Melting of the charge density wave by generation of pairs of topological defects in UTe₂

Topological defects are singularities in an ordered phase that can have a profound effect on phase transitions and serve as a window into the order parameter. Examples of topological defects include dislocations in charge density waves and vortices in a superconductor or pair density wave, where the latter is a condensate of Cooper pairs with finite momentum. Here we demonstrate the role of topological defects in the magnetic-field-induced disappearance of a charge density wave in the heavy-fermion superconductor UTe₂. We reveal pairs of topological defects of the charge density wave with positive and negative phase winding. The pairs are directly correlated with zeros in the charge density wave amplitude and increase in number with increasing magnetic field. A magnetic field generates vortices of the superconducting and pair density wave orders that can create topological defects in the charge density wave and induce the experimentally observed melting of this charge order at the upper critical field. Our work reveals the important role of magnetic-field-generated topological defects in the melting of the charge density wave order parameter in UTe₂ and provides support for the existence of a pair density wave order on the surface.