Abstract
We investigate spin chains with bilinear-biquadratic (BLBQ) spin interactions as a function of an applied magnetic field h. At the Uimin-Lai-Sutherland (ULS) critical point we find a gapless to gapless transition revealed by the dynamical structure factor S(q,ω) as a function of h. At h=0, the envelope of the lowest-energy excitations goes soft at two points, q1=2π/3 and q2=4π/3, dubbed the phase A. With increasing field, the spectral peaks at each of the gapless points bifurcate, making in total four soft modes, and combine to form a new set of excitations that soften at a single point q=π at hc1≈0.94. Beyond hc1 the system enters another gapless B phase until the transition at hc2=4 to the fully polarized phase. We compare the ULS model results with those for the Affleck-Kennedy-Lieb-Tasaki model as a representative of the gapped Haldane phase. We explain the mechanism of the gapless to gapless transition in the ULS model using its conserved charges and a spinon band picture. We also discuss the universality of central charges of the BLBQ family of models subjected to a magnetic field.
| Original language | English |
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| Article number | 014435 |
| Journal | Physical Review B |
| Volume | 105 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 1 2022 |
Funding
We thank Dr. E. Miles Stoudenmire for help with the Intelligent Tensor Library ( itensor ) open source code. Most of the results for the static results were obtained with itensor ; the dynamics (real frequency) results were obtained with , and see also . S.F. and N.T. acknowledge support from U.S. Department of Energy (DOE) Grant No. DE-FG02-07ER46423. Computations were performed using the Unity cluster at the Ohio State University and Ohio super computing center (OSC). G.A. was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences, Division of Materials Sciences and Engineering. G.A. was also supported by the ExaTN ORNL LDRD.