Vanadium Based Compounds

Conductors with Vanadium are good examples for the importance of the orbital degrees of freedom. The most studied system in our group is the quasi-one dimensional BaVS3. The main characteristic of this 3d1 system is the coexistence of a broad one-dimensional dz2 electronic band and a narrow isotropic eg band at the Fermi level. At 70 K a Peierls distortion drives the system into an insulating phase. Deep in this phase the eg electrons form a chiral ferromagnetic order on the chain, but the overall magnetic response is antiferromagnetic.

Single crystals of BaVS3 grown in our laboratory by H. Berger. The typical lenght is 5 mm.

 

The M-I transition is suppressed by 2.0 GPa ofhydrostatic pressure and a metallic phase is stabilized showing a NFL state. Further increase of pressure a Fermi liquid state is recovered.

High pressure suppresses the metal-insulator transition and drives the system into a Non-Fermi liquid state above 2.0 GPa which is testified by the n=1.5 exponent of the temperature dependence of the resistivity. The origin of this state is not known – it is presumably a magnetic one. On further increase of pressure n approaches 2.0 describing the behavior of a Fermi liquid state.

To achieve better understanding of the role of the localized eg electrons, we investigated the properties of the BaVSe3, which, due to the reinforced interchain interactions, may be considered as the high-pressure counterpart of BaVS3. The system is a metallic ferromagnet, in which the strong interaction of dz2 and eg electrons dictates the behavior of transport coefficients.

References:
[1] A. Akrap et al., Transport and magnetic properties of BaVSe3 , Physical Review B78 , 235111 (2008).
[2] T. Ivek et al., Collective charge excitations below the metal-to-insulator transition in BaVS3 Physical Review B78, 035110 (2008).
[3] A. Akrap et al., Influence of point defects on the metal-insulator transition in BaVS3 Physical Review B 77, 115142 (2008).
[4] P. Leininger et al., Ground State of the Quasi-1D Compound BaVS3 Resolved by Resonant Magnetic X-Ray Scattering , Physical Review Letters 106, 167203 (2011).
[5] I. Kezsmarki I. et al., Separation of orbital contributions to the optical conductivity of BaVS3 , Phys Rev Lett.96.186402 (2006).