MSE Department Seminar

Magnesium diboride (MgB₂), a compound known since the 1950s, was unexpectedly discovered to be a superconductor with a transition temperature (Tc) of 39 K in 2001. This discovery sparked tremendous excitement in the superconductivity community and led to a rapid understanding of its fundamental properties, including its conventional BCS superconductivity with two weakly coupled electronic bands and two distinct superconducting energy gaps. The extreme volatility of magnesium strongly constrains the growth of MgB₂ single crystals and thin films.

Advances in ultraclean materials with very long electron mean-free paths, including GaAs/AlGaAs heterostructures and graphene, have opened new opportunities to study electronic transport beyond the conventional Ohmic regime. We experimentally investigate transport in 2D GaAs/AlGaAs electron systems, with mean-free paths 100 micron or longer at cryogenic temperatures, across ballistic, hydrodynamic and diffusive regimes using mesoscopic nonlocal device geometries.

Currently, 70% of all electrical power consumed is routed through power electronics and this fraction is set to increase even faster with further addition of renewable sources to the grid and electrification of transportation. A significant reduction in size, weight, and power loss (SWaP) of power electronics will revolutionize the way the electric grid operates. The lion’s share of power electronics is based on silicon, with a bandgap of 1.1 eV. A significant reduction in SWaP is possible by migrating to semiconductors with wider bandgaps than silicon.

The next generation of polymeric materials will need features typically associated with biological systems: programmable material properties and chemical composition, self-healing and self-regenerating capabilities, and compatibility with sustainable and scalable manufacturing practices. While engineering synthetic materials with such capacities is often challenging, these properties are inherent to biological materials, including biofilms, mycelium, and lichen.

Materials behavior often begins at the atomic scale, making the understanding of how atomic systems behave of vital importance. Atomistic simulation techniques such as molecular dynamics and density functional theory have become instrumental in quantifying how the properties of atomic-level materials systems propagate to larger length and time scales and dictate observed materials behavior.

Moiré superlattices are formed when two van der Waals layers are stacked vertically with a controlled twist angle. Transition metal dichalcogenides (TMDs) are semiconductor building blocks with highly tunable optical properties. After reviewing some early studies, I will discuss the limitations of TMD-based moiré superlattices and propose twisted hBN substrates as a new approach to expand the strategy of moiré engineering to a broader range of photonic materials.

Quantum computing is a transformative technology that will change the world by quickly solving impossible problems, but its fundamental unit of information, the qubit, is nearly impossible to fabricate especially en masse with full functionality.  Single crystal defects form the basis for solid-state qubits; they are materials, and their information is physical in nature requiring extreme precision in fabrication.  This presentation introduce past fs work fabricating single defects in SiC and then it will expand on our very successful preliminary demonstration showing that a singl

With recent advances in detector technology and a new class of ptychographic phase-retrieval algorithms to unscramble multiple scattering, the resolution of the electron microscope is now limited only by the dose applied to the sample, and thermal vibrations of the atoms themselves. At high doses, these approaches have allowed us to image the detailed vibrational envelopes of individual atom columns as well as locating individual interstitial atoms.

In this talk, I will briefly introduce the molecular beam epitaxy (MBE) growth mechanism and then focus on my research, which centers on the MBE growth of quantum materials, spanning from topological materials to interfacial superconductors. I will talk about two solid-state phenomena with zero resistance: the quantum anomalous Hall (QAH) effect and the interface superconductivity. The QAH insulator is a material in which the interior is insulating but electrons can travel with zero resistance along one-dimensional conducting edge channels.

Topological nanowires, topological materials confined in 1D, hold great promise for robust and scalable quantum computing and low-dissipation interconnect applications, for which the desirable properties of topologically protected electronic states must be controlled. In this talk, I will discuss my group’s efforts to develop a precision synthesis method to fabricate 1D topological systems at high throughput. We employ thermomechanical nanomolding to extrude single crystal nanowires of topological materials with controlled diameters.