Abstract
In Eu2ZnIrO6, effectively two atoms are active i.e. Ir is magnetically active, which results in complex magnetic ordering within the Ir sublattice at low temperature. On the other hand, although Eu is a van-vleck paramagnet, it is active in the electronic channels involving 4f 6 crystal-field split levels. Phonons, quanta of lattice vibration, involving vibration of atoms in the unit cell, are intimately coupled with both magnetic and electronic degrees of freedom (DoF). Here, we report a comprehensive study focusing on the phonons as well as intra-configurational excitations in double-perovskite Eu2ZnIrO6. Our studies reveal strong coupling of phonons with the underlying magnetic DoF reflected in the renormalization of the phonon self-energy parameters well above the spin-solid phase (TN ~ 12 K) till temperature as high as ~ 3TN, evidences broken spin rotational symmetry deep into the paramagnetic phase. In particular, all the observed first-order phonon modes show softening of varying degree below ~3TN, and low-frequency phonons become sharper, while the high-frequency phonons show broadening attributed to the additional available magnetic damping channels. We also observed a large number of high-energy modes, 39 in total, attributed to the electronic transitions between 4f-levels of the rare-earth Eu3+ ion and these modes shows anomalous temperature evolution as well as mixing of the crystal-field split levels attributed to the strong coupling of electronic and lattice DoF.
Highlights
A tremendous interest in iridates has been seen in the past few years due to a realization of the exotic quantum phases of matter ascribed to the strong spin-orbit coupling (SOC), electronic correlations, and their entanglement [1,2,3,4,5,6,7,8,9,10,11,12]
Our studies reveal strong coupling of phonons with the underlying magnetic degrees of freedom (DOF) reflected in the renormalization of the phonon self-energy parameters well above the spin-solid phase (TN ∼ 12 K) until temperature as high as ∼3TN evidences broken spin rotational symmetry deep into the paramagnetic phase
It is anticipated that such tuning of these interactions may give rise to the much sought after quantum spin-liquid state in these double perovskites considered to be the holy grail of condensed matter physics
Summary
A tremendous interest in iridates has been seen in the past few years due to a realization of the exotic quantum phases of matter ascribed to the strong spin-orbit coupling (SOC), electronic correlations, and their entanglement [1,2,3,4,5,6,7,8,9,10,11,12]. Raman scattering can be employed to investigate the crucial role of coupling between lattice and electronic degrees of freedom, involving crystal-field excitations of rare-earth elements, to the modulation of magnetic and thermodynamical properties associated with double-perovskite iridates Within this scenario, the crystal-field structure of 4 f levels of rare-earth elements allows further understanding of the fascinating ground-state properties associated with these double-perovskite materials. We report systematic and detailed lattice-dynamics studies and intraconfigurational excitations, involving crystal-field split multiplets of the Eu3+ ion for Eu2ZnIrO6 using inelastic light (Raman) scattering as a function of temperature along with the density functional theory based calculations to understand the complex interactions among spin, lattice, and electronic DOF. The assignment of symmetry of different phonon modes is done in accordance to our density functional theory based calculations
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