Anomalous metallic ground state inBaV13O18

Abstract

We studied single crystals of BaV 13 O 18 , in which V ions with an average valence of +2.62 (3d 2.38 ) form a quasi-fcc lattice. We found that the ground state of the stoichiometric crystal is insulating, whereas that of the off-stoichiometric crystal is metallic with a large effective mass. This metallic state can be explained by the Kondo coupling between the magnetic moment existing at the lone V ion and itinerant carriers in the V tetramers.

Photoinduced phase transitions over three phases in Ba0.9Sr0.1V13O18

“…Figures 1 (b) and (c) show the reflectivity spectrum R(ω) and the optical conductivity spectrum σ(ω) derived from the Kramers-Kronig transformation of R(ω), respectively, at each phase in the equilibrium state. As discussed previously, 17 there is a peak below 0.5 eV and a broad structure between 1.5 and 3 eV in the σ(ω) spectrum in this compound, which can be assigned to the in-gap excitation (the excitation of the d electrons between V 2+ and V 3+ ) and the Mott excitation (between V 3+ and V 3+ ), respectively. Characteristic changes in the σ(ω) spectrum with the phase transitions are observed particularly in the in-gap excitation; the peak athω ∼ 0.2 eV in the HT phase (250 K) shifts to a higher frequency of ∼ 0.3 eV together with an increase in the peak height in the IT phase (160 K), whereas the peak height is decreased and the peak width is increased in the LT phase (30 K).…”

“…AV 13 O 18 (A=Ba, Sr) is a series of compounds that exhibit two different types of ordered states, both of which are dominated by the d electrons on the V ions. [15][16][17] This series of compounds takes a hexagonal structure and the V ions form a quasi-fcc lattice. The HT phase of these compounds is characterized by V tetramers, in which four V ions in a rhombus shape approach each other and form a cluster, as shown in Fig.…”

“…The single crystal used in the present study was grown by the floating-zone technique, as described elsewhere. 17 The resistivity and the magnetic susceptibility of the crystal are shown in the inset of Fig. 1 (a).…”

Trimerization and orbital ordering in Ba1−xSrxV13O18

“…Details were described elsewhere. 12 Electrical resistivity was measured using a conventional four-probe method. Magnetic susceptibility was measured using a SQUID magnetometer.…”

“…Recently, it has been found that BaV 10 O 15 (in which the average valence of V is +2.8) 5-8 , Ba 2 V 13 O 22 (+3.08) 9 , and Ba 1−x Sr x V 13 O 18 (+2.63) [10][11][12] with V ions on a quasi-triangular lattice exhibit ordered states similar to that of LiVO 2 . For example, the trimerization of V ions occurs in BaV 10 O 15 at 123 K, causing the opening of a charge gap of ∼0.3 eV and a sharp increase in resistivity by three orders of magnitude.…”