Emergent topological excitations in a two-dimensional quantum spin system

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	Emergent topological excitations in a two-dimensional quantum spin system
	Shao, H; Guo, WN; Sandvik, AW
刊名	PHYSICAL REVIEW B
	2015
卷号	91 期号:9 页码:94426
通讯作者	Shao, H (reprint author), Beijing Normal Univ, Dept Phys, Beijing 100875, Peoples R China.
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.
学科主题	Physics
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
语种	英语
内容类型	期刊论文
源URL	[http://ir.itp.ac.cn/handle/311006/21048]
专题	理论物理研究所_理论物理所1978-2010年知识产出
推荐引用方式 GB/T 7714	Shao, H,Guo, WN,Sandvik, AW. Emergent topological excitations in a two-dimensional quantum spin system[J]. PHYSICAL REVIEW B,2015,91(9):94426.
APA	Shao, H,Guo, WN,&Sandvik, AW.(2015).Emergent topological excitations in a two-dimensional quantum spin system.PHYSICAL REVIEW B,91(9),94426.
MLA	Shao, H,et al."Emergent topological excitations in a two-dimensional quantum spin system".PHYSICAL REVIEW B 91.9(2015):94426.