Observation of symmetry-protected zero modes in single-flux-quantum vortex cores of UTe₂

Visualization of superconducting vortices provide crucial insights to electron pairing and can nucleate topologically protected states. However, imaging the vortices of bulk spin-triplet superconductors at the atomic scale has remained elusive. Here, we use scanning tunneling microscopy (STM) to visualize vortices on the (011) surface of ultraclean UTe₂ single crystals (T_c = 2.1 K). UTe₂ is a prime candidate of spin triplet superconductors with substantial residual conductance at zero-energy. We introduce and employ d²𝐼/d𝑉² imaging as an effective technique for vortex visualization in such systems. Under an out-of-plane magnetic field, we observe triangular lattice of anisotropic single-flux-quantum vortices, with coherence lengths of ∼12 nm (4 nm) parallel (perpendicular) to the a-axis. The VL symmetry was robust under changes of magnetic field polarity and cooling history strongly supporting time-reversal invariant superconductivity under zero field. At vortex cores (VCs), we detect sharp, nonspliting zero-bias conductance peaks (ZBPs) persisting up to 8 T, consistent with symmetry-protected Majorana zero modes (MZMs) in a topological vortex line. Furthermore, each asymmetric vortex cores exhibits mirror-asymmetric doublet structure - one hosting zero bias and the other with enhanced apparent gap - suggesting the emergence of field induced multi-component order parameter.