Recent progress of scanning tunneling microscopy/spectroscopy study of pair density wave in superconductors

TL;DR

This review summarizes recent experimental advances in detecting and visualizing pair density waves in various superconductors using scanning tunneling microscopy and spectroscopy, highlighting their significance in understanding unconventional superconductivity.

Contribution

It provides a comprehensive overview of how STM/STS techniques have been employed to visualize and analyze PDWs across different superconductor families, advancing the field's understanding.

Findings

Visualization of charge density modulations associated with PDWs

Detection of PDW signatures in diverse superconductors

Discussion of future challenges and research directions

Abstract

A pair density wave (PDW) is a superconducting state characterized by an order parameter with finite center-of-mass momentum in the absence of an external magnetic field, thereby breaking the conventional translational symmetry in homogeneous superconductors. It is proposed that PDW emerges from magnetic interactions, strong electron-electron correlations, and their interplay with competing orders. In this review, we highlight recent advances in the detection and study of PDWs using scanning tunneling microscopy and spectroscopy (STM/STS). We focus on how the signatures of PDW have been experimentally visualized across a variety of extraordinary superconductors, including iron-based superconductors, cuprate superconductors, spin-triplet superconductors, kagome-lattice superconductors, and transition metal dichalcogenides. Beginning with an introduction to the fundamental concept of PDWs and the unique capabilities of STM/STS, particularly its atomic-scale spatial resolution and advanced data analysis techniques, we discuss key experimental findings, including the direct visualization of charge density modulations associated with PDWs. Finally, we discuss emerging challenges and future directions, aiming to inspire future research into the nature of PDWs in superconductors.