Orbital Floquet Engineering of Exchange Interactions in Magnetic Materials

We present a new scheme to control the spin exchange interactions between two magnetic ions by manipulating the orbital degrees of freedom using a periodic drive. We discuss two different protocols for orbital Floquet engineering. In one case, we modify the properties of the ligand orbitals which mediate magnetic interactions between two transition metal ions. While in the other case, we mix the d orbitals on each magnetic ion. In contrast to previous works on Floquet engineering of magnetic properties, the present scheme makes use of the AC Stark shift of the states involved in the exchange process

Evaluation of Neuroprotective effect of medicinal plants in Drosophila melanogaster model

In this study, we investigated the neuroprotective effects of ethanolic extract of Bombax ceiba (EEBC) and ethanolic extract of Gymnemasylvestre (EEGS) against the toxicity induced by rotenone (ROT) in Drosophila melanogaster. Materials and Methods:Adult wild-type flies were concomitantly exposed to ROT (500 μM), EEBC (0.05% w/v and 0.1% w/v) and EEGS (0.05% w/v and 0.1% w/v) in the culture medium for 7 days. Results: ROT treated flies produced marked decreased in locomotor performance (i.e., climbing capability) in the negative geotaxis assay when compared to control group. EEBC and EEGS flies after treatment offered protection (24-42%) against the ROT-induced locomotor impairment in the negative geotaxis assay suggesting attenuation of ROT-induced locomotor deficits. Conclusion: The results of this study suggest that EEBC and EEGS were effective in reducing the toxicity induced by ROT in D. melanogaster as well as it confirms the significance of this model to explore possible therapeutic approaches in Parkinson’s disease (PD)

Evaluation of anti-Parkinson’s activity of ethanolic extract of Tridax procumbens (Asteraceae)

9-17Parkinson's disease (PD) is the second most common neurodegenerative disease characterized by loss of dopaminergic neurons in the substantia nigra. In the present study was designed to evaluate anti-Parkinson’s activity of ethanolic extract of Tridax procumbens (EETP) leaves, family Asteraceae. The experimental paradigm included haloperidol-induced catalepsy in rat model and rotenone-induced locomotor impairment in the fruit fly. In the catalepsy model, the rats received treatment of EETP (100 and 200 mg/kg, p.o.) followed by haloperidol (1 mg/kg, i.p.) for 15 days. The significant (P p.o.). The catalase and reduced glutathione levels were found to be significantly (P P <0.05) improved the performances of locomotor activity in flies when compared with ROT treated flies. Thus, the study proved that EETP treatment significantly attenuated motor defects and also protected the brain from oxidative stress

Central cervical fibroid mimicking as chronic uterine inversion: a case report

Leiomyomas are most common benign gynaecological tumor. Most of the fibroids are situated in the body of the uterus, but only in 1-2% cases, they are confined to cervix.We report a case of 33 years old women, para 2 live 2 diagnosed as myomatous polyp on ultrasound and clinically as chronic inversion of uterus. On surgery, we found it as central cervical fibroid with uterus sitting on the fibroid i.e. lantern on the St. Paul’s

Pragmatic numbers: how the IMF creates policy dialogue for financial reform

Do international organizations generate benchmarks and data as tools for policy enforcement or as tools of knowledge creation? This paper suggests the latter through a case study on the power of numbers in the International Monetary Fund’s (IMF) Financial Sector Assessment Programme (FSAP). While the IMF is typically viewed as an institution that enforces global standards for economic governance through the imposition of quantitative targets (‘numbers’), we suggest that its use of benchmarking tools through the generation of financial data actually serves as knowledge creation tool for policy dialogue. As such, the IMF’s program practices differ from their policy proclamations on the need for universal standards and transparency. Seen through a pragmatist lens, as often found in economic sociology, the IMF seeks to generate ‘learning by monitoring’ with member states within its broader international political and economic constraints. This process must yield to broader principal-agent dynamics in the IMF’s governance structure, as well as tip its cap to private market actors. But it is also not hostage to them. We suggest that the IMF’s use of ‘pragmatic numbers’ within FSAPs demonstrates one method by which an institution seeks to foster learning within an environment of noise and domination

Light Induced Dynamics in Quantum Matter

This thesis presents studies of different schemes to probe and manipulate quantum matter using light with an aim to discover novel routes to efficiently control the properties of quantum materials. A special focus is placed on developing new schemes utilizing light-matter interactions (1) to modify exchange interactions in magnetic insulators, and (2) to probe and modify band topology in quantum matter. In part II, new schemes are presented to probe local band topology of Bloch bands. First, we study the effects of time-dependent band topology on adiabatic evolution of a Bloch wavepacket. We find that it results in an electric-field analog in semi-classical equation of motion, and can be demonstrated in a honeycomb lattice by varying the sublattice offset energy. We then extend these methods to include non-adiabatic processes, and found interesting connections between the anomalous drift during band excitation and a quantum geometric quantity known as shift-vector. We generalize the concept of shift-vector to include different kinds of band transition protocols beyond light-induced dipole transitions. The idea of electric-field analog and the shift-vector are then combined to develop a novel charge pumping scheme. Motivated by these interesting consequences of band topology in non-adiabatic processes, we study shift-current response in moiré materials, and find that the highly topological nature of flat bands along with their very large unit cells significantly enhances these shift-vector related effects. This response also displays a strong dependence on interaction-induced changes in the band structure and quantum geometric quantities. These results suggest that shift-current response can possibly serve as a very reliable probe for interactions in twisted bilayer graphene. In addition to studying consequences of band topology on single-particle transport, we also consider Berry curvature effects on exciton transport. We find that the non-trivial band topology of underlying electron and hole bands allows us to manipulate excitons with a uniform electric field. We examine the conditions necessary to observe such transport and propose that transition metal dichalcogenide heterobilayers with moiré structure can prove an ideal platform for these effects. In part III, we propose novel drive protocols based on manipulating orbital and lattice degrees of freedom in quantum materials with light. We found that light induced changes in orbital hybridization and their electronic energies results in a significant change in exchange interactions in quantum magnets. We also accounted for the role of ligands in periodically driven quantum magnets, and found that the predictions made by the minimal model based on direct-hopping can be wrong in certain regimes of drive parameters. This understanding of light induced modifications in ligand-mediated exchange interactions was used to explain the phase shift observed in coherent phonon oscillations of CrSiTe₃ upon the onset of short-range spin correlations. We also demonstrate that light induced coherent lattice vibrations can provide a new route to realize space-time symmetry protected topological phases. Our results suggest that manipulating additional degrees of freedom (not included in commonly employed minimal models of periodically driven systems) with light can provide novel routes for ultrafast control of quantum materials.</p

Berry electrodynamics: Anomalous drift and pumping from a time-dependent Berry connection

The Berry curvature of a Bloch band can be interpreted as a local magnetic field in reciprocal space. This analogy can be extended by defining an electric field analog in reciprocal space which arises from the time-dependent Berry connection. We explore the term in the semiclassical equation of motion that gives rise to this phenomenon, and show that it can lead to anomalous drift in wave-packet motion. A similar effect arises from changes in the band population due to periodic driving, where the resulting drift depends on the nature of the drive and can be expressed in terms of a shift vector. Finally, these effects can be combined to build a pump with a net anomalous drift during a cyclic evolution in momentum space

Anomalous exciton transport in response to a uniform, in-plane electric field

Excitons are neutral objects, that, naively, should have no response to a uniform, electric field. Could the Berry curvature of the underlying electronic bands alter this conclusion? In this work, we show that Berry curvature can indeed lead to anomalous transport for excitons in 2D materials subject to a uniform, in-plane electric field. By considering the constituent electron and hole dynamics, we demonstrate that there exists a regime for which the corresponding anomalous velocities are in the same direction. We establish the resulting center of mass motion of the exciton through both a semiclassical and fully quantum mechanical analysis, and elucidate the critical role of Bloch oscillations in achieving this effect. We identify transition metal dichalcogenide heterobilayers as candidate materials to observe the effect

Phonon-induced Floquet topological phases protected by space-time symmetries

For systems with spatial and nonspatial symmetries, the topological classification depends not only on these symmetries but also on the commutation/anticommutation relations between spatial and nonspatial symmetries. The coexistence of spatial and nonspatial symmetries together with appropriate commutation/anticommutation relations between them can give rise to crystalline and higher-order topological phases, which host gapless boundary modes. Alternatively, space-time symmetries in a Floquet system can take the role of spatial symmetries in deciding the topological classification. Promoting a spatial symmetry to a space-time symmetry can alter the commutation relations, which in turn can modify the topological properties of the system. We show how a coherently excited phonon mode can be used to promote a spatial symmetry with which the static system is always trivial to a space-time symmetry which supports a nontrivial Floquet topological phase. We demonstrate this effect by considering two systems: The first is a second-order topological superconductor, and the second is a first-order crystalline topological insulator. In both these cases, a coherently excited phonon mode is responsible for promoting the reflection symmetry to a time-glide symmetry. This newly introduced symmetry allows the previously trivial system to host gapless modes. In the first case, these are protected corner modes, while in the second case, these are gapless edge modes