The Department of Physics and Astronomy Colloquium is held on Monday afternoons at 4:15 pm in room SLH 102 unless otherwise noted. Refreshments are served at 4:00 pm.


Fall 2014


September 8

Kondo-Anderson Transitions

Stefan Kettemann
Jacobs University Bremen, Germany


View Abstract

Metal-Insulator transitions
are quantum phase transitions which occur in a wide range of materials
and can be tuned by doping, by pressure or by applying an electric
field. In doped semiconductors both the disorder and the correlations
due to the Coulomb
interaction between the randomly placed dopants are strong and essential
for the understanding of the MIT. At disorder driven metal-insulator
transitions the electrons are known to be in a multifractal state which
is intermediate between being extended and
localized. These states are sparse and concentrated at random spots of
high intensity. They are power law correlated both in energy and space.
Interacting electrons in such states give rise to new phenomena, such as
multifractal superconductivity, multifractal
Kondo effect and new critical semimetal states. We give an overview of
these recent developments and their implications for the theory of
metal-insulator transitions in doped semiconductors. In particular, we
show that magnetic moments at the Anderson-Metal-Insulator
transition can modify these transitions, resulting in new types of phase
transitions, due to the interplay between Kondo screening and Anderson
localisation, named accordingly Kondo-Anderson transitions [1, 2].

[1] S. Kettemann, E. R. Mucciolo, I. Varga and K. Slevin, Kondo-Anderson Transitions, Phys. Rev. B 85, 115112 (2012).
[2] S. Kettemann, E. R. Mucciolo, and I. Varga, Critical Metal Phase at
the Anderson Metal-Insulator Transition with Kondo Impurities, Phys.
Rev. Lett. 103, 126401 (2009).

September 15

No Colloquium


September 22

Understanding Nanomaterials: In-Situ Imaging, Measurements, and Manipulation in the Electron Microscope

Dr. Eli Sutter
Brookhaven National Laboratory


View Abstract

The promise of nanoscience lies in the fact that nanomaterials can show distinct properties that are not simply scaled-down bulk characteristics. Transmission electron microscopy (TEM) provides the necessary spatial resolution to observe individual nanostructures. Beyond imaging, TEM can be used to follow the behavior and measure properties of nanostructures over a wide range of environmental conditions. Finally, the high-energy electron beam often represents an invasive probe that can interact strongly with nano-objects. Used judiciously, this property can make it a unique tool for both activating and tracking processes at the nanoscale.
I will illustrate the power of in-situ imaging, measurements, and manipulation in the quest to understand the distinct properties of nanomaterials, their synthesis, and their transformation via controlled physical and chemical processes at the ultimate size limit.

September 29

Electron Magnetic Resonance Under Extreme Conditions

Stephen Hill
Florida State University, Tallahassee


View Abstract

Most Electron Spin Resonance (ESR) measurements are performed at the X-Band frequency of 9.5 GHz. Highly specialized (and expensive) commercial instruments exist operating at K-Band (25 GHz), Q-Band (35 GHz) and W-Band (95 GHz). The Electron Magnetic Resonance (EMR) facilities at the National High Magnetic Field Laboratory (NHMFL) offer scientists from all over the world opportunities to use several home-built, high-field/high-frequency instruments with continuous coverage from ~10 GHz to >1 THz [1-3]. Magnets are also available providing magnetic fields of up to 45 T—roughly one million times stronger than the earth’s magnetic field. EMR performed at these extremes offers tremendous advantages for problems spanning diverse research fields from condensed matter physics, to chemistry, to biology. After a brief overview of the facilities at the NHMFL and the kinds of research conducted by EMR users (including an explanation of the EMR acronym), the talk will describe the development and application of methods enabling high-field EMR studies of oriented single-crystal samples subjected to hydrostatic pressures of up to 35 kbar. Two applications will be discussed. The first involves a low-dimensional spin-½ quantum anti-ferromagnetic that undergoes a change in effective dimensionality (from 2D to 1D) under pressure [4]. The second example concerns an organic radical (again spin-½) ferromagnet that holds records for both the highest transition temperature and coercivity (for an organic magnet). The latter property is due to an unusually large magnetic anisotropy, attributable to spin-orbit-mediated anisotropic exchange [5]. Ferromagnetic resonance (FMR) measurements performed under pressure provide unique insights into this physics.

[1] http://www.magnet.fsu.edu/usershub/scientificdivisions/emr/index.html

[2] Morley et al., Rev. Sci. Instrum. 79, 064703 (2008).

[3] Takahashi et al., Rev. Sci. Instrum. 76, 023114 (2005).

[4] Prescimone et al., Angew. Chem. Int. Ed. 51, 7490 (2012)

[5] Winter et al., J. Am. Chem. Soc. 133, 8126 (2011); also Phys. Rev. B 85, 094430 (2012).

October 6

Strategies for Teaching Science

Jeffrey Bennett
University of Colorado


View Abstract

What does it take to be a successful science teacher? In this presentation, I’ll focus on the idea that the key to success lies in finding ways to get students to put in the study and effort necessary for true learning. Following a brief introduction on teaching philosophy, I’ll provide concrete examples of principles and strategies that should help in your teaching, regardless of the particular science subject, grade level, or number of students you teach. Note: This presentation follows the organization of my book On Teaching Science (www.onteachingscience.com).

Bio: Astrophysicist and educator Jeffrey Bennett’s extensive experience includes teaching at every level from preschool through graduate school, proposing and helping to develop the Voyage Scale Model Solar System on the National Mall in Washington, DC, and serving two years as a Visiting Senior Scientist at NASA Headquarters, where he helped create numerous programs designed to build stronger links between the research and education communities. He is the lead author of bestselling college textbooks in astronomy, astrobiology, mathematics, and statistics; of critically acclaimed titles for the general public including Beyond UFOs (Princeton University Press, 2008/2011), Math for Life (Big Kid Science 2014), What is Relativity? (Columbia University Press, 2014), and On Teaching Science (Big Kid Science, 2014). His five books for children are currently orbiting Earth and being read by astronauts aboard the International Space Station for the new “Story Time From Space” program (storytimefromspace.com). Dr. Bennett was recently honored with the American Institute of Physics Science Communication Award. His personal web site is www.jeffreybennett.com.