Quantum critical polar metals

Recent years have seen a discovery of a number of polar metals, materials in which itinerant electrons coexist with an inversion-symmetry breaking order. In this talk I will discuss the properties of such systems when the polar ordering temperature is tuned to zero – i.e. at a polar quantum critical point. I will show that unlike other examples of quantum criticality, the soft modes of the polar order do not couple easily to electrons. I will consider the general mechanisms, by which the electrons can interact with the critical modes of the polar order and discuss the consequences of these interactions. In particular, I will demonstrate that exotic metallic phases, including non-Fermi liquid ones, can be realized in multiband systems in the vicinity of band crossings, such as nodal lines or Weyl points. Finally, I will discuss the role of nonlinear interactions in quantum critical polar metals and connect these to the yet unresolved mystery of superconductivity in doped SrTiO3. 

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