The CCDW in 2H-TaSe₂-its phasing onto the lattice and crossover in DC arrays

The phasing of the charge-density wave/periodic structural distortion relative to the 3a 0 commensurate unit cell of low-temperature 2H-TaSe 2 is investigated in the light of recent experimental and theoretical work. In trying to accommodate all the data it becomes apparent that the phasing selected alters substantially with applied magnetic field; interpretation of the NMR and Hall coefficient measurements is at stake, and to a lesser extent the electron microscopy. The phase diagram develops striking resemblance to that modelled by Littlewood and Rice (1982) in connection with the pressure variable. The low-field/low-pressure structure is identified Consequences for the discommensuration array are discussed.