Superfluid density in the slave-boson theory

TL;DR

This paper revises the slave-boson theory to accurately model superfluid density in high-temperature superconductors, addressing previous discrepancies and explaining doping independence of the linear temperature term, with successful application to electron-doped cuprates.

Contribution

It introduces an alternative superfluid density formulation using the London relation, improving agreement with experimental data and explaining doping effects in cuprates.

Findings

Correct temperature dependence of superfluid density achieved

Weakening of doping dependence of the linear temperature term

Qualitative agreement with experiments on electron-doped cuprates

Abstract

Despite of the success of the slave-boson theory in capturing qualitative physics of high-temperature superconductors like cuprates, it fails to reproduce the correct temperature-dependent behavior of superfluid density, let alone the independence of the linear temperature term on doping in the underdoped regimes of hole-doped cuprate, a common experimental observation in different cuprates. It remains puzzling up to now in spite of intensive theoretical efforts. For electron-doped case, even qualitative treatment is not reported at present time. Here we revisit these problems and provide an alternative superfluid density formulation by using the London relation instead of employing the paramagnetic current-current correlation function. The obtained formula, on the one hand, provides the correct temperature-dependent behavior of the superfluid density in the whole temperature regime, on the other hand, makes the doping dependence of the linear temperature term substantially weaken and a possible interpretation for its independence on doping is proposed. As an application, electron-doped cuprate is studied, whose result qualitatively agrees with existing experiments and successfully explains the origin of $d$- to anisotropic $s$-wave transition across the optimal doping. Our result remedies some failures of the slave-boson theory as employed to calculate superfluid density in cuprates and may be useful in the understanding of the related physics in other strongly correlated systems, e.g. Na$_{x}$CoO$_{2}$$\cdot$yH$_{2}$O and certain iron-based superconductors with dominating local magnetic exchange interaction.