Non-density driven liquid-liquid transition in pure gallium melt

A liquid may have two or more isotropic phases of the same composition, the transition between them is called liquid-liquid transition (LLT). LLT has been reported in several systems where LLT is associated with dramatic change of density. However, it is suggested that the structural change in liquid cannot be sufficiently described by density. Several attempts are made to reveal the non-density driven LLT. But the existence of non-density driven LLT is still controversial due to the lack of adequate experimental evidences. In this work, we capture a non-density driven LLT in pure Gallium at far above its melting temperature. The structural change of liquid without significant density change is revealed by a kink in the Knight shift (K_s) curve during heating. The first order character of LLT is revealed by the hysteresis of heating and cooling curve of Knight shift (K_s). The latent heat of LLT can be reflected by an endothermic peak measured in the Differential Scanning Calorimetry experiment. Our observations of the LLT in the single element system support density is not the only order parameter in the description of liquid structure, and additional order parameters are needed.