Diffused metal-insulator transition in NdNiO3 film grown on BaTiO3 : Likely evidence of electronic Griffiths phase

Abstract

This paper reports diffused metal-insulator transitions (MITs) in an oxide with disorder that undergoes a Mott transition. The investigation was carried out in the multilayer film ${\text{NdNiO}}_{3}/{\text{BaTiO}}_{3}/{\text{SrTiO}}_{3}$ (NNO/BTO/STO), where a large mismatch of lattice constants of NNO with those of BTO leads to strain relaxation and creation of quenched disorder in the NNO film. NNO film in the NNO/BTO/STO multilayer structure shows a broad Mott-type MIT at a temperature ${T}_{\text{MI}}=160\phantom{\rule{0.16em}{0ex}}\text{K}$ from a high-temperature bad metallic phase ($\frac{1}{{\ensuremath{\rho}}_{\text{DC}}}\frac{d{\ensuremath{\rho}}_{\text{DC}}}{dT}<0$) with a high value of resistivity ${\ensuremath{\rho}}_{\text{DC}}\ensuremath{\approx}70 \mathrm{m}\mathrm{\ensuremath{\Omega}}$ cm at 300 K to a low temperature insulating phase. Using noise spectroscopy and impedance spectroscopy which can probe the dynamics of the coexisting phases near the MIT, it was observed that in addition to the MIT at ${T}_{\text{MI}}=160\phantom{\rule{0.16em}{0ex}}\text{K}$, there exists a characteristic temperature ${T}_{G}\ensuremath{\approx}230\phantom{\rule{0.16em}{0ex}}\text{K}$ well above the ${T}_{\text{MI}}$, where large low-frequency correlated fluctuations appear, signifying the appearance of a phase with slow dynamics. ${T}_{G}$ signals the onset of a temperature region ${T}_{\text{MI}}<T<{T}_{G}$ with coexisting phases that have been corroborated by the impedance spectroscopy and AC conductivity measurements. It is suggested that the temperature ${T}_{G}$ may signify the onset of an electronic Griffiths phase that has been theoretically proposed for Mott transitions with disorder.