arXiv subjects

Carolina Paiva

Publications and source records attributed to Carolina Paiva.

6 recordsLinked to original sources

arXiv2026

Observation of angular momentum transfer among crystal lattice modes

Transfer of energy and linear momentum between lattice vibrations via anharmonic coupling is an important concept in solid-state physics. However, it remains difficult to directly observe how angular momentum is exchanged and conserved among lattice modes, even though these processes are thought to play an important role in achieving magnetization equilibrium and in spin relaxation effects like the Einstein-de Haas effect. Here, we demonstrate and coherently control angular momentum transfer between two lattice modes using the inverse process of anharmonic decay. The observed rotational phonon-phonon Umklapp scattering enforces the conservation of quantized crystal angular momentum, as dictated by the crystal's discrete rotational symmetry. We thereby experimentally confirm the fundamental analogy between linear and angular momentum conservation in solids. Moreover, we establish axial nonlinear phononics towards ultrafast control of material properties.

cond-mat.other↗

arXiv2026

Quantum Hall States response to toroidal geometry deformation

In this paper, we apply techniques of geometric quantization to study the response of the integer and fractional quantum Hall effects to toroidal geometry deformation. The main method is that of using complex time Hamiltonian evolution to induce the geometry change and then the associated generalized coherent state transforms (gCST) to find the evolution of the Laughlin states. We consider two kinds of deformations. The first are flat toroidal deformations. Although Laughlin states for all flat toroidal geometries have been thoroughly studied before, we believe that our approach via the gCST is novel. It also serves as a testing ground to study the non-flat Kähler deformations. The Hamiltonians used in the flat deformations are quadratic in the generators of translations and therefore non periodic. The second kind of deformations involve nonflat Kähler toroidal deformations, generated by global, thus bi-periodic, Hamiltonians on the torus. The corresponding imaginary time flows are (elliptic curve modulus) $τ$-preserving Mabuchi geodesics in the space of Kähler metrics on the torus, hitting a curvature singularity in finite imaginary time. By restricting to $S^1$-invariant deformations we find explicit analytic expressions for the evolution of the toroidal geometry and of the Laughlin states all the way to the singularity.

math-ph↗

arXiv2025

Geometrical Responses of Generalized Landau Levels: Structure Factor and the Quantized Hall Viscosity

We present a new geometric characterization of generalized Landau levels (GLLs). The GLLs are a generalization of Landau levels to non-uniform Berry curvature, and are mathematically defined in terms of a holomorphic curve -- an ideal Kähler band -- and its associated unitary Frenet-Serret moving frame. Here, we find that GLLs are harmonic maps from the Brillouin zone to the complex projective space and they are critical points of the Dirichlet energy functional, as well as the static structure factor up to fourth order. We also find that filled GLLs exhibit quantized Hall viscosity, similar to the ordinary Landau levels. These results establish GLLs as a versatile generalization of Landau levels.

cond-mat.mes-hall↗

arXiv2024

Conductivity scaling and absence of localization in disordered nodal line semimetals

Transport plays a key role in characterizing topological insulators and semimetals. Understanding the effect of disorder is crucial to assess the robustness of experimental signatures for topology. In this work, we find the absence of localization in nodal line semimetals for long-range scalar disorder and a large range of disorder strengths. Using a continuum transfer matrix approach, we find that the conductivity in the plane and out of the plane of the nodal line increases with system size and disorder strength. We substantiate these findings by a perturbative calculation and show that the conductivity increases with disorder strength using the Kubo formula in the self-consistent Born approximation. We also find that the system remains metallic for vector disorder and that vector disorder can drive a transition from an insulating to a metallic regime. Our results demonstrate the absence of localization in a three-dimensional bulk system.

cond-mat.dis-nn↗

arXiv2024

Shift and Polarization of Excitons from Quantum Geometry

Despite a long history, certain aspects of excitons - the bound inter-band states which form when a valence band hole and a conduction band electron pair - have remained relatively unexplored. This holds particularly true for the wavefunction of an exciton, for which few properties have been explored theoretically in various limiting cases. An intuitive language robustly characterizing the topology of bound electron-hole states is lacking, but needed in order to address the global features of the charge distribution of the excitonic state, to properly understand their transport theory, and to supplement the numerical investigation of excitons in ab-initio approaches. Here, we address these gaps by developing a comprehensive framework for the quantum geometry and topology of two-dimensional exciton states in terms of the exact connections which describe the interaction-renormalized exciton bundle in a periodic lattice. Based on this description, we derive two gauge-invariant quantities, which we identify as the exciton shift vector and the exciton dipole vector. Using the shift vector, we elucidate the topology of exciton bands compared to the topology of the parent electronic band structure, pinpointing precisely how interactions can introduce nontrivial topology to the exciton bands beyond the topology which is contained in the single-particle bands. We further elucidate how shift and polarizations enter into the semiclassical equations of motion for the exciton center of mass coordinates.

cond-mat.mes-hall↗

arXiv2024

Dynamically induced multiferroic polarization

We describe a mechanism by which both ferroelectric polarization and magnetization can be created in nonpolar, nonmagnetic materials. Using a combination of phenomenological modeling and first-principles calculations, we demonstrate that ferroelectric polarization, magnetization, or both simultaneously can be transiently induced by an ultrashort laser pulse upon linearly, circularly, or elliptically polarized excitation of phonon modes in $γ$-LiBO$_2$. The direction and magnitude of the multiferroic polarization can be controlled by the chirality of the laser pulse and the phonon modes, offering a pathway for controlling multiferroicity and magnetoelectricity on ultrafast timescales.

cond-mat.mtrl-sci↗