Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Abstract

The Raman-active phonons and magnetic excitations in the orbitally ordered, quasi-one-dimensional Heisenberg antiferromagnet KCuF 3 are studied as a function of temperature in the range between 3 and 290 K in various scattering configurations. The low-energy E g and B 1g phonon modes show an anomalous softening (~25% and ~13%) between room temperature and the characteristic temperature T S = 50 K. In this temperature range a freezing-in of F -ion dynamic displacements is proposed to occur. In addition, the E g mode at about 260 cm -1 clearly splits below T S . The widths of the phonon lines above T S follow an activated behavior with an activation energy of about 50 K. Our observations clearly evidence a reduction of the lattice symmetry below T S and indicate a strong coupling of lattice, spin, and orbital fluctuations for T > T S . A strongly polarization dependent quasielastic scattering is observed at temperatures above T N = 39 K due to magnetic-energy fluctuations. For temperatures below T N a rich spectrum of additional modes is observed, with different lineshape, polarization and temperatures dependence. We attribute them to longitudinal and transverse magnetic modes as well as to a continuum of magnetic excitations.

Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: The Cr-based dimer system Sr3Cr2O8Wulferding1, Lemmens2, Choi3 et al. 2011Phys. Rev. B161240View full textAdd to dashboardCite

“…Here the ESR absorption line increases exponentially with increasing temperature due to an Orbach spin relaxation process 13 . A similar relation between phonon and ESR linewidth has been observed in the Jahn-Teller system KCuF 3 16,17 . In Fig.…”

Bosonic spinons in anisotropic triangular antiferromagnets

“…Further, we note that the polar plots of the ( bθ ) data unveil that the spinons have the A 1 symmetry and follow a dependence, whereas the triplons have the A 1 + A 2 symmetry (Supplementary Note 3 ). These angular dependencies are incompatible with the dependence expected for two-magnon excitations 34 , 35 . This lends credence to our assignment that the observed magnetic continuum precludes a magnon contribution.…”

“…As the spin chains are frustrated in the low-temperature limit ( T < J ), the spinon excitations may inherit from the TLL physics. Here, we recall that the quasi-1D antiferromagnet KCuF 3 with T N = 39 K features a multi-spinon continuum centered around ω 2 p = 2.6 J in the intrachain polarization 34 , comparable to 3.1 J of Ca 3 ReO 5 Cl 2 . In the interchain polarization, however, the spinon continuum vanishes and only a sharp transverse magnon is visible.…”

Electronic Structure and Magnetic Coupling of Pure and Mg-Doped KCuF3

“…This experimental result is in nice agreement with the LDA + DMFT calculations [2] and supports the conclusion 2 Advances in Condensed Matter Physics that the electron phonon coupling is the most important interaction in stabilizing the peculiar structure of KCuF 3 . The subtle interplay between spin, orbital, and vibrational degrees of freedom of this material is still the subject of experimental and theoretical investigations [7][8][9][10][11][12][13][14][15][16][17][18], adopting a variety of techniques ranging from inelastic Raman and X-rays scattering and absorption, [11,13], neutron scattering [10,14], DFT based electronic structure computations [8], and lattice dynamics [7,15] and, more recently, calculations within the variational Green's function formalism [17,18].…”