arXiv subjects

Sigalit Aharon

Publications and source records attributed to Sigalit Aharon.

7 recordsLinked to original sources

arXiv2026

New Superconductors in the PtPb$_3$Bi Structure Type

The quest for new superconductors is of both fundamental and technological importance. Recently, an artificial intelligence method correctly predicted PtPb$_3$Bi to be a superconductor. In this work, we find superconductivity in the newly synthesized $M$Pb$_{4-x}$Bi$_x$ ($M$ = Au, Pd, and Rh), of which PtPb$_3$Bi is a member. When $M$ = Ni, whose radius is considerably smaller, the structure instead collapses into the different, Pb-substituted NiBi$_3$ type. Interestingly, the stoichiometric parameter $x$ shifts across the three compounds to keep the total valence electron count close to 20 per formula unit. The superconducting transitions occur at 4.9, 4.2, and 3.4 K, for $M$ = Au, Pd, and Rh, respectively. Using electrical resistivity, magnetization, and specific heat measurements, we establish the bulk nature of the superconducting state and determine the critical fields, characteristic length scales, and anisotropy ratios. All three compounds are moderately anisotropic type-II superconductors, with modest upper critical field anisotropies of $H_{c2}^{\parallel c}/H_{c2}^{\perp c} \approx 1.2$ to $1.5$. These results establish $M$Pb$_{4-x}$Bi$_x$ as a family of anisotropic superconductors and a platform for studying how site disorder and Pb-Bi mixing govern superconductivity in heavy-element intermetallics.

cond-mat.supr-con↗

arXiv2024

Bonding Interactions Can Drive Topological Phase Transitions in a Zintl Antiferromagnetic Insulator

While $\sim$30% of materials are reported to be topological, topological insulators are rare. Magnetic topological insulators (MTI) are even harder to find. Identifying crystallographic features that can host the coexistence of a topological insulating phase with magnetic order is vital for finding intrinsic MTI materials. Thus far, most materials that are investigated for the determination of an MTI are some combination of known topological insulators with a magnetic ion such as MnBi$_2$Te$_4$. Motivated by the recent success of EuIn$_{2}$As$_{2}$, we investigate the role of chemical pressure on topologically trivial insulator, Eu$_5$In$_2$Sb$_6$ via Ga substitution. Eu$_5$Ga$_2$Sb$_6$ is predicted to be topological but is synthetically difficult to stabilize. We look into the intermediate compositions between Eu$_5$In$_2$Sb$_6$ and Eu$_5$Ga$_2$Sb$_6$ through theoretical works to explore a topological phase transition and band inversion mechanism. We attribute the band inversion mechanism to changes in Eu-Sb hybridization as Ga is substituted for In due to chemical pressure. We also synthesize Eu$_{5}$In$_{4/3}$Ga$_{2/3}$Sb$_{6}$, the highest Ga concentration in Eu$_{5}$In$_{2-x}$Ga$_{x}$Sb$_{6}$, and report the thermodynamic, magnetic, transport, and Hall properties. Overall, our work paints a picture of a possible MTI via band engineering and explains why Eu-based Zintl compounds are suitable for the co-existence of magnetism and topology.

cond-mat.mtrl-sci↗

arXiv2024

Experimental Evidence for Defect Tolerance in Pb-Halide Perovskites

The term defect tolerance (DT) is used often to rationalize the exceptional optoelectronic properties of Halide Perovskites (HaPs) and their devices. Even though DT lacked direct experimental evidence, it became a "fact" in the field. DT in semiconductors implies that structural defects do not translate to electrical and optical effects (e.g., due to charge trapping), associated with such defects. We present the first direct experimental evidence for DT in Pb-HaPs by comparing the structural quality of 2-dimensional (2D), 2D-3D, and 3D Pb-iodide HaP crystals with their optoelectronic characteristics using high-sensitivity methods. Importantly, we get information from the materials' bulk, because we sample at least a few hundred nanometers, up to several micrometers, from the sample's surface, which allows for assessing intrinsic bulk (and not only surface-) properties of HaPs. The results point to DT in 3D, 2D-3D, and 2D Pb-HaPs. Overall, our data provide an experimental basis to rationalize DT in Pb-HaPs. These experiments and findings can guide the search for, and design of other materials with DT.

cond-mat.mtrl-sci↗

arXiv2023

Anharmonic Fluctuations Govern the Band Gap of Halide Perovskites

We determine the impact of anharmonic thermal vibrations on the fundamental band gap of CsPbBr$_3$, a prototypical model system for the broader class of halide perovskite semiconductors. Through first-principles molecular dynamics and stochastic calculations, we find that anharmonic fluctuations are a key effect in the electronic structure of these materials. We present experimental and theoretical evidence that important characteristics, such as a mildly changing band-gap value across a temperature range that includes phase-transitions, cannot be explained by harmonic phonons thermally perturbing an average crystal structure and symmetry. Instead, the thermal characteristics of the electronic structure are microscopically connected to anharmonic vibrational contributions to the band gap that reach a fairly large magnitude of 450 meV at 425 K.

cond-mat.mtrl-sci↗

arXiv2022

Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals

We show that formamidinium lead bromide is unique among the halide perovskite crystals because its inorganic sub-lattice exhibits intrinsic local static disorder that co-exists with a well-defined average crystal structure. Our study combines THz-range Raman-scattering with single-crystal X-ray diffraction and first-principles calculations to probe the inorganic sub-lattice dynamics evolution with temperature in the range of 10-300 K. The temperature evolution of the Raman spectra shows that low-temperature, local static disorder strongly affects the crystal's structural dynamics and phase transitions at higher temperatures.

cond-mat.mtrl-sci↗

arXiv2022

The Disorder Origin of Raman Scattering In Perovskites Single Crystals

The anharmonic lattice dynamics of oxide and halide perovskites play a crucial role in their mechanical and optical properties. Raman spectroscopy is one of the key methods used to study these structural dynamics. However, despite decades of research, existing interpretations cannot explain the temperature dependence of the observed Raman spectra. We demonstrate the non-monotonic evolution with temperature of the scattering intensity and present a model for 2nd-order Raman scattering that accounts for this unique trend. By invoking a low-frequency anharmonic feature, we are able to reproduce the Raman spectral line-shapes and integrated intensity temperature dependence. Numerical simulations support our interpretation of this low-frequency mode as a transition between two minima of a double-well potential surface. The model can be applied to other dynamically disordered crystal phases, providing a better understanding of the structural dynamics, leading to favorable electronic, optical, and mechanical properties in functional materials.

cond-mat.mtrl-sci↗

arXiv2016

Effect of Halide Composition on the Photochemical Stability of Perovskite Photovoltaic Materials

Photochemical stability of encapsulated films of mixed halide perovskites with a range of MAPb(I1-xBrx)3 compositions (solid solutions) was investigated under accelerated stressing using concentrated sunlight. Evolution of light absorption and the corresponding structural modifications in the films were recorded by UV-vis spectroscopy and X-ray diffraction (XRD), respectively. MAPbBr3 film exhibited no degradation. In MAPbI3 and mixed halide MAPb(I1-xBrx)3 films, decomposition of the perovskite material with crystallization of inorganic PbI2, and the corresponding degradation of light absorption, were recorded. Introduction of bromine into the solid solution was found to stress its structure and accelerate the degradation. The relevance of accelerated testing to standard operational conditions of solar cells was confirmed by comparison to degradation experiments under outdoor sunlight exposure. Reasons for the reduced stability of the mixed halide compositions are discussed.

cond-mat.mtrl-sci↗