Physics & Astronomy Colloquium

Vortex Matter in Superconductors with Nano-Textured Structures

Date: 11/02/2018 - 3:30pm to 4:30pm
Location: CP 155
Speaker(s) / Presenter(s): Wai-K. Kwok, Argonne National Laboratory
 
The advent of nanofabrication has opened new venues for controlling vortex matter, which is responsible for the electro-magnetic response of all applied superconductors. In particular, nano-hole structures with a variety of intriguing patterns have emerged as a versatile platform for controlling and optimizing vortex pinning in superconductors for enhanced critical current. Magnetic field pinning of vortices with meso and nanoscale magnetic structures has also shown great potential for in-situ manipulation of vortex behavior. Here, I will briefly review the vortex response to a variety of nanostructured hole-arrays in superconductors and in particular, demonstrate that a random pattern, an often-overlooked vortex pinning system, can lead to a significant critical current enhancement over a wide magnetic field range. I will also demonstrate the use of ferromagnetic strips on a superconductor to mimic a vortex triode device and lastly, introduce a novel nano-magnetic patterned structure based on artificial spin-ice rules to realize a globally reconfigurable and locally writable magnetic structure that can subsequently be used to control single flux quanta in a superconducting film. The novel ferromagnetic/superconducting hetero-structure enables switchable and reversible rectification effect of the critical current and furthermore, enables the experimental study of geometric frustration in a flux quanta system.
 
This work was supported by the Department of Energy, Office of Basic Energy Sciences which also funds Argonne’s Center for Nanoscale Materials (CNM) where the nano-and magnetic patterning and morphological analysis were performed.
 
Host: DeLong

Solving a puzzling problem of condensed matter physics using inelastic spectroscopy

Date: 10/26/2018 - 3:30pm to 4:30pm
Location: CP 155
Speaker(s) / Presenter(s): Ambrose Seo, University of Kentucky
 
Spectroscopic investigations are essential to understand intriguing phenomena in many areas of physics.  In particular, recent advanced spectroscopic tools such as resonant inelastic x-ray scattering and photoemission spectroscopy play an important role in condensed matter physics.  While research on thin-films or superlattices is expected to reveal hidden novel physical properties, previous inelastic spectroscopic investigations have been unable to detect these properties due to the small cross-section.
 
In this colloquium, I will discuss advanced inelastic light scattering (Raman spectroscopic) studies of two-magnon dynamics in Sr2IrO4 thin-films as functions of strain and temperature.  Recent experimental studies of Sr2IrO4 thin-films have contradicted the widely-accepted Glazer description of octahedral tilting and rotation in perovskite oxides.  However, our experimental observations and density functional theory calculations show that the multi-orbital nature of the Jeff = ½ state is crucial to understanding the magnetic and electronic properties of 5d transition-metal oxides.  This study demonstrates how advanced spectroscopic tools improve our fundamental understanding of strongly correlated, spin-orbit coupled electrons, enabling us to explore the novel phase diagrams of these systems.
 

When the Universe was One Second Old

Date:10/19/2018 - 3:30pm to 4:30pm
Location: CP 155
Speaker(s) / Presenter(s): George Fuller, University of California at San Diego
 
The imminent advent of 30-m class telescopes and Stage-4 cosmic microwave background observatories promises to give us precision measurements of key parameters which are set in the very early universe. For example, we may soon know to fair precision the amount of relic relativistic energy and the deuterium and helium abundances set during the time when the neutrinos fall out of thermal and chemical equilibrium. Given the excitement and ferment right now surrounding new ideas in dark matter, dark sector, and other beyond standard model (BSM) physics, we would very much like to leverage these coming measurements into deeper insights into this epoch, in effect turning the early universe into a precision BSM physics laboratory. Doing so, however, requires theorists to "raise their game” in modeling the neutrino decoupling epoch. We will discuss these issues and reveal some surprising features of the universe when it was roughly one second in age.

The Importance of Being Eccentric

Date: 10/12/ 2018 - 3:30pm to 4:30pm
Location: CP 155
Speaker(s) / Presenter(s): Ann-Marie Madigan (JILA and Department of Astrophysical and Planetary Science, University of Colorado at Boulder)
 
The dynamics of bodies on eccentric orbits largely determines the evolution of planetary systems and stars near massive black holes. In this talk I will review eccentric dynamics and demonstrate wide-ranging implications  such as the orbital clustering of Kuiper Belt objects in the outer solar system (which motivates the planet nine hypothesis),  `double’ galactic nuclei, and the tidal disruptions of stars by massive black holes. 
 
Host: Isaac Shlosman

Spin Phenomena in Jets

Date: 10/05/2018 - 3:30pm to 4:30pm
 
Speaker(s) / Presenter(s):  Renee Fatemi (University of Kentucky)
 
For decades, jets have served as the tool of choice at colliders around the world. They have been used to search for new particles and to probe the inner workings of Quantum Chromodynamics. The jet community continues to innovate and thrive, responding to the experimental and theoretical challenges posed by the TeV scale beam energies at the Large Hadron Collider and the extreme backgrounds produced in the quark gluon plasma. Similarly, the advent of polarized proton beams at the Relativistic Heavy Ion Collider (RHIC)  at the turn of the century motivated the adaptation of jet reconstruction techniques for spin dependent measurements. Close collaboration between theory and experiment has produced a wealth of new data on spin topics ranging from the gluon helicity distribution to novel new probes of transverse momentum distributions. An overview of recent RHIC jet results, as well as new techniques developed for spin measurements will be presented.  The implications for further measurements at RHIC and at a future Electron-Ion-Collider will be discussed
 
Host : Brad Plaster

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