Np) prepared by supercritical hydrothermal synthesis

Shirasaki, Kenji*; Tabata, Chihiro*; Sunaga, Ayaki*; Sakai, Hironori; Li, D.*; Konaka, Mariko*; Yamamura, Tomoo*

Journal of Nuclear Materials, 563, p.153608_1 - 153608_11, 2022/05

https://doi.org/10.1016/j.jnucmat.2022.153608
 Times Cited Count：2 Percentile：50.96(Materials Science, Multidisciplinary)

We focused on the direct synthesis of (U, $$M$$)O$$_2$$ solid solution ($$M$$=Th, Np) by extending our recent progress in hydrothermal synthesis with additives. The homogeneity of the (U, $$M$$)O$$_2$$ ($$M$$ = Th, Np) systems prepared by supercritical hydrothermal reactions was investigated through crystallographic analysis based on Vegard's law, and the $$^{23}$$Na nuclear magnetic resonance (NMR) measurement of (U, Np, Na)O$$_2$$ solid solutions. Our experimental and analytical results revealed that (i) an optimal additive is ammonium carbonate and starting uranium valence is IV in the case of (U, Th)O$$_{2+x}$$, and (ii) an optimal additive is ethanol and starting uranium valence is VI in the case of (U, Np)O$$_{2+x}$$, for producing the homogeneous solid solutions by hydrothermal synthesis.

Journal Articles

Bound spinon excitations in the spin-$$frac{1}{2}$$ anisotropic triangular antiferromagnet Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$

Nawa, Kazuhiro*; Hirai, Daigoro*; Kofu, Maiko; Nakajima, Kenji; Murasaki, Ryo*; Kogane, Satoshi*; Kimata, Motoi*; Nojiri, Hiroyuki*; Hiroi, Zenji*; Sato, Taku*

Physical Review Research (Internet), 2(4), p.043121_1 - 043121_11, 2020/12

https://doi.org/10.1103/PhysRevResearch.2.043121

The spin excitations of the $$S$$ = $$frac{1}{2}$$ anisotropic triangular antiferromagnet Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$ were investigated by inelastic neutron-scattering experiments. The spin excitation spectrum exhibits sharp dispersive modes in addition to a spinonlike continuum. The consistency with the simulated spectrum based on the random-phase approximation is better for Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$ than for Cs$$_{2}$$CuCl$$_{4}$$, indicating that the spin system in the former remains closer to a Tomonaga-Luttinger liquidlike disordered state.

Journal Articles

Dynamical spin-to-charge conversion on the edge of quantum spin Hall insulator

Araki, Yasufumi; Misawa, Takahiro*; Nomura, Kentaro*

Physical Review Research (Internet), 2(2), p.023195_1 - 023195_11, 2020/05

https://doi.org/10.1103/PhysRevResearch.2.023195

Journal Articles

Barnett effect in paramagnetic states

Ono, Masao; Chudo, Hiroyuki; Harii, Kazuya; Okayasu, Satoru; Matsuo, Mamoru; Ieda, Junichi; Takahashi, Ryo*; Maekawa, Sadamichi; Saito, Eiji

Physical Review B, 92(17), p.174424_1 - 174424_4, 2015/11

https://doi.org/10.1103/PhysRevB.92.174424
 Times Cited Count：30 Percentile：74.42(Materials Science, Multidisciplinary)

Journal Articles

Reentrant superconductivity driven by quantum tricritical fluctuations in URhGe; Evidence from $$^{59}$$Co NMR in URh$$_{0.9}$$Co$$_{0.1}$$Ge

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku; Araki, Shingo*

Physical Review Letters, 114(21), p.216401_1 - 216401_5, 2015/05

https://doi.org/10.1103/PhysRevLett.114.216401
 Times Cited Count：51 Percentile：89.64(Physics, Multidisciplinary)

Our measurements of the $$^{59}$$Co NMR spin-spin relaxation in URh$$_{0.9}$$Co$$_{0.1}$$Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at $$H_Rapprox13$$ T, around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We show that critical fluctuations develop in the same limited region near the field $$H_R$$ as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point.

Journal Articles

Theoretical study of resonant inelastic X-ray scattering spectrum in the Hubbard ladder

Tsutsui, Kenji; Toyama, Takami*; Maekawa, Sadamichi*

Physica C, 470(Suppl.1), p.S232 - S233, 2010/12

https://doi.org/10.1016/j.physc.2009.10.042
 Times Cited Count：0 Percentile：0(Physics, Applied)

The spectra of the Cu $$K$$-edge Resonant inelastic X-ray scattering on the ladder cuprates are calculated by using the exact diagonalization method. So far it has been suggested that the momentum-dependence of the spectra on the ladder system is related with the formation of the spin singlet in the ground state. It has also revealed that the stabilization of the spin singlet strongly depends on the sign of the diagonal hopping of holes. In this study, in order to clarify the relationship between the spectra and the formation of the singlet state, the dependence of the spectra on the diagonal hopping of holes is examined. We find that the feature of the spectra is actually changed by the hopping and conclude that the resonant inelastic X-ray scattering can reveal the formation of the spin singlet state in the ladder system.

Journal Articles

Anisotropic transport properties of NpPd$$_5$$Al$$_2$$

Matsuda, Tatsuma; Haga, Yoshinori; Aoki, Dai*; Homma, Yoshiya*; Tateiwa, Naoyuki; Yamamoto, Etsuji; Onuki, Yoshichika

Journal of Physics; Conference Series, 200, p.012113_1 - 012113_4, 2010/02

https://doi.org/10.1088/1742-6596/200/1/012113
 Times Cited Count：2 Percentile：64.43(Materials Science, Multidisciplinary)

The anisotropic superconductor NpPd$$_5$$Al$$_2$$ with ZrNi$$_2$$Al$$_5$$-type tetragonal structure was studied by means of electrical resistivity and Hall effect in the normal state. The temperature dependence of electrical resistivity $$rho(T)$$ shows a large anisotropic behavior. The resistivity for $$J|$$[001] is larger than that for $$J|$$[100] in the whole temperature region. At high temperatures $$rho(T)$$ is proportional to $$-log T$$, which is characteristic behavior in Kondo effect. The field dependence of Hall resistivity $$rho_{rm H}$$ shows a linear dependence up to 55 kOe with a large slope for the field. The slope of $$rho_{rm H}$$ for field along $$c$$-axis is negative, but for field along $$a$$-axis, the slope dramatically changed from negative to positive with increasing temperature.

Journal Articles

Advanced neutron shielding material using zirconium borohydride and zirconium hydride

Hayashi, Takao; Tobita, Kenji; Nakamori, Yuko*; Orimo, Shinichi*

Journal of Nuclear Materials, 386-388, p.119 - 121, 2009/04

https://doi.org/10.1016/j.jnucmat.2008.12.073
 Times Cited Count：81 Percentile：98.22(Materials Science, Multidisciplinary)

Neutron transport calculations have been carried out to assess the capability of zirconium borohydride (Zr(BH$$_{4}$$)$$_{4}$$) and zirconium hydride (ZrH$$_{2}$$) as advanced shield materials, because excellent shields can be used to protect outer structural materials from serious activation. The neutron shielding capability of Zr(BH$$_{4}$$)$$_{4}$$ is lower than ZrH$$_{2}$$, even though the hydrogen density of Zr(BH$$_{4}$$)$$_{4}$$ is slightly higher than that of ZrH$$_{2}$$. High-Z atoms are effective in neutron shielding as well as hydrogen atoms. The combination of steel and Zr(BH$$_{4}$$)$$_{4}$$ can improve the neutron shielding capability. The combinations of (Zr(BH$$_{4}$$)$$_{4}$$ + F82H) and (ZrH$$_{2}$$ + F82H) can reduce the thickness of the shield by 6.5% and 19% compared to (water + F82H), respectively. The neutron flux for Zr(BH$$_{4}$$)$$_{4}$$ is drastically reduced in the range of neutron energy below 100 eV compared to other materials, due to the effect of boron, which can lead to a reduction of radwaste from fusion reactors.

Journal Articles

Ga NQR relaxation rates in superconductor PuRhGa$$_5$$

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Physics and Chemistry of Solids, 68(11), p.2103 - 2106, 2007/11

https://doi.org/10.1016/j.jpcs.2007.08.039
 Times Cited Count：1 Percentile：7.44(Chemistry, Multidisciplinary)

A lot of attention is currently focused on Pu-based superconductors. These systems have relatively high superconducting (SC) transition temperatures, ${it i.e.,}$ $$T_{rm c}simeq$$ 18 K for PuCoGa$$_{5}$$ and $$T_{rm c}simeq$$ 9 K for PuRhGa$$_{5}$$. Both compounds crystallize in the tetragonal HoCoGa$$_{5}$$ (115) structure, which is well known for the heavy-fermion SC systems Ce$$T$$In$$_{5}$$ ($$T$$=Co, Rh, Ir)with $$T_{rm c} sim$$ 2 K at most. Recently, NMR and NQR experiments have been reported for PuCoGa$$_{5}$$ by Curro et al. and for PuRhGa$$_{5}$$ by our group. In both cases, measurements of $$1/T_{1}$$ using NQR have revealed that the Pu115 superconductors show unconventional superconductivity with an anisotropic gap. Now we have measured the more detailed data of $$1/T_{1}$$ for NQR lines in PuRhGa$$_5$$, especially focusing on the low-lying magnetic excitation in the normal state. From the viewpoint of spin-fluctuations, we will discuss the difference between PuRhGa$$_{5}$$ and PuCoGa$$_{5}$$ and between superconducting Pu115 and non-superconducting An115 series.

Journal Articles

Single crystal growth, superconductivity and Fermi surface study of plutonium compounds

Haga, Yoshinori; Aoki, Dai*; Yamagami, Hiroshi*; Matsuda, Tatsuma; Nakajima, Kunihisa; Arai, Yasuo; Yamamoto, Etsuji; Nakamura, Akio; Homma, Yoshiya*; Shiokawa, Yoshinobu*; et al.

Journal of Alloys and Compounds, 444-445, p.114 - 118, 2007/10

https://doi.org/10.1016/j.jallcom.2006.11.206
 Times Cited Count：3 Percentile：28.04(Chemistry, Physical)

We report the first dHvA study in plutonium compound PuIn$$_3$$ with the cubic AuCu$$_3$$ type structure, which can be regarded as a reference compound of PuCoGa$$_5$$. The result of the angular dependence of the dHvA frequency, which corresponds to the extremal cross section of the Fermi surface perpendicular to the field direction, was analyzed by the band calculations. The experimental data agree well with the theory, indicating that the 5f electrons can be treated as itinerant ones. The experimental dHvA study for plutonium-based superconductors such as PuCoGa$$_5$$ are also desired but more challenging because the superconducting mixed state extremely weaken the dHvA amplitude.

Journal Articles

Anisotropic spin fluctuations and anomalies of nuclear quadrupole interactions in the itinerant antiferromagnet NpCoGa$$_5$$; $$^{59}$$Co NMR and $$^{69,71}$$Ga NMR/NQR studies

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Physical Review B, 76(2), p.024410_1 - 024410_14, 2007/07

https://doi.org/10.1103/PhysRevB.76.024410
 Times Cited Count：19 Percentile：62.08(Materials Science, Multidisciplinary)

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)experiments have been performed on a single crystal of NpCoGa$$_5$$ with a N$'e$el temperature $$T_{rm N}$$=47 K. Knight shift, electric field gradient (EFG), frequency, and asymmetry parameter of the EFG are deduced for each site. These parameters are confirmed by NQR measurements in zero field. Hyperfine tensors for each site are deduced. Antiferromagnetic NMR spectra in zero field were also observed. A sharp anisotropy for spin fluctuations in NpCoGa$$_{5}$$ has also been demonstrated.

Journal Articles

Magnetic and magnetotransport properties in nanogranular Co/C$$_{60}$$-Co film with high magnetoresistance

Sakai, Seiji; Yakushiji, Kei*; Mitani, Seiji*; Sugai, Isamu; Takanashi, Koki*; Naramoto, Hiroshi*; Avramov, P.; Lavrentiev, V.*; Narumi, Kazumasa; Maeda, Yoshihito

Materials Transactions, 48(4), p.754 - 758, 2007/04

https://doi.org/10.2320/matertrans.48.754
 Times Cited Count：9 Percentile：51.27(Materials Science, Multidisciplinary)

Magnetic properties were investigated for the alternately deposited film of C$$_{60}$$ and Co which has found to exhibit tunnel magnetoresistance (MR) of 10-80 %. Magnetic field and temperature dependences of magnetization showed typical superparamagnetic behaviors with the blocking temperature of 40 K. The magnetization curve at 300 K was well fitted by the Langevin function with the size distribution of Co particles, and the mean diameter and size distribution were evaluated to be 3.1 nm and 1 nm, respectively. Based on the magnetic properties, the detailed structure and magnetotransport properties are discussed.

Journal Articles

Enhancement of relaxation rates in the normal state of superconductor PuRhGa$$_5$$:NQR relaxation study

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e118 - e119, 2007/03

The spin-lattice relaxation rates ($$1/T_1$$) have been measured under zero fieldusing nuclear quadrupole resonance (NQR) linesin superconductor PuRhGa$$_5$$ and Pauli-paramagnet LuCoGa$$_5$$. In the reference LuCoGa$$_5$$ with fully-occupied $$4f$$ shell, the $$1/T_1$$ shows the constant behavior of $$(T_1T)^{-1}=0.495pm0.002$$ (sec$$cdot$$K)$$^{-1}$$. On the other hand, in PuRhGa$$_5$$, $$1/T_1$$ is much larger than in LuCoGa$$_5$$and the $$1/T_1propto T$$ behavior below $$sim$$30 K is seen, where its $$(T_{1}T)^{-1}$$ value is 3.27 $$pm$$ 0.005 (sec$$cdot$$K)$$^{-1}$$. These results suggest a development of coherent Fermi liquid stateincorporated with $$5f$$ electronsbelow $$sim$$30 K in PuRhGa$$_5$$.

Journal Articles

Transport properties in the ferromagnet UTeS

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Haga, Yoshinori; Onuki, Yoshichika*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1718 - 1720, 2007/03

no abstracts in English

Journal Articles

$$^{57}$$Fe M$"o$ssbauer spectroscopy of NpFeGa$$_{5}$$ in magnetic field

Homma, Yoshiya*; Nasu, Saburo; Nakamura, Akio; Aoki, Dai*; Haga, Yoshinori; Metoki, Naoto; Sakai, Hironori; Ikeda, Shugo; Shiokawa, Yoshinobu*; Onuki, Yoshichika

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.440 - 442, 2007/03

https://doi.org/10.1016/j.jmmm.2006.10.500
 Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)

$$^{57}$$Fe M$"o$ssbauer measurements of NpFeGa$$_{5}$$ has been carried out in external field at 10 kOe. The negative quadrupole splitting QS was enhanced between 70 and 110 K. Negligibly small QS in the paramagnetic state was verified by a measurement of the spectrum in the applied field of 10 kOe. A correlation between the magnetic state and the electric field gradient implies that the origin of hyperfine magnetic field is not only due to the dipole field from magnetic Np atoms, but also from magnetic Fe atoms.

Journal Articles

Magnetic and transport properties in ferromagnet UTeS

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Haga, Yoshinori; Onuki, Yoshichika*

Journal of the Physical Society of Japan, 75(12), p.124706_1 - 124706_5, 2006/12

https://doi.org/10.1143/JPSJ.75.124706
 Times Cited Count：6 Percentile：41.77(Physics, Multidisciplinary)

The ferromagnet UTeS with the Curie temperature $$T_{rm C}$$ = 87 K has been studied by measuring the magnetization, magnetic susceptibility, electrical resistivity, magnetoresistance, Hall resistivity and specific heat. The magnetization was found to be highly anisotropic. The easy-axis was determined as the [001] direction,whereas the hard-axis magnetization for $$H$$ $$parallel$$ [100] decreases below $$T_{rm C}$$, indicating an antiferromagnetic feature. The electrical resistivity also indicates a peak structure at $$T_{rm C}$$. These results suggest that UTeS is a canted ferromagnet. A large negative magnetoresistance was also observed around $$T_{rm C}$$. From the result of the Hall resistivity measurement, UTeS is thought to be a semimetal. This is consistent with the large value of the electrical resistivity and the small electronic specific heat coefficient.

Journal Articles

NMR shift measurements of $$^{69}$$Ga in unconventional superconductor PuRhGa$$_{5}$$

Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.50 - 52, 2006/08

Very recently, we have succeeded in NMR/NQR measurements for PuRhGa$$_{5}$$. PuRhGa$$_{5}$$ is a superconductor with $$T_{c}$$$$approx$$9 K, which is isomorphic to PuCoGa$$_{5}$$ with the higher $$T_{c}$$=18 K. We have reported that PuRhGa$$_{5}$$ is an unconventional superconductor with an anisotropic gap, through the measurement of NQR spin-lattice relaxation rate $$1/T_{1}$$ , while PuCoGa$$_{5}$$ is also reported to be such an anisotropic superconductor. The Knight shift $$K$$ and $$1/T_{1}$$ of NMR under applied field for the normal state of PuRhGa$$_{5}$$ suggest an anisotropic feature of hyperfine and/or spin fluctuation in this system. We will outline the superconducting state and report the nature of the normal state based on the basis of $$K$$ and $$1/T_{1} T$$ results. The difference between PuRhGa$$_{5}$$ and PuCoGa$$_{5}$$ will be also discussed.

66 (Records 1-20 displayed on this page)