Title:String magnetic states: A possible way toward a unified understanding on 1D and 2D quantum magnetic systems

Speaker: Jianda Wu  Shanghai Tsung-Dao Lee Center

Time:2025-02-24 10：00

Venue: Room W105,  Physics Building

Abstract:Based on the algebraic Bethe ansatz formalism, we study spin dynamics in the anti-ferromagnetic spin-1/2 XXZ chain with the Ising anisotropy via the form-factor formulae. Various excitations at different energy scales are identified crucial to the dynamic spin structure factors under the guidance of sum rules. At small magnetic polarization, gapless excitations of psinons and antipsinons corresponding to length-1 string (trivial string), dominate the low energy spin dynamics. In contrast, spin dynamics at intermediate and high energies is characterized by the length two- and three-string states. The dynamic spectra of the identified dominant excitations evolve with clear energy separations when tuning the magnetic field, conveying a simple and straightforward way to clearly identify the novel string excitations as well as its dispersions in proper condensed matter systems. Our predictions have been experimentally confirmed on the quasi-one-dimensional material SrCo₂V₂O₈ and BaCo₂V₂O₈. The concrete progress on string magnetic states further motivates us to develop truncated string state space approach (TS³A) following a simple observation of fast decay of spectra weight in the spin dynamic structure factor with increasing string length. The TS³A then successfully provides a string-state-based unified picture for the spin dynamics observed in different magnetic phase in the material of YbAlO₃ whose effective model becomes non-integrable in the magnetic ordering phases. The TS³A we constructed paves down a possible way toward a unified understanding on 1D and 2D quantum magnetic system.