  Colossal electroresistance (CER) in manganites, i.e., a large change in
electrical resistance under the influence of either an applied electric field
or an applied electric current, has often been described as complimentary to
the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active
t2g and empty eg orbitals, unlike manganites, have not naturally been discussed
in this context, as double exchange based CMR is not realizable in them.
However, presence of coupled spin and orbital degrees of freedom,
metal-insulator transition (MIT) accompanied by orbital order-disorder
transition, etc., anyway make the vanadates an exciting group of materials.
Here we probe a Fe-doped hollandite lead vanadate PbFe1.75V4.25O11 (PFVO),
which exhibits a clear MIT as a function of temperature. Most importantly, a
giant fall in the resistivity, indicative of a CER, as well as a systematic
shift in the MIT towards higher temperature are observed as a function of
applied electric current. Detailed structural, magnetic, thermodynamic and
transport studies point towards a complex interplay between orbital
order/disorder effect, MIT and double exchange in this system.
