arXiv subjects

Abduljelili Popoola

Publications and source records attributed to Abduljelili Popoola.

4 recordsLinked to original sources

arXiv2026

Negative and Zero Linear Compressibility in MCN (M = Ag, Au, Cu): A First-Principles Study

Negative linear compressibility (NLC) is the counterintuitive phenomenon in which a crystallographic axis expands under hydrostatic pressure. A related phenomenon, zero linear compressibility (ZLC), occurs when an axis shows no length change under pressure. Both responses are rare and arise in materials with highly anisotropic mechanical properties. Motivated by recent reports of anomalous behavior in metal cyanides - including negative thermal expansion and NLC - we use first-principles calculations to investigate the potential of the MCN family (M = Ag, Au, Cu) to exhibit ZLC or NLC. Our simulations reveal three main findings. First, we predict the existence of previously unreported phases: the P6mm phase for AgCN and CuCN, and the R3m phase for AuCN. Second, all six members of the MCN family studied exhibit extreme elastic anisotropy, which indeed leads to ZLC or NLC in each case. Third, we identify a mechanism for these responses distinct from previously reported ones. The mechanism arises from the unique "bamboo forest" geometry of the material: weakly interacting rigid rods whose sparse packing allows pressure to be accommodated through changes in packing density rather than rod compression. This mechanism enables the anomalous response to persist over a wide pressure range, contrasting favorably with other materials that exhibit similar behavior. Our findings expand the relatively small family of materials known to exhibit ZLC or NLC and provide deeper insight into the microscopic origin of these unusual mechanical responses.

cond-mat.mtrl-sci↗

arXiv2024

Large electrically and chemically tunable Rashba-Dresselhaus effects in Ferroelectric CsGeX$_3$ (X=Cl, Br, I) perovskites

Rashba-Dresselhaus effects, which originate from spin-orbit coupling and allow for spin manipulations, are actively explored in materials following the pursuit of spintronics and quantum computing. However, materials that possess practically significant Rashba-Dresselhaus effects often contain toxic elements and offer little opportunity for tunability of the effects. We used first-principles simulations to reveal that the recently discovered halide ferroelectrics in the CsGeX$_3$ (X=Cl, Br, I) family possess large and tunable Rashba-Dresselhaus effects. In particular, they give origin to the spin splitting of up to 171meV in valence band of CsGeI$_3$. The value is chemically tunable and can decrease by 25% and 70% for CsGeBr$_3$ and CsGeCl$_3$, respectively. Such chemical tunability could result in engineering of desired values through solid solution technique. Application of electric field was found to result in structural changes that could both decrease and increase spin splitting leading to electrical tunability of the effect. In the vicinity of conduction and valence band extrema, the spin textures are mostly of Rashba type which is promising for spin-to-charge conversion applications. The spin directions are coupled with the polarization direction leading to Rashba-ferroelectricity co-functionality. Our work identifies lead-free perovskite halides as excellent candidates for spin-based applications and is likely to stimulate further research in this direction.

cond-mat.mtrl-sci↗

arXiv2023

First-Principles Property Assessment of Hybrid Formate Perovskites

Hybrid organic inorganic formate perovskites, AB(HCOO)$_3$, is a large family of compounds which exhibit variety of phase transitions and diverse properties. Some examples include (anti)ferroelectricity, ferroelasticity, (anti)ferromagnetism, and multiferroism. While many properties of these materials have already been characterized, we are not aware of any study that focuses on comprehensive property assessment of a large number of formate perovskites. Comparison of the materials property within the family is challenging due to systematic errors attributed to different techniques or the lack of data. For example, complete piezoelectric, dielectric and elastic tensors are not available. In this work, we utilize first-principles density functional theory based simulations to overcome these challenges and to report structural, mechanical, dielectric, piezoelectric, and ferroelectric properties for 29 formate perovskites. We find that these materials exhibit elastic stiffness in the range 0.5 to 127.0 GPa , highly anisotropic linear compressibility, including zero and even negative values; dielectric constants in the range 0.1 to 102.1; highly anisotropic piezoelectric response with the longitudinal values in the range 1.18 to 21.12 pC/N, and spontaneous polarizations in the range 0.2 to 7.8 $μ$C/cm$^2$. Furthermore, we propose and computationally characterize a few formate perovskites, which have not been reported yet.

cond-mat.mtrl-sci↗

arXiv2022

Persistent spin textures in halide perovskites induced by uniaxial stress

Persistent spin textures are highly desirable for applications in spintronics as they may allow for long carrier spin lifetimes. However, they are also rare as only four point groups can host such textures, and even for these four groups, the emergence of persistent spin textures requires a delicate balance between coupling parameters, which control the strength of spin-momentum interactions. We use first-principles density functional simulations to predict the possibility of achieving these desirable spin textures through the application of uniaxial stress. Hybrid organic-inorganic perovskite MPSnBr$_3$ (MP = CH$_3$PH$_3$) is a ferroelectric semiconductor which exhibits persistent spin textures in the near to its conduction band minimum and mostly Rashba type in the vicinity of its valence band maximum. Application of uniaxial stress leads to the gradual evolution of the valence bands spin textures from mostly Rashba type to persistent ones under tensile load and to pure Rashba or persistent ones under compressive load. We also report that the material exhibits flexibility, rubber-like response, and both positive and negative piezoelectric constants. Combination of such properties may create opportunities for a flexible/rubbery spintronic devices.

cond-mat.mtrl-sci↗