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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：5 Percentile：92.42(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

Dry synthesis of brannerite (UTi$$_{2}$$O$$_{6}$$) by mechanochemical treatment

Akiyama, Daisuke*; Mishima, Tomoki*; Okamoto, Yoshihiro; Kirishima, Akira*

High Temperature Materials and Processes, 42(1), p.20220268_1 - 20220268_9, 2023/04

https://www.degruyter.com/document/doi/10.1515/htmp-2022-0268/html

A powder mixture of UO$$_{2}$$ and TiO$$_{2}$$ was mechanochemically treated in a planetary ball mill under Ar atmosphere for 1 h using a tungsten carbide vial and balls as the milling medium. Such mechanochemical (MC) treatment reduced the crystallinity of UO$$_{2}$$ and TiO$$_{2}$$. The mechanochemically treated powder mixture was heated at 973-1573K for 6 h under Ar atmosphere and analyzed by X-ray diffraction analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure analysis. UTi$$_{2}$$O$$_{6}$$ did not form below 1373K without MC treatment and only the starting materials were observed. At 1473 and 1573K, a small amount of UTi$$_{2}$$O$$_{6}$$ and equal amounts of UTi$$_{2}$$O$$_{6}$$ and UO$$_{2}$$ were formed, respectively. The mechanochemically treated sample produced nearly pure UTi$$_{2}$$O$$_{6}$$ containing small amounts of UO$$_{2}$$ impurities when heated above 1173K for 6 h. UTi$$_{2}$$O$$_{6}$$ was highly crystalline and uniform regardless of the synthesis temperature.

Journal Articles

Single crystal growth of superconducting UTe$$_2$$ by molten salt flux method

Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

Physical Review Materials (Internet), 6(7), p.073401_1 - 073401_10, 2022/07

https://doi.org/10.1103/PhysRevMaterials.6.073401
 Times Cited Count：16 Percentile：88.61(Materials Science, Multidisciplinary)

The molten salt flux method is applied as a new synthetic route for the single crystals of the spin-triplet superconductor UTe$$_2$$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at $$T_{rm c}=2.1$$ K, which is the highest $$T_{rm c}$$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below $$T_{rm c}$$. These results indicate that the increase of $$T_{rm c}$$ in UTe$$_2$$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

Journal Articles

Unconventional superconductivity in UTe$$_2$$

Aoki, Dai*; Brison, J.-P.*; Flouquet, J.*; Ishida, Kenji*; Knebel, G.*; Tokunaga, Yo; Yanase, Yoichi*

Journal of Physics; Condensed Matter, 34(24), p.243002_1 - 243002_41, 2022/06

https://doi.org/10.1088/1361-648X/ac5863
 Times Cited Count：54 Percentile：87.73(Physics, Condensed Matter)

Journal Articles

Core-level photoelectron spectroscopy study of UTe$$_{2}$$

Fujimori, Shinichi; Kawasaki, Ikuto; Takeda, Yukiharu; Yamagami, Hiroshi; Nakamura, Ai*; Homma, Yoshiya*; Aoki, Dai*

Journal of the Physical Society of Japan, 90(1), p.015002_1 - 015002_2, 2021/01

https://doi.org/10.7566/JPSJ.90.015002
 Times Cited Count：12 Percentile：79.44(Physics, Multidisciplinary)

Journal Articles

Electronic structure of UTe$$_2$$ studied by photoelectron spectroscopy

Fujimori, Shinichi; Kawasaki, Ikuto; Takeda, Yukiharu; Yamagami, Hiroshi; Nakamura, Ai*; Homma, Yoshiya*; Aoki, Dai*

Journal of the Physical Society of Japan, 88(10), p.103701_1 - 103701_5, 2019/10

https://doi.org/10.7566/JPSJ.88.103701
 Times Cited Count：28 Percentile：85.18(Physics, Multidisciplinary)

Journal Articles

Odd-parity electronic multipolar ordering in URu$$_2$$Si$$_2$$; Conclusions from Si and Ru NMR measurements

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*; Harima, Hisatomo*

Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06

AA2018-0180.pdf:1.09MB

https://doi.org/10.1103/PhysRevB.97.235142
 Times Cited Count：21 Percentile：68.8(Materials Science, Multidisciplinary)

Journal Articles

Magnetoresistance and Hall effect of antiferromagnetic uranium compound URhIn$$_5$$

Haga, Yoshinori; Matsumoto, Yuji*; Pospisil, J.; Tateiwa, Naoyuki; Yamamoto, Etsuji; Yamamura, Tomoo*; Fisk, Z.*

Journal of Physics; Conference Series, 807(1), p.012015_1 - 012015_4, 2017/04

https://doi.org/10.1088/1742-6596/807/1/012015
 Times Cited Count：1 Percentile：34.26(Physics, Condensed Matter)

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：89.51(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

Pressure-temperature-field phase diagram in the ferromagnet U$$_3$$P$$_4$$

Araki, Shingo*; Hayashida, Minami*; Nishiumi, Naoto*; Manabe, Hiroki*; Ikeda, Yoichi*; Kobayashi, Tatsuo*; Murata, Keizo*; Inada, Yoshihiko*; Wi$'s$niewski, P.*; Aoki, Dai*; et al.

Journal of the Physical Society of Japan, 84(2), p.024705_1 - 024705_8, 2015/02

https://doi.org/10.7566/JPSJ.84.024705
 Times Cited Count：9 Percentile：55.91(Physics, Multidisciplinary)

Journal Articles

Resonant magnetic X-ray scattering study of UPd$$_2$$Al$$_3$$

Ishii, Kenji; Kuzushita, Kaori; Murakami, Yoichi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

Journal of the Physical Society of Japan, 75(Suppl.), p.102 - 104, 2006/08

UPd$$_2$$Al$$_3$$ is an attractive material because of the coexistence of the antiferromagnetic order below $$T_N$$ = 14.5 K and superconductivity below $$T_c$$ = 2 K. In order to discuss the coupling between magnetism and superconductivity by resonant magnetic X-ray scattering (RMXS), nature of the resonance at each absorption edge should be clarified before the measurements across $$T_c$$. Therefore we performed RMXS study from U $$M_1$$ to $$M_4$$ edge at $$T_c < T < T_N$$. In addition to a huge resonance at $$M_4$$-edge, we observed a resonant feature at $$M_2$$-edge which corresponds to the transition from $$3p_{1/2}$$ to $$6d$$ orbitals, while resonance at $$M_1$$-edge and $$M_3$$-edge is rather small.

Journal Articles

Soft X-ray magnetic circular dichroism study of ferromagnetic uranium compounds

Okane, Tetsuo; Takeda, Yukiharu; Fujimori, Shinichi; Saito, Yuji; Okamoto, Jun*; Mamiya, Kazutoshi*; Muramatsu, Yasuji*; Fujimori, Atsushi; Ochiai, Akira*; Haga, Yoshinori; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.105 - 106, 2006/08

no abstracts in English

Journal Articles

Soft X-ray magnetic circular dichroism study of UFe$$_2$$

Okane, Tetsuo; Takeda, Yukiharu; Fujimori, Shinichi; Terai, Kota; Saito, Yuji; Muramatsu, Yasuji; Fujimori, Atsushi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

Physica B; Condensed Matter, 378-380, p.959 - 960, 2006/05

https://doi.org/10.1016/j.physb.2006.01.366
 Times Cited Count：4 Percentile：22.76(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Soft X-ray synchrotron radiation photoemission study on uranium compounds

Fujimori, Shinichi; Terai, Kota; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Muramatsu, Yasuji; Fujimori, Atsushi; Yamagami, Hiroshi*; Ikeda, Shugo; Matsuda, Tatsuma; et al.

Physica B; Condensed Matter, 378-380, p.995 - 996, 2006/05

https://doi.org/10.1016/j.physb.2006.01.506
 Times Cited Count：2 Percentile：12.58(Physics, Condensed Matter)

Recently, photoemission experiments in soft X-ray region have attracted much attention due to their high sensitivities for bulk electronic structures of strongly correlated electron system. We have carried out the high-resolution photoemission experiments on some uranium compounds using soft X-ray synchrotron radiation from SPring-8 to understand their electronic structures. Bulk- and U 5$$f$$-sensitive band structure and Fermi surface were obtained for itinerant U 5$$f$$ compounds UFeGa$$_5$$ and USb$$_2$$, and they are compared with the results of the band structure calculations treating U 5$$f$$ states as being itinerant. In addition, we show the results of photoemission study on some heavy fermion compounds such as UPd$$_2$$Al$$_3$$ and UNi$$_2$$Al$$_3$$. The temperature dependences of the U 5$$f$$ electronic structure of UPd$$_2$$Al$$_3$$ will be also reported.

Journal Articles

Itinerant U 5$$f$$ band states in the layered compound UFeGa$$_5$$ observed by soft X-ray angle-resolved photoemission spectroscopy

Fujimori, Shinichi; Terai, Kota; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Muramatsu, Yasuji; Fujimori, Atsushi; Yamagami, Hiroshi*; Tokiwa, Yoshifumi*; Ikeda, Shugo; et al.

Physical Review B, 73(12), p.125109_1 - 125109_6, 2006/03

https://doi.org/10.1103/PhysRevB.73.125109
 Times Cited Count：22 Percentile：67.07(Materials Science, Multidisciplinary)

We have performed angle-resolved photoemission spectroscopy (ARPES) experiments on paramagnetic UFeGa$$_5$$ using soft X-ray synchrotron radiation ($$hnu$$=500 eV) and derived the bulk- and U 5$$f$$-sensitive electronic structure of UFeGa$$_5$$. Although the agreement between the experimental band strucure and the LDA calculation treating U 5$$f$$ electrons as beeing itinerant is qualitative, the morphology of the Fermi surface is well explained by the calculation. This result claims that the importance of the electron correlation effect even for the itinerant U 5$$f$$ compound.

Journal Articles

Electronic properties of transuranium compounds with HoCoGa$$_5$$-type tetragonal crystal structure

Maehira, Takahiro*; Hotta, Takashi; Ueda, Kazuo*; Hasegawa, Akira*

New Journal of Physics (Internet), 8(2), p.24_1 - 24_20, 2006/02

https://doi.org/10.1088/1367-2630/8/2/024
 Times Cited Count：16 Percentile：64.65(Physics, Multidisciplinary)

By using a relativistic band-structrue calculation method, we investigate energy band structures and the Fermi surfaces of NpTGa$$_5$$, PuTGa$$_5$$, and AmCoGa$$_5$$ with transition metal atoms T. It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the large hybridization between $$5f$$ and Ga $$4p$$ electrons. For PuTGa$$_5$$, we observe several cylindrical sheets of Fermi surfaces with large volume for T=Co, Rh, and Ir. It is also found that the Fermi surfaces of NpFeGa$$_5$$, NpCoGa$$_5$$, and NpNiGa$$_5$$ are similar to those of UCoGa$$_5$$, UNiGa$$_5$$, and PuCoGa$$_5$$, respectively, except for small details. For AmCoGa$$_5$$, the Fermi surfaces are found to consist of large cylindrical electron sheets and small closed hole sheets, similar to PuCoGa$$_5$$. The similarity is basically understood by a rigid-band picture.

Journal Articles

Anisotropic superconducting gap in transuranium superconductor PuRhGa$$_{5}$$; Ga NQR study on a single crystal

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, 74(6), p.1710 - 1713, 2005/06

https://doi.org/10.1143/JPSJ.74.1710
 Times Cited Count：78 Percentile：90.09(Physics, Multidisciplinary)

$$^{69,71}$$Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa$$_{5}$$ with $$T_{c}sim 9$$ K. We have observed a $$^{69}$$Ga NQR line at $$sim$$29.15 MHz, and assigned it to the $$4i$$ Ga site using the NMR results. The $$^{69}$$Ga NQR spin-lattice relaxation rate $$1/T_{1}$$ shows no coherence peak just below $$T_{rm c}$$, but obeys $$T^{3}$$ behavior below $$T_{rm c}$$. This result strongly suggests that PuRhGa$$_{5}$$ is an unconventional superconductor having an anisotropic superconducting gap. The gap amplitude 2$$Delta_{0}(Trightarrow 0)simeq5k_{rm B}T_{rm c}$$ and the residual density of states $$N_{rm res}(T=0)/N_{rm 0}(T=T_{rm c})simeq$$ 0.25 have been determined assuming a simple polar function of the form $$Delta(theta,phi)$$=$$Delta_{0}costheta$$, where $$theta$$ and $$phi$$ are angular parameters on the Fermi surface.

Journal Articles

$$^{31}$$P-NMR study of the uranium-based filled skutterudite compound UFe$$_4$$P$$_{12}$$

Tokunaga, Yo; Matsuda, Tatsuma; Sakai, Hironori; Kato, Harukazu*; Kambe, Shinsaku; Walstedt, R. E.; Haga, Yoshinori; Onuki, Yoshichika; Yasuoka, Hiroshi

Physical Review B, 71(4), p.045124_1 - 045124_5, 2005/01

https://doi.org/10.1103/PhysRevB.71.045124
 Times Cited Count：10 Percentile：42.74(Materials Science, Multidisciplinary)

$$^{31}$$P NMR measurements have been performed on the uranium-based ferromagnetic insulator UFe$$_4$$P$$_{12}$$ with $$T_C= 3.15$$ K. The field-orientation dependence of the hyperfine interaction has been measured using a single crystal, and the results compared with a point-dipolar field calculation assuming local moments at the U sites. We have also measured the field and temperature dependence of the nuclear spin-lattice relaxation rate ($$1/T_1$$) in several fields between 1.0 and 5.5 T at temperatures between 1.4 and 300 K. The results are discussed on the basis of a localized picture for the uranium 5f electrons.

Journal Articles

Direct observation of $$^{235}$$U NMR in an itinerant 5${it f}$ electron system, USb$$_{2}$$

Kato, Harukazu*; Sakai, Hironori; Ikushima, Kenji*; Kambe, Shinsaku; Tokunaga, Yo; Aoki, Dai*; Haga, Yoshinori; Onuki, Yoshichika; Yasuoka, Hiroshi; Walstedt, R. E.

Journal of the Physical Society of Japan, 73(8), p.2085 - 2088, 2004/08

https://doi.org/10.1143/JPSJ.73.2085
 Times Cited Count：12 Percentile：57.62(Physics, Multidisciplinary)

Diret AFNMR studies of $$^{235}$$U, $$^{121}$$Sb and $$^{123}$$Sb nuclear spins have been carried out in the antiferromagnetic state of USb$$_{2}$$. The central $$^{235}$$U transition have been found as 217.2MHz based on several tests. The $$^{235}$$U hyperfine coupling constant is estimated as 147T/mB. This is the first observation of $$^{235}$$U NMR in a metallic compound.

Journal Articles

First observation of the de Haas-van Alphen effect in NpNiGa$$_{5}$$

Aoki, Dai*; Yamamoto, Etsuji; Homma, Yoshiya*; Shiokawa, Yoshinobu; Nakamura, Akio; Haga, Yoshinori; Settai, Rikio*; Onuki, Yoshichika

Journal of the Physical Society of Japan, 73(3), p.519 - 522, 2004/03

https://doi.org/10.1143/JPSJ.73.519
 Times Cited Count：37 Percentile：79.57(Physics, Multidisciplinary)

no abstracts in English

68 (Records 1-20 displayed on this page)