Abstract-Excitons in 2D perovskites for ultrafast terahertz photonic devices

Abhishek Kumar,  Ankur Solanki,  Manukumara Manjappa,  Sankaran Ramesh,  Yogesh Kumar Srivastava, Piyush Agarwal,  Tze Chien Sum. Ranjan Singh

https://advances.sciencemag.org/content/6/8/eaax8821

In recent years, two-dimensional (2D) Ruddlesden-Popper perovskites have emerged as promising candidates for environmentally stable solar cells, highly efficient light-emitting diodes, and resistive memory devices. The remarkable existence of self-assembled quantum well (QW) structures in solution-processed 2D perovskites offers a diverse range of optoelectronic properties, which remain largely unexplored. Here, we experimentally observe ultrafast relaxation of free carriers in 20 ps due to the quantum confinement of free carriers in a self-assembled QW structures that form excitons. Furthermore, hybridizing the 2D perovskites with metamaterials on a rigid and a flexible substrate enables modulation of terahertz fields at 50-GHz modulating speed, which is the fastest for a solution-processed semiconductor-based photonic device. Hence, an exciton-based ultrafast response of 2D perovskites opens up large avenues for a wide range of scalable dynamic photonic devices with potential applications in flexible photonics, ultrafast wavefront control, and short-range wireless terahertz communications.

Abstract-Epitaxial strain driven crossover from Drude to Drude-Smith terahertz conductivity dynamics in LaNiO3 thin films

V Eswara Phanindra1, Piyush Agarwal1 and D S Rana

http://iopscience.iop.org/article/10.1088/1361-648X/aa89be/meta

We investigate the hetero-epitaxial strain driven low-energy charge dynamics in compressive and tensile strained LaNiO3 thin films employing terahertz (THz) time-domain spectroscopy. The complex THz conductivity exhibits a crossover from Drude type metallic behavior for the compressive film to a Drude-Smith type disordered behavior for the tensile film. This demonstration of strain driven crossover in THz conductivity dynamics, while the two films have qualitatively similar dc conductivities, (i) brings out the potential of THz technology in distinguishing between similar dc electronic phases and (ii) suggests that LaNiO3 under compressive strain is a better candidate for applications as electrodes in oxides electronics.

Abstract-Epitaxial strain driven crossover from Drude to Drude-Smith terahertz conductivity dynamics in LaNiO3 thin films

V Eswara Phanindra1, Piyush Agarwal2 and Dhanvir Rana3

http://iopscience.iop.org/article/10.1088/1361-648X/aa89be

We investigate the hetero-epitaxial strain driven low-energy charge dynamics in compressive and tensile strained LaNiO3 thin films employing terahertz (THz) time-domain spectroscopy. The complex THz conductivity exhibits a crossover from Drude type metallic behavior for the compressive film to a Drude-Smith type disordered behavior for the tensile film. This demonstration of strain driven crossover in THz conductivity dynamics, while the two films have qualitatively similar dc conductivities, i) brings out the potential of THz technology in distinguishing between similar dc electronic phases and ii) suggests that LaNiO3 under compressive strain is a better candidate for applications as electrodes in oxides electronics.

Abstract-Tuning the terahertz low-energy charge dynamics by simultaneous effect of epitaxial and anisotropic strain in PrNi O 3 thin films

V. Eswara Phanindra, Sarmistha Das, K. Santhosh Kumar, Piyush Agarwal, Rakesh Rana, and D. S. Rana

Phys. Rev. B 95, 085114 – Published 13 February 2017

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.085114

The interplay of charge, spin, and lattice correlations strongly influence the insulator-metal (I-M) transition and magnetic ordering in rare earth nickelates. In this context, we explored the low-energy charge dynamics in structurally modulated $\mathrm{PrNi}{O}_3$ (PNO) thin films to unravel the complexity of ground state across I-M transition using terahertz (THz) spectroscopy. The THz optical constants of compressive film on $\mathrm{LaAl}{O}_3$ (100) substrate and the tensile films on $\mathrm{NdGa}{O}_3$ (100), (001), (110), and (111) substrates with varying orthorhombic distortion exhibit remarkably distinct features as a function of frequency and temperature. The THz conductivity of compressive film sans any I-M transition follows the Drude model. In contrast, the tensile strained films exhibit non-Drude THz conductivity, a giant positive dielectric permittivity, and negative imaginary conductivity, all of which can be explained by the Drude-Smith model. This rich variety of low-energy dynamics manifests as a function of temperature, strain, and crystal orientation. Such distinct THz spectral features, as induced by a subtle variation in strain while crossing over from tensile to compressive strain and with varying degree of orthorhombicity coupled with oxygen vacancies, reveal a novel facet of structure-property relationship of PNO.

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Abstract-Terahertz spectroscopy of PrNiO3 thin films: Strain induced anomalous conductivity, giant dielectric constant, and scaling of optical constants

V. Eswara Phanindra, Sarmistha Das, K. Santhosh Kumar, Piyush Agarwal, Rakesh Rana, and D. S. Rana

https://journals.aps.org/prb/accepted/d7072Ob8F5914b3750bc5439b7a764bc02ee8b8e5

The interplay of charge, spin, and lattice correlations strongly influence the insulator-metal (I-M) transition and magnetic ordering in rare earth nickelates. In this context, we explored the low-energy charge dynamics in structurally modulated PrNiO3 thin films to unravel the complexity of ground state across I-M transition using terahertz (THz) spectroscopy. The THz optical constants of compressive film on LaAlO3 (100) substrate and the tensile films on NdGaO3 (100), (001), (110) and (111) substrates with varying orthorhombic distortion exhibit remarkably distinct features as a function of frequency and temperature. The THz conductivity of compressive film sans any I-M transition follows the Drude model. In contrast, the tensile strained films exhibit non-Drude THz conductivity, a giant positive dielectric permittivity and negative imaginary conductivity, all of which can be explained by Drude-Smith model. This rich variety of low energy dynamics manifest as a function of temperature, strain and crystal orientation. Such distinct THz spectral features, as induced by a subtle variation in strain while crossing over from tensile to compressive strain and with varying degree of orthorhombicity coupled with oxygen vacancies, reveal a novel facet of structure-property relationship of PrNiO3.