37 research outputs found
Electron Spin Resonance in Quasi-One-Dimensional Quantum Antiferromagnets: Relevance of Weak Interchain Interactions
We discuss universal features on the electron spin resonance (ESR) of a
temperature-induced Tomonaga-Luttinger liquid phase in a wide class of weakly
coupled antiferromagnetic spin chains such as spin ladders, spin tubes
and three-dimensionally coupled spin chains. We show that the ESR linewidth of
various coupled chains increases with lowering temperature while the linewidth
of a single spin chain is typically proportional to temperature. This
broadening with lowering temperature is attributed to anisotropic interchain
interactions and has been indeed observed in several kinds of three-dimensional
(3D) magnets of weakly coupled spin chains above the 3D ordering temperature.
We demonstrate that our theory can account for anomalous behaviors of the
linewidths in an four-leg spin tube compound CuClHCSO (abbreviated to Sul-CuCl) and a three-dimensionally
coupled spin chain compound CuClNCH
Spontaneously magnetized Tomonaga-Luttinger liquid in frustrated quantum antiferromagnets
We develop a theory of spontaneously magnetized Tomonaga-Luttinger liquid
(SMTLL) in geometrically frustrated quasi-one-dimensional quantum magnets by
taking an ferrimagnet on a union-jack lattice as an example. We show
that a strong frustration leads to a spontaneous magnetization because of the
ferrimagnetic nature of lattice. Due to the ferrimagnetic order, the local
magnetization has an incommensurate oscillation with the position. We show that
the spontaneously magnetized TLL is smoothly connected to the existence of a
Nambu-Goldstone boson in the canted ferrimagnetic phase of a two-dimensional
frustrated antiferromagnet
Topological transition between competing orders in quantum spin chains
We study quantum phase transitions between competing orders in
one-dimensional spin systems. We focus on systems that can be mapped to a
dual-field double sine-Gordon model as a bosonized effective field theory. This
model contains two pinning potential terms of dual fields that stabilize
competing orders and allows different types of quantum phase transition to
happen between two ordered phases. At the transition point, elementary
excitations change from the topological soliton of one of the dual fields to
that of the other, thus it can be characterized as a topological transition. We
compute the dynamical susceptibilities and the entanglement entropy, which
gives us access to the central charge, of the system using a numerical
technique of infinite time-evolving block decimation and characterize the
universality class of the transition as well as the nature of the order in each
phase. The possible realizations of such transitions in experimental systems
both for condensed matter and cold atomic gases are also discussed.Comment: 8 pages, 7 figure
Electron spin resonance shifts in S=1 antiferromagnetic chains
We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg
antiferromagnetic chains with a weak single-ion anisotropy based on several
effective field theories, the O(3) nonlinear sigma model (NLSM) in the Haldane
phase, free fermion theories around the lower and the upper critical fields. In
the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator
which creates two magnons at the same time and position. Therefore, even inside
a parameter range where free magnon approximation is valid, we have to take
interactions among magnons into account. Though the O(3) NLSM is only valid in
the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov
operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts
near the lower critical field in a similar manner to discussions in Haldane
phase. We present that our theory gives quantitative agreements with recent ESR
experimental results on an spin-1 chain compounds NDMAP
Anomalous behavior of the spin gap of a spin-1/2 two-leg antiferromagnetic ladder with Ising-like rung interactions
Using mainly numerical methods, we investigate the width of the spin gap of a
spin-1/2 two-leg ladder described by \cH= J_\rl \sum_{j=1}^{N/2} [ \vS_{j,a}
\cdot \vS_{j+1,a} + \vS_{j,b} \cdot \vS_{j+1,b} ] + J_\rr \sum_{j=1}^{N/2}
[\lambda (S^x_{j,a} S^x_{j,b} + S^y_{j,a} S^y_{j,b}) + S^z_{j,a} S^z_{j,b}] ,
where denotes the -component of the spin-1/2
operator at the -th site of the chain. We mainly focus on the J_\rr
\gg J_\rl > 0 and case. The width of the spin gap as a
function of anomalously increases near ; for instance,
for when . The gap formation
mechanism is thought to be different for the
cases. Since, in usual cases, the width of the gap becomes zero or small at the
point where the gap formation mechanism changes, the above gap-increasing
phenomenon in the present case is anomalous. We explain the origin of this
anomalous phenomenon by use of the degenerate perturbation theory. We also draw
the ground-state phase diagram.Comment: 4 pages, 11 figures; Proc. "The International Conference on Quantum
Criticality and Novel Phases" (2012), to be published in Phys. Stat. Solidi