# Superconducting materials: the w$hole$ story

## TL;DR

This paper reviews Ted Geballe's extensive work on superconducting materials, emphasizing the central role of hole carriers in enabling superconductivity across various materials and discussing its implications for fundamental physics.

## Contribution

It highlights the unifying importance of hole carriers in superconductivity, proposing that all superconductors studied by Geballe involve hole carriers, including unconventional cases.

## Key findings

- Hole carriers are essential for superconductivity.
- Superconductivity in various materials involves hole carriers.
- Implications for understanding the physics of superconductivity.

## Abstract

Ted Geballe has contributed enormously to the knowledge of superconducting materials during an illustrious scientific career spanning seven decades, encompassing groundbreaking discoveries and studies of both so-called conventional and unconventional superconductors. On the year of his 100th birthday I would like to argue that all superconducting materials that Ted investigated, as well as those he did not, have one thing in common that is not generally recognized: hole carriers. This includes $PbTe$ doped with $Tl$, for which Ted has proposed that superconductivity is driven by negative-U pairing. I will discuss why hole carriers are necessary for a material to be a superconductor, and the implications of this for the understanding of the fundamental physics of superconductivity.