Reflectance Spectra and Electrical Resistivity of (Me₂-DCNQI)₂Li_1-xCu_x

Charge-Ordering Signatures in the Optical Properties ofβ−Na0.33V2O5

“…It has been argued that for Fe 3 O 4 [9] and many other materials [10] the mid-infrared band can be understood as a polaronic response. However, also materials where Hubbard physics dominates may show a relatively strong mid-infrared band resulting from intraband transitions [5,6,11,12].The recent discovery[13] of a clear metal-insulator transition (MIT) in the vanadium bronze β−Na 0.33 V 2 O 5 has sparked a revival of interest in this quasi onedimensional (1D) metallic system. The room temperature crystal structure[14] of β−Na x V 2 O 5 presents three crystallographically distinct Vanadium sites, labelled V 1 , V 2 and V 3 .…”

“…In charge density wave systems, like [5,6], a MI transition may occur due to charge ordering resulting from electronic coulomb interactions (Wigner crystal). Materials of which the properties are dominated by electronphonon interaction often show the appearance in the insulating state of a large number of phonons in the infrared spectrum along the chain direction.…”

“…The metal-insulator transition at TMI leads to the opening of a psuedogap (hω = 1700 cm −1 ), and to the appearance of a large number of optical phonons. These observations, and the presence of a mid-infrared band (typical for low dimensional metals) strongly suggests that the charge carriers in β−Na0.33V2O5 are small polarons.Low dimensional metals feature a variety of MI transitions resulting from electron-phonon or electron-electron interactions.In charge density wave systems, like [5,6], a MI transition may occur due to charge ordering resulting from electronic coulomb interactions (Wigner crystal). Materials of which the properties are dominated by electronphonon interaction often show the appearance in the insulating state of a large number of phonons in the infrared spectrum along the chain direction.…”

“…In Fe 3 O 4 and Ti 4 O 7 [4], which are polaronic materials, a MI transition is induced by small polaron ordering (Verwey state). Finally, in systems lacking sufficiently strong electron-phonon interaction, such as for instance (M e 2 − DCN QI) 2 Li 1−x Cu x [5,6], a MI transition may occur due to charge ordering resulting from electronic coulomb interactions (Wigner crystal). Materials of which the properties are dominated by electronphonon interaction often show the appearance in the insulating state of a large number of phonons in the infrared spectrum along the chain direction.…”

“…It has been argued that for Fe 3 O 4 [9] and many other materials [10] the mid-infrared band can be understood as a polaronic response. However, also materials where Hubbard physics dominates may show a relatively strong mid-infrared band resulting from intraband transitions [5,6,11,12].…”