Electronic and Sturctural Transitions in Dense Liquid Sodium

Raty, J Y ; Schwegler, E R ; Bonev, S A

Lawrence Livermore National Laboratory

关键词: Sodium;    Liquid Metals;    Fermi Level;    75 Condensed Matter Physics, Superconductivity And Superfluidity;    Melting;   

DOI  :  10.2172/923615
RP-ID  :  UCRL-TR-233403
RP-ID  :  W-7405-ENG-48
RP-ID  :  923615

美国|英语

来源: UNT Digital Library

【 摘 要 】

At ambient conditions, the light alkali metals are free-electron like crystals with a highly symmetric structure. However, they were shown recently to exhibit unexpected complexity under pressure. It was predicted from theory and later confirmed by experiment that Li and Na undergo a sequence of symmetry breaking transitions driven by a Peierls mechanism. Most recently, measurements of the Na melting curve revealed an unprecedented and still unexplained drop in the melting temperature from 1000 K at 30 GPa to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behavior in dense Na. We show that molten Na undergoes a series of pressure-induced structural and electronic transitions analogous to that observed in solid Na, but commencing at much lower pressure in the presence of disorder. With increasing pressure, liquid Na initially evolves by assuming a more compact local structure. However, a transition to a lower coordinated liquid takes place at a pressure around 65 GPa, accompanied by a threefold drop in electrical conductivity. A pseudogap opening at the Fermi level, an effect previously not observed in a liquid metal, drives this transition. Remarkably, the lower coordinated liquid emerges at rather elevated temperatures and above the stability region of a closed packed free electron-like metal. We predict that similar exotic behavior is possible in other materials as well.