Optical 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">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>sheets and their strong dependence on Cu-O coordination and bond length

Arima, T.; Kikuchi, Kôichi; Kasuya, M.; Koshihara, Shin‐ya; Tokura, Y.; Ido, T.; Uchida, S.

doi:10.1103/physrevb.44.917

Cited by 68 publications

(24 citation statements)

References 13 publications

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“…The spectrum has a sharp absorption peak at 1.7 eV and a broad side peak at 2.2 eV, similarly to the bulk feature. 12 The main absorption peak corresponds to the charge-transfer ͑CT͒ transition from the O 2p band to the Cu 3d x 2 −y 2 upper Hubbard band ͑UHB͒, 13 and its fairly sharp profile indicates the exitonic character of the transition. Within the CT gap, optical absorption is negligibly small.…”

Section: Resultsmentioning

confidence: 99%

Optical probe of electrostatic-doping in ann-type Mott insulator

et al. 2007

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Electrostatic-doping into an n-type Mott insulator Sm 2 CuO 4 has been successfully achieved with use of the heterojunction with an n-type band semiconductor Nb-doped SrTiO 3 . The junction exhibits rectifying currentvoltage characteristics due to the interface band discontinuity and the formation of depleted region. The application of reverse bias electric field on this junction enables the field-effect electron doping ͑presumably up to 6% per Cu atom͒ to the Mott insulator. The electromodulation absorption spectroscopy could clearly show a large modification of the Mott-gap state accompanying the spectral weight transfer to the lower-energy region, reminiscent of formation of a metallic state.

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Section: Resultsmentioning

confidence: 99%

Optical probe of electrostatic-doping in ann-type Mott insulator

et al. 2007

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“…Note that many 2D insulating cuprates also have a strong peak in this energy range. 2,3,4 Therefore peaks C and D are attributed to β transitions from LHB to NB states.…”

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Optical excitations inSr2CuO3

Kim

2009

Phys. Rev. B

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We investigated excitation spectra of the one-dimensional chain compound Sr2CuO3. The small peak at 2.3 eV in the loss function turned out to correspond to the strong charge transfer transition at 1.8 eV in conductivity. It has the excitonic character expected in one dimensional extended Hubbard model of the transition from the lower Hubbard band to the Zhang-Rice singlet state. The strongest peak at 2.7 eV in the loss function is attributed to the continuum excitation of the excitonic charge transfer transition. The spectral weight sum rule is satisfied within these transitions.PACS numbers: 71.27.+a, 71.35.-y, 78.20.-e, 78.67.-n Superconducting cuprates have a CuO 2 plane in common which is composed of a two dimensional (2D) cornersharing network of CuO 4 plaquettes. The electronic property of an undoped CuO 2 plane should be metallic without strong onsite Coulomb repulsion at Cu sites, which divides the Cu d x 2 −y 2 state into two Hubbard bands of upper Hubbard band (UHB) and lower Hubbard band (LHB) opening a charge transfer gap between LHB (from a hole point of a view) and O 2p states. Charge doping changes the electronic structure of the CuO 2 plane finally giving rise to the high temperature superconductivity. It is important to understand the properties of insulating cuprates to solve the mystery of the high temperature superconductivity.Optical spectroscopy is one of fundamental tools to investigate electronic structure, which can directly measure the charge transfer gap. By absorbing light, holes in LHB can be excited to O 2p states. When a hole is introduced into the CuO 2 plane, the ground state becomes a well known Zhang-Rice singlet (ZRS) state evenly residing at surrounding O 2p orbitals. 1 Because an optical excitation is a charge conserving process, to be involved in optical excitations for the ZRS state, one CuO 4 plaquette should give a hole to a neighboring CuO 4 plaquette, which is possible in corner-sharing CuO 4 plaquette structures. Therefore, the first optical excitation crossing the charge transfer gap should be from LHB to the ZRS state in the CuO 2 plane as depicted in fig. 1. The second excitation is expected to be from LHB to nonbonding (NB) O 2p states in the CuO 2 plane, which is localized within one plaquette. Energies of these two excitations are essential to model the electronic structure of the CuO 2 plane.However, the electronic structure of insulating cuprates remains still unclear. Optical spectra of insulating cuprates of 1D and 2D corner-sharing structure show similar spectral feature of two peaks around 2 eV like the peaks A and B in fig. 2. It is clear that the lowest energy peak, which is rather sharp and has a large spectral weight in common, should be the charge transfer transition α from LHB to ZRS. But the origin of the other peak, which comes at about 0.5 eV higher, is still unclear. This peak is relatively broad and the strength varies depending on materials. It is rather small and appear as a hump-like shape in RE 2 CuO 4 (RE: rare earth ions) and Sr 2 CuO 3...

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“…2-5 are in good agreement with known literature data obtained by reflection spectroscopy. [17][18][19][20] It is well known that ellipsometry measurements allow one to obtain more accurate data. However, to the best of our knowledge, ellipsometry measurements were done only for La and Bi cuprates.…”

Section: Resultsmentioning

confidence: 99%

“…3-5. We note, that no decomposition into Lorentz oscillators was undertaken before on the basis of reflection data [17][18][19][20] for these copper oxides. The band gap in TЈ cuprates is noticeably red shifted by about 0.6 eV as compared to La cuprate.…”

Section: Resultsmentioning

confidence: 99%

“…32 Thus, in terms of the cluster model discussed above the energy spectrum of the Pr, Nd, and Sm cuprates can be associated with the charge transfer within the square-planar complexes CuO 4 6− ͑p-d CT transitions͒, or between the neighboring complexes ͑d-d CT transitions͒ 30,31 with properly taken into account effects of neighboring planes above and below the CuO 2 plane as well as Cu-O bond lengths. 17,18,33 Thus, important experimental observation of strong 0.6 eV "redshift" of the fundamental band gap in the Pr, Nd, and Sm cuprates ͑TЈ phase͒ with respect to the R = La cuprate ͑T phase͒ can be easily explained by decrease of the average negative charge in the nearest environment of CuO 4 6− complexes. In fact, the transition from the T-type structure to the TЈ-type structure leads to the energy increase of the b 1g hole.…”

Section: Discussionmentioning

confidence: 99%

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Near-band gap electronic structure of the tetragonal rare-earth cupratesR2CuO4and the bismuth cuprateBi2
Pisarev
¹
,
Павлов
²
,
Kalashnikova
³

et al. 2010
Phys. Rev. B
27
0
11
0
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Complex optical dielectric function in the tetragonal rare-earth cuprates R 2 CuO 4 ͑R = La, Pr, Nd, and Sm͒ and in the tetragonal bismuth cuprate Bi 2 CuO 4 is studied in the spectral range of 0.6-5.4 eV using a method of optical ellipsometry. The dielectric spectra are studied for the two main polarizations and analyzed in terms of a cluster model for CuO 4 6− complexes taking into account intracenter p-d and intercenter d-d charge-transfer ͑CT͒ transitions. The band gap in the rare-earth cuprates is defined by an electric-dipole-allowed CT transitions centered at 1.54-1.59 eV in Pr, Nd, and Sm cuprates, and 2.1 eV in La cuprate. Optical response of Bi 2 CuO 4 strongly differs from the rare-earth cuprates which we relate with strong covalency of Bi-O bonding and strong ionicity of Cu͑3d͒-O͑2p͒ bonding. These features are manifested in suppression of low-energy intense intracenter p-d and intercenter d-d CT transitions, and by appearance of strong intense absorption bands near 5 eV. Regardless the strong distinctions of optical response, on one hand, of La, Pr, Nd, and Sm cuprates, and on the other hand, of the Bi cuprate, the dielectric gap in these compounds shows comparable values defined by a superposition of intracenter p-d CT transitions and two-center d-d CT transitions. Thus these cuprates should be classified as compounds intermediate between CT and Mott-Hubbard insulators.

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Optical excitations inCuO2sheets and their strong dependence on Cu-O coordination and bond length

Cited by 68 publications

References 13 publications

Optical probe of electrostatic-doping in ann-type Mott insulator

Optical probe of electrostatic-doping in ann-type Mott insulator

Optical excitations inSr2CuO3

Near-band gap electronic structure of the tetragonal rare-earth cupratesR2CuO4and the bismuth cuprateBi2
Pisarev
¹
,
Павлов
²
,
Kalashnikova
³

et al. 2010
Phys. Rev. B
27
0
11
0
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Optical excitations inCuO2sheets and their strong dependence on Cu-O coordination and bond length

Cited by 68 publications

References 13 publications

Optical probe of electrostatic-doping in ann-type Mott insulator

Optical probe of electrostatic-doping in ann-type Mott insulator

Optical excitations inSr2CuO3

Near-band gap electronic structure of the tetragonal rare-earth cupratesR2CuO4and the bismuth cuprateBi2Pisarev1, Павлов2, Kalashnikova3 et al. 2010Phys. Rev. B270110View full textAdd to dashboardCite

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Near-band gap electronic structure of the tetragonal rare-earth cupratesR2CuO4and the bismuth cuprateBi2
Pisarev
¹
,
Павлов
²
,
Kalashnikova
³

et al. 2010
Phys. Rev. B
27
0
11
0
View full text Add to dashboard Cite