Anisotropic in-plane thermal conductivity of single-crystal YBa2Cu4O8

We report measurements of the in-plane thermal conductivity (kappa) of YBa2Cu4O8 (Y-124) single crystals in the temperature range 4 less than or equal to T less than or equal to 300 K and compare them with previous results on YBa2Cu3O6+x (Y-123). For transport perpendicular to the CuO chains, kappa(a)(300 K) similar or equal to 10 W/mK, and along the chains, kappa(b)(300 K) similar or equal to 40 W/mK. The temperature dependence of kappa for both transport directions is much stronger than in YBa2Cu3O6+x (Y-123), indicative of substantially superior lattice heat conduction in Y-124, and resulting in maximum values for kappa at T similar to 20 K exceeding 200 W/mK. The data imply a surprisingly large anisotropy in the lattice conduction. kappa(a) and kappa(b) are enhanced in the superconducting state as in other cuprates. The magnitude and anisotropy of the enhancement are discussed and compared to those of Y-123. [S0163-1829(98)06445-5].