Spring 2017

Kagome Spin Liquids and Nuclear Relaxation Rates in Herbertsmithites

Rajiv Singh
Tuesday, February 28, 2017 -
4:00pm to 5:00pm

The Kagome Lattice Heisenberg Model is one of the simplest realistic spin models with a quantum spin-liquid ground state. We discuss the current status of our understanding of this well-studied model. The precise nature of the spin-liquid state and the existence of a spin-gap in the model still remain in dispute. We also discuss experimental studies of Herbertsmithite material Kagome-antiferromagnet ZnCu_3(OH)_6Cl_2. We focus on NMR measurements by Imai and collaborators, who have presented strong evidence for a spin-gap in the excitation spectra. Through a Numerical...

Using Ultrafast Laser Pulses and Computational Modeling to Understand Nonproportionality in Spectroscopic Gamma-Ray Detectors

Richard Williams
Thursday, March 23, 2017 -
12:00pm to 1:30pm

Under gamma-ray or charged-particle excitation, scintillation light yield is a complicated function of carrier diffusion and cooling in the track along with kinetic rate terms depending on local excitation density. Up to 1021 electron-hole pairs/cm3 are produced in an initial track radius of about 3 nm. Extracting the fundamental rate constants directly from such conditions would require solving the diffusion and cooling problems in complex track structures first. Laser interband photon density response and time-resolved pump-probe studies are surrogate experiments that...

Nanotechnology: Small Things Matter

Chad Mirkin
Thursday, February 2, 2017 -
4:30pm to 6:00pm

Nanotechnology is an interdisciplinary field focused on studying and manipulating ultraminiaturized structures, ones with at least one dimension 10,000 times smaller than the diameter of a human hair. This field has the potential to transform almost every aspect of our lives for the better – from enabling our cell phones and computers to run faster to generating our power more efficiently to making our tennis racquets and golf clubs lighter and more durable to making our medicines and drugs more efficacious. How can such small materials lead to such big advances in...

In Silico Searches for Efficient Renewable Energy Catalysts Through Chemical Compound Space

John Keith
Friday, February 3, 2017 -
11:30am to 12:30pm

This talk will provide an overview of our group’s work using both standard and atypical high-performance computational chemistry modeling to elucidate atomic scale reaction mechanisms of catalytic reactions. I will introduce our toolkit of in silico methods for accurately modeling solvating environments and realistic nanoscale architectures. I will then present how these methods can be used for predictive insights into chemical and material design. The talk will then summarize our progress in unraveling reaction mechanisms for 1) electrochemical CO2 reduction with...

Magnetic Interface Anisotropy, Domain Walls, and Skyrmions

Vincent Sokalski
Thursday, February 23, 2017 -
4:30pm to 5:30pm

The recently discovered Dzyaloshinskii-Moriya Interaction (DMI) in thin films has spawned a new direction for magnetism in spintronic application. This phenomenon stabilizes topological magnetic features including skyrmions and chiral domain walls (DWs) that can be manipulated by electric current with unprecedented efficiency. In this talk, I will review consequences of DMI on the structure of “Dzyaloshinskii” DWs and introduce the creep scaling law, which is paramount to describing a range of elastic interfaces including also superconductor flux lines and fluids being...

Understanding Anomalies and Variations in Magnetic Random Access Memory Devices

Eric Evarts
Thursday, January 12, 2017 -
2:30pm to 3:30pm

Spin-transfer torque magnetic random access memory (STT-MRAM) is a scalable, low-power, non-volatile memory structure based on the magnetic tunnel junction (MTJ). In this talk, I will present the common techniques used for characterizing MTJ thin films and devices using ferromagnetic resonance (FMR) and high-speed pulsed switching with a focus on devices with in-plane magnetization, At the nanodevice level, average thin film properties do not reflect the specifics of individual devices, but instead are representative of ensemble measurements of multiple devices. Minor...