Search

The perovskite manganites host a range of charge- and orbital-ordered phases wherein the intrinsic and extrinsic controls of magnetic field, doping, epitaxial strain, chemical pressure, etc., induce subtleties of phase transition. The Pr0.5Sr0.5MnO3 (PSMO) is one such system that possesses a unique stripe-type charge-order manifesting in anisotropic transport. It exhibits a Drude-type and charge-density-wave (CDW) type of low-energy phases; the magnetic field is contemplated as a key control for both these phases; however, it has not yet been explored. Here, we have investigated the magnetic-field dependence of Drude-type terahertz (THz) carriers dynamics and the CDW type of low-energy excitations along two non-identical orthogonal in-plane axes of the (110) epitaxial thin film in the energy range of 1–7 meV using magneto-THz time-domain spectroscopy in Faraday geometry. While THz Drude conductivity expectedly increases with the increasing magnetic field, the CDW type of resonance absorption peak anomalously strengthens with the field. The origin of this unusual field-induced stabilization of the CDW-type mode is expected to lie in the d(x2–y2) orbital ordering in the A-type antiferromagnetic ordered state and anisotropic charge ordering. This study brings out a unique facet of the effect of magnetic field on orbital ordering of anisotropic stripe-type charge-ordered PSMO, which has potential THz modulation and switching applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The magnetic field control of quantum matter enables to study various exotic phenomena which emerge in complex oxide materials. The thin film heterostructures of these systems, potentially relevant in oxide electronics, require a great deal of care in distinguishing the properties of the film from those of the substrate underneath. Here, we unravel a low-energy excitation mode in NdGaO3 crystals which is an important constituent of oxide thin film heterostructures. Employing terahertz (THz) time-domain spectroscopy with control of the external magnetic field, an excitation mode resonating at a frequency of 0.2THz was observed along two key (001) and (110) crystallographic orientations. The mode develops and strengthens with an application of increasing magnetic field and weakens with increasing temperature; all attributes conforming to the predictions for the energetics of Zeeman splitting and intra-level transition within Kramer's doublet ground state. A dominance of the magnetic field control of this mode along (110) compared to that along (001) orientation also further unveils a structural control. NdGaO3crystals are widely used as substrates in oxide thin film heterostructures; hence, while realizing ultrafast control of magnetic order, specifically in oxide thin films, the Kramer crystal field splitting mode should be carefully separated from ordered spin resonance mode. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) are among the most contemporary topics in condensed matter research. For over the past three decades, the most astounding discoveries of high temperature superconductivity, colossal magnetoresistance, multiferroics, topological matter, and several other novel electronic and magnetic phases have been realized and hosted in the TMOs. Almost simultaneously and specifically during the past 5 years, the implementation of terahertz (THz) spectroscopy to unveil the complexity of such materials has delivered unprecedented success. THz spectroscopy extracts material parameters such as dynamic conductivity, dielectric constant, and magnetic permeability in spectral range of 1–20 meV. This imparts the capability to probe a variety of quasiparticles emerging from the electrodynamics of collective, bound and free charge carriers, and complex spin orders, which is the key to decode the complex phases of TMOs class of quantum matter. Herein, the THz spectroscopic investigations of quasiparticle electrodynamics of correlated TMOs are reviewed. Several long‐standing issues are resolved and there is enormous potential for a lot more to offer, emphasizing the growing indispensability of THz technology in condensed matter. [ABSTRACT FROM AUTHOR]

Electron-doped Ca 0.96 Ce 0.04 MnO 3 (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 state 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., (© 2023 IOP Publishing Ltd.)