Do electrons change their c-axis kinetic energy upon entering the superconducting state?

TL;DR

This paper discusses how electrons in cuprate high-temperature superconductors significantly lower their c-axis kinetic energy when transitioning to the superconducting state, supporting the interlayer tunneling mechanism over conventional theories.

Contribution

It provides a theoretical and experimental analysis showing electrons lower their c-axis kinetic energy in the superconducting state, supporting the interlayer tunneling mechanism.

Findings

Recent measurements support c-axis kinetic energy reduction in superconductivity

Proper sum rule application resolves optical and penetration depth puzzles

Supports interlayer tunneling as a key mechanism in cuprates

Abstract

The interlayer tunneling mechanism of the cuprate high temperature superconductors involves a conversion of the confinement kinetic energy of the electrons perpendicular to the CuO-planes ($c$-axis) in the normal state to the pair binding energy in the superconducting state. This mechanism is discussed and the arguments are presented from the point of view of general principles. It is shown that recent measurements of the $c$-axis properties support the idea that the electrons substantially lower their $c$-axis kinetic energy upon entering the superconducting state, a change that is nearly impossible in any conventional mechanism. The proper use of a $c$-axis conductivity sum rule is shown to resolve puzzles involving the penetration depth and the optical measurements.