Is there a liquid-liquid phase transition in supercooled water?

TLDR: In this paper, a two-level model of liquid supercooled water is proposed to show evidence of a liquid-liquid phase transition in liquid super-cooled liquid. But this model is based on the two known forms of amorphous ice: the low-density amorphus ice (LDA) and the high-density Amorphous Ice (HDA).

Abstract: Previous studies of the structure of liquid water under pressure performed by neutron diffraction allowed us to establish two structural limits in liquid water. These two limits are closely connected to the two known forms of amorphous ice: the low-density amorphous ice (LDA) and the high-density amorphous ice (HDA). In the present paper, we propose some interpretation of our data in terms of a "two-level"–type model of water. This leads to show some evidence of a liquid-liquid phase transition in liquid supercooled water. The result looks in agreement with recent computer simulations that incorporate the two forms of amorphous ice.