A translator gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. That's roughly how disorder in a crystal slows electrons: tiny inhomogeneities make them wander, and resistance grows. In the Dirac semimetal PdTe, this effect has now been observed in its pure form for the first time.

A single crystal of PdTe, grown by slow cooling of the melt, was placed in a magnetic field up to 14 tesla. At 5 kelvin, the resistance increased by 112%. Initially, it grew quadratically, as expected for an ordinary metal, but after a critical field of about 2–3 tesla, the dependence became linear. Such behavior is often attributed to quantum effects, but here everything was explained more simply.

Linear magnetoresistance arose from mobility fluctuations: in different regions of the crystal, electrons move at different speeds, and in a strong field these differences add up to a direct increase in resistance. The critical field depended linearly on the inverse mobility, exactly as predicted by the classical Parish–Littlewood model. The quantum limit, where all electrons would occupy the lowest Landau level, would require a field of 2.49 kilotesla, hundreds of times stronger than the most powerful steady-state magnet.

A parametric plot of transverse resistance versus longitudinal resistance gave a shock-wave-like shape, a characteristic signature of anisotropic orbital magnetoresistance. Electrons scatter differently depending on the field direction, and this creates the planar Hall effect without any topology.

The translator who gets distracted by rustles still eventually translates, just more slowly. So does PdTe: despite its Dirac nature, its transport anomalies turn out to be classical. This result offers a simple criterion for other materials: before invoking topology, check for disorder.