초록: Using holographic entanglement entropy, we determine the gravity dual of systems with Fermi surfaces, such as metals.We find a very strong restriction on it, and it proves out that systems like usual metals (Landau Fermi Liquids) cannot have classical
gravity dual, and only special kinds of so-called strange metals (non-Fermi Liquids) are allowed. 

Reference :  arXiv:1111.1023