Nuclear Disarmament Verification via Resonant Phenomena

Prof. Areg Danagoulian
Massachusetts Institute of Technology

Hosted by Prof. Aprahamian…

Core-Collapse Supernovae from 1D to 3D

Prof. Evan O'Connor
Stockholm University

Core-Collapse supernovae are triggered by the implosion and subsequent explosion of the iron core in an evolved massive star. Since the core is shrouded from us by the overlying layers of the star, numerical simulations (and the odd neutrino detection of a Galactic supernova) are our best look into this extreme engine that powers one of the most energetic events in the Universe. Nature is 3D, and it is critical to simulate core-collapse supernovae in three dimensions because of the important hydrodynamic instabilities that can be present, however they are computationally expensive. With 2D models, we now starting to be able to perform systematic studies across a range of stars, and in 1D codes we are able to achieve excellent agreement between otherwise completely independent codes. In this talk I will present a global comparison in 1D between six core-collapse codes, the beginnings of a systematic study of core-collapse in 2D, and simulations where we explore fundamentally 3D phenomena.

Magnetic Weyl and Dirac Kondo semimetal phases in heterostructures

Dr. Ashley Cook
Postdoctoral Researcher
UC Berkeley

A key challenge of modern condensed matter physics is characterization of topologically non-trivial phases of matter - those phases of matter with signatures unaffected by sufficiently small perturbations - and their relationships to one another. An important branch of this work is characterization of correlated topological phases of matter, including study of topological Kondo phases of matter and the fractional quantum Hall effect among other phenomena. In this work, we extend the set of topologically non-trivial phases of matter and their relationships to one another by studying layered three-dimensional heterostructures in which two types of Kondo insulators are stacked alternatingly. One of them is the topological Kondo insulator SmB6, the other one an isostructural Kondo insulator AB6, where A is a rare-earth element, e.g., Eu, Yb, or Ce. We find that if the latter orders ferromagnetically, the heterostructure generically becomes a magnetic Weyl Kondo semimetal, while antiferromagnetic order can yield a magnetic Dirac Kondo semimetal. We detail both scenarios with general symmetry considerations as well as concrete tight-binding and ab-initio calculations and show that type-I as well as type-II magnetic Weyl/Dirac Kondo semimetal phases are possible in these heterostructures. Our results demonstrate that Kondo insulator heterostructures are a versatile platform for design of strongly correlated topological semimetals.

The History of Supernova Neutrinos

Prof. John LoSecco
Department of Physics, University of Notre Dame

Many physics concepts like relativity and quantum mechanics emerged as theories during the mid 19th to the late 20th century. Join us as we discuss the evolution of astrophysics from this period and how that enabled us to develop an understanding of energy production in stars and the end point of stellar evolution.…

Generalized Lieb-Schultz-Mattis constraints on phases of quantum magnets

Dr. Chao-Ming Jian
Kavli Institute for Theoretical Physics
UC Santa Barbara

Quantum magnetic systems with a large number of spins often enable the emergence of a great variety of interesting phases at zero temperature. Yet, there are fundamental constraints on the infrared behavior of quantum magnets from the ultraviolet data encoded in the microscopic lattice of spins. As the first and the most well-known example, the Lieb-Schultz-Mattis (LSM) constraint forbids trivial phases from arising in certain quantum magnets with SU(2) spin rotation and the lattice translation symmetries. As an important experimental consequence, it enables the confirmation of exotic phases like quantum spin liquids, whose intrinsic properties are often hard to probe directly, through the examination of the absence of spontaneous symmetry breaking which is more accessible with standard spectroscopy measurements. In this talk, we will present a new topological perspective of the LSM constraint. We will show how the LSM constraint is related to the constraints on the surface modes of symmetry-protected topological states. Using this relation, we will discuss a large class of generalizations of the LSM constraint incorporating different space groups (including both translations and point group symmetries) and different spin symmetries. The range of applicability of such generalized LSM constraints is vastly extended compared to the original version. We will also discuss how the generalized LSM constraints enforce the “exotic-ness” of continuous phase transitions in quantum magnets.