arXiv subjects

Fauzia Mujid

Publications and source records attributed to Fauzia Mujid.

3 recordsLinked to original sources

arXiv2025

Spectra-orthogonal optical anisotropy in wafer-scale molecular crystal monolayers

Controlling the spectral and polarization responses of two-dimensional (2D) crystals is vital for developing ultra-thin platforms for compact optoelectronic devices. However, independently tuning optical anisotropy and spectral response remains challenging in conventional semiconductors due to the intertwined nature of their lattice and electronic structures. Here, we report spectra-orthogonal optical anisotropy, where polarization anisotropy is tuned independently of spectral response, in wafer-scale, one-atom-thick 2D molecular crystal (2DMC) monolayers synthesized on monolayer transition metal dichalcogenide (TMD) crystals. Utilizing the concomitant spectral consistency and structural tunability of perylene derivatives, we demonstrate tunable optical polarization anisotropy in 2DMCs with similar spectral profiles, as confirmed by room-temperature scanning tunneling microscopy and cross-polarized reflectance microscopy. Additional angle-dependent analysis of the single- and polycrystalline molecular domains reveals an epitaxial relationship between the 2DMC and the TMD. Our results establish a scalable, molecule-based 2D crystalline platform for unique and tunable functionalities unattainable in covalent 2D solids.

cond-mat.mes-hall↗

arXiv2023

The Role of Self-Torques in Transition Metal Dichalcogenide/Ferromagnet Bilayers

Recently, transition metal dichalcogenides (TMDs) have been extensively studied for their efficient spin-orbit torque generation in TMD/ferromagnetic bilayers, owing to their large spin-orbit coupling, variety in crystal symmetries, and pristine interfaces. Although the TMD layer was considered essential for the generation of the observed SOTs, recent reports show the presence of a self-torque in single-layer ferromagnetic devices with magnitudes comparable to TMD/ferromagnetic devices. Here, we perform second-harmonic Hall SOT measurements on metal-organic chemical vapor deposition (MOCVD) grown MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices and compare them to a single-layer permalloy/Al$_{2}$O$_{3}$ device to accurately disentangle the role of self-torques from contributions from the TMD layer. We report a damping-like self-torque conductivity of opposite sign in our single-layer permalloy/Al$_{2}$O$_{3}$ device compared to one MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ device, and find no significant one for all other MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices. This indicates a competition between the self-torque and the torque arising from the TMD layer, which would reduce the observed torque in these bilayers. In addition, we find a field-like spin-torque conductivity of comparable magnitude to control MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices, indicating only a minor role of the MoS$_{2}$ layer. Finally, we find a linear dependence of the SOT conductivity on the Hall bar leg/channel width ratio of our devices, indicating that the Hall bar dimensions are of significant importance for the reported SOT strength. Our results accentuate the importance of delicate details, like device asymmetry, Hall bar dimensions, and self-torque generation, for the correct disentanglement of the microscopic origins underlying the SOTs, essential for future energy-efficient spintronic applications.

cond-mat.mes-hall↗

arXiv2019

Spatiotemporal Mapping of Photocurrent in a Monolayer Semiconductor Using a Diamond Quantum Sensor

The detection of photocurrents is central to understanding and harnessing the interaction of light with matter. Although widely used, transport-based detection averages over spatial distributions and can suffer from low photocarrier collection efficiency. Here, we introduce a contact-free method to spatially resolve local photocurrent densities using a proximal quantum magnetometer. We interface monolayer MoS2 with a near-surface ensemble of nitrogen-vacancy centers in diamond and map the generated photothermal current distribution through its magnetic field profile. By synchronizing the photoexcitation with dynamical decoupling of the sensor spin, we extend the sensor's quantum coherence and achieve sensitivities to alternating current densities as small as 20 nA per micron. Our spatiotemporal measurements reveal that the photocurrent circulates as vortices, manifesting the Nernst effect, and rises with a timescale indicative of the system's thermal properties. Our method establishes an unprecedented probe for optoelectronic phenomena, ideally suited to the emerging class of two-dimensional materials, and stimulates applications towards large-area photodetectors and stick-on sources of magnetic fields for quantum control.

cond-mat.mtrl-sci↗