Magnetically controlled optical effects in Eu-based conductors

Ana Akrap

Europium is a fascinating element. In its 2+ valence state, it has a large spin of 7/2. In this talk, we will delve into what we learned about EuCd2X2 (where X= As, P and Sb) from infrared spectroscopy and magneto-optical experiments. Although we hoped to find evidence of a magnetic Weyl semimetal, instead we found multiple experimental confirmations of a sizeable band gap, just shy of 1 eV. Most interesting is our finding that the band gap is remarkably sensitive to a small external magnetic field. EuCd2X2 start off as antiferromagnets in zero external field, but become fully spin polarized already below 2 T. It appears that there is a large exchange coupling between the f-states and the conduction and valence bands, and this shrinks the band gap by 20% under only 2 T in EuCd2As2. We will discuss how this strong influence of magnetism on conducting states leads to several remarkably strong and potentially useful optical effects—Faraday effect and giant circular dichroism—in EuCd2X2.