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VERSION:2.0
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BEGIN:VEVENT
DTSTAMP:20260917T020553Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20080425T160000Z
DTEND:20080425T170000Z
UID:event226@bu.edu
URL:http://physics.bu.edu/internal/events/show/226
SUMMARY:Precise Measurement of Electronic States Above and Below the Fermi 
	Level
DESCRIPTION:Featuring Ray Ashoori\, MIT\nHosted by: Claudio Chamon\n\nPart 
	of the Biophysics/Condensed Matter Seminar Series.\n\nAbstract: In many way
	s\, electrons in a metal behave much like sand in a jar. The sand fills the
	 jar up to a certain level\, just as electrons fill energy levels in a meta
	l up to an energy known as the Fermi-level. Any sand grains put in above th
	is level will fall down to the sand-level\, and plucking a sand grain from 
	below the sand level will create a vacancy (or hole) that will work its way
	 up to the sand-level as grains fall into the vacancy. The same process wor
	ks for injecting an electron above the Fermi-level or pulling out an electr
	on from below the Fermi level to leave a hole. This injection or ejection o
	f electrons into and out of a system can be accomplished by means of quantu
	m mechanical tunneling. We have developed a method to measure tunneling int
	o a two-dimensional metal with extraordinary resolution and precision. We c
	all our method "Time Domain Capacitance Spectroscopy" (TDCS)\, and it works
	 by averaging results from using millions of very short (50 ns) pulses to i
	nject electrons into the system of interest with negligible heating. We use
	 TDCS to study the two-dimensional electron system\, host to the integer an
	d fractional quantum Hall effects. We can precisely measure energies of and
	 tunneling strengths for quantum states above and below the Fermi energy. T
	he measurements allow us to determine the lifetimes of electrons in these s
	tates (the time they spend in the states before they fall down to the Fermi
	 energy) and measure the effects of magnetism and many-body physics on the 
	spectra. They have also led us to discover new "quasiparticles" whose origi
	n is at present a mystery.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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