Ehrenfest Relations and Magnetoelastic Effects in Field-induced Ordered Phases

Matsumoto, M.; Sigrist, Manfred

doi:10.1143/jpsj.74.2310

Cited by 13 publications

(6 citation statements)

References 34 publications

(49 reference statements)

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“…In addition, by understanding the BEC phenomenology in idealized U(1)-invariant magnets we can treat U(1) symmetry-breaking terms perturbatively (Oshikawa and Affleck, 1997;Kolezhuk et al, 2004;Misguich and Oshikawa, 2004;Sirker, Weiße, and Sushkov, 2004;Matsumoto and Sigrist, 2005;Orignac and Citro, 2005;Sebastian, Tanedo et al, 2006;.…”

Section: B Uniaxial Symmetry Breaking and Superfluid Currentsmentioning

confidence: 99%

Bose-Einstein condensation in quantum magnets

2014

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This article reviews experimental and theoretical work on Bose-Einstein condensation in quantum magnets. These magnets are natural realizations of gases of interacting bosons whose relevant parameters such as dimensionality, lattice geometry, amount of disorder, nature of the interactions, and particle concentration can vary widely between different compounds. The particle concentration can be easily tuned by applying an external magnetic field which plays the role of a chemical potential. This rich spectrum of realizations offers a unique possibility for studying the different physical behaviors that emerge in interacting Bose gases from the interplay between their relevant parameters. The plethora of other bosonic phases that can emerge in quantum magnets, of which the Bose-Einstein condensate is the most basic ground state, is reviewed. The compounds discussed in this review have been intensively studied in the last two decades and have led to important contributions in the area of quantum magnetism. In spite of their apparent simplicity, these systems often exhibit surprising behaviors. The possibility of using controlled theoretical approaches has triggered the discovery of unusual effects induced by frustration, dimensionality, or disorder.

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Section: B Uniaxial Symmetry Breaking and Superfluid Currentsmentioning

confidence: 99%

Bose-Einstein condensation in quantum magnets

2014

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“…The physics of BEC is also altered in the presence of coupling between spins and lattice distortions. Fortunately, it is possible to use our good control and knowledge of the pure BEC system to treat theoretically these weak deviations as well [26,28,29,55,56]. Finally the spin systems are excellent to study the critical behavior around the quantum critical points, since the boson density can be finely controlled by the external magnetic field, and the system is fully homogeneous.…”

Section: Comparison With Other Boson Systemsmentioning

confidence: 99%

Bose–Einstein condensation in magnetic insulators

2008

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The Bose–Einstein condensate (BEC) is a fascinating state of matter predicted to occur for particles obeying Bose statistics. Although the BEC has been observed with bosonic atoms in liquid helium and cold gases, the concept is much more general. We here review analogous states, where excitations in magnetic insulators form the BEC. In antiferromagnets, elementary excitations are magnons, quasiparticles with integer spin and Bose statistics. In certain experiments their density can be controlled by an applied magnetic field leading to the formation of a BEC. Furthermore, interactions between the excitations and the interplay with the crystalline lattice produce very rich physics compared with the canonical BEC. Studies of magnon condensation in a growing number of magnetic materials thus provide a unique window into an exciting world of quantum phase transitions and exotic quantum states, with striking parallels to phenomena studied in ultracold atomic gases in optical lattices

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“…This instability should be a universal feature of magnetic BEC systems at their magnetic phase transition, and it is not expected to occur in axially symmetric Bose gases composed of real particles such as superfluid 4 He or atomic condensates, where the condensate cannot create an axial-symmetry breaking term by itself. In a microscopic picture, the tendency of a magnetic condensate to spontaneously violate the axial symmetry can be interpreted as a natural consequence of the transverse magnetic ordering that develops in the condensate phase and that locks to the crystal lattice due to unavoidable magnetoelastic coupling [3,37,38]. As soon as the transverse magnetic moments point to a specific, energetically preferred crystal direction, the phase φ that is associated with the angle between these moments and the crystal axes [16] is indeed fixed (in TlCuCl 3 with an angle α ≈ 39 • to the a-axis [37]), and the magnetic analogue to a supercurrent velocity v s = /m ⋆ ∇φ (where m ⋆ is the effective mass of a triplon) is naturally zero for excitation energies below the anisotropic gap ∆.…”

Section: B Instability Of the Condensate Towards Violation Of Axial S...mentioning

confidence: 99%

U(1)symmetry breaking and violated axial symmetry inTlCuCl3and other insulating spin systems

2009

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We describe the Bose-Einstein condensate of magnetic bosonic quasiparticles in insulating spin systems using a phenomenological standard functional method for T = 0. We show that results that are already known from advanced computational techniques immediately follow. The inclusion of a perturbative anisotropy term that violates the axial symmetry allows us to remarkably well explain a number of experimental features of the dimerized spin-1/2 system TlCuCl3. Based on an energetic argument we predict a general intrinsic instability of an axially symmetric magnetic condensate towards a violation of this symmetry, which leads to the spontaneous formation of an anisotropy gap in the energy spectrum above the critical field. We, therefore, expect that a true Goldstone mode in insulating spin systems, i.e., a strictly linear energy-dispersion relation down to arbitrarily small excitations energies, cannot be observed in any real material.

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Ehrenfest Relations and Magnetoelastic Effects in Field-induced Ordered Phases

Cited by 13 publications

References 34 publications

Bose-Einstein condensation in quantum magnets

Bose-Einstein condensation in quantum magnets

Bose–Einstein condensation in magnetic insulators

U(1)symmetry breaking and violated axial symmetry inTlCuCl3and other insulating spin systems

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