Raman scattering by crystal-field excitations

Schaack, G.

doi:10.1007/bfb0103385

Cited by 19 publications

(15 citation statements)

References 160 publications

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“…Optical spectroscopy is well-suited to the study of strongly correlated insulators [25,26] and has provided key insights into the spin-orbit coupled Mott state [27][28][29][30][31]. Raman scattering is also sensitive to electronic excitations, albeit of different symmetry than optical spectroscopy, and is therefore an excellent complementary probe [32]. The high energy resolution (< 1 meV) of our optical techniques is also advantageous for studying the effects of the modest λ ∼ 100 meV of 4d elements such as Ru.…”

Section: +mentioning

confidence: 99%

Spin-orbit excitations and electronic structure of the putative Kitaev magnetα−RuCl3

Sandilands¹,

Tian²,

Reijnders³

et al. 2016

Phys. Rev. B

186

161

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Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4d system α-RuCl3 has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations involving localized total angular momentum states of the Ru ion, implying that strong spin-orbit coupling and electron-electron interactions coexist in this material. Analysis of these features allows us to estimate the spin-orbit coupling strength as well as other parameters describing the local electronic structure, revealing a well-defined hierarchy of energy scales within the Ru d states. By comparing our experimental results with density functional theory calculations, we also clarify the overall features of the optical response. Our results demonstrate that α-RuCl3 is an ideal material system to study spin-orbit coupled magnetism on the honeycomb lattice.Introduction.-A variety of novel electronic phases are predicted to emerge in the solid state due to the cooperative action of spin-orbit coupling and electron correlation [1]. One prominent example is the proposed realization of the Heisenberg-Kitaev model in a strongly spin-orbit coupled Mott insulator on the honeycomb lattice [2,3]. In this scenario, the combination of spin-orbit coupling and orbital degeneracy leads to the formation of j ef f = 1/2 pseudospins. The spatial anisotropy inherent to these pseudospins in turn yields bond-dependent, anisotropic exchange interactions that can be mapped onto a generalized Heisenberg-Kitaev model [4], which hosts a variety of unusual magnetic states, including the Kitaev quantum spin liquid [5]. Experimental work in this direction has focussed on honeycomb lattice iridates [6,7], although the electronic structure of these materials is complicated by structural distortions and electron itinerancy [8].

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Section: +mentioning

confidence: 99%

Spin-orbit excitations and electronic structure of the putative Kitaev magnetα−RuCl3

Sandilands¹,

Tian²,

Reijnders³

et al. 2016

Phys. Rev. B

186

161

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“…Notable advantages of RS are its high spectral resolution and its ability to reveal excitation symmetry properties by utilizing well-defined light polarization configurations. Apart from vibration mode studies, RS has also been utilized for investigating electronic excitations, including a few studies of CF excitations in rare earth materials [20]. To our knowledge, to arXiv:1611.03402v1 [cond-mat.str-el] 10 Nov 2016 this date all published Raman results from 4f electrons originate from bulk samples [21][22][23][24].…”

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confidence: 99%

“…This seems to be a natural choice since the main difference of Ce with respect to La consists of the extra 4f electron, and CF excitations generally acquire more intensity at low temperature [20]. The appropriateness of this attribution may once again be discussed based on the polarization dependence of the new features, which is similar to that of V1.…”

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confidence: 99%

“…The appropriateness of this attribution may once again be discussed based on the polarization dependence of the new features, which is similar to that of V1. In the CF picture the hexagonal symmetry of the Ce site in CePt 5 leads to a splitting of the j = 5/2 multiplet into three Kramers doublets of pure m j = ±1/2, ±3/2, and ±5/2 character, which belong to the double group representations Γ − 7 , Γ − 9 , and Γ − 8 [20,31]. Since the quadrupole selection rules for CE Raman transition in the present geometry require ∆m j = ±2, only the transitions involving the m j = ±1/2 doublet are symmetry allowed, i.e.…”

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confidence: 99%

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Study of crystal-field splitting in ultrathinCePt5films by Raman spectroscopy

et al. 2017

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Low-temperature electronic properties of rare-earth intermetallics are substantially influenced by the symmetry and magnitude of the crystal electric field. The direct spectroscopic analysis of crystal field splitting can be challenging, especially in low-dimensional systems, because it requires both high spectral resolution and pronounced sensitivity. We demonstrate the eligibility of electronic Raman spectroscopy for this purpose by the direct determination of the 4f level splitting in ultrathin ordered CePt5 films down to 1.7 nm thickness on Pt(111). Crystal field excitations of Ce 4f electrons give rise to Raman peaks with energy shifts up to ≈ 25 meV. Three distinct peaks occur which we attribute to inequivalent Ce sites, located (i) at the interface to the substrate, (ii) next to the Pt-terminated surface, and (iii) in the CePt5 layers in between. The well-resolved Raman signatures allow us to identify a reduced crystal field splitting at the interface and an enhancement at the surface, highlighting its strong dependence on the local atomic environment.

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“…In very rare cases, Ce III compounds exhibit electronic Raman transitions [6][7][8], but usually only at lower temperatures. If suitable single crystals are available, the polarization properties of these transitions possibly allow their assignments to be made.…”

Section: Introductionmentioning

confidence: 99%