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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

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

Element-specific insight into ferromagnetic stability in UCoGe revealed by soft X-ray magnetic circular dichroism

Takeda, Yukiharu; Posp$'i$$v{s}$il, J.*; Yamagami, Hiroshi; Yamamoto, Etsuji; Haga, Yoshinori

Physical Review B, 108(8), p.085129_1 - 085129_10, 2023/08

Journal Articles

Ferromagnetic crossover within the ferromagnetic order of U$$_{7}$$Te$$_{12}$$

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

Journal of the Physical Society of Japan, 92(3), p.034704_1 - 034704_5, 2023/03

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

We investigate the physical properties of a single crystal of uranium telluride U$$_{7}$$Te$$_{12}$$. We have confirmed that U$$_{7}$$Te$$_{12}$$ crystallizes in the hexagonal structure with three nonequivalent crystallographic uranium sites. The paramagnetic moments are estimated to be approximately 1 $$mu_{B}$$ per the uranium site, assuming a uniform moment on all the sites. A ferromagnetic phase transition occurs at $$T_{rm C}$$= 48 K, where the in-plane magnetization increases sharply, whereas the out of-plane component does not increase significantly. With decreasing temperature further below $$T_{rm C}$$ under field-cooling conditions, the out-of-plane component increases rapidly around T$$^{star}$$= 26 K. In contrast, the in-plane component hardly changes at T$$^{star}$$. Specific heat measurement indicates no $$lambda$$-type anomaly around T$$^{star}$$, so this is a cross-over suggesting a reorientation of the ordering moments or successive magnetic ordering on the part of the multiple uranium sites.

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

 Times Cited Count:9 Percentile:85.45(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

Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe$$_2$$

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

Journal of Physics; Condensed Matter, 34(17), p.175601_1 - 175601_7, 2022/04

 Times Cited Count:14 Percentile:90.93(Physics, Condensed Matter)

Journal Articles

Electronic structure of ThPd$$_2$$Al$$_3$$; Impact of the U $$5f$$ states on the electronic structure of UPd$$_2$$Al$$_3$$

Fujimori, Shinichi; Takeda, Yukiharu; Yamagami, Hiroshi; Posp$'i$$v{s}$il, J.*; Yamamoto, Etsuji; Haga, Yoshinori

Physical Review B, 105(11), p.115128_1 - 115128_6, 2022/03

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

Journal Articles

Anisotropic physical properties of layered antiferromagnet U$$_2$$Pt$$_6$$Ga$$_{15}$$

Matsumoto, Yuji*; Haga, Yoshinori; Yamamoto, Etsuji; Takeuchi, Tetsuya*; Miyake, Atsushi*; Tokunaga, Masashi*

Journal of the Physical Society of Japan, 90(7), p.074707_1 - 074707_6, 2021/07

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

Journal Articles

Observation of longitudinal magnetic fluctuations at a first-order ferromagnetic quantum phase transition in UGe$$_2$$

Noma, Yuichiro*; Kotegawa, Hisashi*; Kubo, Tetsuro*; To, Hideki*; Harima, Hisatomo*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*; Ito, Kohei*; Nakamura, Ai*; et al.

Journal of the Physical Society of Japan, 90(7), p.073707_1 - 073707_5, 2021/07

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

Journal Articles

Electronic structure of URu$$_2$$Si$$_2$$ in paramagnetic phase; Three-dimensional angle resolved photoelectron spectroscopy study

Fujimori, Shinichi; Takeda, Yukiharu; Yamagami, Hiroshi; Yamamoto, Etsuji; Haga, Yoshinori

Electronic Structure (Internet), 3(2), p.024008_1 - 024008_8, 2021/06

Journal Articles

Intriguing behavior of UCo$$_{1-x}$$Rh$$_x$$Ge ferromagnets in magnetic field along the $$b$$ axis

Posp$'i$$v{s}$il, J.*; Haga, Yoshinori; Miyake, Atsushi*; Kambe, Shinsaku; Tokunaga, Yo; Tokunaga, Masashi*; Yamamoto, Etsuji; Proschek, P.*; Voln$'y$, J.*; Sechovsk$'y$, V.*

Physical Review B, 102(2), p.024442_1 - 024442_13, 2020/07

 Times Cited Count:5 Percentile:40.68(Materials Science, Multidisciplinary)

Journal Articles

The $$f$$-electron state of the heavy fermion superconductor NpPd$$_5$$Al$$_2$$ and the isostructural family

Metoki, Naoto; Aczel, A. A.*; Aoki, Dai*; Chi, S.*; Fernandez-Baca, J. A.*; Griveau, J.-C.*; Hagihara, Masato*; Hong, T.*; Haga, Yoshinori; Ikeuchi, Kazuhiko*; et al.

JPS Conference Proceedings (Internet), 30, p.011123_1 - 011123_6, 2020/03

Rare earths (4$$f$$) and actinides (5$$f$$) provide variety of interesting states realized with competing interactions between the increasing number of $$f$$ electrons. Since crystal field splitting of many-body $$f$$ electron system is smaller than the bandwidth, (1) high resolution experiments are needed, (2) essentially no clear spectrum with well defined peaks is expected in itinerant Ce and U compounds, and (3) Np and Pu is strictly regulated. Therefore, systematic research on magnetic excitations by neutron scattering experiments of localized compounds and rare earth iso-structural reference is useful. We describe the $$f$$ electron states of heavy electron compounds NpPd$$_5$$Al$$_2$$ and actinide and rare earth based iso-structural family.

Journal Articles

Structural characterization and magnetic behavior of uranium compound U$$_2$$Pt$$_6$$Al$$_{15}$$

Haga, Yoshinori; Sugai, Takashi*; Matsumoto, Yuji*; Yamamoto, Etsuji

JPS Conference Proceedings (Internet), 29, p.013003_1 - 013003_5, 2020/02

Journal Articles

NMR studies on antiferromagnetic fluctuation in UPt$$_3$$

Aoyama, Taisuke*; Kotegawa, Hisashi*; To, Hideki*; Kimura, Noriaki*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*

Physica B; Condensed Matter, 570, p.349 - 351, 2019/10

Journal Articles

Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance

Tateiwa, Naoyuki; Haga, Yoshinori; Sakai, Hironori; Yamamoto, Etsuji

Physical Review B, 100(6), p.064413_1 - 064413_7, 2019/08

 Times Cited Count:1 Percentile:4.96(Materials Science, Multidisciplinary)

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures $$T_{rm C}$$ $$sim$$ 85 and 23 K, respectively. We determine the critical exponents, $$beta$$ for the spontaneous magnetization $$M_{rm s}$$, $$gamma$$ for the magnetic susceptibility $$chi$$, and $$delta$$ for the magnetization isotherm at $$T_{rm C}$$ with several analytical methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising system. Similar exponents have been reported for the uranium ferromagnetic superconductors UGe$$_2$$ and URhGe. An important finding is that the novel critical phenomenon appears regardless of the charge carrier density or the degree of the itinerancy of the $$5f$$ electrons.

Journal Articles

Evidence for weak spin-orbit interaction experienced by Cooper pairs in the spin-triplet superconductor UPt$$_3$$; $$^{195}$$Pt-NMR study

Aoyama, Taisuke*; Kotegawa, Hisashi*; Kimura, Noriaki*; Yamamoto, Etsuji; Haga, Yoshinori; Onuki, Yoshichika*; To, Hideki*

Journal of the Physical Society of Japan, 88(6), p.064706_1 - 064706_7, 2019/06

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

Journal Articles

Electronic structure in heavy fermion compound UPd$$_2$$Al$$_3$$ through directional Compton profile measurement

Koizumi, Akihisa*; Kubo, Yasunori*; Yamamoto, Etsuji; Haga, Yoshinori; Sakurai, Yoshiharu*

Journal of the Physical Society of Japan, 88(3), p.034714_1 - 034714_6, 2019/03

 Times Cited Count:2 Percentile:21.69(Physics, Multidisciplinary)

Journal Articles

Novel critical behavior of magnetization in URhSi; Similarities to the uranium ferromagnetic superconductors UGe$$_2$$ and URhGe

Tateiwa, Naoyuki; Haga, Yoshinori; Yamamoto, Etsuji

Physical Review B, 99(9), p.094417_1 - 094417_12, 2019/03

 Times Cited Count:6 Percentile:34.01(Materials Science, Multidisciplinary)

We study the critical behavior of dc magnetization in the uranium ferromagnet URhSi around the ferromagnetic phase transition at $$T_{rm C}{,}{sim}{,}$$10 K. The critical exponent $$beta$$ for the spontaneous magnetization below $$T_{rm C}$$, $$gamma$$ for the magnetic susceptibility, and $$delta$$ for the magnetic isotherm at $$T_{rm C}$$ have been determined as $$beta$$ = 0.300 $$pm$$ 0.002, $$gamma$$ = 1.00 $$pm$$ 0.02, and $$delta$$ = 4.32 $$pm$$ 0.04 by the scaling analysis and the critical isotherm analysis. Magnetization has strong uniaxial magnetic anisotropy in the ferromagnetic state of URhSi. However, the universality class of the critical phenomenon does not belong to the 3D Ising system ($$beta$$ = 0.325, $$gamma$$ = 1.241, and $$delta$$ = 4.82). The obtained exponents in URhSi are similar to those in uranium ferromagnetic superconductors UGe$$_2$$ and URhGe. We discuss the static and dynamical magnetic properties of URhSi in comparison with those in UGe$$_2$$, URhGe and UCoGe.

Journal Articles

Manifestation of electron correlation effect in 5$$f$$ states of uranium compounds revealed by 4$$d$$-5$$f$$ resonant photoelectron spectroscopy

Fujimori, Shinichi; Kobata, Masaaki; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*

Physical Review B, 99(3), p.035109_1 - 035109_5, 2019/01

 Times Cited Count:9 Percentile:54.51(Materials Science, Multidisciplinary)

Journal Articles

Strong correlation between ferromagnetic superconductivity and pressure-enhanced ferromagnetic fluctuations in UGe$$_2$$

Tateiwa, Naoyuki; Haga, Yoshinori; Yamamoto, Etsuji

Physical Review Letters, 121(23), p.237001_1 - 237001_6, 2018/12

 Times Cited Count:7 Percentile:55.03(Physics, Multidisciplinary)

We have measured magnetization at high pressure in the uranium ferromagnetic superconductor UGe$$_2$$ and analyzed the magnetic data using Takahashi's spin fluctuation theory. There is a peak in the pressure dependence of the width of the spin fluctuation spectrum in the energy space $$T_0$$ at $$P_x$$, the phase boundary of FM1 and FM2 where the superconducting transition temperature $$T_{rm sc}$$ is highest. This suggests a clear correlation between the superconductivity and pressure-enhanced magnetic fluctuations developed at $$P_x$$. The pressure effect on $${T_{rm Curie}}/{T_0}$$, where $${T_{rm Curie}}$$ is the Curie temperature, suggests that the less itinerant ferromagnetic state FM2 is changed to a more itinerant one FM1 across $$P_x$$. Peculiar features in relations between $$T_0$$ and $$T_{rm sc}$$ in uranium ferromagnetic superconductors UGe$$_2$$, URhGe and UCoGe are discussed in comparison with those in high-$$T_c$$ cuprate and heavy fermion superconductors.

Journal Articles

Localized 5$$f^2$$ states in UPd$$_5$$Al$$_2$$ and valence crossover in the Vicinity of Heavy-Fermion superconductivity

Metoki, Naoto; Haga, Yoshinori; Yamamoto, Etsuji; Matsuda, Masaaki*

Journal of the Physical Society of Japan, 87(11), p.114712_1 - 114712_9, 2018/11

 Times Cited Count:3 Percentile:29.86(Physics, Multidisciplinary)

The localized 5$$f$$ states with 5$$f^2$$ ($$^3H_4$$) configuration of U$$^{4+}$$ ion have been revealed in UPd$$_5$$Al$$_2$$. We found that the low-lying states are the same as PrPd$$_5$$Al$$_2$$ flat orbitals with large $$J_z$$ are stabilized by a two-dimensional CEF potential in the unique crystal structure. The present study involves the valence crossover from tetravalent to trivalent in a series of AnPd$$_5$$Al$$_2$$, demonstrated by lattice and/or transport anomaly as well as many body effects in the vicinity of the boundary. The valence instability plays important role for the unusual heavy fermion superconductivity in NpPd$$_5$$Al$$_2$$.

505 (Records 1-20 displayed on this page)