Mass renormalization in the bandwidth-controlled Mott-Hubbard systemsSrVO3andCaVO3studied by angle-resolved photoemission spectroscopy

Abstract

Ca 1−x Sr x VO 3 is a Mott-Hubbard-type correlated electron system whose bandwidth can be varied by the V-O-V bond angle, but the actual effect of bandwidth control on the electronic structure has been controversial in previous photoemission experiments. In this work, band dispersions and Fermi surfaces of SrVO 3 and CaVO 3 are studied by angle-resolved photoemission spectroscopy.Near the Fermi level (E F ), three bands forming cylindrical Fermi surfaces derived from the three V 3d t 2g orbitals have been observed. The observed band widths for both compounds are almost half of those predicted by local-density-approximation band-structure calculation, confirming mass renormalization caused by electron correlation. It has been clearly demonstrated that the width of the d band in CaVO 3 is narrower than that in SrVO 3 , qualitatively consistent with the result of band-structure calculation. Roles of the orthorhombic lattice distortion and electron correlation in the observed band narrowing are discussed. The complex nature of correlated electrons in transition-metal oxides (TMO's) causes various interesting phenomena including high-T c superconductivity and colossal magnetoresistance 1 . Light transition-metal oxides such as perovskite-type Ti and V oxides are ideal systems to study the fundamental physics of electron correlation because they are prototypical Mott-Hubbard-type systems, in which the O 2p band is located below the transition-metal 3d band, in the framework of the Zaanen-Sawatzky-Allen classification scheme. 2 Those systems have a relatively small number of electrons in the degenerate t 2g bands, and their electronic properties have been modeled by the Hubbard model without explicit consideration of the oxygen p orbitals. In the Mott-Hubbard regime, the MIT occurs when the ratio of the on-site Coulomb repulsion (U) to the one-electron band width (W ) exceeds a critical value (U/W ) c . In those light TMO's, the electronic properties are those of normal Fermi liquids on the metallic side, while they are Mott insulators (with orbital ordering) on the insulating side of the MIT. Electron correlation effects and metal-insulator transitions (MITs) in light TMO's have been described based on theoretical predictions of dynamical mean-field theory (DMFT) for the Hubbard model 3 .To address the nature of electron correlation in light TMO's experimentally, photoemission spectroscopy has provided rich information. In the photoemission spectra of the perovskite-type Ti and V oxides, 4-7 the coherent part around the Fermi level (E F ) corresponding to band-like electronic excitations and incoherent part 1-2 eV away from E F corresponding to atomic-like excitations or the remnant of the lower Hubbard band (LHB) have been observed. DMFT has predicted that the effective mass of conduction electron is enhanced concomitant with decreasing spectral weight in the coherent part 3 and that spectral weight transfer occurs from the coherent part to incoherent part as the system approaches an MIT from the metallic side. For ex...

Enhanced electron correlations at theSrxCa1−xVO3surface

“…Photoelectrons with kinetic energies of 2.2 keV and 4.2 keV are estimated to have an IMFP, λ, of 3.6 nm and 6.1 nm respectively in Sr x Ca 1−x VO 3 within the TPP-2M model, 23 compared with 0.5 nm at ultraviolet energies (∼ 80 eV). 3,7 Owing to the different densities of CaVO 3 and SrVO 3 , the IMFP within this model is anticipated to be ∼ 8% smaller in SrVO 3 than in CaVO 3 (mean values, roughly corresponding to Sr 0.5 Ca 0.5 VO 3 , are quoted above). Samples were cleaved ex-situ, and immediately loaded into the ultra-high vacuum chamber.…”

“…Additionally, band dispersions and Fermi surfaces have been clearly observed in both end-members. 5,7,12 However, the behavior of the spectra at the surface compared with the bulk has received little experimental attention, despite the role of the surface being questioned and studied in detail theoretically. 13,15 Moreover, our knowledge of the "bulk" spectra from PES has so far been limited to analytical differences between spectra containing both bulk and surface components.…”

“…2 Sr x Ca 1−x VO 3 are prototypical strongly-correlated perovskites, with similar spectral weight in both the incoherent (strongly correlated) Hubbard subbands and the coherent (one electron-like) quasiparticle states. Although the spectral function of these materials has been well studied experimentally [3][4][5][6][7][8][9][10][11][12] and theoretically, [13][14][15][16][17] there is not a well established consensus on the form of the surface and bulk components, or as the Sr content (x) is varied. Both endmembers are correlated metals * Present address: Department of Physics, IISER Bhopal, MP-462023, India and have been reported to exhibit metal-insulator transitions in ultrathin films due to a reduction in the dimensionality and corresponding narrowing of the V 3d bandwidth.…”

Screened exchange dynamical mean-field theory and its relation to density functional theory: SrVO 3 and SrTiO 3

“…Due to the relatively localized nature of the corresponding orbitals and a non-negligible Coulomb interaction, the spectral properties are however not well-described by simple band theory. Various experimental probes, in particular photoemission [27][28][29][30][31][32], inverse photoemission [33] and angle-resolved photoemission [34][35][36][37] have been used to characterize the spectral properties of this compound. The resulting picture is that of a moderately correlated metal, with quasi-particle mass enhancement of the order of 2 and a well-defined lower Hubbard band that has been identified in various spectroscopic probes.…”

Proceedings of Computational Science Workshop 2014 (CSW2014)

“…The GW+DMFT scheme is illustrated by applying it to the much studied cubic perovskite SrVO 3 , generally considered to be a prototype of correlated metals, as is evident from the large number of both experimental [14][15][16][17][18][19][20][21][22] and theoretical works [23][24][25][26][27][28][29][30][31], There are two main discrepancies of the LDA electronic structure when compared with experiment. Experimentally, a substantial t 2g band narrowing by a factor of two compared with the LDA bandwidth is observed [20].…”