In-plane optical spectral weight transfer in optimally doped Bi$_{2}$Sr$_{2}$Ca$_{2}$Cu$_{3}$O$_{10}$

TL;DR

This study investigates how the in-plane optical spectral weight redistributes in optimally doped Bi2223 superconductors, revealing a kinetic energy lowering below Tc that challenges conventional BCS theory and scales with Tc.

Contribution

It provides the first detailed analysis of spectral weight transfer in tri-layer Bi2223, showing a kinetic energy decrease below Tc, which is larger than in bi-layer compounds and scales with critical temperature.

Findings

Spectral weight increases below Tc at 1 eV cutoff.

Kinetic energy of holes decreases in the superconducting state.

Effect size correlates with the critical temperature.

Abstract

We examine the redistribution of the in-plane optical spectral weight in the normal and superconducting state in tri-layer \bbb (Bi2223) near optimal doping ($T_c$ = 110 K) on a single crystal via infrared reflectivity and spectroscopic ellipsometry. We report the temperature dependence of the low-frequency integrated spectral weight $W(\Omega_c)$ for different values of the cutoff energy $\Omega_c$. Two different model-independent analyses consistently show that for $\Omega_c$ = 1 eV, which is below the charge transfer gap, $W(\Omega_c)$ increases below $T_c$, implying the lowering of the kinetic energy of the holes. This is opposite to the BCS scenario, but it follows the same trend observed in the bi-layer compound \bb (Bi2212). The size of this effect is larger in Bi2223 than in Bi2212, approximately scaling with the critical temperature. In the normal state, the temperature dependence of $W(\Omega_c)$ is close to $T^2$ up to 300 K.