Dynamical spin structure factor from a variational Monte Carlo perspective*

The spin dynamical structure factor is computed within a variational framework to study frustrated Heisenberg models in one and two dimensions. Starting from Gutzwiller-projected fermionic wave functions, the low-energy spectrum is constructed by considering two-spinon excitations. Benchmarks on the one-dimensional J₁-J₂ model are considered. Here, an excellent description of both the gapless and gapped (dimerized) phases is obtained [1]. In the square lattice, we obtain the distinctive spectral signatures of the transition between the Neel and the spin-liquid phases that takes place for J₂/J₁ ∼0.45. By increasing the frustration, the magnon excitation at q=(π,0) and (0,π) broadens, suggesting the tendency towards a spin fractionalization. In addition, its energy softens, indicating the presence of gapless states at the transition and within the spin-liquid phase [2]. On the triangular lattice, we assess the possibility to have the magnon decay, as suggested by using spin-wave approaches for non-collinear magnetic orders [3]. The evolution of the spin dynamical structure factor when approaching the magnetically disordered phase in presence of a next-nearest-neighbor coupling J₂ is also included [4]. Preliminary calculations on the kagome lattice are also discussed.

[1] F. Ferrari, A. Parola, S. Sorella, and F. Becca, Physical Rev. B 97, 235103 (2018).
[2] F. Ferrari and F. Becca, Phys. Rev. B 98, 100405 (2018).
[3] A.L. Chernyshev and M.E. Zhitomirsky, Phys. Rev. Lett. 97, 207102 (2006).
[4] F. Ferrari and F. Becca, in preparation.