####################################################
# Martin Holt <mvholt@uiuc.edu>
# requesting 3 days, at minimum=2 days
# beamline 33ID, "Phonon softening and critical exponents in SrTiO3"
####################################################
# top:/home/www/beamtime-requests/req00309.txt
# UNICAT Member Beam Time Request  #309
# created Thu Dec 05 13:13:34 CST 2002
####################################################

beamline:
	33ID

collaboration:
	Yes

contact:
	mvholt@uiuc.edu

days:
	3

description:
	The antiferrodistortive phase transition in SrTiO3 involves the softening and freezing of a zone-boundary phonon mode upon cooling resulting in a (2x2x2) superlattice at temperatures below Tc= 104 K. This softening behavior, characterized by a power-law dependence of the phonon frequency on temperature, has been measured over a wide temperature range by x-ray thermal diffuse scattering. Well above Tc the results are in excellent agreement with both available neutron data and a mean-field behavior. In a critical region near the transition temperature the softening behavior crosses over to result in a non-classical exponent.  Our present results in this region are in agreement with a renormalization-group calculation for the universality class of the Heisenberg antiferromagnet.  However, more data in this region (the current data set is only 5 data points) is necessary  for a precise determination of the critical softening behavior.  
	
	As well the present data might be influenced by the appearance of a central peak due to a surface contribution.  To this end a second sample with a treated surface will be analyzed in which hopefully the appearance of this component will move away from the onset of the critical region.

equipment+required:
	33-ID-D Newport Kappa, He Displex

experiment:
	Phonon softening and critical exponents in SrTiO3

foreign+nationals:
	

hazards:
	cryogenic hazard - standard methods with closed-cycle He displex

minimumdays:
	2

name:
	Martin Holt

new+request:
	on

nonmembers:
	

unacceptable+dates:
	Preferably on a weekend


#REMOTE_HOST: chiangpc2.mrl.uiuc.edu
#REMOTE_ADDR: 130.126.102.86
#CONTENT_LENGTH: 1646
#HTTP_REFERER: http://www.uni.aps.anl.gov/unireq.htm
#HTTP_USER_AGENT: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0