Contains reports on three research projects

Harrison, R. J.

Harvey, George G.

Kingston, R. H.

Klein, M. J.

Meckler, A.

Piore, E. R.

Tisza, Laszlo

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III. SOLID STATE PHYSICSProf, G. G. Harvey Dr. E. R. PioreProf. L. Tisza R. J. HarrisonDr. M. J. Klein R. H. KingstonA. MecklerA. CRITICAL POINT FLUCTUATIONSTechnical Report No. ill, "Critical Point Fluctuations", introducedthe notion of macroparameters in contrast to microparameters. In particu-lar for crystals the former are the invariants of the translational groupof the system. An investigation has been started to elucidate the connec-tion of these parameters with those describing the state of long and shortrange order obtained from x-ray studies.Prof. L. Tisza, Dr. M. J. KleinB. VACUUM SPECTROGRAPHMost of the parts of the vacuum spectrograph have been completed andwill shortly be assembled. Measurements are in progress on experimentalgun designs for the x-ray tube. It is expected that the x-ray tube designwill shortly be completed and the final tube constructed.Prof. G. G. Harvey, Dr. E. R. Piore, A. Meckler, R. H. KingstonC. THEORY OF LIQUID HELIUMWe are continuing to study the thermodynamics of the A-point phenomenain liquid helium. We have previously discussed the fact that the A-pointcan be considered as a critical point in the sense of the general theory ofphase transitions (1). The theory distinguishes between the "normal case"and the "exceptional case". In the exceptional case the thermodynamicvariables may be divided into two independent classes such that the criti-cal phenomena are associated with the interaction of the variables in thefirst class. The compliance coefficients involving the variables belongingto this class become infinite at the critical point; while the compliancesinvolving the remaining set of variables stay finite. Thus the singularbehavior of Rochelle salts may be described to a very good approximationby the interaction of just one strain and one polarization variable, whilethe other strain-coordinates, (entropy, etc.), exhibit no singularities.A similar situation seems to exist in helium.This division into two cases, normal and exceptional, has been criti-cized on the grounds that in nature one never has completely independentsets of variables. (There is in fact a small coupling in the Rochelle-19-(III. SOLID STATE PHYSICS)salts case.) This criticism refers to the fact that the formalism predictsa distinct difference between the normal and exceptional cases with respectto the appearance or non-appearance of infinities so that on the surfaceit seems as if the "nearly exceptional" case would be quite different fromthe (non-realizable) exactly exceptional case.We have shown by a closer examination that this is not so, that thereis in fact a gradual transition from the nearly exceptional to the excep-tional case, as one might expect physically. The unavoidable "washing out"of infinities, inherent in the fact that measurements are averages overfinite intervals, will cause the nearly exceptional case to be experimen-tally indistinguishable from the exactly exceptional case.Prof. L. Tisza, R. J. HarrisonReference(1) L. Tisza, "On the General Theory of Phase Transitions" (written forthe N.R.C. Symposium at Cornell University).-20-__ ^ YI^~-~~L-~- ~_L--XII~L^-__I~-II -~-LI_~CII -1.. I_ X .1II~~iill.*r~ - --XII ~-*~L l-- ~I^ -. ~Ctll (li-. CL-III^I.I~~I~LW-~~IsI^.-111 il-~ -- . -4111119--1~- - --*1111111---- ----~-1-

Solid State Physics

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Solid State Physics

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