Magnetic-Field-Induced Bound States in Spin- 12 Ladders

Abstract

Motivated by the intriguing mode splittings in a magnetic field recently observed with inelastic neutron scattering in the spin ladder compound (C5H12N)2CuBr4 (BPCB), we investigate the nature of the spin ladder excitations using DMRG and analytical arguments. Starting from the fully frustrated ladder, for which we derive the low-energy spectrum, we show that bound states are generically present close to k = 0 in the dynamical structure factor of spin ladders above Hc1, and that they are characterized by a field-independent binding energy and an intensity that grows with H − Hc1. These predictions are shown to explain quantitatively the split modes observed in BPCB. arXiv:1912.01576v2 [cond-mat.str-el]

Investigating field-induced magnetic order in Han purple by neutron scattering up to 25.9 T

“…Thus the summary from our INS experiments is that the observed intensities are fully consistent with theoretical modeling based on Zeeman-split triplet modes over the full field range of the measurements up to 25 T, with no significant deterioration of data quality or fitting quality. Returning to the question of whether additional modes might appear in the spectrum around H c1 as a result of bound-state formation, we comment that this type of physics is strongly favored by interdimer frustration [77]. Recalling from the inset of Fig.…”

“…As an initial model for our spectral data, we will assume that the effect of the applied field is only to cause a Zeeman splitting of the three excited triplet states |t −,0,+ . However, it has been shown for the quasi-1D spin dimer system BPCB that additional bound states can form between excited triplets and the condensed triplets that are present above H c1 [77], and below we comment on the possible applicability of such a scenario in BaCuSi 2 O 6 . For the triplets |t −,0,+ , the ratio of the transition probabilities p −,0,+ s from the singlet ground state is given by p − s : p 0 s : p + s = 1:2:1 [41].…”

Investigating field-induced magnetic order in Han Purple by neutron scattering up to 25.9 T

“…Thus the summary from our INS experiments is that the observed intensities are fully consistent with theoretical modelling based on Zeeman-split triplet modes over the full field range of the measurements up to 25 T, with no significant deterioration of data quality or fitting quality. Returning to the question of whether additional modes might appear in the spectrum around H c1 as a result of bound-state formation, we comment that this type of physics is strongly favored by inter-dimer frustration [78]. Recalling from the inset of Fig.…”

“…As an initial model for our spectral data, we will assume that the effect of the applied field is only to cause a Zeeman splitting of the three excited triplet states, |t −,0,+ . However, it has been shown for the quasi-1D spin dimer system BPCB that additional bound states can form between excited triplets and the condensed triplets that are present above H c1 [78], and below we comment on the possible applicability of such a scenario in BaCuSi 2 O 6 . For the triplets |t −,0,+ , the ratio of the transition probabilities, p −,0,+ s , from the singlet ground state is given by p − s : p 0 s : p + s = 1:2:1 [41].…”

Accessing Multi-triplons in Spin Ladders using Resonant Inelastic X-ray Scattering

“…These dynamical correlation functions were also studied using numerical technqiues [18,19,29]. While these numerical approaches can provide high-resolution spectral functions [30,31], they do not yield an intrinsic physical understanding of the underlying processes and structure of the spectra. In contrast, the study of dynamical correlation functions using exact methods in the thermodynamic limit allow for a detailed characterization in terms of quasi-particle excitations.…”