Evolution of the electronic structure from electron-doped to hole-doped states in the two-dimensional Mott-Hubbard systemLa1.17−xPbx

Abstract

The filling-controlled metal-insulator transition ͑MIT͒ in a two-dimensional Mott-Hubbard system La 1.17Ϫx Pb x VS 3.17 has been studied by photoemission spectroscopy. With Pb substitution x, chemical potential abruptly jumps by ϳ0.07 eV between xϭ0.15 and 0.17, indicating that a charge gap is opened at x Ӎ0.16 in agreement with the Mott insulating state of the d 2 configuration. When holes or electrons are doped into the Mott insulator of xӍ0.16, the gap is filled and the photoemission spectral weight at , (), gradually increases in a similar way to the electronic specific-heat coefficient, although the spectral weight remains depressed around compared to that expected for a normal metal, showing a pseudogap behavior in the metallic samples. The observed behavior of ()→0 for x→0.16 is contrasted with the usual picture that the electron effective mass of the Fermi-liquid system is enhanced towards the metal-insulator boundary. With increasing temperature, the gap or the pseudogap is rapidly filled up, and the spectra at Tϭ300 K appears to be almost those of a normal metal. Near the metal-insulator boundary, the spectra around are consistent with the formation of a Coulomb gap, suggesting the influence of long-range Coulomb interaction under the structural disorder intrinsic to this system.

Effects of strong correlations on the disorder-induced zero-bias anomaly in the extended Anderson–Hubbard model

“…The Mott transition may occur as a function of any number of parameters [6], such as temperature [7] or magnetic field [8], but more commonly occurs in transition metal oxides as a result of chemical doping. A number of experiments [9][10][11][12][13] have found that chemical doping introduces sufficient disorder that there is a regime between the Mott-insulating and gapless phases that is characterized by a ZBA. This naturally raises the question of how the strong electron-electron correlations that are prevalent in the gapless phase near the Mott transition affect the physics of the ZBA.…”

Dielectric breakdown and current switching effect in the incommensurate layered compound(LaS)1.196VS2

“…On the other hand, recent photoemission studies have revealed that La 1.17−x Pb x VS 3.17 is a classical Mott-Hubbard system for x = 0.17 while long range Coulomb interactions seems to remain in the undoped compound ͑x =0͒. 13 All these ingredients-the proximity of a Mott-insulating state, the importance of the Coulomb interactions, the very strong modulation of the V-V distance which modulates as well the energy integrals-lead us to suggest that the criteria for a Mottinsulator state may be realized locally. This is presumably at the origin of the heterogeneous charge distribution.…”

Ultrafast filling of an electronic pseudogap in an incommensurate crystal

“…Its large dispersion of 0.7 eV along Γ-M is close to that expected in the calculation. This large bandwidth and the large filling factor appear incompatible with the simple picture of a Mott insulating phase in the degenerate t 2g manyfold [10].…”

“…(LaS) 1.196 VS 2 may in fact share more properties with quasicrystals. Indeed, a pseudogap was observed by angular integrated photoemission, although it was first attributed to strong correlations [10]. Such a pseudogap would explain the lack of metallicity [11] observed despite the non integer filling of the band (each LaS unit should transfer one electron to each V, yielding an expected d band filling for V near 2.196).…”