# All Videos

Randy Feenstra (CMU) discusses the use of both first-principles computational methods and low-energy electron microscopy in the investigation of two-dimensional transition-metal dichalcogenide materials as potential candidates for interlayer tunneling devices.

He uses the former to realistically estimate the values of tunneling currents and the latter to characterize the layers. He discusses as well the progress towards fabricating a full interlayer tunneling device.

Ken Jordan (Pitt) shows how electronic correlation in a system can be taken into account via a Drude oscillator.

First he demonstrates Feyman's "conjecture", which states that two atoms at long distance acquire permanent dipoles due to dispersion interactions. The dipole and atomic force both vary as R-7.

He shows that the permanent dipole on an atom is induced by the coupling of the instantaneous dipole on the other atom and its hyperpolarizability, and that, as predicted by Feynman, the two negative ends of the dipoles point toward each other.

David Pekker's (Pitt) talk is about emergent conserved quantities in strongly disordered matter.

He explains how the conventional wisdom that states that interacting systems are their own heat baths breaks down via the spontaneous appearance of local quantum numbers and describes the renormalization method he used to find them. This approach, called a Wegner flow, could be a foundation for the analytical theory of many-body localization transitions.

Vincent Sokalksi (CMU) presents his new study on the energetic molding of fermion-like magnetic bubbles.

He first introduces the Dzyaloshinskii-Moriya interaction (DMI), which is the origin of skyrmions and magnetism, and then proceeds to describe how to measure this interaction.

He shows, using a Wolff construction, how DMI impacts the growth behavior of magnetic bubbles.

In her talk, Grace Xing (Cornell University) describes the recent progress accomplished in her group in the field of 2D materials towards the fabrication of Thin-Tunneling Field-Effect Transistor (TFET) devices, where Thin stands for Two-dimensional Heterojunction Interlayer Tunnel.

Indeed, she describes how the group has been able to observe a 40 mV/decade subthreshold slope in 2D materials, which is an experimental first.

Sean Garrett-Roe (Pitt) presents the collaborative work fostered by PQI, between his experimental lab and the theoretical group of Daniel Lambrecht.

He describes the use of ultra fast spectroscopic techniques to provide molecular details about the interaction and dynamics of a molecule with its environment in the framework of CO2 capture in ionic liquids. The group uses the anti-symmetric stretch of the CO2 molecule as a probe to investigate the intermolecular interactions that lead to bulk properties.

In his talk, entitled "Bridging QM and Chemical Intuition", Daniel Lambrecht (Pitt) shows how quantum mechanics can inform conceptual thinking in chemistry.

He walks us through a well defined procedure that allows the calculation of "chemical" quantities that are not observables, for example the notion of charge transfer. The approach he describes is a flavor of energy decomposition analysis, and it can be applied to the calculation of properties such as vibrational spectra as demonstrated in their study.

The main topic of Ben Hunt's (CMU) talk is superconductivity in two dimensions.

He describes the new approach he developed with his team to make superconductors with the van der Waals heteromaterial NbSe2...and the surprising observation of a metallic state at non-zero temperatures.

This state is characterized by a resistance that is finite, independent of the temperature, and has a power-law dependence on the magnetic field.

Cyrus Umrigar (Cornell University) gives an in-depth description of various variational and projector Quantum Monte Carlo (QMC) methods that are used to computationally solve problems in chemistry and physics. He also addresses some of the current challenges in method development and application, namely the sign problem, as well as the current approaches to overcome the issue. Several methods are thus compared and contrasted throughout the lecture.

Nader Engheta (University of Pennsylvania) talks about some of the aspects of near-zero optics and applications in "extreme" optical materials. He introduces the notion of ‘static optics’, a state in which the the electric and magnetic fields are temporally dynamic but decoupled. This occurs in materials where both the relative effective permittivity and permeability attain near-zero values. Such "Near-Zero" structures show promise as platforms for quantum emitters, long-range entanglement, and quantum interference.