Dr. Judy Wu, University of Houston (Pitt Chemistry Seminar)

Judy Wu
Thursday, February 25, 2021 - 2:30pm

Title: Molecules in a Hurry to Escape Antiaromaticity

Abstract: Antiaromatic molecules, unless kinetically trapped, fused to aromatic frameworks, or stabilized by chemical modifications, often are short-lived and difficult to work with experimentally—they always find ways of escaping the state of being called “antiaromatic.” Cyclobutadiene, cyclopentadiene, pentalene, and other cyclic, π-conjugated compounds, with formal [4n] ring π-electrons, easily dimerize to get rid of antiaromaticity. Upon irradiation, benzene rather isomerize to fulvene and...

Why Engineers Should Care about Quantum Computing -- From Quantum Hardware to Programming

Abraham Asfaw
Tuesday, February 9, 2021 - 11:00am

This talk will attempt to answer the question, "Why Should Engineers Care about Quantum Computation." In the talk, I will lay out key concepts and potential uses of quantum computers in quantum simulation and computation. As part of the discussion, I will emphasize the urgency of building a quantum-ready workforce, highlighting the relevance of training in engineering for building the physical quantum computing systems and understanding their potential applications. I will not assume knowledge of quantum mechanics and quantum computation, and will take a systems...

Dr. Moïra Hocevar, Institut Néel CNRS, France (CMU MSE Seminar)

Dr. Moïra Hocevar
Friday, April 2, 2021 - 11:30am

Growth of Nanowires Heterostructures for Quantum Devices and Nanotechnology

Abstract: Nanowires are crystals with the morphology of a hair but ten thousand times smaller. They measure several microns in length and tens of nanometers in diameter. For the past twenty years, nanowires have been at the root of important breakthrough in both basic science and nanotechnology in a multitude of scientific areas. They are now commonly developed for transistor and sensor applications, light emitting diodes or solar cells. In quantum technologies, their unique properties enabled the development of bright single photon sources, spin quantum bits and nanomechanical resonators. We fabricate nanowires with crystalline semiconductor materials such as silicon which is the backbone of electronics or gallium arsenide, which emits light and is used to manufacture light emitting diodes. For a certain number of applications, it is necessary to juxtapose different semiconductors to form a heterostructure. Yet, creating heterostructures is not an easy task, especially in thin films. As different crystalline materials have different lattice parameters (distance between atoms), the lattice is strained at the junction (or interface) between two materials. This induces the formation of defects, among them dislocations which deteriorate the targeted physical properties. Thanks to their morphology, nanowires have more flexibility to release strain, preventing the formation of defects. Nanowires have the potential to host heterostructures that cannot be fabricated in standard technologies, enabling the discovery of new physical phenomena and the improvement of existing devices. During the seminar, I will present an overview of my ongoing research on nanowire heterostructures. The first part will be dedicated to embedding light emitters in silicon technology. Different semiconductor families or high-mismatch semiconductors are combined in nanowires. I will show how interfaces are built without structural defects, a prerequisite for optoelectronic devices [1]. Then, I will present superconductor-semiconductor nanowire hybrids. A particular focus will be on the development and study of Sn/InSb interfaces which have recently shown high potential for superconducting and topological quantum circuits [2]. Finally, I will present the development of an ultrasensitive tool to study the mechanical properties of nanowires using a focused electron beam [3].

[1] Beznasyuk et al (2020)

[2] Pendharkar et al (2020)

[3] Pairis et al (2019)

Biography: Moïra Hocevar is a researcher at CNRS Néel Institute in Grenoble since January 2015. She received an Engineering degree in Materials Science from INSA de Lyon in France (2004), a master degree in Environmental Science from Université Denis Diderot in Paris (2005) and her PhD in Electronics from INSA de Lyon in 2008. Prior to joining Néel Institute in Grenoble, she was a Marie Curie postdoctoral fellow at the Technical University of Delft in the Netherlands and a Nanoscience Foundation postdoctoral fellow in Grenoble. Her research focuses on creating novel nanowire heterostructures by molecular beam epitaxy and uncovering their unique physical properties using Mhigh-end characterization tools.

Dr. Patrick Rinke, Aalto University, Finland (CMU MSE Seminar)

Dr. Patrick Rinke
Friday, February 12, 2021 - 11:30am

Data generation in materials science is often limited by the time it takes to perform experiments or simulations. To facilitate the exploration and characterization of complex materials, we have developed the Bayesian Optimization Structure Search (BOSS) code. BOSS uses an active learning technique that strategically samples the parameter space of material-science tasks be it experimental or computational. BOSS proposes new data acquisition points for maximum knowledge gain, balancing exploitation with exploration. I will demonstrate BOSS' smart and efficient data strategy for two examples...

Timothy Berkelbach (Columbia & Flatiron Institute)

Timothy Berkelbach
Thursday, February 18, 2021 - 4:00pm

Ab initio wavefunction-based quantum chemistry represents a tantalizing alternative to density functional theory for problems in materials science, due to the former's ability to achieve high accuracy with systematic improvability. I will give an overview of our group's research efforts in this direction, describing theoretical and methodological developments at the periodic Hartree-Fock and post-Hartree-Fock levels (especially perturbation theory and coupled-cluster theory) and connections to popular Green's function-based techniques such as the random-phase...

Vikesh Siddhu (Carnegie Mellon University)

Vikesh Siddhu
Thursday, February 11, 2021 - 4:00pm

Entanglement lies at the root of quantum theory. It is a remarkable resource that is generally believed to diminish when entangled systems interact with their environment. On the contrary, we find that engaging a system with its environment increases its ability to retain entanglement. The maximum rate of retaining entanglement is given by the quantum channel capacity. We counter-intuitively boost the quantum capacity of a channel by allowing it to leak almost all quantum information to...

My escape from the lab: scientific publishing

Dr. Matteo Cavalleri
Thursday, March 14, 2019 - 4:00pm

Across the world and across disciplines, numbers reveal that the term “alt-ac” – referring to positions within higher education and research alternative to the professoriate – is a misnomer. Permanent academic jobs are, in fact, the “alt-ac”. In this talk, I’ll share my (happy) experience going from a computational chemistry lab to my current career on the “other side” of scientific publishing, and explores roles for STEM Ph.D.s in the publishing industry.

Interfacial Coupling and Magnetic Competition in Magnetic and Magnetoelectric Systems

Mikel Holcomb
Thursday, February 7, 2019 - 4:00pm

In the American economic system, competition is a critical driver of performance and innovation. The same can be said for materials physics.  My group focuses on studying a variety of strongly correlated quantum systems, where the competition between charge, spin and orbital degrees of freedom can lead to novel or enhanced properties. It is this sensitivity that makes these materials useful for devices. A good device has a measured property (such as resistance or magnetization) that changes dramatically with an external stimulus (such as current, temperature or magnetic field). Competition is a valuable strategy for creating this interplay of parameters. Magnetic competition in magnetic systems, on the other hand, has often been seen as a hindrance. While it typically decreases the overall net magnetization, I will show that it can be utilized to generate novel phenomena useful for devices, such as giant negative magnetization and enhanced magnetization at small applied fields. While much research on magnetism utilizes large fields to strengthen the net magnetization, most devices will need to utilize small fields. While my group also collaborates on a wide range of other systems (such as topological insulators, delafossites and transition edge sensors), much of our focus has been to grow high-quality films and understand the interfacial interactions in magnetic and magnetoelectric layers. I will discuss our first observation of a magnetoelectric dead layer, which motivated our recent interest and successes in magnetic phase competition and then some of the interesting features we have discovered in complex oxide thin films.