Superconductivity from a Confinement Transition out of a Fractionalized Fermi Liquid with Z2 Topological and Ising-Nematic Orders
Figure 2. Mean-field dispersion E+(k) of the fermionic spinons for the parameters (Δ1x, Δ1y, Δ2, t2x, t2y) = (0.9, 1, 0.4, 0.2, 0.2). The other band is not shown for clarity 1. [Reprinted by permission from APS © 2016.]
A ℤ2 fractionalized Fermi liquid (FL*) is a novel state of strongly correlated quantum matter. Although it is metallic, it violates Luttinger’s theorem on the volume enclosed by the Fermi surface obeyed by conventional metals; this is possible due to the presence of emergent gauge excitations. In a new Physical Review B editors' suggested article describes a study of the superconducting states that can arise out of instabilities of such a topological metal. The study is by a Harvard physics grad student Shubhayu Chatterjee, Prof. Subir Sachdev, grad student Julia Steinberg, and a colleague from the Perimeter Institute, Yang Q.
The authors focus on a FL* topological metal that has favorable energetics on the square lattice with nematic order, relevant to the cuprate superconductors. They find that a Higgs transition out of this FL* results in confinement of the anyonic degrees of freedom, and the resulting state is a superconductor with broken translation symmetry or time-reversal invariance. In the process, they also establish a complete mapping between bosonic and fermionic descriptions of time-reversal invariant gapped insulating ℤ2 spin liquid states on the rectangular lattice, which, on doping with charge carriers, can give rise to FL* phases. They also note a possible connection to the recent observation of pair density waves in the superconducting state of the underdoped cuprates.
1 See Shubhayu Chatterjee, Yang Qi, Subir Sachdev, and Julia Steinberg, "Superconductivity from a confinement transition out of a fractionalized Fermi liquid with ℤ2 topological and Ising-nematic orders ," Phys. Rev. B 94, 024502 (5 July 2016) DOI: http://dx.doi.org/10.1103/PhysRevB.94.024502.