Pseudogap State in High-$T_c$ Superconductors: an Infrared Study

TL;DR

This study investigates the pseudogap state in high-T_c superconductors across various doping levels using infrared spectroscopy, revealing how the pseudogap evolves with doping, temperature, and impurities through a comprehensive electromagnetic response analysis.

Contribution

It provides a detailed infrared analysis of the pseudogap state across the entire doping range, employing a memory-function approach to clarify the charge dynamics in underdoped superconductors.

Findings

Pseudogap response varies with doping and temperature.

Memory-function analysis highlights the pseudogap's impact on charge dynamics.

Infrared data correlates with other experimental techniques.

Abstract

We report on a study of the electromagnetic response of three different families of high-T_c superconductors that in combination allowed us to cover the whole doping range from under- to overdoped. The discussion is focused on the ab-plane charge dynamics in the {\it pseudogap state} which is realized in underdoped materials below a characteristic temperature T^*; a temperature that can significantly exceed the superconducting transition temperature T_c. We explore the evolution of the pseudogap response by changing the doping level, by varying the temperature from the above to below T^*, or by introducing impurities in the underdoped compounds. We employ a memory-function analysis of the ab-plane optical data that allows us to observe the effect of the pseudogap most clearly. We compare the infrared data with other experimental results, including c-axis optical response, dc transport, and angular resolved photoemission.