Topological spin texture and d -vector rotation in spin-triplet superconductors: A case of UTe 2

A novel spin texture formed by Cooper pair spins is found theoretically with a phase string attached by half-quantized vortices at both ends in a unit cell and characterized by its topologically rich vortex structure in a spin-triplet pairing. It is stable at an intermediate field below a conventional singular vortex phase. The $d$-vector direction of this spin texture is tilted from the principal crystal axes, whose spin susceptibility is neither the normal Pauli one ${\ensuremath{\chi}}_{\mathrm{N}}$ nor zero, describing microscopically the process of the $d$-vector rotation phenomena observed recently in ${\mathrm{UTe}}₂$. We compare the spin texture and singular vortex state in relation to the quasiparticle structure with Majorana zero modes for STM, the nuclear spin resonance spectral line width for NMR and $\ensuremath{\mu}\mathrm{SR}$, and the vortex form factors for SANS to facilitate the identification of the pairing symmetry in ${\mathrm{UTe}}₂$.