Phonon contribution to the transport properties of single-crystal MgB₂

We extract phonon contributions from the transport properties of a MgB₂ single crystal. The temperature dependence of the in-plane resistivity is well explained by the Bloch-Grüneisen formula with the Debye temperature θ_D∼400 K, taking into account an additional contribution of the E_2g phonon mode (∼890 K). In the thermoelectric power, we find a phonon drag peak around 70 K, which gives a consistent estimation of θ_D with the resistivity result. The pressure dependence of the in-plane resistivity reveals a major contribution of the E_2g phonon mode to superconductivity.