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题名: Emergent topological excitations in a two-dimensional quantum spin system
作者: Shao, H;  Guo, WN;  Sandvik, AW
刊名: PHYSICAL REVIEW B
出版日期: 2015
卷号: 91, 期号:9, 页码:94426
学科分类: Physics
DOI: http://dx.doi.org/10.1103/PhysRevB.91.094426
通讯作者: Shao, H (reprint author), Beijing Normal Univ, Dept Phys, Beijing 100875, Peoples R China.
文章类型: Article
英文摘要: We study the mechanism of decay of a topological (winding-number) excitation due to finite-size effects in a two-dimensional valence-bond solid state, realized in an S = 1/2 spin model (J- Q model) with six-spin interactions and studied using projector Monte Carlo simulations in the valence bond basis. A topological excitation with winding number |W| > 0 contains domain-walls, which are unstable due to the emergence of long valence bonds in the wave function, unlike in effective descriptions with the quantum dimer model (which by construction includes only short bonds). We find that the lifetime of the winding number in imaginary time, which is directly accessible in the simulations, diverges as a power of the system length L. The energy can be computed within this time (i.e., it converges toward a "quasieigenvalue" before the winding number decays) and agrees for large L with the domain-wall energy computed in an open lattice with boundary modifications enforcing a domain-wall. Constructing a simplified two-state model which can be solved in real and imaginary time, and using the imaginary-time behavior from the simulations as input, we find that the real-time decay rate out of the initial winding sector is exponentially small in L. Thus, the winding number rapidly becomes a well-defined conserved quantum number for large systems, supporting the conclusions reached by computing the energy quasieigenvalues. Including Heisenberg exchange interactions which bring the system to a quantum-critical point separating the valence-bond solid from an antiferromagnetic ground state (the putative "deconfined" quantum-critical point), we can also converge the domain-wall energy here and find that it decays as a power law of the system size. Thus, the winding number is an emergent quantum number also at the critical point, with all winding number sectors becoming degenerate in the thermodynamic limit. This supports the description of the critical point in terms of a U(1) gauge-field theory.
类目[WOS]: Physics, Condensed Matter
关键词[WOS]: PEIERLS GROUND-STATES ;  VALENCE-BOND STATE ;  HEISENBERG-ANTIFERROMAGNET ;  2 DIMENSIONS ;  SUPERCONDUCTIVITY ;  MODEL ;  EXPANSION ;  PHASE
收录类别: SCI
项目资助者: NSFC [11175018] ;  NSF [DMR-1410126, PHY-1211284] ;  Simons Foundation
语种: 英语
Citation statistics: 
内容类型: 期刊论文
URI标识: http://ir.itp.ac.cn/handle/311006/21048
Appears in Collections:理论物理所2015年知识产出_期刊论文

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Recommended Citation:
Shao, H,Guo, WN,Sandvik, AW. Emergent topological excitations in a two-dimensional quantum spin system[J]. PHYSICAL REVIEW B,2015,91(9):94426.
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