arXiv subjects

Raquel Esteban-Puyuelo

Publications and source records attributed to Raquel Esteban-Puyuelo.

3 recordsLinked to original sources

arXiv2021

Role of defects in ultrafast charge recombination in monolayer MoS$_2$

In this work, we have systematically studied the role of point defects in the recombination time of monolayer MoS$_2$ using time-dependent ab initio non-adiabatic molecular dynamics simulations. Various types of point defects, such as S vacancy, S interstitial, Mo vacancy and Mo interstitial have been considered. We show that defects strongly accelerate the electron-hole recombination, especially interstitial S atoms do that by 3 orders of magnitude higher compared to pristine MoS$_2$. Mo defects (both vacancy and interstitial) introduce a multitude of de-excitation pathways via various defect levels in the energy gap. The results of this study provide some fundamental understanding of photoinduced de-excitation dynamics in presence of defects in highly technologically relevant 2D MoS$_2$.

cond-mat.mtrl-sci↗

arXiv2020

Structural phase transition in monolayer gold(I) telluride: From a room-temperature topologicalinsulator to an auxetic semiconductor

Structural phase transitions between semiconductors and topological insulators have rich applications in nanoelectronics but are rarely found in two-dimensional (2D) materials. In this work, by combining ab initio computations and evolutionary structure search, we investigate two stable 2D forms of gold(I) telluride (Au$_{2}$Te) with square symmetry, noted as s(I)- and s(II)-Au$_{2}$Te. s(II)-Au$_{2}$Te is the global minimum structure and is a room-temperature topological insulator. s(I)-Au$_{2}$Te is a direct-gap semiconductor with high carrier mobilities and unusual in-plane negative Poisson's ratio. Both s(I) and s(II) phases have ultra-low Young's modulus, implying high flexibility. By applying a small tensile strain, s(II)-Au$_{2}$Te can be transformed into s(I)-Au$_{2}$Te. Hence, a structural phase transition from a room-temperature topological insulator to an auxetic semiconductor is found in the 2D forms of Au$_{2}$Te, which enables potential applications in phase-change electronic devices. Moreover, we elucidate the mechanism of the phase transition with the help of phonon spectra and group theory analysis.

cond-mat.mtrl-sci↗

arXiv2020

Tailoring the opto-electronic response of graphene nanoflakes by size and shape optimization

The long spin-diffusion length, spin-lifetimes and excellent optical absorption coefficient of graphene provide an excellent platform for building opto-electronic devices as well as spin-based logic in a nanometer regime. In this study, by employing density functional theory and its time-dependent version, we provide a detailed analysis of how the size and shape of graphene nanoflakes can be used to alter their magnetic structure and optical properties. As the edges of zigzag graphene nanoribbons are known to align anti-ferromagnetically and armchair nanoribbons are typically non-magnetic, a combination of both in a nanoflake geometry can be used to optimize the ground-state magnetic structure and tailor the exchange coupling decisive for ferro- or anti-ferromagnetic edge magnetism, thereby offering the possibility to optimize the external fields needed to switch magnetic ordering. Most importantly, we show that the magnetic state alters the optical response of the flake leading to the possibility of opto-spintronic applications.

cond-mat.mtrl-sci↗