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Sarma, D. D.; Shanthi, N.; Krishnakumar, S.; Saitoh, T.; Mizokawa, T.; Sekiyama, A.; Kobayashi, Katsuyoshi; Fujimori, A.; Weschke, E.; Meier, Robert J.; Kaindl, G.; Takeda, Yasuo; Takano, Mikio

doi:10.1103/physrevb.53.6873

Cited by 113 publications

(66 citation statements)

References 25 publications

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“…The integrated oscillator strength for this two-component Drude absorption changes down to the very low temperature where the ferromagnetic moment already saturates, which suggests that other degrees of freedom still remain active. (2) The photoemission spectra shows only a small discontinuity at the Fermi energy E F followed by a gap like behavior [13][14][15]. On the other hand, the specific heat is not enhanced with γ ∼ 5mJ/K 2 mol [15].…”

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confidence: 97%

Orbital liquid in perovskite transition-metal oxides

1997

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We study the effects of the degeneracy of the eg orbitals as well as the double exchange interaction with t2g spins in perovskite transition-metal oxides. In addition to the spin field Si, the isospin field Ti is introduced to describe the orbital degrees of freedom. The isospin is the quantum dynamical variable, and is represented by the boson with a constraint. The dispersion of this boson is flat along (π/a, π/a, kz) (a: lattice constant) and the other two equivalent directions. This enables the orbital disordered phase down to low temperatures. We interpret some of the anomalous experiments, i.e., optical absorption and d.c. resistivity, in the low temperature ferromagnetic phase of La1−xSrxMnO3 with x > 0.2 in terms of this orbital liquid picture. 71.27.+a, 71.30.+h, 75.30.Et The colossal negative magneto-resistance observed in transition-metal oxides with perovskite structure, e.g., the double exchange system La 1−x Sr x MnO 3 , has revived the interest in these systems [1][2][3][4]. The valency of Mn ion is Mn 3+ for x = 0, whose electron configuration is (t 2g ) 3 (e g ) 1 , and all the spins are aligned ferromagnetically due to the strong Hund coupling. Because of the strong on-site repulsion, the double occupancy of e g orbitals is forbidden [5,6], and the system is a Mott insulator. When one La is replaced by Sr, one hole is introduced to Mn and Mn 3+ turns into Mn 4+ . These doped holes, which contribute to the conduction, can not be described in terms of the one-body theory. For a single band case, which is relevant to high-Tc cuprates, extensive studies have been focused on these doped holes to a Mott insulator. One of the promising approaches is resonating valence bond (RVB) theory [7,8], where the spin and charge are separated. In the orbital-degenerate case, this idea can be generalized also to the orbital degrees of freedom as shown below [9].Experimentally the orbital ordering has been established in the low hole-concentration region, i.e., x ∼ 0.0 [10], where the system is insulating with the A-type antiferromagnetic long range ordering (AFLRO) [11]. As x increases the system becomes more and more conductive, and finally shows the metallic conduction below the ferromagnetic transition temperature T c . In this metallic state (x > 0.2), there are several anomalous features.(1) The optical conductivity shows a narrow coherent peak up to around 0.02eV followed by a broader "Drude like" band up to around 1eV [12]. The integrated oscillator strength for this two-component Drude absorption changes down to the very low temperature where the ferromagnetic moment already saturates, which suggests that other degrees of freedom still remain active.(2) The photoemission spectra shows only a small discontinuity at the Fermi energy E F followed by a gap like behavior [13][14][15]. On the other hand, the specific heat is not enhanced with γ ∼ 5mJ/K 2 mol [15]. (3) The anisotropy of the conduction and the spin excitation, which is expected with the orbital ordering, is not observed even at low temperature...

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Orbital liquid in perovskite transition-metal oxides

1997

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“…However, this is not always true, particu-larly in strongly correlated electron systems like LSMO. Although the low-temperature electrical conductivity for LSMO is as high as about 10 5 (Ω cm) −1 at x = 0.4, 13 angle-integrated photoemission studies have failed to observe large near-E F spectral weight 14,15 as can be seen in Ti or V oxides. 16 Instead, only a few angle-resolved studies on layered manganites have succeeded in observing an extremely small quasiparticle peak in very limited k-space areas.…”

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Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

Hishida

Ohbayashi

Kobata

et al. 2013

Journal of Applied Physics

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By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/corelevel x-ray photoemission spectral weight and electrical conductivity in La 1−x Sr x MnO 3 as a function of x. In the Mn 2p 3/2 HX-PES spectra, we observed the shoulder structure due to the Mn 3+ well-screened state. However, the intensity at x=0.8 was too small to explain its higher electrical conductivity than x=0.0, which confirms our recent analysis on the Mn 2p 3/2 XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight.

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“…It has also been noted 5,6 that doped manganites are unusual metals having resistivities greater than the maximum Mott resistivity (1 to 10 mohm cm) and a very low density of states at the Fermi level 14 .…”

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Electronic Raman scattering fromLa0.7Sr0.3Mn
Gupta
¹
,
Sood
²
,
Mahesh
³

et al. 1996
Phys. Rev. B
141
3
19
0
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Raman and Photoluminescence (PL) experiments on correlated metallic La 0.7 Sr 0.3 MnO 3 have been carried out using different excitation wavelengths as a function of temperature from 15 K to 300 K. Our data suggest a Raman mode centered at 1800 cm −1 and a PL band at 2.2 eV. The intensities of the two peaks decrease with increasing temperature. The Raman mode can be attributed to a plasmon excitation whose frequency and linewidths are consistent with the measured resistivities. The PL involves intersite electronic transitions of the manganese ions.

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Temperature-dependent photoemission spectral weight inLa0.6Sr0.4

Cited by 113 publications

References 25 publications

Orbital liquid in perovskite transition-metal oxides

Orbital liquid in perovskite transition-metal oxides

Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

Electronic Raman scattering fromLa0.7Sr0.3Mn
Gupta
¹
,
Sood
²
,
Mahesh
³

et al. 1996
Phys. Rev. B
141
3
19
0
View full text Add to dashboard Cite

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Temperature-dependent photoemission spectral weight inLa0.6Sr0.4

Cited by 113 publications

References 25 publications

Orbital liquid in perovskite transition-metal oxides

Orbital liquid in perovskite transition-metal oxides

Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

Electronic Raman scattering fromLa0.7Sr0.3MnGupta1, Sood2, Mahesh3 et al. 1996Phys. Rev. B1413190View full textAdd to dashboardCite

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Electronic Raman scattering fromLa0.7Sr0.3Mn
Gupta
¹
,
Sood
²
,
Mahesh
³

et al. 1996
Phys. Rev. B
141
3
19
0
View full text Add to dashboard Cite