Incommensurate dynamic correlations in the quasi-two-dimensional spin liquid BiCu2PO6

TL;DR

This study uses inelastic neutron scattering to explore the incommensurate dynamic correlations in the spin liquid BiCu2PO6, revealing two dispersing spin excitation branches with incommensurate wavevectors and energy gaps, influenced by frustration and anisotropic interactions.

Contribution

It provides detailed experimental evidence of incommensurate spin excitations and highlights the role of frustration and anisotropic interactions in BiCu2PO6's spin liquid state.

Findings

Two spin excitation branches with gaps of 1.90 and 3.95 meV

Incommensurate wavevectors due to frustration

Temperature-dependent activation of excitations

Abstract

We report detailed inelastic neutron scattering measurements on single crystals of the frustrated two-leg ladder BiCu2PO6, whose ground state is described as a spin liquid phase with no long-range order down to 6 K. Two branches of steeply dispersing long-lived spin excitations are observed with excitation gaps of \Delta_1 = 1.90(9) meV and \Delta_2 = 3.95(8) meV. Significant frustrating next-nearest neighbour interactions along the ladder leg drive the minimum of each excitation branch to incommensurate wavevectors \zeta_1 = 0.574\pi and \zeta_2 = 0.553\pi for the lower and upper energy branches respectively. The temperature dependence of the excitation spectrum near the gap energy is consistent with thermal activation into singly and doubly degenerate excited states. The observed magnetic excitation spectrum as well as earlier thermodynamic data could be consistently explained by the presence of strong anisotropic interactions in the ground state Hamiltonian.