Comet Calendar, The Official Event Calendar for UT Dallas en-us This week's events for Natural Sciences & Mathematics at UT Dallas Physics Colloquium: Hybridizing Superconductors and Topological Matters Friday, Apr 24
(2 p.m. - 3:15 p.m.)

Dr. Xiaoyan Shi (Sandia National Laboratories)

The topological matters family expands greatly ever since the first observed topological matter, the integer quantum Hall system. Currently, many new types of materials are experimentally available, such as topological insulators (both 2D and 3D), topological crystalline insulators and topological Kondo insulators. In another interesting yet more than 100 years old field, researches in superconductivity keep surprising us with novel materials and phenomena. In this talk, I will briefly review both materials families and present our recent transport experiments on a superconductor-2D topological insulator-superconductor junction. In this hybrid system, giant proximity induced supercurrent is observed in both edge and bulk channels. In addition, the supercurrent can survive in a surprisingly large temperature-magnetic field parameter space. Lastly, I will conclude with an outlook of the field.

Physics Colloquium: Scanning SQUID Microscopy of Emergent Phenomena Monday, Apr 27
(2 p.m. - 3:15 p.m.)

Dr. Ilya Sochnikov (Stanford)

Scanning Superconducting QUantum Interference Device (SQUID) microscopy is a versatile technique that is efficiently used to study various emergent phenomena, such as interface superconductivity in complex oxides, magnetism in complex oxides, and protected normal- and super-currents in topological insulators. Following an introduction, I will focus on another intriguing phenomena of magnetic fluctuations in a so-called ‘spin-ice’ material.

Spin-ices are frustrated magnets that are predicted to host exotic magnetic excitations akin to freely diffusing electrostatic charges. We use scanning SQUID microscopy on classical spin-ice Ho2Ti2O7 to discover a magnetization landscape that fluctuates in both time and space. The temperature and frequency dependence of the magnetic fluctuations reveals a gapped distribution of activation energies of the fluctuations. In contrast to theoretical expectations, this gapped distribution indicates a finite energy barrier for spin flipping. Our experiment demonstrates that scanning SQUID microscopy will powerfully complement other techniques in studies of emergent phenomena in various classical and quantum magnets by enabling space-, time-, and energy- resolved detection of spin fluctuations.


Physics Colloquium: Ultracold Molecules in Crystals of Light: A Highly Tunable System for Exploring Novel Materials, Quantum Dynamics, and Quantum Complexity Wednesday, Apr 29
(4 p.m. - 5:15 p.m.)

Dr. Lincoln Carr (Colorado School of Mines)

Ultracold molecules at sub-microKelvin temperatures and trapped in crystals of light (optical lattices) present a new regime of physical chemistry and a new state of matter: complex dipolar matter.  Such systems open up the prospect of tunable quantum complexity.  We present models for the quantum many-body statics and dynamics of present experiments on polar bi-alkali dimer molecules.  We are developing and will discuss Hamiltonians and simulations for upcoming experiments on dimers beyond the alkali metals, including biologically and chemically important naturally occurring free radicals like the hydroxyl free radical (OH), as well as symmetric top polyatomic molecules like methyl fluoride (CH3F).  These systems offer surprising opportunities in modeling and design of new materials, in addition to well-known exciting possibilities in quantum computing applications.  For example, symmetric top polyatomics can be used to study quantum molecular magnets and quantum liquid crystals.  Our numerical method of choice is massively parallel high performance computing via variational matrix-product-state (MPS) algorithms, a highly successful form of data compression used to treat lowly entangled dynamics and statics of many-body systems with large Hilbert spaces; we supplement our calculations with exact diagonalization and simpler variational, perturbative, and other approaches.  We use MPS algorithms not only to produce experimentally measurable quantum phase diagrams but also to explore the dynamical interplay between internal and external degrees of freedom inherent in complex dipolar matter.  Our group maintains open source code (openTEBD and openMPS) available freely and used widely.  We have worked and will continue to work closely with experimentalists throughout our projects, and make detailed use of ultracold molecular properties and constants to provide concrete and accurate explanations, guidance, and inspiration.

Mathematics Colloquium by Yunkai Zhou Thursday, Apr 30
(2:30 p.m. - 3:30 p.m.)

Yunkai Zhou

Mathematics, SMU

Fast algorithms for large scale eigenvalue problems

Eigenvalue problems are of fundamental importance and arise frequently in many scientific disciplines, including materials science and data mining. Many modern applications can benefit from algorithms that can solve large scale eigenvalue problems more efficiently. In this talk, we first give a brief overview of large scale eigenvalue problems, and survey a few representative algorithms by pointing out their essential common features. Then we discuss some main challenges for solving ever larger scale eigenvalue problems. We present some recent progress on the 'preconditioned' eigen-solvers related to solving the Kohn-Sham equation in density functional theory, both in the plane-wave setting and in the real-space setting. We will also discuss a novel spectrum decomposition algorithm that addresses several main difficulties encountered in state-of-the-art algorithms for solving large scale eigenvalue problems.

Sponsored by the Department of Mathematical Sciences