Nanowerk  June 10, 2021 Acoustic waves in gases, liquids, and solids usually travel at an almost constant speed of sound. However, rotons, quasiparticles, are an exception: their speed of sound changes significantly with the wavelength, and it is also possible that the waves travel backwards. Rotons were predicted in 1962 in the context of superfluidity. Until now, they could only be observed under special quantum-physical conditions at very low temperatures – and were therefore not suitable to technical applications. An international team of researchers (Germany, France) propose an artificial material that can produce rotons without any quantum effects under normal […]