Zeeman splitting and dynamical mass generation in Dirac semimetal ZrTe$_{\mathrm{5}}$

Dirac semimetals have attracted extensive attentions in recent years. It has been theoretically suggested that many-body interactions may drive exotic phase transitions, spontaneously generating a Dirac mass for the nominally massless Dirac electrons. So far, signature of interaction-driven transition has been lacking. In this work, we report high-magnetic-field transport measurements of the Dirac semimetal candidate ZrTe5. Owing to the large g factor in ZrTe5, the Zeeman splitting can be observed at magnetic field as low as 3 Tesla. Most prominently, high pulsed magnetic field up to 60 Tesla drives the system into the ultra-quantum limit, where we observe abrupt changes in the magnetoresistance, indicating field-induced phase transitions. This is interpreted as an interaction-induced spontaneous mass generation of the Dirac fermions. Our work establishes Dirac semimetals as ideal platforms for investigating emerging correlation effects in topological matters. Reference: Yanwen Liu, et al. Nature Communications 7, 12516 (2016)