The College of Science will present a "Science Night Live!" event next Wednesday, January 25th, from 5:30 p.m. to 7:00 p.m. at Keys on Main, 242 South Main St. (next to Sam Weller's bookstore). Invite a friend, make a date, and stop by after work!

Kyle Dawson, assistant professor of physics & astronomy at the U, will discuss how astronomers at the U and across the world are "Revealing the Secrets of the Universe."

Daily Utah Chronicle Article here.

MRSEC Seminar: Dr. Vardeny

Wednesday January 25, 2012
4:10-5:00 p.m.
L103 WEB

Professor Z. Valy Vardeny
Distinguished Professor, Department of Physics & Astronomy, University of Utah

Presented by the Departments of Materials Science and Engineering & Metallurgical Engineering

“Organic Spintronics”

Organic semiconductors have been used as active layer in devices such as organic light-emitting diodes (OLEDs), photovoltaic cells, field-effect transistors, and lasers. Recently there has been a growing interest in spin and magnetic field effects in these materials. This include optically detected magnetic resonance where long spin coherence time was demonstrated; OLEDs where substantive magneto-electroluminescence and magneto-conductance were obtained; and organic spin valves (OSV) where spin injection from ferromagnetic (FM) electrodes was obtained. The interest in spin transport in organic semiconductors has been motivated by the weak spin-orbit interaction that is caused by the light building block elements such as carbon and hydrogen, and the small hyperfine interaction (HFI) with the nuclei.

In this talk the status of the young field of ‘Organic Spintronics’ will be reviewed. The necessary ingredients needed for the success of this field will be summarized, and evaluated by recent experiments. In particular the role of the HFI in magneto-transport will be elucidated via the isotope effect. Three applications of Organic Spintronics will be discussed: organic diodes with two FM electrodes for use as OSV; with one FM electrode for magnetic detectors; and organic diodes with no FM electrodes as magnetic sensors.

Kai Sun
University of Maryland - College Park

Tuesday, Jan. 24, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (102 JFB)

Title: Topological Insulators, Topological Semimetals, & Quantum Hall Effects Without Landau Levels

Abstract:

The search for novel topological states of matter, where the quantum phase is characterized not by an order parameter but by some underlying topology, has been the focus of extensive studies since the discovery of the integer and fractional quantum Hall effects in two-dimensional semiconductors. These studies not only improve our understanding about topological states, but also have important potential applications (e.g. topological quantum computing), due to the unique and nontrivial topological properties of these systems. In band insulators, it has been known that the key ingredient to stabilize a topologically nontrivial insulating state is to introduce either some external magnetic fields (e.g. the integer quantum Hall effect) or spin-orbit couplings (e.g. the Z_2 topological insulators). In this talk, I present the theoretical discovery of a novel class of topological insulators, which are stabilized by interaction effects in the absence of external field or spin-orbit coupling. In particular, I will focus on two systems (2D topological semimetals and 3D heavy-fermion Kondo insulators), in which such phenomena can be investigated using well-controlled theoretical techniques. I will further demonstrate that these ideas can be generalized to stabilize fractional topological insulators in the absence of Landau levels or external magnetic fields. Experimental implications will also be discussed.

References:
[1] Kai Sun, W. Vincent Liu, Andreas Hemmerich and S. Das Sarma, Nature Physics, 8, 67–70 (2012).
[2] Kai Sun, Zhengcheng Gu, Hosho Katsura and S. Das Sarma, Phys. Rev. Lett. 106, 236803 (2011).
[3] Maxim Dzero, Kai Sun, Victor Galitski and Piers Coleman, Phys. Rev. Lett. 104, 106408 (2010).
[4] Kai Sun, Hong Yao, Eduardo Fradkin and Steven A. Kivelson, Phys. Rev. Lett. 103, 046811 (2009).