Charge and orbital excitations in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Li</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Kim, Yong Baek; Hill, J. P.; Chou, F. C.; Casa, D.; Gög, T.; Venkataraman, C.

doi:10.1103/physrevb.69.155105

Cited by 40 publications

(46 citation statements)

References 35 publications

(40 reference statements)

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“…In Li 2 CuO 2 , the situation is more controversial, because in previous experiments with RIXS [22] and other experimental techniques [29][30][31], the ZRS exciton could not be unambiguously observed.…”

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confidence: 93%

Determining the Short-Range Spin Correlations in the Spin-ChainLi2CuO2andCuGeO3Compounds Using Resonant Inelastic X-Ray Scattering

et al. 2013

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We report a high-resolution resonant inelastic soft x-ray scattering study of the quantum magnetic spin-chain materials Li2CuO2 and CuGeO3. By tuning the incoming photon energy to the oxygen Kedge, a strong excitation around 3.5 eV energy loss is clearly resolved for both materials. Comparing the experimental data to many-body calculations, we identify this excitation as a Zhang-Rice singlet exciton on neighboring CuO4-plaquettes. We demonstrate that the strong temperature dependence of the inelastic scattering related to this high-energy exciton enables to probe short-range spin correlations on the 1 meV scale with outstanding sensitivity.PACS numbers: 78.70. En,71.27.+a,74.72.Cj Two-dimensional cuprate materials play an essential role in condensed matter physics as they show high temperature superconductivity upon charge doping. For better understanding these complex materials, it is important to tackle simpler model systems sharing similar key components and showing reduced complexity, namely one dimensional cuprate chains made out of CuO 4 plaquettes. In this context, Zhang-Rice singlets (ZRS) are fundamental elementary excitations being composite objects generic to hole doped or photon excited strongly correlated charge transfer insulators, and that are especially well-known in the cuprates [1]. However, more than two decades after their theoretical discovery and numerous observations afterwards, there is still significant theoretical and experimental activity aimed at clarifying their complex details e.g. with respect to additional orbitals [2] or specific magnetic correlations beyond their centers [3].Edge-shared cuprate chains represent a particular class of quantum magnets in which the local geometry gives rise to competing nearest ferromagnetic (FM) or antiferromagnetic (AFM) exchange coupling J 1 and frustrating next-nearest neighbor AFM J 2 superexchange couplings. The AFM one-dimensional spin-1/2 J 1 -J 2 Heisenberg model describes such frustrated magnetic interactions, due to which quantum fluctuations can alter both * Deceased ground state and spin correlations [4]. Generalizing this model by varying the signs and ratio of J 1 and J 2 gives rise to a rich phase diagram with ground states spanning FM, AFM, helical, and gapped singlet states. In real materials, the presence of interchain coupling and occasionally coupling to the lattice adds complexity to this behavior, rendering theoretical treatment more difficult [5]. It is therefore desirable to obtain experimental access to nearest neighbor spin correlations both within the ground state probed at very low-temperature and in thermally occupied excited spin-states as a function of temperature (T ) [6]. Both Li 2 CuO 2 and CuGeO 3 realize frustrated edge-shared chain systems that exhibit ground states with completely different intrachain spin correlations. While CuGeO 3 , on the one hand, displays the well-established spin-Peierls phase below T SP = 14 K resulting in a gapped singlet state with pronounced AFM nearest neighbor spin correlations ...

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Determining the Short-Range Spin Correlations in the Spin-ChainLi2CuO2andCuGeO3Compounds Using Resonant Inelastic X-Ray Scattering

et al. 2013

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“…More recently this technique has been applied to various cuprates including high-T c materials 2,3,4,5,6,7,8,9,10,11 and other highly-correlated electron systems. 12,13,14 A recent RIXS study near the Cu K edge in undoped La 2 CuO 4 (LCO) has revealed three features in its charge excitation spectrum. 5 Two features, labeled A and B, appear at energy transfers ω = 2.2 eV and 3.9 eV, respectively; these features show the largest intensity enhancement at an incident photon energy of E i = 8.991 keV.…”

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Resonant inelastic x-ray scattering study of overdopedLa2−xSrxCuO4

Wakimoto

Kim

et al. 2005

Phys. Rev. B

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Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge has been performed for heavily overdoped samples of La2−xSrxCuO4 with x = 0.25 and 0.30. We have observed the charge transfer and molecular-orbital excitations which exhibit resonances at incident energies of Ei = 8.992 and 8.998 keV, respectively. From a comparison with previous results on undoped and optimally-doped samples, we determine that the charge-transfer excitation energy increases monotonically as doping increases. In addition, the Ei-dependences of the RIXS spectral weight and absorption spectrum exhibit no clear peak at Ei = 8.998 keV in contrast to results in the underdoped samples. The low-energy (≤ 3 eV) continuum excitation intensity has been studied utilizing the high energy resolution of 0.13 eV (FWHM). A comparison of the RIXS profiles at (π 0) and (π π) indicates that the continuum intensity exists even at (π π) in the overdoped samples, whereas it has been reported only at (0 0) and (π 0) for the x = 0.17 sample. Furthermore, we also found an additional excitation on top of the continuum intensity at the (π π) and (π 0) positions.

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“…4 where the RIXS peak near 2.1 eV has been ascribed to the ZRS using a lowspin GS. Probably, the 2.1 eV-peak should be ascribed to d-d excitations 10,11 . A similar feature has been found in CuGeO 3 (in σ(ω) at lower ω ≈ 1.7 ± 0.1 eV) while the ZRS is clearly observed at 3.4 ± 0.2 eV 17,18 .…”

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confidence: 99%

“…This will cause a strong T -dependence of various response functions, here presented for the case of the optical conductivity σ(ω). For an illustration of our approach we consider Li 2 CuO 2 being of current interest 1,2,3,4,5,6,7,8,9,10,11,12 , structurally simple, and most importantly, where single crystal data are available in a broad ω-range 1,2 . This system stands for a class of frustrated spin-1/2 chain materials with both small ferromagnetic (FM) NN Cu-Cu exchange coupling J 1 and AFM next-nearest neighbor (NNN) Cu-Cu in-chain exchange J 2 1,3 in terms of a 1D spin-1/2 Heisenberg model…”

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Temperature-dependent optical conductivity of undoped cuprates with weak exchange

et al. 2008

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The optical conductivity σ(ω) is calculated at finite temperature T for CuO2 chain clusters within a pd-Hubbard model. Data at T = 300 K for Li2CuO2 are reanalyzed within this approach. The relative weights of Zhang-Rice singlet and triplet charge excitations near 2.5 and 4 eV, respectively, depend strongly on T , and a rather dramatic dependence of σ(ω) on the ratio of the 1 st to 2 nd neighbor exchange integrals is predicted. On the basis of these results, information about exchange interactions for frustrated edge-shared cuprates can be obtained from T -dependent optical spectra. Our results are also relevant for magnetically weakly coupled wide-gap insulators in general.PACS numbers: 71.15. Mb, 71.27.+a, 74.72.Jt, 75.10.Jm, 75.10.Pq, Standard wisdom on wide gap insulators says that their optical spectra above 1 eV excitation energy are hardly affected by temperature T , magnetic fields H, and by the magnetic nature of their ground state (GS). Moreover, spin and charge degrees of freedom are often decoupled in one dimension (1D). Here, we present exact theoretical results qualitatively valid for several cuprates to be specified below which prove just the opposite in all these respects. Our study bases on the fact that different magnetic states with different symmetries obey different selection rules, which -in case of soft magnetic materials -can lead to sizable T -dependence of the optical spectra. For systems with small enough exchange integrals, the energy difference between the GS and the excited magnetic states of the system will be small enough so that they can be thermally populated. This will cause a strong T -dependence of various response functions, here presented for the case of the optical conductivity σ(ω). For an illustration of our approach we consider Li 2 CuO 2 being of current interest 1,2,3,4,5,6,7,8,9,10,11,12 , structurally simple, and most importantly, where single crystal data are available in a broad ω-range 1,2 . This system stands for a class of frustrated spin-1/2 chain materials with both small ferromagnetic (FM) NN Cu-Cu exchange coupling J 1 and AFM next-nearest neighbor (NNN) Cu-Cu in-chain exchange J 2 1,3 in terms of a 1D spin-1/2 Heisenberg modelIn Li 2 CuO 2 chains running along the b-axis are formed by the edge-sharing of CuO 4 plaquettes. The most exciting puzzle addressed here is the missing of the ZhangRice singlet peak (ZRS) in reflectivity and electron energy loss spectroscopy (EELS) data at T = 300 K 1,2 . Its detection in resonant inelastic x-ray scattering (RIXS) spectra is under debate, too 4,5 . There is also no consensus on the role of two scenarios for the FM in-chain order below the Néel temperature T N = 9 K. Scenario I is given by a dominant FM J 1 9 defined by the inequality α = −J 2 /J 1 < α c ≈ 0.25, if J 3 is weak 13 , where

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Charge and orbital excitations inLi2CuO2

Cited by 40 publications

References 35 publications

Determining the Short-Range Spin Correlations in the Spin-ChainLi2CuO2andCuGeO3Compounds Using Resonant Inelastic X-Ray Scattering

Determining the Short-Range Spin Correlations in the Spin-ChainLi2CuO2andCuGeO3Compounds Using Resonant Inelastic X-Ray Scattering

Resonant inelastic x-ray scattering study of overdopedLa2−xSrxCuO4

Temperature-dependent optical conductivity of undoped cuprates with weak exchange

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