2018/02/28 by E. A. Ghioldi, M. G. Gonzalez, Shang-Shun Zhang +5 · 2 citations
Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Antiferromagnetism #Bound state #Condensed matter physics #Ferromagnetism #Ground state #Heisenberg model #Magnetic and transport properties of perovskites and related materials #Magnon #Physics #Physics of Superconductivity and Magnetism #Quantum #Quantum fluctuation #Quantum mechanics #Quantum phase transition #Semiclassical physics #Spinon #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.98.184403
published as Phys. Rev. B 98, 184403 (2018) · 28 pages + 8 figures. Extended version
arxiv created 2018/09/10 · openalex created_date 2018/09/27 · openalex publication_date 2018/11/02 · arxiv updated 2018/11/06 · openalex updated_date 2026/08/06
We compute the zero-temperature dynamical structure factor S(\mathbitq,\ensuremathω) of the triangular lattice Heisenberg model (TLHM) using a Schwinger boson approach that includes the Gaussian fluctuations (1/N corrections) of the saddle-point solution. While the ground state of this model exhibits a well-known 120^\ensuremath∘ magnetic ordering, experimental observations have revealed a strong quantum character of the excitation spectrum. We conjecture that this phenomenon arises from the proximity of the ground state of the TLHM to the quantum melting point separating the magnetically ordered and spin-liquid states. Within this scenario, magnons are described as collective modes (two-spinon bound states) of a spinon condensate (Higgs phase) that spontaneously break the SU(2) symmetry of the TLHM. Crucial to our results is the proper account of this spontaneous symmetry breaking. The main qualitative difference relative to semiclassical treatments (1/S expansion) is the presence of a high-energy spinon continuum extending up to about three times the single-magnon bandwidth. In addition, the magnitude of the ordered moment (m=0.224) agrees very well with numerical results and the low-energy part of the single-magnon dispersion is in very good agreement with series expansions. Our results indicate that the Schwinger boson approach is an adequate starting point for describing the excitation spectrum of some magnetically ordered compounds that are near the quantum melting point separating this Higgs phase from the deconfined spin-liquid state.