Unusual terahertz spectral weight and conductivity dynamics of the insulator-metal transition in Pr_0.5Nd_0.5NiO₃ thin films

Abstract

The metal-insulator transition (MIT) in correlated systems is a central phenomenon that possesses potential for several emerging technologies. We investigate the kinetics of such MIT in perovskite nickelates by studying the terahertz (THz) low-energy charge dynamics in orthorhombic and tetragonal symmetries of Pr0.5Nd0.5NiO3 thin films. The THz conductivity of the orthorhombic thin film is dominated by Drude behavior in the entire temperature range, albeit a dominant anomaly at and around the MIT region. The tetragonal thin film exhibits different overall THz conductivity dynamics though, i.e. of a Drude–Smith (DS) type in the entire temperature range, the DS coefficient signifying dominant backscattering peaks in the MIT region. While the overall THz dynamics profile is different for the two films, a unique yet similar sensitivity of the I–M transition regions of both films to THz frequencies underlines the fundamental origin of the bi-critical phase around MIT of the nickelates. The peculiar behavior around the I–M transition, as evaluated in the framework of a percolative path approximation based Dyre expression, emphasizes the importance of critical metallic volume fraction (fc) for the percolation conduction, as an fc of ~0.645 obtained for the present case, along with evidence for the absence of super-heating.

Digital- to Analog-Type Terahertz Modulation Controlled by Mosaicity of the Substrate Template in Rare-Earth Nickelate Thin Films

“…It is a modified form of the Drude model, which incorporates the backscattering of carriers due to the presence of defects/impurity. The Drude–Smith model has so far been successfully used to explain non-Drude-like behavior of many nanostructured metals, semiconductors, oxides, disordered materials, etc. − To explain non-Drude conductivity of disordered materials containing impurity, dislocations, size mismatch, etc., Smith generalized the Drude formula assuming that collisions are anisotropic, resulting in scattering of carriers in preferential directions as expressed below ,, where, c n is persistence of velocity parameter signifying fraction of carrier’s initial velocity retained after n successive collisions. For the sake of simplicity, we have considered persistence of velocity parameter only for the case of one collision as c n = c ; (−1< c < 0).…”

Surface Electronic States Induced High Terahertz Conductivity of Co3O4 Microhollow Structure

“…σ(ω) dω, where ω 1 = 0.2 THz and ω 2 = 1.2 THz are the upper and lower cut-off frequencies, which can provide the valuable insights of the condensed and uncondensed states of the charge carriers. 30 In addition, it can effectively track the charge distribution and kinetic energy as well. Interestingly, the SW of THz conductivity due to bulk is found to be significantly low as compared to the surface one and becomes approximately zero below T N , indicating predominant role of surface spin frustration for determining the THz conductivity even in the charge-ordered antiferromagnetic state.…”

Terahertz Electrodynamics in Transition Metal Oxides

“…The carrier tunneling between the metallic domains existed up to the fractional metallic volume of 0.645. [228] Further, OPTP measurements in the insulating phase of SmNiO 3 revealed that the photo-excitation drive the coexistence of metallic and insulating phases. These phases relax to the ground state within the picosecond timescale and the photon density of 4.4 mJ cm −2 can drive the metallic state (Figure 30).…”

“…In the superconducting regime, the superconducting carriers increase at the expense of normal carriers. [228] Copyright 2017, IOP Publishing. The peak in real conductivity was attributed to a large enhancement in carrier scattering time (τ) due to the formation of large phase correlation in superconducting state which was not present in the normal state.…”

“…The conductivity of the metallic and insulating domains is represented as Drude (D) part, the conductivity due to the tunneling of carriers between the domains is represented as Drude-Smith (DS) and total conductivity D + DS. Reproduced with permission [228]. Copyright 2017, IOP Publishing.…”