6 January 2023 Fri 3 pm

We study the nonlinear response of non-integrable 1D spin models using infinite matrix-product state techniques. As a benchmark and demonstration of the method, we first calculate the 2D coherent spectroscopy for the exactly soluble ferromagnetic transverse field Ising model, where excitations are fractionalized particles (spinons). We then investigate the distinct signatures of confined bound states by introducing a longitudinal field and observe the emergence of strong off-diagonal signals. To interpret the observed phenomena, we use a two-kink approximation to perturbatively compute the 2D spectra. We find good agreement in comparison with the exact results of the infinite matrix-product state method in the strongly confined regime. We discuss the relevance of our results for quasi−1D Ising spin chain materials such as CoNb2O6.

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