Magnetic field control of absorption coefficient and group index in an impurity doped quantum disc Ecaterina C. Niculescu, Cristina Stan, Gabriela Tiriba and Cristina Truşcǎ Eur. Phys. J. B, 90 5 (2017) 100 Published online: 24 May 2017 DOI: 10.1140/epjb/e2017-80138-0