Spectral and thermodynamic properties of a strong-leg quantum spin ladder

TL;DR

This study combines theoretical and experimental methods to explore the unique spectral and thermodynamic behaviors of a strong-leg quantum spin ladder, revealing persistent bound states and attractive excitations in magnetic fields.

Contribution

It provides new insights into the spectral properties and excitations of strong-leg spin ladders, highlighting differences from strong-rung systems and effects of inter-ladder interactions.

Findings

Long-lived two-triplon bound state persists across the Brillouin zone.

Elementary excitations in the spin liquid phase are attractive.

Weak inter-ladder interactions promote 3D ordering.

Abstract

The strong-leg S=1/2 Heisenberg spin ladder system (C7H10N)2CuBr4 is investigated using Density Matrix Renormalization Group (DMRG) calculations, inelastic neutron scattering, and bulk magneto-thermodynamic measurements. Measurements showed qualitative differences compared to the strong-rung case. A long-lived two-triplon bound state is confirmed to persist across most of the Brillouin zone in zero field. In applied fields, in the Tomonaga-Luttinger spin liquid phase, elementary excitations are attractive, rather than repulsive. In the presence of weak inter-ladder interactions, the strong-leg system is considerably more prone to 3-dimensional ordering.