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1. Realizing tunable Fermi level in SnTe by defect control

   https://doi.org/10.1088/1361-648X/adb408  

   Onipede, Bamidele; Metcalf, Matthew; Fletcher, Nisha; Cai, Hui (February 2025, Journal of Physics: Condensed Matter)

   Abstract The tuning of the Fermi level in tin telluride, a topological crystalline insulator, is essential for accessing its unique surface states and optimizing its electronic properties for applications such as spintronics and quantum computing. In this study, we demonstrate that the Fermi level in tin telluride can be effectively modulated by controlling the tin concentration during chemical vapor deposition synthesis. By introducing tin-rich conditions, we observed a blue shift in the x-ray photoelectron spectroscopy core-level peaks of both tin and tellurium, indicating an upward shift in the Fermi level. This shift is corroborated by a decrease in work function values measured via ultraviolet photoelectron spectroscopy, confirming the suppression of Sn vacancies. Our findings provide a low-cost, scalable method to achieve tunable Fermi levels in tin telluride, offering a significant advancement in the development of materials with tailored electronic properties for next-generation technological applications. 

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2. Superconductor–insulator transition in two-dimensional indium–indium-oxide composite

   https://doi.org/10.1073/pnas.2015970118  

   Hen, Bar; Zhang, Xinyang; Shelukhin, Victor; Kapitulnik, Aharon; Palevski, Alexander (December 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   The magnetic-field–tuned superconductor-to-insulator transition was studied in a hybrid system of superconducting indium islands, deposited on an indium oxide (InOx) thin film, which exhibits global superconductivity at low magnetic fields. Vacuum annealing was used to tune the conductivity of the InOx film, thereby tuning the inergrain coupling and the nature of the transition. The hybrid system exhibits a “giant” magnetoresistance above the magnetic-field–tuned superconductor-to-insulator transition (H-SIT), with critical behavior similar to that of uniform InOx films but at much lower magnetic fields, that manifests the duality between Cooper pairs and vortices. A key feature of this hybrid system is the separation between the quantum criticality and the onset of nonequilibrium behavior. 

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3. Violation of the Pauli limit at KTaO3 (110) interfaces

   https://doi.org/10.1103/PhysRevB.111.214506  

   Poage, Samuel J; Gao, Xueshi; Baksi, Merve; Salmani-Rezaie, Salva; Muller, David A; Kumah, Divine P; Lau, Chun Ning; Lorenzana, José; Gastiasoro, Maria N; Ahadi, Kaveh (June 2025, Physical Review B)

   The superconducting order parameter at the KTaO3 interfaces and its dependence on interface orientation remains a subject of debate. The superconductivity at these interfaces exhibits strong resilience against in-plane magnetic field and violates Pauli limit. The interface orientation dependence of critical field and violation of Pauli limit, however, have not been investigated. To address this problem, we grew epitaxial LaMnO3/KTaO3 heterostructures using molecular beam epitaxy. We show that superconductivity is extremely robust against the in-plane magnetic field. The critical field to the Pauli limiting field coincides with the (111) interfaces for the same carrier density. This suggests that the orientation of the surface does not play a critical role in determining the ratio, despite the strong impact on the critical temperature. These results offer opportunities to engineer superconductors which are resilient against magnetic field. 

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4. Electronic, vibrational, and electron–phonon coupling properties in SnSe ₂ and SnS ₂ under pressure

   https://doi.org/10.1039/D0TC04356G  

   Kafle, Gyanu Prasad; Heil, Christoph; Paudyal, Hari; Margine, Elena R. (December 2020, Journal of Materials Chemistry C)

   The tin-selenide and tin-sulfide classes of materials undergo multiple structural transitions under high pressure leading to periodic lattice distortions, superconductivity, and topologically non-trivial phases, yet a number of controversies exist regarding the structural transformations in these systems. We perform first-principles calculations within the framework of density functional theory and a careful comparison of our results with available experiments on SnSe 2 reveals that the apparent contradictions among high-pressure results can be attributed to differences in experimental conditions. We further demonstrate that under hydrostatic pressure a superstructure can be stabilized above 20 GPa in SnS 2 via a periodic lattice distortion as found recently in the case of SnSe 2 , and that this pressure-induced phase transition is due to the combined effect of Fermi surface nesting and electron–phonon coupling at a momentum wave vector q = (1/3, 1/3, 0). In addition, we investigate the contribution of nonadiabatic corrections on the calculated phonon frequencies, and show that the quantitative agreement between theory and experiment for the high-energy A 1g phonon mode is improved when these effects are taken into account. Finally, we examine the nature of the superconducting state recently observed in SnSe 2 under nonhydrostatic pressure and predict the emergence of superconductivity with a comparable critical temperature in SnS 2 under similar experimental conditions. Interestingly, in the periodic lattice distorted phases, the critical temperature is found to be reduced by an order of magnitude due to the restructuring of the Fermi surface. 

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5. Colorimetric quantification of linking in thermoreversible nanocrystal gel assemblies

   https://doi.org/10.1126/sciadv.abm7364  

   Kang, Jiho; Valenzuela, Stephanie A.; Lin, Emily Y.; Dominguez, Manuel N.; Sherman, Zachary M.; Truskett, Thomas M.; Anslyn, Eric V.; Milliron, Delia J. (February 2022, Science Advances)

   Nanocrystal gels can be responsive, tunable materials, but designing their structure and properties is challenging. By using reversibly bonded molecular linkers, gelation can be realized under conditions predicted by thermodynamics. However, simulations have offered the only microscopic insights, with no experimental means to monitor linking leading to gelation. We introduce a metal coordination linkage with a distinct optical signature allowing us to quantify linking in situ and establish structural and thermodynamic bases for assembly. Because of coupling between linked indium tin oxide nanocrystals, their infrared absorption shifts abruptly at a chemically tunable gelation temperature. We quantify bonding spectroscopically and use molecular simulation to understand temperature-dependent bonding motifs, revealing that gel formation is governed by reaching a critical number of effective links that extend the nanocrystal network. Microscopic insights from our colorimetric linking chemistry enable switchable gels based on thermodynamic principles, opening the door to rational design of programmable nanocrystal networks. 

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