TRIPLET BIPOLARONS IN DISORDERED CONDUCTING POLYMERS - AN ESR STUDY

Electron spin resonance measurements on a disordered conducting polyme r were performed from 4 K up to 400 K for the first time in order to i nvestigate the nature of the so-called <<Pauli-like>> regime. The usua l departure of the susceptibility from a Curie law, a shift in the g-f actor value and a transition from a line broadening regime to a line n arrowing one were observed for T > 200 K. We argue that all of these h igh-temperature ESR properties are due to thermal excitation of bipola rons from the singlet to the triplet state. The appearance of Pauli pa ramagnetism is ruled out for this system. A detailed discussion of the susceptibility, spin relaxation and g-factor is given.