Ultrafast dynamical charge-lattice coupling in rare-earth nickelate thin films studied by time-resolved terahertz spectroscopy

J. Phys.: Condens. Matter

Dagar

Sahoo

et al. 2023

Self Cite

Electron-doped Ca0.96Ce0.04MnO3 (CCMO) possesses a unique band structure and exhibits a giant topological Hall effect contrary to other correlation-driven manganites known for insulator-to-metal transition, magnetoresistance, complex magnetic order, etc. The interaction mechanisms among the fundamental entities and their dynamical evolutions responsible for this unusual topological phase are yet to be understood. Here, we employ time-averaged and sub-picosecond time-resolved terahertz (THz) spectroscopy to explore the low-energy steady-state and ultrafast carrier dynamics, respectively, to unravel the complexity of charge carriers during their transition from a non-equilibrium to the ground state in CCMO thin film. The THz optical conductivity confirms the presence of dichotomic charge carriers, i.e., heavy and light carriers throughout the temperature range of 15-300 K. A rare observation of both positive and negative photoconductivities along with a sharp crossover between the two resolved to a few picoseconds of illumination confirms the formation of polaron with a lifetime of a few nanoseconds. These optical evidences of dichotomic charge carriers, along with manipulation of the sign of photoconductivity induced by dynamics of related quasiparticles could facilitate a new mechanism for ultrafast optoelectronic switching devices.

Section: Methodsmentioning

confidence: 99%

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

J. Phys.: Condens. Matter

Dagar

Sahoo

et al. 2023

Self Cite

Coherent acoustic modulation and defect-sensitive ultrafast carrier dynamics of Pr0.5Ca0.5MnO3 thin films investigated by time-resolved terahertz spectroscopy

Journal of Applied Physics

Udeshi

Dagar

et al. 2022

In transition metal oxides, the potential of competing energetics of interacting fundamental entities is best displayed in perovskite manganites via the formation of a variety of exotic phases; however, there are limitations of extreme sensitivity to extrinsic and intrinsic defects and the slightest of structural modulations. Here, we report the effect of oxygen annealing and epitaxial strain on the ultrafast carrier excitation and relaxation mechanism in charge-ordered (CO) manganite Pr0.5Ca0.5MnO3 (PCMO) thin films of 60 and 150 nm thicknesses, both as-grown and oxygen annealed, as investigated by optical pump–terahertz (THz) probe measurements. Transient THz transmittance is negative for both films. Bi-exponential relaxation behavior accompanied with acoustic modulations was observed that varies along with strain and oxygen content of the films. As fitted by the sum of exponentials, the fast relaxation time constant is found to be fluence independent, while the slow relaxation time constant decreases with pump fluence for both films and is less for the annealed film suggesting that the relaxation in PCMO strongly depends on strain and oxygen content. This study on non-equilibrium carrier dynamics depicting the sensitivity of defects and subtle structural modifications is unprecedented in demonstrating the ultrafast control of CO manganites.

Precise measurement of correlation parameters driving optical transparency in CaVO3 thin film by steady state and time resolved terahertz spectroscopy

Anagha

Journal of Applied Physics

Khare

et al. 2022

Transparent conducting materials are inevitable in the fast-developing optoelectronic and photovoltaic industries. Correlated metals are emerging classes of materials that possess a charge density comparable to the metals in which the correlation effects provide transparency. So, understanding the fundamental physics of these materials is equally important to improve the performance of devices. We have investigated the low energy and non-equilibrium dynamics of the CaVO3 (CVO) thin film using terahertz time-domain and time-resolved terahertz spectroscopic measurements. Though the electrical resistivity of the CVO thin film shows a Fermi liquid-like signature, the terahertz conductivity dynamics unveil the presence of metal-insulator transition. Furthermore, the mass renormalization effects indicate the competition between electron correlations and phonon interactions in driving the ground state of this system. It is clear that the relaxation of photo-excited carriers is through electron–phonon thermalization, and comprehensive studies show the metallic nature of the system with electron correlations. Thus, the extracted optical and electrical parameters of CVO are comparable with the existing transparent conducting materials and, hence, make this system another potential candidate for transparent electronics.