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 F(4)TCNQ (F(4)TCNQ = 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 F(4)TCNQ contact. Formation of K-F(4)TCNQ nanocrystals at the TCNQ 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.