Frohlich. Nonpairing Model for Superconductivity

The BCS and Little models for superconductivity are both based on the formation of pairs of electrons with an effective attractive interaction due to phonons or excitons respectively. Recently, J. Bardeen (8,28) revived a model, originally presented by Frohlich in 1954 (152), as a possible explanation of the reported anomalous conductivity behavior of (TTF)(TCNQ) (97). This model predates the BCS theory and relies on the direct interaction between electrons and the one-dimensional lattice resulting in the formation of charge density waves. The model has also been applied to the one-dimensional metal K2Pt(CN)4Bro.3o(H20)s (72, 457). 

In the Frohlich model (367), as in the Peierls transition and Kohn anomaly, the lattice vibration of wavevector Ikp produces a periodic variation in the lattice site positions. This new lattice periodicity results in an additional periodic 

A very important feature of the Frohlich model is that the lattice distortion and the charge density wave need not be fixed to the frame of reference of the lattice (i.e., the phase of the distortion need not be fixed). The electrons which make up the charge density wave may then move as a unit (collective charge transport) with a large effective charge and large effective mass leading to enhanced conductivity. 

Additional experiments and theoretical calculations are important for understanding the potential role of these effects in one-dimensional systems. 

---