Speaker
Description
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 EuCd$_2$X$_2$ (where X= As, P and Sb) from infrared spectroscopy and magneto-optical experiments. Although we had initially 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, however, is our finding that the band gap is remarkably sensitive to a small external magnetic field. EuCd$_2$X$_2$ starts off as an antiferromagnet in zero external field, but becomes fully spin polarized already below 2 T. A large exchange coupling between the f-states and the conduction and valence bands shrinks the band gap by 20% under only 2 T in EuCd$_2$As$_2$. The splitting of the bands reaches about 240 meV.
We will discuss how this strong influence of magnetism on conducting states leads to several remarkably strong and potentially useful optical effects in EuCd$_2$X$_2$.