Magnetic order and magnon coherent state in double exchange s=1/2 lattices

Journal Article · Mon Feb 15 00:00:00 EST 2010 · Annals of Physics (New York)

DOI:https://doi.org/10.1016/j.aop.2009.11.001· OSTI ID:21336098

Lopez-Aguilar, F. ^[1]

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1. Electromagnetism Group, Department of Physics, Autonomous Barcelona University, Bellaterra, E-08193 Barcelona (Spain), E-mail: [e-mail]

Starting from trial wave functions and by minimizing the total energy, we obtain the ground state (GS) of a magnetic system in which there is competition between two exchange interactions: one of them between localized and unlocalized spins and another one among the spins of a Heisenberg s=1/2 lattice. This analysis allows us to analyze directly a particular case of a magnetic ground state: a magnon gas whose collective wave function presents similarities with the coherent state of the electromagnetic field which is the basis for the laser. The Kondo coupling becomes concomitant with the external magnetic field which can control the number of magnons. The corresponding Zeeman effect provoked by the magnetic external field plus the Kondo interaction energy compete with the spin-spin Heisenberg exchange of the localized magnetic lattices. The fruit of the competition of these three interactions is the existence of a collective state which can be represented with an oscillation with one only frequency which has a minimum uncertainty and therefore it is a most similar quantum state to a classical wave. This collective state for determined crystal conditions, values of Kondo coupling strength, external B values and Heisenberg J{sub ij}-parameters tends to be a minimal energy state, and then, this coherent state, can transit to a magnon Bose-Einstein condensate (BEC). The passing from the minimal coherent state towards the BEC condensation is thermodynamically analyzed and we have deduced the critical temperature of this phase transition.

• OSTI ID: 21336098
• Journal Information: Annals of Physics (New York), Vol. 325, Issue 2; Other Information: DOI: 10.1016/j.aop.2009.11.001; PII: S0003-4916(09)00219-X; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-4916
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANNIHILATION OPERATORS
BOSE-EINSTEIN CONDENSATION
CRITICAL TEMPERATURE
CRYSTALS
EIGENSTATES
ELECTROMAGNETIC FIELDS
EXCHANGE INTERACTIONS
GROUND STATES
LASERS
MAGNETIC FIELDS
MAGNONS
OSCILLATIONS
PHASE TRANSFORMATIONS
SPIN
WAVE FUNCTIONS
ZEEMAN EFFECT