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論文

Photoelectron diffraction for probing valency and magnetism of 4$$f$$-based materials; A View on valence-fluctuating EuIr$$_2$$Si$$_2$$

Usachov, D. Yu*; Tarasov, A. V.*; Schulz, S.*; Bokai, K. A.*; Tupitsyn, I. I.*; Poelchen, G.*; Seiro, S.*; Caroca-Canales, N.*; Kliemt, K.*; Mende, M.*; et al.

Physical Review B, 102(20), p.205102_1 - 205102_11, 2020/11

 被引用回数:2 パーセンタイル:24.67(Materials Science, Multidisciplinary)

Using photoelectron diffraction (PED) and magnetic dichroism measurements, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material EuIr$$_2$$Si$$_2$$. We present and discuss the methodology for modeling of the 4$$f$$ photoemission spectra, PED patterns and magnetic dichroism for rare-earth-based materials. For the Eu-terminated surface we found that the topmost Eu layer is divalent and exhibits a ferromagnetic order below 10 K. The valency of the next Eu layer, that is the 5th atomic layer, is about 2.8 at low temperature that is close to the valency in the bulk. The properties of the Si-terminated surface are drastically different. The first subsurface Eu layer (4th atomic layer below the surface) behaves divalently and orders ferromagnetically at much higher temperature. Experimental data indicate, however, that there is an admixture of trivalent Eu in this layer, resulting in its valency of about 2.1. The next deeper lying Eu layer (8th atomic layer below the surface) behaves mixed-valently, but the estimated valency of 2.4 is notably lower than the value in the bulk. The obtained results create a background for further studies of exotic surface properties of 4$$f$$-based materials, and allow to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.

論文

Divalent EuRh$$_2$$Si$$_2$$ as a reference for the Luttinger theorem and antiferromagnetism in trivalent heavy-fermion YbRh$$_2$$Si$$_2$$

G$"u$ttler, M.*; Generalov, A.*; 藤森 伸一; Kummer, K.*; Chikina, A.*; Seiro, S.*; Danzenb$"a$cher, S.*; Koroteev, Yu. M.*; Chulkov, E. V.*; Radovic, M.*; et al.

Nature Communications (Internet), 10(1), p.796_1 - 796_7, 2019/02

 被引用回数:6 パーセンタイル:67.47(Multidisciplinary Sciences)

Application of the Luttinger Theorem (LT) to the canonical heavy-fermion Kondo Lattice (KL) material YbRh$$_2$$Si$$_2$$ suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local moment anti-ferromagnet (AFM) EuRh$$_2$$Si$$_2$$ in its PM regime. This leads to the tempting opportunity to explore a new experimental realization of the LT in general and how the large FS may change upon the AFM transition below 70 mK in YbRh$$_2$$Si$$_2$$ in particular. A detailed knowledge of the FS reconstruction might be essential to disclose the properties of this phase, which is a precursor of quantum criticality and superconductivity. Using angle-resolved photoemission spectroscopy (ARPES), we observe a large FS for PM EuRh$$_2$$Si$$_2$$ essentially the same as the one seen in YbRh$$_2$$Si$$_2$$ in the KL state at a temperature of 1 K. Across the EuRh$$_2$$Si$$_2$$ AFM transition we found an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Doughnut and Jungle gym Fermi-surface sheets. Our results on EuRh$$_2$$Si$$_2$$ indicate that the formation of the AFM state in YbRh$$_2$$Si$$_2$$ is very likely also connected with large changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system.

論文

High-energy magnetic excitations in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ studied by neutron and resonant inelastic X-ray scattering

脇本 秀一; 石井 賢司; 木村 宏之*; 藤田 全基*; Dellea, G.*; Kummer, K.*; Braicovich, L.*; Ghiringhelli, G.*; Debeer-Schmitt, L. M.*; Granroth, G.*

Physical Review B, 91(18), p.184513_1 - 184513_7, 2015/05

 被引用回数:20 パーセンタイル:71.29(Materials Science, Multidisciplinary)

We have performed neutron inelastic scattering and resonant inelastic X-ray scattering (RIXS) at the Cu-$$L_3$$ edge to study high-energy magnetic excitations at energy transfers of more than 100 meV for overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ with $$x$$ = 0.25 ($$T_c$$ = 15 K) and $$x$$ = 0.30 (nonsuperconducting) using identical single-crystal samples for the two techniques. Our results indicate consistency between neutron inelastic scattering and RIXS, and elucidate the entire magnetic excitation in the $$(pi, pi)$$ direction by the complementary use of two probes. The paramagnon along $$(pi, 0)$$ agrees well with the LCO spin-wave dispersion, while the paramagnon in the $$(pi, pi)$$ direction probed by RIXS appears to be less dispersive.

論文

High-energy spin and charge excitations in electron-doped copper oxide superconductors

石井 賢司; 藤田 全基*; 佐々木 隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山 貴己*; et al.

Nature Communications (Internet), 5, p.3714_1 - 3714_8, 2014/04

 被引用回数:75 パーセンタイル:94.66(Multidisciplinary Sciences)

We combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper $$L_3$$ resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone center and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the $$Gamma$$-point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin-excitations (paramagnons) recently observed in hole-doped compounds even at high doping-levels.

口頭

共鳴非弾性X線散乱による電子ドープ型銅酸化物超伝導体の磁気・電荷励起

石井 賢司; 藤田 全基*; 佐々木 隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山 貴己*; et al.

no journal, , 

銅酸化物超伝導体において、母物質の反強磁性モット絶縁体からキャリアドープにより金属・超伝導体化していく過程で磁気・電荷励起がどのように変遷してくか、また、それがホールドープと電子ドープでどのように異なるかは、超伝導のみならず強相関電子系のより基本的で重要な問題である。磁気励起については、これまで主に利用されてきた中性子非弾性散乱(INS)に加えて、銅のL$$_3$$吸収端を利用した共鳴非弾性X線散乱(RIXS)が有力な実験手法となってきている。RIXSは高エネルギー磁気励起を広いブリルアンゾーンに渡って観測でき、INSとの相補性が高い。一方、電荷励起のエネルギー・運動量空間での全容解明は、RIXSで研究が可能になったことで緒に就いたばかりである。本講演では、RIXSを用いた電子ドープ型銅酸化物超伝導体Nd$$_{2-x}$$Ce$$_x$$CuO$$_4$$の磁気・電荷励起の研究結果について報告する。

口頭

X線・中性子非弾性散乱による電子ドープ型銅酸化物超伝導体のスピン・電荷励起の観測

石井 賢司; 藤田 全基*; 佐々木 隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山 貴己*; et al.

no journal, , 

銅酸化物超伝導体において、母物質の反強磁性モット絶縁体からキャリアドープにより金属・超伝導体化していく過程でスピン・電荷励起がどのように変遷してくか、また、それがホールドープと電子ドープでどのように異なるかは重要な問題である。これまでスピン励起に対して主に利用されてきた中性子非弾性散乱に加えて、内殻共鳴を利用したX線非弾性散乱(RIXS)を相補的に利用して行った電子ドープ型銅酸化物超伝導体のスピン・電荷励起の研究結果について報告する。

口頭

共鳴非弾性X線散乱による電子ドープ型銅酸化物超伝導体の磁気励起と電荷励起

石井 賢司; 藤田 全基*; 佐々木 隆了*; Minola, M.*; Dellea, G.*; Mazzoli, C.*; Kummer, K.*; Ghiringhelli, G.*; Braicovich, L.*; 遠山 貴巳*; et al.

no journal, , 

本講演では、RIXSを用いた電子ドープ型銅酸化物超伝導体Nd$$_{2-x}$$Ce$$_x$$CuO$$_4$$の磁気・電荷励起の研究結果について報告する。銅の$$L_3$$吸収端RIXSで観測されたおよそ100meV以上の高エネルギー磁気励起は、電子ドープが進むにつれて幅を広げながら高エネルギーにシフトすることが明らかになった。このような変化は、ドーピングをしてもほとんど分散が変わらず、母物質の局在スピンの特徴を残したホールドープ型の結果とは対照的である。さらに、電子ドープした試料の$$L_3$$吸収端RIXSでは、$$Gamma$$点の近くで磁気励起よりも高エネルギー側に励起が観測された。その運動量依存性は、$$K$$吸収端で観測されている電荷励起(上部ハバードでのバンド内励起)の分散に滑らかにつながっていることから、同じ起源の電荷励起と考えられ、$$K$$吸収端では観測が難しかった$$Gamma$$点近くの電荷励起の特徴も明らかにすることができた。

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