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Journal Articles

$$^{125}$$Te-NMR study on a single crystal of heavy fermion superconductor UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

We report $$^{125}$$Te-NMR studies on a newly discovered heavy fermion superconductor UTe$$_2$$. Using a single crystal, we have measured the $$^{125}$$Te-NMR Knight shift $$K$$ and spin-lattice relaxation rate $$1/T_1$$ for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static ($$K$$) and dynamical susceptibilities ($$1/T_1$$) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate $$1/T_2$$, when the field is applied along the easy axis of magnetization (=$$a$$ axis). This behavior suggests the development of longitudinal magnetic fluctuations along the $$a$$ axis at very low frequencies below 20 K.

Journal Articles

Microscopic approach to magnetism and superconductivity of $$f$$-electron systems with filled skutterudite structure

Hotta, Takashi

Journal of the Physical Society of Japan, 74(4), p.1275 - 1288, 2005/04

 Times Cited Count:24 Percentile:24.89(Physics, Multidisciplinary)

In order to understand electronic properties of filled skutterudite materials, the Anderson model is analyzed by using the numerical renormalization group method to evaluate magnetic susceptibility and entropy of $$f$$ electron for each case of $$n$$=1$$sim$$13, where $$n$$ is the number of $$f$$ electrons per rare-earth ion. For the $$f^2$$-electron system corresponding to the Pr-based filled skutterudite, it is found that magnetic fluctuations significantly remain at low temperatures, even when the ground state is $$Gamma_1$$ singlet, if $$Gamma_4^{(2)}$$ triplet is the excited state with small excitation energy. By analyzing an orbital degenerate Hubbard model constructed based on the $$j$$-$$j$$ coupling scheme, we find that anisotropic Cooper-pair mediated by magnetic fluctuations appears in a limited region in which the singlet and triplet ground states are interchanged.

Journal Articles

Effect of orbital fluctuations on magnetic properties of $$f$$-electron systems

Hotta, Takashi

Physica B; Condensed Matter, 359-361, p.1003 - 1005, 2005/04

 Times Cited Count:1 Percentile:92.68(Physics, Condensed Matter)

In order to understand magnetic properties of filled skutterudite materials, we evaluate magnetic susceptibility of the Anderson model with orbital degeneracy by using the numerical renormalization group method. Even when the local ground state is $$Gamma_1$$, magnetic fluctuations significantly remain, if $$Gamma_4^{(2)}$$ is the excited state with small excitation energy, as experimentally proposed for Pr-based filled skutterudite compounds.

Journal Articles

Magnetic fluctuations of filled skutterudites emerging in the transition region between singlet and triplet states

Hotta, Takashi

Physical Review Letters, 94(6), p.067003_1 - 067003_4, 2005/02

 Times Cited Count:15 Percentile:34.1(Physics, Multidisciplinary)

In order to clarify magnetic properties of filled skutterudites, we analyze the Anderson model including seven $$f$$ orbitals hybridized with an $$a_{rm u}$$ conduction band using a numerical technique. For $$n$$=2 corresponding to Pr-based filled skutterudites, where $$n$$ is the local $$f$$-electron number, even if the ground state is a singlet, there remain significant magnetic fluctuations from a triplet state with a small excitation energy. This result can be understood by the fact that $$f$$-electron states are clearly distinguished as itinerant and localized ones in the filled skutterudite structure. This picture also explains the complex results for $$f$$-electron magnetic susceptibility and entropy for $$n$$=1$$sim$$13.

Journal Articles

Ferromagnetism in ErTi$$_{2}$$Ga$$_{4}$$

Abe, Hideki*; Yoshii, Kenji; Kitazawa, Hideaki*

Journal of the Physical Society of Japan, 70(10), p.3042 - 3045, 2001/10

 Times Cited Count:6 Percentile:55.02(Physics, Multidisciplinary)

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