Infrared study of the interplay of charge, spin, and lattice excitations in the magnetic topological insulator EuIn2As2

We report an infrared spectroscopy study of the axion topological insulator candidate EuIn2As2 for which the Eu moments exhibit an A-type antiferromagnetic (AFM) order below T-N similar or equal to 18 K. The low-energy response is composed of a weak Drude peak at the origin with a plasma frequency of about 2000 cm(-1) and a pronounced infrared-active phonon mode at 185 cm(-1). The interband transitions start above 800 cm(-1) and give rise to a series of weak absorption bands at 5000 and 12 000 cm(-1) and strong ones at 20 000, 27 500, and 32 000 cm(-1). The AFM transition leads to pronounced anomalies of the charge response in terms of a cusp-like maximum of the free carrier scattering rate around T-N and large magnetic splittings of the interband transitions at 5000 and 12 000 cm(-1). The phonon mode at 185 cm(-1) has also an anomalous temperature dependence around T-N which suggests that it couples to the fluctuations of the Eu spins. The combined data provide evidence for a strong interaction among the charge, spin, and lattice degrees of freedom.

Automated summary

The study on EuIn2As2 using infrared spectroscopy revealed anomalous phenomena associated with antiferromagnetic order, indicating a strong interaction among the charge, spin, and lattice degrees of freedom.