Sketch of the phase diagram of the SYK+U array. Inset a) Temperature dependence of the resistivity in the insulating (pseudogap) phase.

Contexts in source publication

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... [21- 23], which we do not discuss in details and introduce phenomenologically as a negative Hubbard U [24]. We show that the same pairing mechanism is responsible for the existence of the insulating phase. The latter is separated from the superconductor by a quantum phase transition (QPT) at a critical value of the pairing strength, U c , Fig. 1. Within the insulating phase the low temperature resistivity exhibits the activation behavior, R ∝ exp{ 1 /T }, with an activation energy 1 (U). Importantly, the activation energy tends to zero upon approaching the insulator to superconductor QPT, 1 (U) → 0 when U → U c − 0. This gives rise to a wide quantum critical regime above the ...

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... power laws represent Gaussian exponents of the QPT. We do not attempt here to discuss if fluctuation corrections affect the critical exponents. The quantum critical regime extends above the T = 0 QPT point, Fig. 1, flanked by the lines T = 1 (U, T ) on the left and 1 (U, T ) = 0 on the right. The insulating phase crosses over into the SYK strange metal phase with the linear in T resistivity, at a temperature where the mean-field local pairing amplitude disappears ∆(T ) = 0. This temperature marks closing the gap in the single-particle spectrum ...

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... higher than the Josephson energy but still below the superconducting energy gap, the phase coherence between the grains in the array is lost, while each grain in the array remains superconducting. Therefore the single particle transport is suppressed and the normal current is carried by incoherent Cooper pairs. It is thus denoted as Bose metal in Fig. ...

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... Bose metal appears at higher temperature T E J ≈ t 2 0 /J and extends up to the in-grain critical temperature. The latter is determined by the condition g(T ) = 16∆ 2 (U, T )/J = E 1 /2, where the Kuramoto synchronization within the grain is lost. At higher temperature the array enters the quantum critical region described above, see Eq. (13) and Fig. ...