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Alessandra Ames

Publications and source records attributed to Alessandra Ames.

3 recordsLinked to original sources

Optical memory in a MoSe$_2$/Clinochlore device

Two-dimensional heterostructures have been crucial in advancing optoelectronic devices utilizing van der Waals materials. Semiconducting transition metal dichalcogenide monolayers, known for their unique optical properties, offer extensive possibilities for light-emitting devices. Recently, a memory-driven optical device, termed a Mem-emitter, was proposed using these monolayers atop dielectric substrates. The successful realization of such devices heavily depends on selecting the optimal substrate. Here, we report a pronounced memory effect in a MoSe$_2$/clinochlore device, evidenced by electric hysteresis in the intensity and energy of MoSe$_2$ monolayer emissions. This demonstrates both population-driven and transition-rate-driven Mem-emitter abilities. Our theoretical approach correlates these memory effects with internal state variables of the substrate, emphasizing that clinochlore layered structure is crucial for a robust and rich memory response. This work introduces a novel two-dimensional device with promising applications in memory functionalities, highlighting the importance of alternative insulators in fabricating van der Waals heterostructures.

cond-mat.mtrl-sci

The Emergence of Mem-Emitters

The advent of memristors and resistive switching has transformed solid state physics, enabling advanced applications such as neuromorphic computing. Inspired by these developments, we introduce the concept of Mem-emitters, devices that manipulate light emission properties of semiconductors to achieve memory functionalities. Mem-emitters, influenced by past exposure to stimuli, offer a new approach to optoelectronic computing with potential for enhanced speed, efficiency, and integration. This study explores the unique properties of transition metal dichalcogenides-based heterostructures as a promising platform for Mem-emitter functionalities due to their atomic-scale thickness, tunable electronic properties, and strong light-matter interaction. By distinguishing between population-driven and transition rate-driven Mem-emitters, we highlight their potential for various applications, including optoelectronic switches, variable light sources, and advanced communication systems. Understanding these mechanisms paves the way for innovative technologies in memory and computation, offering insights into the intrinsic dynamics of complex systems.

cond-mat.mes-hall

Strong magneto-optical responses of an ensemble of defect-bound excitons in ambient exposed WS$_{2}$ and WSe$_{2}$ monolayers

Transition metal dichalcogenide (TMD) monolayers present a singular coupling in their spin and valley degrees of freedom. Moreover, by applying an external magnetic field it is possible to break the energy degeneracy between their K and $-$K valleys. This valley Zeeman effect opens the possibility of controlling and distinguishing the spin and valley characters of charge carriers in TMDs by their optical transition energies, making these materials promising for the next generation of spintronic and photonic devices. However, the free excitons of pristine TMD monolayers present a moderate valley Zeeman splitting of $\approx 0.23$ meV/T. Therefore, alternative excitonic states with higher magnetic responses are mandatory for application purposes. Here, we investigate the magneto-optical properties of ambient exposed WS$_2$ and WSe$_2$ monolayers by circularly polarized magneto-photoluminescence experiments at cryogenic temperatures. A broad lower energy photoluminescence emission related to an ensemble of defects is observed, presenting remarkable valley-related splittings of $\approx 1.45$ meV/T and $\approx 1.11$ meV/T for WS$_2$ and WSe$_2$ monolayers, respectively. In addition, we report a significant valley polarization of charge carriers in the defect mid-gap states induced by the external magnetic field. We explain this valley-polarized population and enhanced valley-related splitting in terms of imbalanced intervalley relaxations, leading to a magnetic field-dependent distribution of charge carriers in multiple defect levels. This effect, together with the individual Zeeman shiftings of the mid-gap states, explains the strong magneto-optical responses observed. Our work uncovers the singular potential of manipulating the light emission of ambient exposed TMD monolayers by an external magnetic field.

cond-mat.mes-hall