Liquid helium, anomaly

The liquid helium temperature coefficient of resistivity also changes from positive to negative in going from (Ero.gAl A Bo.2 to (Ero,65Feo.35)o.9Bo.i as can be seen in fig. 90. This is interpreted in terms of the structure factor an of eq. (71) which is due to magnetic ions. Fig. 90 further shows that anomalies are observable in p at 80K for the Er alloys containing Ga and Au. The authors deduce from the shape of the hysteresis loop of the Au alloys that these... 

As known, at a temperature of 4.2 K under normal pressure, gaseous helium turns into a liquid (helium 1), but at 2.2 K helium 1 transforms into another modification of liquid which is called helium 2. Helium 1 is an ordinary liquid which differs from other liquids by nothing but low temperature. Helium 2, on the contrary, has unusual properties, the most interesting of which is superfluidity. By its anomalous pa-operties helium 2 radically differs not only from helium 1 but also from all other hquids in nature. However, what is stranger is the very existence of two quite different liquids of hehum. The existence of helium 2, the second liquid of helium, is an exception to the rule, which displays itself as a unique physical and logical anomaly. 

The mysteries of the helium phase diagram further deepen at the strange A-line that divides the two liquid phases. In certain respects, this coexistence curve (dashed line) exhibits characteristics of a line of critical points, with divergences of heat capacity and other properties that are normally associated with critical-point limits (so-called second-order transitions, in Ehrenfest s classification). Sidebar 7.5 explains some aspects of the Ehrenfest classification of phase transitions and the distinctive features of A-transitions (such as the characteristic lambda-shaped heat-capacity curve that gives the transition its name) that defy classification as either first-order or second-order. Such anomalies suggest that microscopic understanding of phase behavior remains woefully incomplete, even for the simplest imaginable atomic components. 

The existence of helium 2 is an established fact meanwhile, the existent idea of sublimation reflects only the level of our present-day knowledge. The facts are admitted to be of greater logical weight than theoretical notions. So, it should be more correct to agree that our notion of sublimation, rather than the existence of second liquid of hehum, is a real anomaly. 

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