Decoupling of electronic thermal conductivity and electrical conductivity in the magnetic nodal semimetal CeAlGe

Wiedemann-Franz (WF) law is a robust empirical law stating that the ratio between the electronic thermal conductivity and electrical conductivity is related by a universal Lorenz number. For conventional materials, this law is strictly obeyed even when the electronic thermal conductivity and electrical conductivity are suppressed by magnetic fields. In the magnetic nodal semimetal CeAlGe, we observed a decoupling of electronic thermal conductivity and electrical conductivity.

CeAlGe possesses a ferrimagnetic ordering in the ab plane below 4.5 K. The magnetic field applied along the c axis diminishes the ferrimagnetic ordering and induces a ferromagnetic ordering along thec axis. At a certain temperature, the positive magnetoresistance (MR) originating from the enhanced electron cyclotron motion and the negative MR originating from the spin reorientation compensates completely, which makes the MR is zero at this temperature. However, at this temperature, the thermal conductivity does not keep a constant as expected by the WF law. In contrast, we found the magnetic field suppressed the thermal conductivity to the largest extent at this temperature. This indicates a new mechanism dominating the relationship between the electronic thermal conductivity and electrical conductivity.