Abstract-Pinned and bound modes of charge density wave type collective excitation in SmNiO 3 as revealed by terahertz spectroscopy

                                           

Sarmistha Das, G. L. Prajapati, and D. S. Rana

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.102.214403

The terahertz (THz) optical conductivity of charge-ordered nickelate ${\mathrm{SmNiO}}_3$ thin films depicts a unique dependence of the charge-density-wave (CDW) type instability on the film thickness. Here, we report a rare observation of two dominant resonance modes in the THz conductivity spectrum. Corroborated by structural and electrical conductivity data, we demonstrate that these doublet excitations are the attribution of the CDW type pinned and bound modes. Both the peak position and the peak strength can be controlled by the film thickness and the defect density associated with oxygen stoichiometry. The oxygen vacancies in these films act like defects/impurities and induce charge oscillation around them which get coupled with unperturbed CDW mode of the charge-ordered phase. Thus, an additional bound mode emerges alongside the pinned mode. The defect density as controlled by the film thickness allows modulation of the resonance excitations in the desired THz frequency range.

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Abstract-Terahertz charge dynamics unveil fundamental transport anisotropy in charge-ordered Pr 0.5 Eu 0.5 NiO 3 nickelate thin films

Sarmistha Das, G. L. Prajapati, Anagha P, and D. S. Rana

https://journals.aps.org/prb/accepted/ad074O16Ea9E1c1763c31290edb7c0df04b9f8b35

Electrons, condensed in a collective mode and behaving as free charge carriers, are two important facets induced by complex intertwining of charge, spin, orbital and lattice degrees of freedom. Existence of these two electronic ground states in the same structural/chemical phase is as much desired as much is elusive in complex oxides. Using some unique attributes of terahertz (THz) spectroscopy, we show existence of two fundamentally different electronic phenomena in Pr0.5Eu0.5NiO3, member of contemporary rare-earth nickelates, in the same orthorhombic phase but along two different orthogonal in-plane axes [001] and [1-10] of thin films. While a collective response of charge manifests via charge-density-wave (CDW) excitation along [001] direction, an entirely different Drude-Smith type free carrier response manifests along the other in-plane orthogonal axis. This anisotropy, on one hand, unveils the strained engineered crystallographic preferences of the underlying charge-ordering phenomenon, on the other hand, the different conduction channels open up the possibilities of application of nickelates such as in THz transmission modulators.