A study published in Nature Communications yields crucial new insights on their behaviour: researchers at Politecnico di Milano, in collaboration with the Institute of Photonics and Nanotechnologies IFN-CNR and a theory group from the Tsukuba University (Japan) and the Max Plank Institute for the Structure and Dynamics of matter at Hamburg (Germany), have discovered that an exciton can simultaneously adopt two radically different characters when it is stimulated by light: a solid-like character and an atomic-like character. The researchers managed to observe the dynamics of excitons in an ultrafast regime, on time scales of the billionth of billionth of second, thanks to the experiments carried out at the Attosecond Research Center within the ERC project AuDACE (Attosecond Dynamics in AdvanCed matErials). With advanced theoretical simulations they have demonstrated the co-existence of the dual characters.