Magnetic field-controlled phonon softening in topological semimetal Co2MnGa

One of the several promising applications of topological semimetals (TSMs) is magnetic-field enhanced thermoelectric performance. Time-reversal-symmetry (TRS)-broken TSMs further enable enhanced transport properties even at zero field and give rise to a range of intriguing phenomena such as chiral magnetic effects as well as large anomalous Hall and Nernst effects. Magnetic topological semimetal Co2MnGa has received considerable attention due to exotic magnetic nodal-line, Weyl points and linked-loop phases and giant anomalous Nernst effect, which is attributed to a large net Berry curvature near the Fermi level. The phonon and magnon properties of this material, including the possible interactions between them, remain elusive. In this talk, we present inelastic scattering measurements performed on Co2MnGa performed at room temperature under a magnetic field to map the field-dependent phonon dispersions. We observe an anomalous strong tuning of an optical phonon to external magnetic field, when the magnetic field is located in the plane of the phonon wavevector. The tuning does not appear when the field is applied perpendicular to the plane of the phonon wavevector. The observed phenomena may originate from magnon-phonon interactions in the material at the crossing point which may lead to further discussions on topics such as non-Hermitian physics.