Width of the longitudinal magnon in the vicinity of the O(3) quantum critical point

Abstract

We consider a three-dimensional quantum antiferromagnet in the vicinity of a quantum critical point separating the magnetically ordered and the magnetically disordered phases. A specific example is TlCuCl${}_3$ where the quantum phase transition can be driven by hydrostatic pressure and/or by external magnetic field. As expected two transverse and one longitudinal magnetic excitation have been observed in the pressure driven magnetically ordered phase. According to the experimental data, the longitudinal magnon has a substantial width, which has not been understood and has remained a puzzle. In the present work, we explain the mechanism for the width, calculate the width and relate value of the width with parameters of the Bose condensate of magnons observed in the same compound. The method of an effective quantum field theory is employed in the work.

6 pages, 3 figures

References in corpus (8)

• Quantum Criticality
• Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3
• Bose-Einstein Condensation of Magnons in TlCuCl3: Phase diagram and specific heat from a self-consistent Hartee-Fock calculation with a realistic dispersion relation
• Spin-resonance modes of the spin-gap magnet TlCuCl_3
• Consequences of spin-orbit coupling for the Bose-Einstein condensation of magnons
• Softening of Magnetic Excitations Leading to Pressure-Induced Quantum Phase Transition in Gapped Spin System KCuCl${}_3$
• Pressure-Induced Reentrant Oblique Antiferromagnetic Phase in Spin Dimer System TlCuCl_3
• Bose-Einstein condensation of magnons in TlCuCl${}_3$

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