In situ electron spin resonance experiments on polyacetylene during electrochemical doping

Abstract

We present results obtained from in situ e.s.r. measurements on both n-type [Na y +(CH) − y ] x and p-type [(CH) + y (ClO 4 −) y ] x during electrochemical doping. For [Na y +(CH) − y ] x , data were obtained over an extended concentration range out to ∼15 mol% (or well into the metallic regime); for p-type [(CH) + y (ClO 4 −) y ] x we have succeeded in achieving doping sufficiently high in situ to observe the abrupt first-order onset of the Pauli spin susceptibility. Comparison of the results obtained from p-type and n-type electrochemical doping shows remarkable similarities between the two. For both p-type and n-type doping, at dilute concentrations charge is stored in nonmagnetic spinless charged solitons. For both p-type and n-type doping, a first-order phase transition is observed at a dopant concentration of y ∼ 0.06. For both p-type and n-type doping, there is an abrupt increase in the Pauli spin susceptibility at the transition with a corresponding increase in N(0) by a factor of more than 200 to a metallic value of N(0) ≈ 0.08 states/eV C (both signs of spin). For both p-type and n-type doping, there is a qualitative change in spin dynamics at the transition. The precise symmetry of the results obtained from n-type and p-type doping demonstrates without ambiguity the charge conjugation symmetry of trans-(CH) x . The mechanism for the first-order electronic phase transition is discussed.