Macroscopic properties of triplon Bose-Einstein condensates

Journal Article · Thu Sep 15 04:00:00 EDT 2011 · Annals of Physics (New York)

DOI:https://doi.org/10.1016/j.aop.2011.06.003· OSTI ID:21583338

Rakhimov, Abdulla ^[1]; Mardonov, Shuhrat ^[2]

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1. Institute of Nuclear Physics, Tashkent 100214 (Uzbekistan)
2. Samarkand State University, Samarkand (Uzbekistan)

Magnetic insulators can be characterized by a gap separating the singlet ground state from the lowest-energy triplet, S=1 excitation. If the gap can be closed by the Zeeman interaction in applied magnetic field, the resulting quasiparticles, triplons, can have concentrations sufficient to undergo the Bose-Einstein condensates transition. We consider macroscopic properties of the triplon Bose-Einstein condensates in the Hartree-Fock-Bogoliubov approximation taking into account the anomalous averages. We prove that these averages play the qualitative role in the condensate properties. As a result, we show that with the increase in the external magnetic field at a given temperature, the condensate demonstrates an instability related to the appearance of nonzero phonon damping and a change in the characteristic dependence of the speed of sound on the magnetic field. The calculated magnetic susceptibility diverges when the external magnetic field approaches this instability threshold, providing a tool for the experimental verification of this approach. - Highlights: > A consistent theory of the triplon BEC should consider the anomalous density terms. > These terms strongly modify the macroscopic properties of the BEC. > They lead to the instability of the BEC in strong enough magnetic fields. > The instability can be observed in neutron scattering and magnetization experiments.

• OSTI ID: 21583338
• Journal Information: Annals of Physics (New York), Journal Name: Annals of Physics (New York) Journal Issue: 9 Vol. 326; ISSN 0003-4916; ISSN APNYA6
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
APPROXIMATIONS
BOSE-EINSTEIN CONDENSATION
CALCULATION METHODS
COHERENT SCATTERING
CONDENSATES
DAMPING
DENSITY
DIFFRACTION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
GROUND STATES
HARTREE-FOCK-BOGOLYUBOV THEORY
INSTABILITY
INTERACTIONS
MAGNETIC FIELDS
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MAGNETIZATION
MULTIPLETS
NEUTRON DIFFRACTION
PHONONS
PHYSICAL PROPERTIES
QUASI PARTICLES
SCATTERING
SOUND WAVES
SPECIFIC HEAT
THERMODYNAMIC PROPERTIES
TRIPLETS
VELOCITY
ZEEMAN EFFECT