Universal Fermionic Spectral Functions from String Theory

We carry out the first holographic calculation of a fermionic response function for a strongly coupled $d=3$ system with an explicit $D=10$ or $D=11$ supergravity dual. By considering the supersymmetry current, we obtain a universal result applicable to all $d=3$ $N=2$ SCFTs with such duals. Surprisingly, the spectral function does not exhibit a Fermi surface, despite the fact that the system is at finite charge density. We show that it has a phonino pole and at low frequencies there is a depletion of spectral weight with a power-law scaling which is governed by a locally quantum critical point.

Figure 1

The spectral function $A(\omega ,k)$ The top panel is for $T/\mu =0.44$ and momenta $k\ell \in (0.1,1.1)$, with larger values of $k$ in darker shades of gray. The bottom panel is for $T=0$ and $k\ell \in (1.2,2.1)$.