${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$, a quasi-2D ferrimagnetic nodal-line semiconductor with $T_{\mathrm{c}}=78$ K, exhibits strongly angular-dependent colossal magnetoresistance (CMR) in its magnetically ordered state, which is featured by the development of a unique metallic state under magnetic fields along the $c$ axis. Recently, a peculiar chiral orbital current (COC) state has been proposed to exist in this compound, evidenced by the effective manipulation of magnetotransport properties via applying electrical currents. A field-induced insulator-to-metal transition (IMT) and field-controlled electron scattering off COC domain boundaries thus serve as two feasible origins of the CMR in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$. Here, we further explore the current- and field-driven variations of electronic states in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ by scrutinizing its electrical transport, thermoelectric, and thermal transport properties. A combination of $I\text{−}V$ characteristics and Ettingshausen effect studies allows us to pinpoint the predominant impact of Joule heating on triggering the current-induced IMT. Measurement of the Seebeck effect unambiguously reveals a reduction of the band gap occurring concomitantly with the CMR, in accordance with the field-driven IMT scenario. A remarkable enhancement of thermal conductivity below $T_{\mathrm{c}}$ is observed when magnetic field is applied along $c$ but is absent under in-plane magnetic fields. Such an anisotropic positive magnetothermal conductivity most likely reflects increase of the phonon mean free path stemming from the field-induced suppression of boundary scattering, hence it implies the presence of certain types of field-tunable structural domain walls in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$. Our findings not only underscore the intricate interplay between the spin, charge, and lattice degrees of freedom in ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$, but also point toward cooperative mechanisms for its CMR: Whereas the field-driven IMT appears to be the most essential cause, domain boundary scattering may still play a secondary role.

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• Colossal magnetoresistance
• Electrical properties
• Ettingshausen effect
• Magnetotransport
• Metal-insulator transition
• Seebeck effect
• Thermal conductivity
• Ferrimagnets
• Magnetic insulators
• Magnetic semiconductors
• Resistivity measurements
• Thermometry
• Transport techniques