Dynamical properties of an antiferromagnet near the quantum critical point: Application to LaCuO{sub 2.5}
- Theoretische Physik, ETH-Hoenggerberg, CH-8093 Zuerich (Switzerland)
For a system of two-chain spin ladders, the ground state for weak interladder coupling is the spin-liquid state of the isolated ladder, but is an ordered antiferromagnet (AF) for sufficiently large interactions. We generalize the bond-operator mean-field theory to describe both regimes, and to focus on the transition between them. In the AF phase near the quantum critical point (QCP) we find both spin waves and a low-lying but massive amplitude mode which is absent in a conventional AF. The static susceptibility has the form {chi}(T)={chi}{sub 0}+aT{sup 2}, with {chi}{sub 0} small for a system near criticality. We consider the dynamical properties to examine features arising from the presence of the amplitude mode, and compute the dynamic structure factor. LaCuO{sub 2.5} is thought to be such an unconventional AF, whose ordered phase is located very close to the QCP of the transition to the spin liquid. From the N{acute e}el temperature we deduce the interladder coupling, the small ordered moment, and the gap in the amplitude mode. The dynamical properties unique to near-critical AF{close_quote}s are expected to be observable in LaCuO{sub 2.5}. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 632630
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 56, Issue 14; Other Information: PBD: Oct 1997
- Country of Publication:
- United States
- Language:
- English
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