Single crystals of the perovskite-type 3d 1 metallic alloy system Ca 1Ϫx Sr x VO 3 were synthesized in order to investigate metallic properties near the Mott transition. The substitution of a Ca 2ϩ ion for a Sr 2ϩ ion reduces the bandwidth W due to a buckling of the V-O-V bond angle from ϳ180°for SrVO 3 to ϳ160°for CaVO 3 . Thus, the value of W can be systematically controlled without changing the number of electrons making Ca 1Ϫx Sr x VO 3 : one of the most ideal systems for studying bandwidth effects. The Sommerfeld-Wilson ratio (Ӎ2), the Kadowaki-Woods ratio ͑in the same region as heavy fermion systems͒, and a large T 2 term in the electric resistivity, even at 300 K, substantiate a large electron correlation in this system, though the effective mass, obtained by thermodynamic and magnetic measurements, shows only a systematic but moderate increase in going from SrVO 3 to CaVO 3 , in contrast to the critical enhancement expected from the Brinkmann-Rice picture. It is proposed that the metallic properties observed in this system near the Mott transition can be explained by considering the effect of a nonlocal electron correlation. ͓S0163-1829͑98͒03232-9͔ PHYSICAL REVIEW B 15 AUGUST 1998-II VOLUME 58, NUMBER 8 PRB 58 0163-1829/98/58͑8͒/4372͑12͒/$15.00 4372

We investigate the electronic structure of Ca1−xSrxVO3 using photoemission spectroscopy. Core level spectra establish an electronic phase separation at the surface, leading to distinctly different surface electronic structure compared to the bulk. Analysis of the photoemission spectra of this system allowed us to separate the surface and bulk contributions. These results help us to understand properties related to two vastly differing energy-scales, namely the low energy-scale of thermal excitations (∼ kBT ) and the high-energy scale related to Coulomb and other electronic interactions.PACS numbers 71.30.+h, 71.27.+a, 73.20.At, 79.60.Bm The electronic structure of strongly correlated transition metal oxides has attracted a great deal of attention both theoretically [1] and experimentally [2] due to many exotic properties exhibited by these systems such as high temperature superconductivity and colossal magnetoresistance. In order to investigate such issues, photoemission spectroscopy has been extensively employed due to its ability to probe the electronic structure directly. While this technique is highly surface sensitive as observed in rare earth intermetallics [3], its extensive use to understand the bulk properties of transition metal (TM) oxides [4] is based on the implicit assumption of very similar electronic structures at the surface and in the bulk. We observe a spectacular failure of this assumption in Ca 1−x Sr x VO 3 .Ca 1−x Sr x VO 3 is a solid solution of CaVO 3 and SrVO 3 where the bandwidth W can be systematically controlled due to a buckling of the V-O-V bond angle from ∼ 180• in SrVO 3 to ∼ 160. Thus, Ca 1−x Sr x VO 3 is ideally suited for the systematic study of the competition between local interactions and itineracy, which leads to several strong correlation effects. This system is arguably the simplest strongly correlated transition metal oxide, since it remains paramagnetic down to the lowest temperature measured so far (T = 50 mK), has typical Fermi liquid behavior and has nominally just one conduction electron per site of V 4+ . Despite these facts, important aspects of its fundamental physics remain unclear, particularly in terms of its contrasting high-energy spectroscopic and low-energy thermodynamic properties [1,6]. The spectroscopic properties and the thermodynamic properties belong to vastly different energy scales: the former corresponds to a high energy (typically 10 ∼ 10 3 eV) perturbation to the system, while the latter probes electrons typically within k B T (∼ 1 meV) of E F . There is indeed a-priori no reason to believe that the same model physics will be valid in both the regimes.In this study, we observe a strong dependence of the photoemission spectra from Ca 1−x Sr x VO 3 with the escape depth λ of the photoelectrons, siginifying very different surface and bulk electronic structures. The core level spectra exhibit an electronic phase separation at the surface, possibly due to an enhanced correlation effect and leading to a distinctly different surface electronic stru...

The electronic specific heat coefficients for single crystals of a perovskite-type vanadate system, , are reported. Wilson's ratio has been determined by comparing the data to the Pauli-paramagnetic susceptibility; the value indicates a strong electron correlation in this system. Nevertheless, the effective masses are not so large as expected from the critical-mass-enhancement picture near the Mott transition.

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