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Exchange interactions in solid [superscript 3]He on a parallel computer


Callahan, Sean Macauley (1989) Exchange interactions in solid [superscript 3]He on a parallel computer. Dissertation (Ph.D.), California Institute of Technology.


NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

We have developed a method of calculating the Gruneisen parameter, [...] (J - exchange splitting; [...] - molar volume), for energy splittings that are due to atoms exchanging lattice sites in fermionic systems for which the exchange splittings are small compared with the lattice kinetic and potential energies. The method involves making two separate path integral Monte Carlo calculations, one for a path (sequence of particle positions in time) that doesn't involve atoms exchanging lattice sites, and one for a path in which the atoms do exchange lattice sites. The difference between a quantity calculated for the two systems is related to the Gruneisen parameter.

The central results of this thesis are firstly, that there is no significant variation of the Gruneisen parameters for two, three and four particle exchange ([...], [...] and [...], respectively) for solid [superscript 3]He, in going from 24 cm3/mole, which is near melting, to 22 cm3/mole. This result was extended to 20 cm3/mole for [...]. Since no significant variation was observed, the values calculated for different molar volumes were combined to give best estimates for the Gruneisen constants, [...] = 15.9 ± .8, [...] = 16.4 ± 1.4 and [...] = 13.8 ± 1.5. The second result is that the magnitudes of the Gruneisen parameters are very similar for the three types of exchange despite their significantly different geometry. Some very limited runs were done for a system of hard spheres. It is interesting that for the hard sphere diameter chosen, the Gruneisen parameters are of the same order as for solid [superscript 3]He, [...] = 21.7 ± .8, [...] = 16.8 ± 2.1 and [...] = 19.3 ± 1.9 for the small test systems checked. The final result relates to [superscript 3]He deposited on a graphite surface. The Gruneisen parameter for three particle exchange for a two-dimensional system with a triangular mesh is found to be consistent with [...] = 50 ± 5 for a range of nearest-neighbor, lattice spacings from 3.2 [...] to 3.6 [...]. This is inconsistent with experiment, indicating that three particle exchange confined to two dimensions does not account for the ferromagnetic properties of this system, as was claimed previously.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Cross, Michael Clifford (advisor)
  • Fox, Geoffrey C. (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 August 1988
Record Number:CaltechETD:etd-06072007-135648
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2511
Deposited By: Imported from ETD-db
Deposited On:25 Jun 2007
Last Modified:26 Dec 2012 02:52

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