arXiv subjects

Aneesh Agarwal

Publications and source records attributed to Aneesh Agarwal.

5 recordsLinked to original sources

arXiv2026

Geometric Ginzburg-Landau theory of charge ordering and commensurability

The concept of quantum geometry has recently led to reinvigorated insights in a wide range of fields including physical responses, superconductivity, and optical transitions, with effects most pronounced in systems with nearly flat dispersion. Here, we show that it plays an essential role in charge density wave formation (CDW) -- an important physical phenomenon that is responsible for driving various sharp changes in material transport properties including metal-insulator transitions. We derive an effective Ginzburg-Landau theory including uncharted contributions and, as a highlight, discover a general criterion for both CDW formation and commensurability transitions where underlying electron-phonon interactions manifest purely as electronic quantum geometric enhancements/suppressions. We benchmark our framework in a class of transition-metal dichalcogenides and resolve a longstanding puzzle where well-established purely kinetic CDW criteria fail in describing the correct ordering wavevector. Besides rendering robust criteria and fundamental insights that are immediately relevant to several experimental charge ordering systems, our theory can also be applied directly to other phonon-mediated phases such as superconductivity, and can be used as an important tool to explore the interplay between various such states. More generally, our framework provides a recipe for investigating the role of quantum geometry in phase transitions.

cond-mat.str-el↗

arXiv2025

Modelling the non-linear dynamics of the looping pendulum

The Looping pendulum phenomenon was first introduced in 2019 at the 32nd edition of the IYPT, wherein a lighter bob sweeps around a cylindrical rod to support the weight of a heavier bob. In this paper, the phenomenon was divided based on rotating and non-rotating forces, and differential equations were derived for each. To verify the theoretical derivation, an experimental analysis was done, varying the mass ratio with the vertical distance travelled by the heavier bob. (Tracked using tracker) Experimental findings fit a logarithmic curve fit -- falling succinctly with a similar trend with the simulation run with MATLAB solving the derived differential equations. Furthermore, to verify the simulation, the trajectory of both the lighter and heavier mass was also compared for the simulation and experimental findings. The experimental findings fit very closely to the simulation findings, accrediting the validity and accuracy of the derived theory.

physics.class-ph↗

arXiv2025

Shift photocurrent vortices from topological polarization textures

Following the recent interest in van der Waals (vdW) ferroelectrics, topologically nontrivial polar structures have been predicted to form in twisted bilayers. However, these structures have proven difficult to observe experimentally. We propose that these textures may be probed optically by showing that topological polarization textures result in exotic nonlinear optical responses. We derive this relationship analytically using non-Abelian Berry connections and a quantum-geometric framework, supported by tight-binding and first-principles calculations. For the case of moiré materials without centrosymmetry, which form networks of polar merons and antimerons, the shift photoconductivity forms a vortex-like structure in real space. For a range of frequencies where transitions between topologically trivial bands occur at the Brillouin zone edge, the shift photocurrents are antiparallel to the in-plane electronic polarization field. Our findings highlight the interplay between complex polarization textures and nonlinear optical responses in vdW materials and provide a sought-after strategy for their experimental detection.

cond-mat.mes-hall↗

arXiv2025

Field-driven band asymmetry and non-reciprocal transport in a helimagnet

Helimagnets exhibit noncollinear spin arrangements characterized by a periodic helical modulation, giving rise to emergent chiral properties. These materials have attracted significant interest due to their potential applications in spintronics, particularly for robust information storage and the realization of topological spin textures such as skyrmions. In this work, we focus on Yoshimori-type helimagnets, where competing exchange interactions mediated by conduction electrons stabilize helical spin structures without requiring Dzyaloshinskii-Moriya interaction. We introduce a minimal model describing the electronic structure of a one-dimensional helimagnet in the presence of an external magnetic field and investigate its impact on non-reciprocal transport. We demonstrate how band asymmetry emerges in the conical phase induced by the external field, leading to a nonzero second-order electronic conductivity and injection photoconductivity. Our results provide insight into the interplay between the real space magnetic texture and electronic properties, paving the way for future studies on chirality-driven transport phenomena in centrosymmetric helimagnets.

cond-mat.mes-hall↗

arXiv2024

Polarization textures in crystal supercells with topological bands

Two-dimensional materials are a highly tunable platform for studying the momentum space topology of the electronic wavefunctions and real space topology in terms of skyrmions, merons, and vortices of an order parameter. Such textures for electronic polarization can exist in moiré heterostructures. A quantum-mechanical definition of local polarization textures in insulating supercells was recently proposed. Here, we propose a definition for local polarization that is also valid for systems with topologically non-trivial bands. We introduce semilocal hybrid polarizations, which are valid even when the Wannier functions in a system cannot be made exponentially localized in all dimensions. We use this definition to explicitly show that nontrivial real-space polarization textures can exist in topologically non-trivial systems with non-zero Chern number under (1) an external superlattice potential, and (2) under a stacking-induced moiré potential. In the latter, we find that while the magnitude of the local polarization decreases discontinuously across a topological phase transition from trivial to topologically nontrivial, the polarization does not completely vanish. Our findings suggest that band topology and real-space polar topology may coexist in real materials.

cond-mat.mes-hall↗