358 research outputs found
NMR relaxation rate and dynamical structure factors in nematic and multipolar liquids of frustrated spin chains under magnetic fields
Recently, it has been shown that spin nematic (quadrupolar) or higher
multipolar correlation functions exhibit a quasi long-range order in the wide
region of the field-induced Tomonaga-Luttinger-liquid (TLL) phase in spin-1/2
zigzag chains. In this paper, we point out that the temperature dependence of
the NMR relaxation rate 1/T_1 in these multipolar TLLs is qualitatively
different from that in more conventional TLLs of one-dimensional quantum
magnets (e.g., the spin-1/2 Heisenberg chain); 1/T_1 decreases with lowering
temperature in multipolar TLL. We also discuss low-energy features in spin
dynamical structure factors which are characteristic of the multipolar TLL
phases.Comment: 4+epsilon pages, 2 figures, published versio
Spin-Nematic and Spin-Density-Wave Orders in Spatially Anisotropic Frustrated Magnets in a Magnetic Field
We develop a microscopic theory of finite-temperature spin-nematic orderings
in three-dimensional spatially anisotropic magnets consisting of weakly-coupled
frustrated spin-1/2 chains with nearest-neighbor and next-nearest-neighbor
couplings in a magnetic field. Combining a field theoretical technique with
density-matrix renormalization group results, we complete finite-temperature
phase diagrams in a wide magnetic-field range that possess spin-bond-nematic
and incommensurate spin-density-wave ordered phases. The effects of a four-spin
interaction are also studied. The relevance of our results to
quasi-one-dimensional edge-shared cuprate magnets such as LiCuVO4 is discussed.Comment: 5 pages (2 column version), 4 figures, Revtex, published versio
Octupolar order in the multiple spin exchange model on a triangular lattice
We show how a gapless spin liquid with hidden octupolar order arises in an
applied magnetic field, in a model applicable to thin films of 3He with
competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions.
Evidence is also presented for nematic -- i.e., quadrupolar -- correlations
bordering on ferromagnetism in the absence of a magnetic field.Comment: 4 pages, 5 figure
Instability of isolated triplet excitations on the Shastry-Sutherland lattice (SSL)
Configurations of singlets and triplets on the SSL have been proposed in the
literature as variational ground states of the Shastry-Sutherland model at
fixed magnetization M. We prove, that isolated triplet excitations on the SSL
are unstable if the coupling alpha falls below a critical value alpha_c=2.0
(approx.). The instability should be visible in the compound SrCu_2(BO_3)_2
where a coupling alpha^*=1.48 is realized.Comment: 4 pages, 4 figures, RevTe
Dilute-Bose-Gas Approach to ground state phases of 3D quantum helimagnets under high magnetic field
We study high-field phase diagram and low-energy excitations of
three-dimensional quantum helimagnets. Slightly below the saturation field, the
emergence of magnetic order may be mathematically viewed as Bose-Einstein
condensation (BEC) of magnons. The method of dilute Bose gas enables an
unbiased quantitative analysis of quantum effects in three-dimensional
helimagnets and thereby three phases are found: cone, coplanar fan and an
attraction-dominant one. To investigate the last phase, we extend the usual BEC
approach so that we can handle 2-magnon bound states. In the case of 2-magnon
BEC, the transverse magnetization vanishes and long-range order occurs in the
quadrupolar channel (spin-nematic phase). As an application, we map out the
phase diagram of a 3D helimagnet which consists of frustrated J1-J2 chains
coupled by an interchain interaction J3.Comment: 4pages, 3figures, International Conference on Magnetism (ICM) 2009
(Karlsruhe, Germany, July 26-31, 2009)
Duality relations and exotic orders in electronic ladder systems
We discuss duality relations in correlated electronic ladder systems to
clarify mutual relations between various conventional and unconventional
phases. For the generalized two-leg Hubbard ladder, we find two exact duality
relations, and also one asymptotic relation which holds in the low-energy
regime. These duality relations show that unconventional (exotic) density-wave
orders such as staggered flux or circulating spin-current are directly mapped
to conventional density-wave orders, which establishes the appearance of
various exotic states with time-reversal and/or spin symmetry breaking. We also
study duality relations in the SO(5) symmetry that was proposed to unify
antiferromagnetism and d-wave superconductivity. We show that the same SO(5)
symmetry also unifies circulating spin current order and s-wave
superconductivity.Comment: 9 pages, 2 figures; Proceedings of SPQS2004 (Sendai
Quantum fluctuations in quantum lattice-systems with continuous symmetry
We discuss conditions for the absence of spontaneous breakdown of continuous
symmetries in quantum lattice systems at . Our analysis is based on
Pitaevskii and Stringari's idea that the uncertainty relation can be employed
to show quantum fluctuations. For the one-dimensional systems, it is shown that
the ground state is invariant under the continuous transformation if a certain
uniform susceptibility is finite. For the two- and three-dimensional systems,
it is shown that truncated correlation functions cannot decay any more rapidly
than whenever the continuous symmetry is spontaneously broken.
Both of these phenomena occur owing to quantum fluctuations. Our theorems cover
a wide class of quantum lattice-systems having not-too-long-range interactions.Comment: 14 pages. To appear in J.Stat.Phy
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