Pseudogap, Superconducting Energy Scale, and Fermi Arcs in Underdoped Cuprate Superconductors

TL;DR

This study links the pseudogap, Fermi arcs, and superconducting energy scale in underdoped cuprates, showing their interdependence and suggesting superconductivity arises from gap formation on Fermi arcs, consistent with RVB theory.

Contribution

It provides experimental evidence connecting the pseudogap, Fermi arcs, and superconducting gap, supporting the RVB-based SU(2) slave boson theory in cuprates.

Findings

The nodal slope of the quasiparticle gap follows the pseudogap temperature dependence.

The maximum gap relates to the pseudogap temperature as Δ_q=0.46k_B T^*.

Superconducting transition temperature depends on the residual density of states and nodal gap slope.

Abstract

Through the measurements of magnetic field dependence of specific heat in $La_{2-x}Sr_xCuO_4$ in zero temperature limit, we determined the nodal slope $v_\Delta$ of the quasiparticle gap. It is found that $v_\Delta$ has a very similar doping dependence of the pseudogap temperature $T^*$ or value $\Delta_p$. Meanwhile the virtual maximum gap at ($\pi,0$) derived from $v_\Delta$ is found to follow the simple relation $\Delta_q=0.46k_BT^*$ upon changing the doping concentration. This strongly suggests a close relationship between the pseudogap and superconductivity. It is further found that the superconducting transition temperature is determined by both the residual density of states of the pseudogap phase and the nodal gap slope in the zero temperature limit, namely, $T_c \approx \beta v_\Delta \gamma_n(0)$, where $\gamma_n(0)$ is the extracted zero temperature value of the normal state specific heat coefficient which is proportional to the size of the residual Fermi arc $k_{arc}$. This manifests that the superconductivity may be formed by forming a new gap on the Fermi arcs near nodes below $T_c$. These observations mimic the key predictions of the SU(2) slave boson theory based on the general resonating-valence-bond (RVB) picture.