Charge Carrier Doping into the Peierls Insulator of the TCNQ Anion Radical Salt (TCNQ = 7,7,8,8-Tetracyanoquinodimethane)

Hole-doping into K–TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) crystals with segregated TCNQ anion radical columns with dimeric deformation (Peierls state) has been performed by a contact doping method using F4TCNQ (F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) crystals or powder. The sheet resistance of the K–TCNQ surface has been found to decrease by the F4TCNQ contact. Formation of K–F4TCNQ nanocrystals at the contact interface has been observed, but conductive AFM images indicate that current paths form along the hole-doped K–TCNQ surface. Interestingly, hole-doping into K–TCNQ suppresses the phase transition to the high-temperature phase (Mott insulator). This is considered to result from the energy gain by the delocalization of the doped carriers.