Spin susceptibility in a pseudogap state with fluctuating spiral magnetic order

We compute the electron spin susceptibility in the pseudogap regime of the two-dimensional Hubbard model within an SU(2) gauge theory of fluctuating magnetic order. Electrons are fractionalized into fermionic chargons and bosonic spinons. The chargons, described by a renormalized mean-field theory, order in a Néel or spiral pseudospin state below a transition temperature T*. Spinon fluctuations, governed by a nonlinear sigma model with microscopically computed stiffnesses, higgs the SU(2) gauge group, and thus prevent breaking of the physical spin symmetry at any finite temperature. The resulting spin susceptibility reproduces key pseudogap phenomenology: a spin gap in S(q, ω), a strong suppression of the uniform spin susceptibility κₛ below T*, and an exponentially vanishing NMR relaxation rate T₁^-1 at low T in the quantum disordered regime. At low hole doping, S(q, ω) exhibits nematicity below Tₙₑₘ < T*, which persists at larger dopings for any T<T*.