# $K$ -edge and $L_{3}$ -edge RIXS study of columnar and staggered quantum dimer phases of the square lattice Heisenberg model

## TL;DR

This study calculates the RIXS spectra at $K$ and $L_3$ edges for quantum dimer phases in the square lattice Heisenberg model, revealing characteristic excitation boundaries, a novel local constraint contribution, and implications for experimental identification of quantum states.

## Contribution

It introduces a detailed RIXS spectral analysis for columnar and staggered quantum dimer states, including a new contribution from local dimer constraints, aiding experimental differentiation of quantum phases.

## Key findings

- Two-triplon excitation energies range from 78-124 meV to 414-345 meV.
- A finite RIXS signal at (0,0) momentum transfer due to local constraints.
- Predicted RIXS signatures for various quantum dimer states and crystal effects.

## Abstract

We compute the $K$ and $L_{3}$ -edge resonant inelastic x-ray scattering (RIXS) spectrum of the columnar and the staggered quantum dimer states accessible to the square lattice Heisenberg magnet. Utilizing a bond operator representation mean field theory we investigate the RIXS features of the one- and two-triplon excitation spectrum supported by the quantum dimer model in the background of condensed singlet excitation. We find that the two-triplon excitation boundary lies within a 124 (78) meV to (414) 345 meV energy range for the columnar (staggered) phase. We estimated the two-triplon gap to be 124 (78) meV for the columnar (staggered) dimer phase. The highest intensity of the $K$ -edge RIXS spectrum is centralized approximately around the $(\pi/2,\pi/2)$ point for both the columnar and the staggered phases. At the $L_{3}$ -edge we study the one- and two- triplon signal considering experimental scattering geometry, polarization restriction, and experimental resolution effects. Our calculations find an additional contribution to the two-triplon RIXS signal, not previously reported in the literature, that originates from the local hard-core dimer constraint. This leads to a finite non-zero signal at the (0,0) momentum transfer which can offer an explanation for the existing ladder RIXS experiments and also predicts a non-zero signal for the two-dimensional quantum dimer system. We find that the $L_3$ edge RIXS response of the one- and two-triplon signal could exist in antiphase rung modulation for zero and $\pi$ as found in inelastic neutron scattering. We also consider static crystal twinning at the $L_3$ -edge RIXS signal to mimic realistic crystal effects. Since the disordered phase has the potential to harbor a variety of quantum paramagnetic states, our RIXS calculations provide useful signatures to identify the true nature of the ordering pattern.