Multi-triplet bound states and finite-temperature dynamics in highly frustrated quantum spin ladders

Abstract

Low-dimensional quantum magnets at finite temperatures present a complex interplay of quantum and thermal fluctuation effects in a restricted phase space. While some information about dynamical response functions is available from theoretical studies of the one-triplet dispersion in unfrustrated chains and ladders, little is known about the finite-temperature dynamics of frustrated systems. Experimentally, inelastic neutron scattering studies of the highly frustrated two-dimensional material SrCu${}_2$(BO${}_3$)${}_2$ show an almost complete destruction of the one-triplet excitation band at a temperature only 1/3 of its gap energy, accompanied by strong scattering intensities for apparent multi-triplet excitations. We investigate these questions in the frustrated spin ladder and present numerical results from exact diagonalization for the dynamical structure factor as a function of temperature. We find anomalously rapid transfer of spectral weight out of the one-triplet band and into both broad and sharp spectral features at a wide range of energies, including below the zero-temperature gap of this excitation. These features are multi-triplet bound states, which develop particularly strongly near the quantum phase transition, fall to particularly low energies there, and persist to all the way to infinite temperature. Our results offer valuable insight into the physics of finite-temperature spectral functions in SrCu${}_2$(BO${}_3$)${}_2$ and many other highly frustrated spin systems.

22 pages, 19 figures; published version: many small modifications

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Cited by in corpus (11)

• Topological Triplon Modes and Bound States in a Shastry-Sutherland Magnet
• Thermodynamic properties of the Shastry-Sutherland model throughout the dimer-product phase
• Thermal Critical Points and Quantum Critical End Point in the Frustrated Bilayer Heisenberg Antiferromagnet
• Finite-Temperature Dynamics and Thermal Intraband Magnon Scattering in Haldane Spin-One Chains
• Bound states and field-polarized Haldane modes in a quantum spin ladder
• Three-body bound states in antiferromagnetic spin ladders
• Magnetic field induced bound states in spin-$\frac{1}{2}$ ladders
• Magnetization process in a frustrated plaquette dimerized ladder
• Anomalous thermal broadening in the Shastry-Sutherland model and SrCu${}_2($BO${}_3{)}_2$
• Effects of Interactions on Dynamic Correlations of Hard-Core Bosons at Finite Temperatures
• Spin-singlet dimer phase in a frustrated square lattice under a magnetic field