Charge dynamics of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">Na</mml:mi></mml:mrow><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cl

Waku, Kiminori; Katsufuji, T.; Kohsaka, Y.; Sasagawa, T.; Takagi, H.; Kishida, Hideo; Okamoto, Hiroshi; Azuma, Masaki; Takano, Mikio

doi:10.1103/physrevb.70.134501

Cited by 36 publications

(46 citation statements)

References 28 publications

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“…When first observed, the 1.5 eV peak was thought to be of extrinsic origin 13 . Measurements of this peak in samples that were hole-doped by oxygen, 22 photodoping measurements, 23 and a comparison between materials 24 have together demonstrated that the 1.5 eV feature comes solely from the presence of holes in the copper-oxygen plane, although this last study extended only to x=0.10.…”

Section: 19mentioning

confidence: 99%

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

et al. 2011

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We report a comprehensive Cu K-edge RIXS investigation of La2−xSrxCuO4 (LSCO) for 0≤x≤0.35, stripe-ordered La1.875Ba0.125CuO4 (LBCO), and La2Cu0.96Ni0.04O4 (LCNO) crystals. The RIXS spectra measured at three high-symmetry momentum transfer (q) positions are compared as a function of doping and for the different dopants. The spectra in the energy range 1-6 eV can be described with three broad peaks, which evolve systematically with increased doping. The most systematic trend was observed for q=(π, 0) corresponding to the zone boundary. As hole doping increased, the spectral weight transfer from high energies to low energies is nearly linear with x at this q. We interpret the peaks as interband transitions in the context of existing band models for this system, assigning them to Zhang-Rice band→upper Hubbard band, lower-lying band→upper Hubbard band, and lower-lying band→Zhang-Rice band transitions. The spectrum of stripe-ordered LBCO was also measured, and found to be identical to the correspondingly doped LSCO, except for a relative enhancement of the near-infrared peak intensity around 1.5-1.7 eV. The temperature dependence of this near-infrared peak in LBCO was more pronounced than for other parts of the spectrum, continuously decreasing in intensity as the temperature was raised from 25 K to 300 K. Finally, we find that 4% Ni substitution in the Cu site has a similar effect on the spectra as does Sr substitution in the La site.

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Section: 19mentioning

confidence: 99%

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

et al. 2011

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“…The samples of x = 0.06, 0.08 and 0.12 are insulators, insulators (in the close vicinity of the insulator-superconductor critical doping) and underdoped superconductors of T c = 21 K, respectively 21,22 . The samples were cleaved at 77 K or below and immediately transferred to the heads of microscopes cooled down beforehand.…”

Section: Methodsmentioning

confidence: 99%

Visualization of the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator

et al. 2012

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Superconductivity emerges from the cuprate antiferromagnetic Mott state with hole doping. The resulting electronic structure 1 is not understood, although changes in the state of oxygen atoms seem paramount 2-5 . Hole doping first destroys the Mott state, yielding a weak insulator 6,7 where electrons localize only at low temperatures without a full energy gap. At higher doping levels, the 'pseudogap', a weakly conducting state with an anisotropic energy gap and intra-unit-cell breaking of 90 • rotational (C 4v ) symmetry, appears 3,4,8-10 . However, a direct visualization of the emergence of these phenomena with increasing hole density has never been achieved. Here we report atomic-scale imaging of electronic structure evolution from the weak insulator through the emergence of the pseudogap to the superconducting state in Ca 2− x Na x CuO 2 Cl 2 . The spectral signature of the pseudogap emerges at the lowest doping level from a weakly insulating but C 4v -symmetric matrix exhibiting a distinct spectral shape. At slightly higher hole density, nanoscale regions exhibiting pseudogap spectra and 180 • rotational (C 2v ) symmetry form unidirectional clusters within the C 4v -symmetric matrix. Thus, hole doping proceeds by the appearance of nanoscale clusters of localized holes within which the broken-symmetry pseudogap state is stabilized. A fundamentally two-component electronic structure 11 then exists in Ca 2− x Na x CuO 2 Cl 2 until the C 2v -symmetric clusters touch at higher doping levels, and the long-range superconductivity appears.To visualize at the atomic scale how the pseudogap and superconducting states are formed sequentially from the weak insulator state, we performed spectroscopic imaging scanning tunnelling microscopy (SI-STM) studies on Ca 2−x Na x CuO 2 Cl 2 (0.06 ≤ x ≤ 0.12; see also the Methods sections). The crystal structure is simple tetragonal (I 4/mmm) and thereby advantageous because the CuO 2 planes are unbuckled and free from orthorhombic distortion. More importantly Ca 2 CuO 2 Cl 2 can be doped from the Mott insulator to the superconductor by introduction of Na atoms. Figure 1c,d shows differential conductance images measured using SI-STM of bulk-insulating x = 0.06 and x = 0.08 samples taken in the field of views of the topographic images in Fig. 1a,b. The wavy, bright, arcs in Fig. 1c,d have never been observed in superconducting samples (x > 0.08) but appear only in such quasi-insulating samples (x ≤ 0.08). They are created by spectral peaks in differential conductance spectra whose energy is dependent on location (Fig. 1f). Consequently, the wavy arcs shrink with increasing bias voltages and finally disappear. This behaviour, due to tip-induced impurity charging [12][13][14] , is characteristic of poor electronic screening in a weakly insulating state.A wide variety of spectral shapes originating from electric heterogeneity were found in these samples. A typical example of the spectra is, as spectrum number 1 in Fig. 1e, the V-shaped pseudogap (∼0.2 eV) spectrum with a small dip (∼20...

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“…In our √ 18 × √ 18 and √ 20 × √ 20 clusters, however, the doping dependence of the in-gap weight near half-filling shows the same tendency and is consistent with the experimental data. 1,2,3,4 We note that a dramatic increase of the low-energy peak at n = 12/18 ∼ 0.667 in Fig. 3(c) is probably due to nonzero total momentum of the ground state [K = (±2π/3, ±2π/3) (Ref.…”

mentioning

confidence: 99%

Exact diagonalization study of optical conductivity in the two-dimensional Hubbard model

et al. 2005

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The optical conductivity σ(ω) in the two-dimensional Hubbard model is examined by applying the exact diagonalization technique to small square clusters with periodic boundary conditions up to √ 20 × √ 20 sites. Spectral-weight distributions at half filling and their doping dependence in the 20-site cluster are found to be similar to those in a √ 18× √ 18 cluster, but different from 4×4 results. The results for the 20-site cluster enable us to perform a systematic study of the doping dependence of the spectral-weight transfer from the region of the Mott-gap excitation to lower-energy regions. We discuss the dependence of the Drude weight and the effective carrier number on the electron density at a large on-site Coulomb interaction.

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Charge dynamics ofCa2−xNaxCuO2Cl

Cited by 36 publications

References 28 publications

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

Visualization of the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator

Exact diagonalization study of optical conductivity in the two-dimensional Hubbard model

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