Correlated paramagnetism and interplay of magnetic and phononic degrees of freedom in 3d-5d coupled La₂CuIrO₆

Abstract

Conventional Paramagnetism -a state with finite magnetic moment per ion sans long range magnetic ordering, but with lowering temperature the moment on each ion picks up a particular direction, breaking rotational symmetry, and results into long-range magnetic ordering.However, in systems with competing multiple degrees of freedom this conventional notion may easily break and results into short range correlation much above the global magnetic transition temperature. La2CuIrO6 with complex interplay of spins (s =1/2) on Cu site and pseudo-spin (j =1/2) on Ir site owing to strong spin-orbit coupling provides fertile ground to observe such correlated phenomena. By a comprehensive temperature dependent Raman study, we have shown the presence of such a correlated paramagnetic state in La2CuIrO6 much above the long-range magnetic ordering temperature (TN ). Our observation of strong interactions of phonons, associated with Cu/Ir octahedra, with underlying magnetic degrees of freedom mirrored in the observed Fano asymmetry, which remarkably persists as high as ~ 3.5TN clearly signals the existence of correlated paramagnetism hence broken rotational symmetry. Our detailed analysis also reveals anomalous changes in the self-energy parameters of the phonon modes, i.e. mode frequencies and linewidth, below TN, providing a useful gauge for monitoring the strong coupling between phonons and magnetic degrees of freedom. 12  eff J Mott-insulator, quantum-spin liquids, Weyl semimetals, axion insulators, unconventional superconductors and realization of the Kitaev model with spin-spin correlation [1-8]. In the current studies of double perovskite iridates and iridium based oxides i.e. Na4Ir3O8, Sr2IrO4, and Na2IrO3, in +4 (Ir 4+ , 5d 5 ) and +5 (Ir 5+ , 5d 4 ) oxidation state [9-16] shows Mott-insulating ground state with effective total angular momentum 12  eff J driven by strong SOC. Despite of intense research on double perovskite iridates, the factors facilitating the rich magnetic ground state are still under debate. Recently, the focus is on double perovskites with co-existence of 3d and 5d transition metals, such as La2RIrO6 (R = Zn, Mn, Ni, Fe, Co and Cu) [17-23], which have provided new frontier in unrevealing the complex quantum state of these materials owing to competing nature of multiple degrees of freedom. Due to the compact nature of 3d-orbitals, they have strong electronic correlation and highly quenched orbital angular momentum due to presence of non-degeneracy of d-orbitals originated from the Jahn-Teller effect, however, in contrast spatially extended 5dorbitals exhibit opposite behaviour i.e. strongly pronounced SOC and weak electronic correlation.Also, in case of 3d transition metal oxides, the pseudo-spin degrees of freedom are active owing to very weak SOC and as a result Jahn-Teller effect generate strong coupling between phonons and pseudo-spin degrees of freedom [24]. On the other hand, for 5d systems, strong SOC is expected to quench pseudo-spin dynamics. However, it has been suggested in recent studie...

Davydov Splitting, Resonance Effect and Phonon Dynamics in Chemical Vapor Deposition Grown Layered MoS2

“…In the present work, we report a comprehensive study of the temperature dependent vibrational properties for chemical vapor deposition (CVD) grown horizontally aligned (HA) layered MoS 2 using the Raman spectroscopic technique under a resonance condition. Raman spectroscopy is a nondestructive and fast technique that has been widely used to explore the vibrational and electronic properties of a wide range of materials [14][15][16][17][18][19]. MoS 2 is one of the early members of the TMDC family and is crucial from a fundamental as well as application point of view.…”

Phonon dynamics in lead free perovskite (1-x)KNN-xBAN (x = 0.0–0.1): a temperature dependent raman study

“…This coupling is the primary reason for the observed non-zero linewidth and variation of frequency with temperature in the phonon modes. To understand the underlying physics behind the observed behavior, one may expand the potential V (r) about the equilibrium position using the Taylor expansion [54]:…”

Anisotropic electron–photon–phonon coupling in layered MoS2

“…This anisotropy may be gauged via an indirect probe by an external perturbation such as probing by light, in particular Raman scattering. Raman scattering has proved to be a very powerful technique to understand intricate coupling between different quasi-particles in both nano systems and bulk via coupling of electrons and phonons with the incoming and outgoing photons [16][17][18][19][20][21][22][23]. An anisotropy in the thermal conductivity was reported for the case of MoS 2 , where in-plane conductivity is reported to be ∼5-6 times more than the out-of-plane conductivity [24] suggesting the more dominant role of the inplane lattice vibrations such as E 1 2g phonon mode as phonons coupling controls the thermal behavior of a material.…”