112 research outputs found
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)
Quantum Interactions of Topological Solitons from Electrodynamics
The Casimir energy for the classically stable configurations of the
topological solitons in 2D quantum antiferromagnets is studied by performing
the path-integral over quantum fluctuations. The magnon fluctuation around the
solitons saturating the Bogomol'nyi inequality may be viewed as a charged
scalar field coupled with an effective magnetic field induced by the solitons.
The magnon-soliton couping is closely related to the Pauli Hamiltonian, with
which the effective action is calculated by adapting the worldline formulation
of the derivative expansion for the 2+1d quantum electrodynamics in an external
field. The resulting framework is more flexible than the conventional
scattering analysis based on the Dashen-Hasslacher-Neveu formula. We obtain a
short-range attractive well and a universal long-range -type repulsive
potential between two solitons.Comment: 17 pages, 3 figures, added an experimental setup using a skyrmion
racetrack; matches published versio
Ground-state phase diagram and magnetic properties of a tetramerized spin-1/2 J_1-J_2 model: BEC of bound magnons and absence of the transverse magnetization
We study the ground state and the magnetization process of a spin-1/2
- model with a plaquette structure by using various methods. For
small inter-plaquette interaction, this model is expected to have a spin-gap
and we computed the first- and the second excitation energies. If the gap of
the lowest excitation closes, the corresponding particle condenses to form
magnetic orders. By analyzing the quintet gap and magnetic interactions among
the quintet excitations, we find a spin-nematic phase around
due to the strong frustration and the quantum effect. When high magnetic moment
is applied, not the spin-1 excitations but the spin-2 ones soften and dictate
the magnetization process. We apply a mean-field approximation to the effective
Hamiltonian to find three different types of phases (a conventional BEC phase,
``striped'' supersolid phases and a 1/2-plateau). Unlike the BEC in spin-dimer
systems, this BEC phase is not accompanied by transverse magnetization.
Possible connection to the recently discovered spin-gap compound (CuCl)LaNb2O7
is discussed.Comment: 18pages, 17figures; title changed, typos correcte
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