Events at Physics |
Events During the Week of May 31st through June 7th, 2009
Monday, June 1st, 2009
- No events scheduled
Tuesday, June 2nd, 2009
- No events scheduled
Wednesday, June 3rd, 2009
- No events scheduled
Thursday, June 4th, 2009
- No events scheduled
Friday, June 5th, 2009
- R. G. Herb Condensed Matter Seminar
- Electronic refrigeration of two-dimensional electron gases
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Jon Prance, Cambridge University
- Abstract: Two-dimensional electron gases (2DEGs) in semiconductors are the basis for studies of a wide range of physical phenomena, particularly at sub-kelvin temperatures. However, efforts to cool these systems much below 10 mK quickly encounter the problems of reduced thermal conductivities and the necessity for increasingly complex refrigeration techniques.
One possible solution is direct electronic refrigeration of the 2DEG. The Quantum Dot Refrigerator (first proposed by Edwards et al.[1]) employs energy-selective tunneling through a pair of quantum dots to cool an otherwise isolated electron gas, potentially below the temperature of its host lattice. Such a device does not require specialised fabrication techniques and, in theory, can operate at arbitrarily low temperatures.
In this talk, we will present measurements of a Quantum Dot Refrigerator designed to cool an isolated 2DEG with an area of 6 square microns [2]. To interpret the results, a model has been developed which extends previous work to the regime of strong electrostatic coupling between the components of the device. Within the context of this model, the data show strong evidence for active cooling. We will discuss the practical limitations of such devices, methods for improving performance and evaluation, and potential applications.
[1] Edwards et al., PRB 52, p5714 (1995)
[2] Prance et al., PRL 102, 146602 (2009) - Host: Mark Eriksson
- SPECIAL SEMINAR TALK
- Clustering of accreting supermassive blackholes: An X-ray perspective
- Time: 3:30 pm - 5:00 pm
- Place: 4534 Sterling Hall
- Speaker: Yuxuan Yang, University of Illinois
- Abstract: > n the CDM structure formation scenario galaxies traces the large scale structure in a biased way. On large scales, the bias is determined by the mass of the galaxies. Recent advances in large area surveys have made it possible for very accurate statistical studies of galaxies in the context of structure formation. Such studies have revealed some interesting correlations between galaxy properties and their large scale bias. Active galactic nuclei (AGNs) play an important role in galaxy formation. Correlations between AGN properties and their bias provides an interesting perspective on the host galaxy of AGNs and their dark matter halos. Observationally, AGNs selected in different electromagnetic wave bands selects particular features of AGNs in those bands. Hard X-ray emission from AGNs originates from the inner accretion disk. The radiation is close to isotropic and is not strongly affected by absorption. Comparing to selection methods optical or IR, hard X-ray yields the least biased sample of accreting supermassive blackholes. In this talk, I discuss some recent progress in the study of AGN clustering using hard X-ray observations. I also present some new results using data from Chandra surveys (CLASXS, CLANS, CDFN, CDFS), and the SWIFT/BAT survey. The combination of low and high redshift AGN sample allow us to constrain on the evolutionary stage of AGN host galaxies.