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

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 $T<T_C$ . 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 ${\Delta }_k$ . 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 $\left(E\right)\le \Delta$ , so that bulk ${\Delta }_k$ 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 $q_i:i=1-6$ of interference wavevectors, showing that QSB dispersions $k$ (E) occur only for energies $\left(E\right)\le {\Delta }_{max}$ and only within the range of Fermi momenta projected onto the (0-11) crystal surface. In combination, these phenomena are consistent with a bulk ${\Delta }_k$ exhibiting spin-triplet, time-reversal conserving, odd-parity, a-axis nodal, B _3u symmetry in UTe₂.