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Journal Articles

Revising the 4${it f}$ symmetry in CeCu$$_{2}$$Ge$$_{2}$$; Soft X-ray absorption and hard X-ray photoemission spectroscopy

Aratani, Hidekazu*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Kawada, Moeki*; Kanai, Yuina*; Yamagami, Kohei*; Fujioka, Shuhei*; Hamamoto, Satoru*; Kuga, Kentaro*; Kiss, Takayuki*; et al.

Physical Review B, 98(12), p.121113_1 - 121113_6, 2018/09

AA2018-0352.pdf:1.16MB

 Times Cited Count:3 Percentile:63.29(Materials Science, Multidisciplinary)

Journal Articles

Evidence for momentum-dependent heavy fermionic electronic structures; Soft X-ray ARPES for the superconductor CeNi$$_{2}$$Ge$$_{2}$$ in the normal state

Nakatani, Yasuhiro*; Aratani, Hidekazu*; Fujiwara, Hidenori*; Mori, Takeo*; Tsuruta, Atsushi*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; et al.

Physical Review B, 97(11), p.115160_1 - 115160_7, 2018/03

AA2018-0003.pdf:1.65MB

 Times Cited Count:1 Percentile:87.28(Materials Science, Multidisciplinary)

Journal Articles

Experimental observation of temperature and magnetic-field evolution of the 4${it f}$ states in CeFe$$_{2}$$ revealed by soft X-ray magnetic circular dichroism

Saito, Yuji; Yasui, Akira*; Fuchimoto, Hiroto*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Imada, Shin*; Narumi, Yasuo*; Kindo, Koichi*; Takahashi, Minoru*; Ebihara, Takao*; et al.

Physical Review B, 96(3), p.035151_1 - 035151_5, 2017/07

AA2017-0611.pdf:0.36MB

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We revisit the delocalized character of the 4$$f$$ states of CeFe$$_2$$ in the ferromagnetically ordered phase by X-ray magnetic circular dichroism (XMCD) in X-ray absorption spectroscopy (XAS) with improved data quality using single crystals. Surprisingly, the Ce $$M_{4,5}$$ XMCD spectral shape changes significantly as a function of temperature and applied magnetic field, with no concomitant changes in the spectral shape of the Ce $$M_{4,5}$$ XAS as well as the Fe $$L_{2,3}$$ XAS and XMCD. This unusual behavior is characterized by the $$J=7/2$$ states in a 4$$f^1$$ configuration mixed into the $$J=5/2$$ ground state. Such extreme sensitivity of the Ce 4$$f$$ states to the external perturbations can be related to the magnetic instability toward an antiferromagnetic phase in CeFe$$_2$$. Our experimental data presented here provide valuable insights into the underlying physics in strongly-hybridized ferromagnetic Ce compounds.

Journal Articles

Circular dichroism in resonant angle-resolved photoemission spectra of LaNi$$_{2}$$Ge$$_{2}$$

Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Aratani, Hidekazu*; Mori, Takeo*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; Yamagami, Hiroshi*; et al.

Journal of Electron Spectroscopy and Related Phenomena, 220, p.50 - 53, 2017/01

 Times Cited Count:1 Percentile:83.16(Spectroscopy)

We report the soft X-ray angle-resolved photoemission study for LaNi$$_{2}$$Ge$$_{2}$$ to reveal the electronic structures derived from non-4$$f$$ bands of the heavy fermion compound CeNi$$_{2}$$Ge$$_{2}$$. The photoemission spectra recorded at the La M$$_{4,5}$$ absorption edges clearly show the enhancement of the La 5$$d$$ components in the valence band spectra. The circular dichroism of photoemission spectra reveals the band-dependent dichroic response due to the orbital symmetry.

Journal Articles

Electronic structures of ferromagnetic CeAgSb$$_{2}$$; Soft X-ray absorption, magnetic circular dichroism, and angle-resolved photoemission spectroscopies

Saito, Yuji; Fujiwara, Hidenori*; Yamaguchi, Takashi*; Nakatani, Yasuhiro*; Mori, Takeo*; Fuchimoto, Hiroto*; Kiss, Takayuki*; Yasui, Akira*; Miyawaki, Jun*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 85(11), p.114713_1 - 114713_7, 2016/11

 Times Cited Count:7 Percentile:38.94(Physics, Multidisciplinary)

We report on the electronic structures of ferromagnetic CeAgSb$$_{2}$$ using soft X-ray absorption (XAS), magnetic circular dichroism (XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce $$M_{4,5}$$ XAS spectra show very small satellite structures, reflecting a strongly localized character of the Ce 4${it f}$ electrons. The linear dichroism effects in the Ce $$M_{4,5}$$ XAS spectra demonstrate the ground-state Ce 4${it f}$ symmetry of $$Gamma$$$$_{6}$$, the spatial distribution of which is directed along the ${it c}$-axis. Nevertheless, ARPES spectra at the Ce 3$$d$$-4$$f$$ resonance show the momentum dependence of the intensity ratio between Ce 4$$f^{1}_{5/2}$$ and 4$$f^{1}_{7/2}$$ peaks in a part of the Brillouin zone, suggesting the non negligible momentum-dependent hybridization effect between the Ce 4${it f}$ and the conduction electrons. This is associated with the moderate mass enhancement in CeAgSb$$_{2}$$.

Journal Articles

Probing strongly correlated 4$$f$$-orbital symmetry of the ground state in Yb compounds by linear dichroism in core-level photoemission

Mori, Takeo*; Kitayama, Satoshi*; Kanai, Yuina*; Naimen, Sho*; Fujiwara, Hidenori*; Higashiya, Atsushi*; Tamasaku, Kenji*; Tanaka, Arata*; Terashima, Kensei*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 83(12), p.123702_1 - 123702_5, 2014/12

 Times Cited Count:14 Percentile:27.43(Physics, Multidisciplinary)

We show that the strongly correlated 4$$f$$-orbital symmetry of the ground state is revealed by linear dichroism in core-level photoemission spectra, as we have discovered for YbRh$$_{2}$$Si$$_{2}$$ and YbCu$$_{2}$$Si$$_{2}$$. Theoretical analysis shows us that the linear dichroism reflects the anisotropic charge distributions resulting from a crystalline electric field. We have successfully determined the ground-state 4$$f$$ symmetry for both compounds from the polarization-dependent angle resolved core-level spectra at a temperature well below the first excitation energy. The excited-state symmetry is also probed by temperature dependence of the linear dichroism where the high measurement temperatures are on the order of the crystal-field-splitting energies.

Journal Articles

Valence state in Ce-based heavy fermion compounds at high magnetic fields

Matsuda, Yasuhiro*; Her, J.-L.*; Michimura, Shinji*; Inami, Toshiya; Ebihara, Takao*; Amitsuka, Hiroshi*

JPS Conference Proceedings (Internet), 3, p.011044_1 - 011044_6, 2014/06

Synchrotron X-ray absorption spectroscopy of CeRh$$_2$$Si$$_2$$ has been performed in pulsed high magnetic fields of up to 32 T. The Ce valence is slightly larger than 3+ at 5 K and decreases with increasing magnetic above 20 T. The field-induced valence change seems to correspond to the metamagnetic transition in the magnetization process. This phenomena is similar to our previous result on CeRu$$_2$$Si$$_2$$ and seems to be common in Ce-based heavy fermion compounds.

Journal Articles

Temperature and magnetic field dependent Yb valence in YbRh$$_2$$Si$$_2$$ observed by X-ray absorption spectroscopy

Nakai, Hirohito*; Ebihara, Takao*; Tsutsui, Satoshi*; Mizumaki, Masaichiro*; Kawamura, Naomi*; Michimura, Shinji*; Inami, Toshiya; Nakamura, Toshiyuki*; Kondo, Akihiro*; Kindo, Koichi*; et al.

Journal of the Physical Society of Japan, 82(12), p.124712_1 - 124712_5, 2013/12

 Times Cited Count:7 Percentile:46.64(Physics, Multidisciplinary)

The temperature and magnetic field dependences of Yb valence were observed in the heavy fermion compoundYbRh$$_2$$Si$$_2$$ by X-ray absorption spectroscopy. The measurements revealed that the Yb valence decreases with decreasing temperature in the range from 200 to 2 K and increases with increasing magnetic field in the range from 0 to 33 T without showing an abrupt change in the Yb valence. The Yb valence is in the range from 2.92 to 2.96 depending on temperature and magnetic field. With respect to the valence being 2.92 at 0 T and 2.93 at 33 T in 2 K, YbRh$$_2$$Si$$_2$$ is a valence fluctuation compound and does not reach the integer trivalent state at high magnetic field. These results endorse the conventional knowledge that the valence of Yb is very close to the integer value of 3+, decreases with decreasing temperature, and becomes closer to 3+ with increasing magnetic field.

Journal Articles

Suppression of $$f$$-electron itinerancy in CeRu$$_2$$Si$$_2$$ by a strong magnetic field

Matsuda, Yasuhiro*; Nakamura, Toshiyuki*; Her, J. L.*; Michimura, Shinji*; Inami, Toshiya; Kindo, Koichi*; Ebihara, Takao*

Physical Review B, 86(4), p.041109_1 - 041109_4, 2012/07

 Times Cited Count:8 Percentile:59.12(Materials Science, Multidisciplinary)

The valence state of Ce in a typical heavy fermion compound CeRu$$_2$$Si$$_2$$ has been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high magnetic fields of up to 40T. The valence was slightly larger than for the pure trivalent state, as expected in heavy fermion compounds, and it decreased toward the trivalent state as the magnetic field was increased. The field-induced valence reduction indicates that the itinerant character of the 4$$f$$ electrons in CeRu$$_2$$Si$$_2$$ was suppressed by a strong magnetic field. The suppression was gradual and showed a characteristic magnetic field dependence, which reflects the metamagnetism around $$H_{rm m}$$ $$sim$$ 8T.

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