2D Transition Metal Dichalcogenides: Controlling Disorder and Superconductivity

Abstract:
Electrostatic control over states that interact with superconductivity and understanding how these states compete with or enhance superconductivity is a longstanding goal in the condensed matter community. Part of realizing these interactions is solving materials challenges posed by considerable amounts of disorder, both extrinsic and intrinsic in the 2D limit. I will begin this talk by highlighting the difficulties and challenges that face the 2D community when it comes to exploring new kinds of 2D materials and some potential solutions to overcoming these challenges, particularly for transition metal dichalcogenides. Subsequently, I will follow up with an example of the new kinds of physics that such control over materials quality can allow us to explore. In particular, the interaction between ferroelectricity, carrier density, magnetic field, and superconductivity in a specific class of transition metal dichalcogenides: the 1T’ family. Studying the interaction between superconductivity and ferroelectricity has been impeded by their seemingly contradictory conditions: one requiring low carrier density with little electronic screening and the other requiring significant carrier densities with substantial electronic screening. Clean 2D materials with interlayer polarization present a new opportunity to study this interaction, as well as a host of other interesting electronic phenomena like: quantum spin Hall insulator stands and the quantum Hall effect. I will discuss the first observation of such a material, bilayer 1T’-MoTe2, where both ferroelectricity and superconductivity can be realized under the same conditions and their interaction can be directly probed via magnetotransport measurements. In addition, I will elaborate on how the influence of an electrostatic gate allows us to identify a unique superconducting state in bilayer Td-MoTe2 and its profound influence even when no change in the chemical potential is made.

Bio:
Dr. Daniel Rhodes has been an assistant professor in the Department of Materials Science and Engineering and an affiliate of the Department of Physics since 2020 at the University of Wisconsin - Madison. Dr. Rhodes specializes in bulk single crystal synthesis and magnetotransport experiments for two-dimensional materials, with a focus on topological, magnetic, superconducting, and ferroelectric properties. Dr. Rhodes earned his Ph.D. degree in physics working on Weyl semimetals from Florida State University in 2016. From 2016 to 2019, he was postdoctoral researcher at Columbia University, where he focused on synthesis of transition metal dichalcogenide single crystals and defect characterization and superconductivity of two-dimensional materials. His notable discoveries include synthesis of transition metal dichalcogenides with extremely low defect densities, and the first observations of coupled ferroelectricity and superconductivity in a two-dimensional material. He is a recipient of the NSF CAREER award and the Grainger Professorship at UW-Madison.