Sushmita Chandra
Humboldt Fellow as of July 2024
Overview of my Research Project:
In recent years, the exploration of 2D materials has emerged as a captivating frontier in materials science, revolutionizing various fields from electronics and optoelectronics to energy storage and biomedicine. Unlike traditional bulk materials, which extend in three dimensions, 2D materials possess remarkable properties confined within a single atomic or molecular layer. In 2004, the discovery of graphene was a significant breakthrough in the field of 2D materials. Composed of a single layer of carbon atoms arranged in a hexagonal lattice, graphene exhibits extraordinary mechanical strength, exceptional thermal and electrical conductivity, and remarkable optical transparency. Moreover, by further manipulating the motion of electrons, unconventional superconductivity (SC) was observed in twisted bilayer graphene (TBG), a superstructure forming moiré pattern. Motivated by the unique structural motif of TBG, various van der Waals (vdW) layered heterostructures, and transition metal dichalcogenides (TMDs) have been widely explored till date for their novel electronic and magnetic properties in the ultrathin limit. Among several 2D materials, the MISFIT layered compounds (MLCs) have significantly acquired attention due to their unique structure, crystallographic diversity, and chemical tunability. Like TBG, MLCs also share the similar concept of lattice mismatch between the layers which can lead to the formation of a moiré pattern or strain-induced modifications in the electronic structure. Typically, MLCs can be represented by the general formula [(MX)(1+δ)]m[(TX2)n] with m, n = 1, 2, 3, where M denotes elements such as Sn, Sb, Pb, Bi, rare-earth elements; T represents Ta, Nb, Mo, etc., and X represents chalcogen atoms such as S, Se, Te. These compounds resemble the natural vdW heterostructure and consist of alternating layers of distorted rock salt MX and hexagonal TX2 structural units stacked on top of each other. Interestingly, there is an effective charge transfer takes place in MLCs from the MX layers to the TX2 layers, giving rise to a plethora of intriguing physical phenomena. To date, MISFIT compounds have been extensively studied for their potential applications in optoelectronics, catalysis, energy storage, and thermoelectrics. However, the fabrication of nanodevices for manipulation of electronic property with mono- or multilayered MISFIT crystals is a challenging task and thus remains underexplored.
As an awardee of prestigious Alexander von Humboldt fellowship, I will fabricate nanodevices of few layers of MISFIT single crystals. Since, MLCs are itself composed of separate MX and TX2 layers, there is a high probability that conflicting physical phenomena will occur in a single material. Thus, by controlling the number of layers and the composition of the TMDs, their properties can be precisely engineered, making them a potential candidate in the application of next-generation quantum devices. During the tenure of my fellowship, my goal is to study the coexistence of complementary physical phenomenon such as charge density wave with SC or ferroelectricity with Ising SC in these MISFIT superlattices. The MISFIT materials will be synthesized in their single crystalline form, and subsequently fabricated into thin flake devices via exfoliation.
Electrical and thermal transport properties will be measured under varying temperatures and magnetic fields at the Max Planck Institute for Chemical Physics of Solids in Dresden, under the supervision of Prof. Claudia Felser with collaboration with Dr. Nicola Poccia at IFW, Dresden. Prof. Felser has an extensive experience and expertise in the area of 2D topological quantum materials, and transition metal di-chalcogenide based superconductors. Moreover, the group's proficiency in solid-state chemistry and physics provides a robust foundation for the successful execution of my proposed research project.