“…These include, but are not limited to electron JHEP07(2020)081 transitions: in atoms and semiconductors [9][10][11][12][13][14][15][16][17], superconductors [18][19][20], topological insulators [21,22] and Dirac materials [23][24][25]. Sub-GeV DM can be searched for also via the Migdal effect [26][27][28][29], single phonon [30,31] and magnon [32] excitations in crystals, in superfluid helium [33,34], through dissociation or excitation in molecules [35,36] and also through other methods [37][38][39][40][41][42] proposed recently.…”