N. W. Preyer

Frequency dependence of the conductivity and dielectric constant of La2CuO4+y near the insulator-metal transition

Abstract Measurement are reported of the conductivity and the dielectric constant (ɛ 1 ) at frequencies (ω) up to 20 MHz and magnetic fields up to 15 T for a single crystal of La 2 CuO 4+y with y varied in the range 0.001 – 0.01. The frequency dependence of the conductivity at low temperatures follows a power law, which is typical of conventional doped semiconductors. ɛ 1 at high ω is independent of ω and grows as the insulator to metal transition (IMT) is approached, but only for the electric field in the CuO 2 layers, indicating that the IMT is two-dimensional. For the highest oxygen concentration, this excess ɛ 1 was reduced by a factor of 2 at a magnetic field of 15 T perpendicular to the CuO 2 layers.

Magnetoresistance and the spin flop transition in pure single - Crystal La2CuO4+y

Abstract Magnetoresistance (MR) measurements are reported for pure single crystals of La 2 CuO 4+y at magnetic fields up to 23T. With the magnetic field →H‖→c, parallel to the staggered moment, the MR shows evidence of a spin flop transition, which provides a measure of both the antisymmetric and the symmetric anisotropies of the nearest-neighbour exchange. The MR, which arises from the interlayer hopping conductivity, is proportional to M † + , the order parameter of the antiferromagnetism (AF) with propagation vector →gt‖→c.

Weak localization effects in conductance measurements of La2−xSrxCuO4−y

Abstract Conductivity data from many La 2−x Sr x CuO 4−y crystals is presented. All sufficiently conductive crystals (with conductances of order e 2 /h per square per CuO 2 layer) show a logarithmic temperature dependent correction to the conductance, of order e 2 /h, predicted by weak localization theory.