# Visualizing the Odd-Parity Superconducting Order Parameter and Its Quasiparticle Surface Band in UTe2

## TL;DR

This paper uses advanced imaging techniques to visualize the unique superconducting properties of UTe2, revealing a non-chiral topological superconducting state.

## Contribution

The study provides direct visualization of the quasiparticle surface band and confirms the odd-parity, spin-triplet superconducting order in UTe2.

## Key findings

- An intense zero-energy Andreev conductance peak is observed at the UTe2 (0–11) crystal termination.
- Quasiparticle interference patterns reveal a sextet of interference wavevectors, indicating a specific dispersion of Bogoliubov quasiparticles.
- The findings are consistent with a spin-triplet, time-reversal conserving, odd-parity superconducting order in UTe2.

## Abstract

A distinctive identifier of nodal intrinsic topological superconductivity (ITS) would the appearance of an Andreev bound state on crystal surfaces parallel to the nodal axis, in the form of a topological quasiparticle surface band (QSB) appearing only for \documentclass[12pt]{minimal}
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\begin{document}$$T < T_{C}$$\end{document}T<TC. Moreover, the theory shows that specific QSB characteristics observable in tunneling to an s-wave superconductor can distinguish between chiral and non-chiral ITS order parameter \documentclass[12pt]{minimal}
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\begin{document}$$\Delta_{{\boldsymbol{k}}}$$\end{document}Δk. To search for such phenomena in UTe2, s-wave superconductive scan-tip scanning tunneling microscopy (STM) imaging was employed. It reveals an intense zero-energy Andreev conductance maximum at the UTe2 (0–11) crystal termination. The development of the zero-energy Andreev conductance peak into two finite-energy particle-hole symmetric conductance maxima as the tunnel barrier is reduced and then signifies that UTe2 superconductivity is non-chiral. Quasiparticle interference imaging (QPI) for an ITS material should be dominated by the QSB for energies within the superconductive energy gap \documentclass[12pt]{minimal}
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\begin{document}$$\left| E \right| \le {\Delta }$$\end{document}E≤Δ, so that bulk \documentclass[12pt]{minimal}
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\begin{document}$$\Delta_{{\boldsymbol{k}}}$$\end{document}Δk characteristics of the ITS can only be detected excursively. Again using a superconducting scan-tip, the in-gap quasiparticle interference patterns of the QSB of UTe2 were visualized. Specifically, a band of Bogoliubov quasiparticles appears as a characteristic sextet \documentclass[12pt]{minimal}
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\begin{document}$${\boldsymbol{q}}_{i} :i = 1 - 6{ }$$\end{document}qi:i=1-6 of interference wavevectors, showing that QSB dispersions \documentclass[12pt]{minimal}
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\begin{document}$$\boldsymbol{k}$$\end{document}k(E) occur only for energies \documentclass[12pt]{minimal}
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\begin{document}$$\left| E \right| \le \Delta_{\max }$$\end{document}E≤Δmax and only within the range of Fermi momenta projected onto the (0–11) crystal surface. In combination, these phenomena are consistent with a bulk \documentclass[12pt]{minimal}
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\begin{document}$$\Delta_{{\boldsymbol{k}}}$$\end{document}Δk exhibiting spin-triplet, time-reversal conserving, odd-parity, a-axis nodal, B3u symmetry in UTe2.