Session K01: Lustig Award Talks (Plenary Session K01)

Discovery of Bose-Einstein Condensation in a Strongly Spin-Orbit Coupled Quantum Magnet

A canonical example of Bose-Einstein condensation (BEC) is the that of the ultracold gas, however, an often-overlooked example of BEC is that which occurs in quantum magnets. BEC occurs in quantum magnets when two spins are closely separated and entangle to form a singlet state. The system is then tuned to a BEC state by applying a magnetic field, the strength of which is determined by the single-triplet energy gap. This type of BEC has only been observed in 3d transition metal compounds, which typically have exchange interactions on the order of 1-10 meV. This leads to a large single-triplet gap and thus, large critical fields to enter the BEC. In this work we have discovered a BEC in a rare-earth magnet (Yb2Si2O7), which naturally exhibits lower energy exchange interactions (\textless 1 meV). This has allowed us to bring previously inaccessible techniques to bear on the entire phase diagram. We have performed specific heat and ultrasound velocity measurements to map out the edges of the phase diagram, showing smaller critical fields then ever previously observed. For the first time ever we have directly probed the singlet-triplet excitations throughout the entire BEC phase diagram with inelastic neutron scattering. The discovery of this system allows for a new testing ground of BEC physics that is accessible to almost all conventional condensed matter probes.   

Effects of Boundary Conditions and Alignment Methods on Liquid Crystal Performance in Microwave Wave Devices

Microwave devices are ubiquitous in our daily lives; cell phones, satellite communications, automobile safety radars all depend on microwaves. We are working on a technology, a merger of microwave science with liquid crystal physics, that has the potential to revolutionize microwave technology by reducing the size and cost of these devices by a factor of 100. As part of this effort, we are investigating a variety of the techniques used to control the initial state of the liquid crystal in a device to determine the optimum method to use with this emerging microwave technology. From our work, we see that a treated thin film of polyimide provides the best results. However, our work also demonstrates that, if a specialized liquid crystal known as dual frequency liquid crystal is used, the initial state of the liquid crystal does not significantly impact the performance of the device. This discovery reduces the number of steps necessary to manufacture microwave devices, saves on chemical and treatment costs, and eliminates several manufacturing challenges unique to liquid crystal based microwave devices. These benefits add up to a significant savings in time and cost during the design and manufacture of microwave components based on liquid crystal technology.   

Enabling offline optical intensity interferometry for the study of stars at high resolution

Over the last decade, there has been a renewed interest in developing a modern Stellar Intensity Interferometry (SII) observatory for high angular resolution measurements of stars at optical wavelengths. The SII technique is relatively insensitive to atmospheric turbulence allowing for very large telescope baselines, thus probing small angular scales, as well as the ability to operate at short visible wavelengths, generally inaccessible to current state-of-the-art interferometers. Here, I present astrophysical results from observations with an SII system installed onto the VERITAS gamma-ray telescopes. The system utilizes an off-line approach, where the light intensity measured at each telescope is synchronously recorded to disk at nanosecond timescales, and correlated post-observation. This off-line capability allows it to be readily scaled up to an arbitrary number of telescopes, enabling an optical interferometer analogous to radio/mm observatories. The work demonstrates the feasibility of using imaging air Cherenkov telescope (IACT) arrays as SII observatories, and serves as a technological pathway for implementing SII on future IACT arrays such as the Cherekov Telescope Array.