Figure 1
Right-hand curves adapted from She et al. [2].

Figure 1: (Left) To carry out future experiments on quantum critical superconductors as proposed by She et al. [2], a two-layer tunnel junction could be used that consists of a high-transition-temperature superconductor (HTSC) next to a low-transition-temperature superconductor in the normal state (LTSC). The two layers are separated by a thin insulating barrier. In the HTSC all the electrons are paired (colors indicate spins), whereas in the LTSC some of the Cooper pairs can tunnel into the normal material from the superconductor. This effect is larger when the pair susceptibility increases as indicated by the tunneling current. (Right) Experimental measurements of the pair susceptibility could distinguish between conventional BCS behavior (top curve) and exotic quantum critical superconductivity (bottom panel).