Visualizing the low-energy electronic structure of the triplet superconductor UTe$_2$ through quasiparticle interference

TL;DR

This study uses quasiparticle interference imaging to map the Fermi surface of the triplet superconductor UTe2, revealing how uranium-derived bands contribute to intertwined charge density wave and pair density wave phases, with implications for topological surface states.

Contribution

It provides the first detailed visualization of UTe2's Fermi surface and links quasiparticle interference patterns to its complex intertwined orders and band structure.

Findings

Identification of uranium-derived bands influencing CDW and PDW phases

Observation of small Fermi pockets near the Fermi energy

Spectroscopic evidence of the CDW gap and its temperature dependence

Abstract

The identification, control and theoretical modelling of spin-triplet superconductors (STC) remain a central theme in quantum materials research. Intrinsic STC are rare but offer rich condensate properties and unique surface properties allowing insights into the nature of the spin-triplet order, and promising applications in quantum technologies. Owing to interactions, the order parameter in STCs can often be intertwined with other symmetry breaking orders like charge/spin density waves (CDW/SDW) or pair density waves (PDW) complicating their phase diagrams. UTe2 stands out as the only known odd-parity, STC that harbors such intertwined orders on the surface and possible topological surface states composed of Majorana fermions. While the (0-11) facet is the most heavily studied, the fermiology of this surface that gives rise to such exotic phenomena is still lacking and continues to be an area of active interest. Here, we employ low-temperature spectroscopic imaging to reveal the Fermi surface of UTe2 through quasiparticle interference. We find scattering originating from the uranium-derived bands that play a major role in the formation of the CDW and the PDW phases. Tunneling spectroscopy further reveals spectral signatures of the CDW gap, corroborating its onset temperature. Suppressing the CDW with a magnetic field, highlights the presence of small, circular Fermi pockets that disperse strongly near the Fermi energy. We discuss the nature of the interference patterns and the origin of the small Fermi pockets in the context of the calculated band structure and the unconventional CDW phase.