Many-body electronic structure in pyrochlore superconductor CsBi2 and spin liquid Pr2Ir2O7

TL;DR

This study uses atomic-scale scanning tunneling microscopy to explore the complex electronic states of pyrochlore superconductors CsBi2 and spin liquid Pr2Ir2O7, revealing novel surface structures, superconducting gaps, vortex lattices, and Kondo resonances.

Contribution

First atomic-scale imaging of (111) surfaces in pyrochlore CsBi2 and Pr2Ir2O7, uncovering their electronic structures and many-body phenomena related to geometric frustration.

Findings

CsBi2 exhibits a strong-coupling superconducting gap with a 4.7 ratio of 2Δ/kBTC.

Applied magnetic fields induce vortex lattices with three-fold symmetry in CsBi2.

Pr2Ir2O7 shows a spatially modulated Kondo resonance with Zeeman splitting under magnetic field.

Abstract

The pyrochlore lattice materials can exhibit geometrical frustration, while the related many-body electronic states remain elusive. In this work, we performed scanning tunneling microscopy measurements on the pyrochlore superconductor CsBi2 and spin liquid Pr2Ir2O7 at 0.3 K. For the first time, we obtained atomically resolved images of their (111) surfaces, revealing a hexagonal lattice or a kagome lattice. Tunneling spectroscopy in CsBi2 reveals a nearly fully opened superconductivity gap. The ratio of 2{\Delta}/kBTC = 4.7 suggests relatively strong coupling superconductivity, as compared with that in kagome superconductors AV3Sb5 (A = K, Rb, Cs). In contrast to the previous study categorizing CsBi2 as a type-I superconductor, the applied magnetic field induces a hexagonal vortex lattice in which each vortex core exhibits an intriguing three-fold symmetry state. In Pr2Ir2O7, we observed a spatially homogeneous Kondo-lattice resonance, which is compared with that in the kagome Kondo-lattice material CsCr6Sb6. We further discover that the Kondo resonance exhibits a spatial modulation with three-fold symmetry, and the applied magnetic field induces a Zeeman splitting of the Kondo resonance with intriguing atomic site dependence. We discuss the relations of these many-body electronic phenomena with the pyrochlore lattice geometry and its charge or spin frustration. Our systematic observations offer atomic-scale insights into the many-body electronic structures of the geometrically frustrated pyrochlore superconductors and spin liquids.