arXiv subjects

Raagya Arora

Publications and source records attributed to Raagya Arora.

5 recordsLinked to original sources

arXiv2026

Classification of Metal - Insulator Transitions: Relating characteristic Properties to Quantum Chemical Bonding Descriptors

Pressure induced metal insulator transitions (MIT) are classified by the evolution of characteristic optoelectronic and vibrational properties calculated with density functional theory. Three classes emerge: ionic solids metallize continuously at band-gap closure with hardening phonons; covalent solids show discontinuous changes in atomic arrangement and optical phonon frequencies; a third class exhibits complete lattice softening and drastically enhanced electron phonon coupling. A one dimensional hydrogen chain reproduces this behavior and serves as a toy model of the underlying bonding mechanism, termed metavalent. Two quantum-chemical descriptors capture the distinct bonding changes behind the three classes. In metavalent solids, competing electron localization and delocalization yield soft optical modes and Peierls distortions on the insulating side, superconductivity on the metallic side, and low lattice thermal conductivity near the MIT.

cond-mat.mtrl-sci↗

arXiv2026

First-Principles Insights into Surface and Ligand Effects in Stoichiometric HgTe Quantum Dots

HgTe quantum dots are promising mid-infrared nanomaterials owing to their exceptional bandgap tunability, yet their electronic structure is strongly influenced by surface coordination and ligand passivation at ultrasmall sizes. Here, we employ atomistic simulations to systematically investigate stoichiometric HgTe nanoclusters with sizes 0.86 to 1.85 nm. The in silico exploration uncovers a transition from confinement-dominated electronic structures with delocalized frontier states in small self-passivated clusters to surface influenced characteristics in larger nanoclusters. Increased coordination and bond-length inhomogeneity in the larger nanoclusters generate localized near-gap states centered on undercoordinated surface atoms. At intermediate sizes, the band edge states become spatially separated on different regions of the cluster without forming deep gap states, marking the onset of surface induced electronic asymmetry. In larger clusters (1.8 nm), common neutral ligands like amines, thiols, phosphines, and alcohols effectively eliminate surface-derived localized states by restoring local coordination and altering the band edge electronic structure through ligand surface hybridization. The sensitivity of the bandgap to ligand identity and binding site underscores the interplay between surface coordination and ligand chemistry in shaping the electronic structure of these nanoclusters. These insights provide an atomistic understanding of size-dependent electronic structures in ultrasmall HgTe clusters. The study further establishes neutral ligands as powerful chemical handles for engineering frontier electronic states relevant to infrared optoelectronic functionality.

cond-mat.mtrl-sci↗

arXiv2024

Stacking-dependent electronic structure of ultrathin perovskite bilayers

Twistronics has received much attention as a new method to manipulate the properties of 2D van der Waals structures by introducing moir\'e patterns through a relative rotation between two layers. Here we begin a theoretical exploration of twistronics beyond the realm of van der Waals materials by developing a first-principles description of the electronic structure and interlayer interactions of ultrathin perovskite bilayers. We construct both an ab initio tight-binding model as well as a minimal 3-band effective model for the valence bands of monolayers and bilayers of oxides derived from the Ruddlesden-Popper phase of perovskites, which is amenable to thin-layer formation. We illustrate the approach with the specific example of Sr$_2$TiO$_4$ layers but also provide model parameters for Ca$_2$TiO$_4$ and Ba$_2$TiO$_4$ .

cond-mat.mtrl-sci↗

arXiv2024

Engineering Interfacial Charge Transfer through Modulation Doping for 2D Electronics

Two-dimensional (2D) semiconductors are likely to dominate next-generation electronics due to their advantages in compactness and low power consumption. However, challenges such as high contact resistance and inefficient doping hinder their applicability. Here, we investigate workfunction-mediated charge transfer (modulation doping) as a pathway for achieving high-performance p-type 2D transistors. Focusing on type-III band alignment, we explore the doping capabilities of 27 candidate materials, including transition metal oxides, oxyhalides, and {\alpha}-RuCl3, on channel materials such as transition metal dichalcogenides (TMDs) and group-III nitrides. Our extensive first-principles density functional theory (DFT) reveal p-type doping capabilities of high electron affinity materials, including {\alpha}-RuCl3, MoO3, and V2O5. We predict significant reductions in contact resistance and enhanced channel mobility through efficient hole transfer without introducing detrimental defects. We analyze transistor geometries and identify promising material combinations beyond the current focus on WSe2 doping, suggesting new avenues for hBN, AlN, GaN, and MoS2. This comprehensive investigation provides a roadmap for developing high-performance p-type monolayer transistors toward the realization of 2D electronics.

cond-mat.mtrl-sci↗

arXiv2024

2D Nitride Ordered Alloys: A Novel Class of Ultra-Wide Bandgap Semiconductors

Ultra-wide bandgap (UWBG) semiconductors are poised to transform power electronics by surpassing the capabilities of established wide bandgap materials, such as GaN and SiC, owing to their capability to operate at higher voltage, frequency, and temperature ranges. While bulk group-III nitrides and their alloys have been extensively studied in the UWBG realm, their two-dimensional counterparts remain unexplored. Here, we examine the stability and electronic properties of monolayers of ordered boron-based group-III nitride alloys with general formula BxM1-xN, where M = Al, Ga. On the basis of ab initio calculations we identify a number of energetically and dynamically stable structures. Instrumental to their stability is a previously overlooked out-of-plane displacement (puckering) of atoms, which induces a polar ordering and antiferroelectric ground state. Our findings reveal the energy barrier between metastable ferroelectric states is lowered by successive switching of out-of-plane displacements through an antiferroelectric state.

cond-mat.mtrl-sci↗