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Article: Nearly deconfined spinon excitations in the square-lattice spin-1=2 Heisenberg antiferromagnet
Title | Nearly deconfined spinon excitations in the square-lattice spin-1=2 Heisenberg antiferromagnet |
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Authors | |
Issue Date | 2017 |
Publisher | American Physical Society. The Journal's web site is located at http://journals.aps.org/prx/ |
Citation | Physical Review X, 2017, v. 7 n. 4, article no. 041072 , p. 1-26 How to Cite? |
Abstract | We study the spin-excitation spectrum (dynamic structure factor) of the spin-1=2 square-lattice Heisenberg antiferromagnet and an extended model (the J-Q model) including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on CuðDCOOÞ2 · 4D2O, where a broad spectral-weight continuum at wave vector q ¼ ðπ; 0Þ was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at ðπ; 0Þ show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q ¼ ðπ=2; π=2Þ (as also seen experimentally). We further investigate the reasons for the small magnon weight at ðπ; 0Þ and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J-Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at ðπ; 0Þ in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile ðπ; 0Þ-magnon pole in the Heisenberg model and its depletion in the J-Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at ðπ; 0Þ in the Heisenberg model, as well as the energy maximum and smaller continuum at ðπ=2; π=2Þ. It can also account for the rapid loss of the ðπ; 0Þ magnon with increasing Q and the remarkable persistence of a large magnon pole at q ¼ ðπ=2; π=2Þ even at the deconfined critical point. The fragility of the magnons close to ðπ; 0Þ in the Heisenberg model suggests that various interactions that likely are important in many materials—e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions—may also destroy these magnons and lead to even stronger spinon signatures than in CuðDCOOÞ2 · 4D2O. |
Persistent Identifier | http://hdl.handle.net/10722/268481 |
ISSN | 2023 Impact Factor: 11.6 2023 SCImago Journal Rankings: 5.896 |
ISI Accession Number ID |
DC Field | Value | Language |
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dc.contributor.author | Shao, Hui | - |
dc.contributor.author | Qin, Yan Qi | - |
dc.contributor.author | Capponi, Sylvain | - |
dc.contributor.author | Chesi, Stefano | - |
dc.contributor.author | Meng, Zi Yang | - |
dc.contributor.author | Sandvik, Anders W. | - |
dc.date.accessioned | 2019-03-25T07:59:48Z | - |
dc.date.available | 2019-03-25T07:59:48Z | - |
dc.date.issued | 2017 | - |
dc.identifier.citation | Physical Review X, 2017, v. 7 n. 4, article no. 041072 , p. 1-26 | - |
dc.identifier.issn | 2160-3308 | - |
dc.identifier.uri | http://hdl.handle.net/10722/268481 | - |
dc.description.abstract | We study the spin-excitation spectrum (dynamic structure factor) of the spin-1=2 square-lattice Heisenberg antiferromagnet and an extended model (the J-Q model) including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on CuðDCOOÞ2 · 4D2O, where a broad spectral-weight continuum at wave vector q ¼ ðπ; 0Þ was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at ðπ; 0Þ show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q ¼ ðπ=2; π=2Þ (as also seen experimentally). We further investigate the reasons for the small magnon weight at ðπ; 0Þ and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J-Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at ðπ; 0Þ in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile ðπ; 0Þ-magnon pole in the Heisenberg model and its depletion in the J-Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at ðπ; 0Þ in the Heisenberg model, as well as the energy maximum and smaller continuum at ðπ=2; π=2Þ. It can also account for the rapid loss of the ðπ; 0Þ magnon with increasing Q and the remarkable persistence of a large magnon pole at q ¼ ðπ=2; π=2Þ even at the deconfined critical point. The fragility of the magnons close to ðπ; 0Þ in the Heisenberg model suggests that various interactions that likely are important in many materials—e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions—may also destroy these magnons and lead to even stronger spinon signatures than in CuðDCOOÞ2 · 4D2O. | - |
dc.language | eng | - |
dc.publisher | American Physical Society. The Journal's web site is located at http://journals.aps.org/prx/ | - |
dc.relation.ispartof | Physical Review X | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.title | Nearly deconfined spinon excitations in the square-lattice spin-1=2 Heisenberg antiferromagnet | - |
dc.type | Article | - |
dc.description.nature | published_or_final_version | - |
dc.identifier.doi | 10.1103/PhysRevX.7.041072 | - |
dc.identifier.scopus | eid_2-s2.0-85039839919 | - |
dc.identifier.volume | 7 | - |
dc.identifier.issue | 4 | - |
dc.identifier.spage | article no. 041072, p. 1 | - |
dc.identifier.epage | article no. 041072, p. 26 | - |
dc.identifier.isi | WOS:000418920000001 | - |
dc.identifier.issnl | 2160-3308 | - |