Random Singlets and Permutation Symmetry in the Disordered Spin-2 Heisenberg Chain: A tree tensor strong disorder renormalization group study

Yen-Tung Lin^1*, Shao-Fu Liu¹, Pochung Chen¹, Yu-Cheng Lin²

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Graduate Institute of Applied Physics, National Chengchi University, Taipei, Taiwan

* Presenter:Yen-Tung Lin, email:aronton0502@gmail.com

We employ a tree tensor network strong disorder renormalization group (tSDRG) to study how randomness R affects the ground state of a disordered S=2 antiferromagnetic Heisenberg chain with bond alternation D. In the clean limit, dimerization produces two quantum critical points that separate three valence-bond solid (VBS) states, (σ,4−σ)=(2,2),(3,1),(4,0). As randomness increases, these clean limit critical points broaden into random-singlet (RS) critical lines that divide the corresponding random VBS phases. The RS lines merge at a multicritical point P3 at finite D and intermediate R. In the undimerized limit D=0, we further identify another multicritical point, P3′, which separates a gapless Haldane phase from an infinite-randomness critical line. These results establish a unified phase diagram in the (R,D) plane, demonstrate RS universality in a high-spin (S=2) system, and highlight the efficiency of tSDRG for exploring infinite-randomness criticality.

Keywords: Random Singlet (RS) (隨機單重態), Permutation Symmetry (置換對稱性), tree tensor strong disorder renormalization group, Disordered Spin Chain (無序自旋鏈), Valence Bond Solid (VBS) (價鍵固態)