arXiv subjects

Vitor Dantas

Publications and source records attributed to Vitor Dantas.

4 recordsLinked to original sources

arXiv2026

Majorana Signatures in Planar Tunneling through a Kitaev Spin Liquid

We propose a planar tunneling setup to probe vacancy-bound Majorana modes in the chiral Kitaev spin liquid. In this geometry, the inelastic tunneling conductance can be expressed directly in terms of real-space spin correlations, establishing a link between measurable spectra and the underlying fractionalized excitations. We show that spin vacancies host localized Majorana states that generate sharp near-zero-bias features, well separated from the continuum of bulk spin excitations. Compared to local STM measurements, the planar configuration naturally enhances the signal by coherently summing over multiple vacancies, reducing spatial resolution requirements. Our results demonstrate a realistic and scalable route to detect Majorana excitations in Kitaev materials.

cond-mat.str-el↗

arXiv2025

Raman scattering from moir\'e phonons

We develop a theoretical framework for probing moir\'e phonon modes using Raman spectroscopy, and illustrate it with the example of twisted bilayer graphene (TBG). These moir\'e phonons arise from interlayer sliding motion in twisted 2D materials and correspond to fluctuations of the stacking order in reconstructed moir\'e superlattices. These include both acoustic-like phason modes and a new set of low-energy optical modes originating from the zone-folding of monolayer graphene's acoustic modes, which are accessible via Raman spectroscopy. We show that the Raman response of TBG exhibits a series of low-frequency peaks that clearly distinguish it from that of decoupled layers. We further examine the role of anharmonic interactions in shaping the phonon linewidths and demonstrate the strong dependence of the Raman spectra on both the twist angle and the polarization of the incident light. Our findings establish Raman spectroscopy as a powerful tool for exploring moir\'e phonons in a broad class of twisted van der Waals systems.

cond-mat.str-el↗

arXiv2024

Phonon dynamics in the site-disordered Kitaev spin liquid

The Kitaev honeycomb model provides a paradigmatic example of an exactly solvable quantum spin liquid (QSL), in which the spin degrees of freedom fractionalize into itinerant Majorana fermions coupled to a static background of $\mathbb{Z}_{2}$ gauge fluxes. This model has attracted significant attention in recent years due to the possibility of its experimental realization in some spin-orbit Mott insulators such as $ \alpha $-RuCl$ _3 $. Among various experimental probes, ultrasound experiments measuring sound attenuation have emerged as a promising avenue to unveil the fractionalization of spins in these materials. Yet, candidate materials often deviate from the ideal Kitaev model due to the presence of disorder, leading to the emergence of localized modes governing low-energy physics. To provide further insight into the effects of these defect-induced modes on the phonon dynamics, we calculate the sound attenuation coefficient in the site-disordered Kitaev honeycomb model with an applied magnetic field, which breaks the time-reversal symmetry. In order to obtain a more accurate perspective on the temperature-dependent sound attenuation in this model, the impact of thermally excited fluxes on the disordered system is also analyzed.

cond-mat.str-el↗

arXiv2022

Disorder, Low-Energy Excitations, and Topology in the Kitaev Spin Liquid

The Kitaev model is a fascinating example of an exactly solvable model displaying a spin-liquid ground state in two dimensions. However, deviations from the original Kitaev model are expected to appear in real materials. In this Letter, we investigate the fate of Kitaev's spin liquid in the presence of disorder -- bond defects or vacancies -- for an extended version of the model. Considering static flux backgrounds, we observe a power-law divergence in the low-energy limit of the density of states with a nonuniversal exponent. We link this power-law distribution of energy scales to weakly coupled droplets inside the bulk, in an uncanny similarity to the Griffiths phase often present in the vicinity of disordered quantum phase transitions. If time-reversal symmetry is broken, we find that power-law singularities are tied to the destruction of the topological phase of the Kitaev model in the presence of bond disorder alone. However, there is a transition from this topologically trivial phase with power-law singularities to a topologically nontrivial one for weak to moderate site dilution. Therefore, diluted Kitaev materials are potential candidates to host Kitaev's chiral spin-liquid phase.

cond-mat.str-el↗