Sibin Yang: Single-hole spectral function of the t-J-Q model

Thanks to improved methods for numerical analytic continuation, spectral functions with sharp features (peaks and edges) can now be extracted from imaginary-time correlation functions computed by quantum Monte Carlo (QMC) simulations. Here we test these new approaches on various one-dimensional spin systems with a single injected fermion, i.e., the single-hole spectral function. We focus on the different characteristics of systems with spin-charge separation and those in which a spin-polaron forms due to attractive interactions between the spin and the charge. Spin-charge separation is well understood in the conventional $t$-$J$ chain, which we confirm here. Turning on a multi-spin interaction $Q$ that eventually drives the system into a spontaneously dimerized (valence-bond solid) state, we see evidence of a spin-polaron formation already at small values of $Q$. Such instability of the fractionalized excitation was recently proposed also within an approximate scheme for a different class of models. In the dimerized chain and in a spin ladder, we see very clear signs of spin-polarons with two internal modes. Our results overall demonstrate the power of modern analytic continuation tools in combination with large-scale quantum Monte Carlo simulations.