arXiv subjects

Muhsin Abdul Karim

Publications and source records attributed to Muhsin Abdul Karim.

4 recordsLinked to original sources

arXiv2026

RHEED pattern classification by a convolutional neural network for the growth of chalcogenide thin films and nanostructures

The use of reflection high energy electron diffraction (RHEED) plays a critical role for in-situ characterization in molecular beam epitaxy, pulsed laser deposition and sputtering. While sensitive to crystal symmetries and morphology, it is used ubiquitously to determine the growth modes of thin films. However, analysis of RHEED patterns depends on skilled experts and is therefore difficult to incorporate into the growth strategy in real-time. The development of machine learning (ML) processes, specifically convolutional neural networks (CNNs), presents a unique opportunity towards real-time RHEED pattern recognition. In this study, we develop a CNN model that can accurately classify four common and distinct RHEED patterns present in chalcogenide thin film growth. Its reached accuracy reached 94.9% for single run and 91.2% when averaged over 20 seeds. Our network is able to distinguish the nucleation of three common growth modes encountered in epitaxy, namely Volmer Weber, Stransky-Krastanov and Frank-van der Merwe, potentially enabling future automation of substrate temperature and shutter control informed by RHEED data. The network is material-agnostic and distinguishes the VW process with greater than 98% accuracy but is somewhat more limited in its ability to properly classify roughening and the initiation of Stransky-Krastanov growth. Our findings show that ML techniques can be successfully implemented even in cases where there is no detailed knowledge of growth chemistry providing an avenue towards real-time incorporation of ML to control nanostructure nucleation and thin film morphology.

cond-mat.mtrl-sci↗

arXiv2025

g-Factor Enhanced Upper Critical Field in Superconducting PdTe2 due to Quantum Confinement

The Pauli limiting field of superconductors determines the maximal possible value of magnetic field at which superconductivity remains possible. For weak-coupling superconductors, it is determined by an established relation that can be found by setting the condensation energy equal to the magnetization free energy. The latter is a function of the carrier g-factor. Here, we demonstrate in a van der Waals superconductor PdTe2, that quantum confinement can tune the effective g-factor causing the Pauli limit to become thickness dependent. We experimentally probe the in-plane upper critical field (Hc2||) of PdTe2 at intermediate thicknesses down to 20mK. Hc2|| is enhanced by more than an order of magnitude as the thickness is varied from 50nm down to 19nm. We model its temperature and thickness dependence, revealing that both orbital and spin Zeeman depairing mechanisms impact its value. While the variation of the orbital interaction is expected, our findings reveal how the Zeeman interaction impacts superconductivity in thin films. They aid in the search for mixed and odd pairing superconductivity where an enhancement of Hc2|| can be occasionally associated with those unconventional pairing symmetries.

cond-mat.supr-con↗

arXiv2025

Spectral analysis of the magneto-optical response in valley polarized Pb$_{1-x}$Sn$_x$Se

Since the last century, considerable efforts have been devoted to the study of valley-degenerate narrow gap semiconductors, such as the Pb$_{1-x}$Sn$_x$Se alloy. This material possesses band edges at the $L$-points of their Brillouin zone, yielding a valley degeneracy of four. However, in (111)-oriented films, it is still not fully understood how differences between the longitudinal valley, oriented along the growth axis, and the oblique valleys, oriented at an angle with respect to that axis, appear in infrared magneto-optical spectroscopy. In this work, we report a magneto-optical study on this family of alloys, focusing on an anomaly in the interband transition of the absorption strength ratio between longitudinal and oblique valleys under a magnetic field applied along the [111] direction. Based on the Mitchell-Wallis model, we provide a theoretical fit for the experimental transmission data, which quantitatively explains the spectral shape of the data at magnetic fields as high as 35T. In particular, we attribute this anomalous absorption strength variation to the carrier density difference between the two types of valleys as well as the field-dependent multiple-beam interference or the Fabry-Pérot interference. Our analysis also allows for the extraction of the real and imaginary parts of the dielectric function.

cond-mat.mes-hall↗

arXiv2023

MBE growth of axion insulator candidate EuIn2As2

The synthesis of thin films of magnetic topological materials is necessary to achieve novel quantized Hall effects and electrodynamic responses. EuIn2As2 is a recently predicted topological axion insulator that has an antiferromagnetic ground state and an inverted band structure, but that has only been synthesized and studied as a single crystal. We report on the synthesis of c-axis oriented EuIn2As2 films on sapphire substrates by molecular beam epitaxy. By carefully tuning the substrate temperature during growth, we stabilize the Zintl phase of EuIn2As2 expected to be topologically non-trivial. The magnetic properties of these films reproduce those seen in single crystals, but their resistivity is enhanced when grown at lower temperatures. We additionally find that the magnetoresistance of EuIn2As2 is negative even up to fields as high as 31T. while it is highly anisotropic at low fields, it becomes nearly isotropic at high magnetic fields above 5T. Overall, the transport characteristics of EuIn2As2 appear similar to those of chalcogenide topological insulators, motivating the development of devices to gate tune the Fermi energy and reveal topological features in quantum transport.

cond-mat.mtrl-sci↗