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Examples of Phase Transitions
Published in Teunis C. Dorlas, Statistical Mechanics, 2021
A very interesting phase diagram is that of helium. It has the peculiarity that there is no solid phase for pressures below 26 atm. Instead, the liquid becomes superfluid for temperatures below the λ-line or λ-curve indicated in figure 12.6. Superfluidity means that the liquid flows without viscosity, that is, it can flow through the smallest opening without experiencing any resistance. Superfluid helium is called He-II. It has many extraordinary properties. See for example the book by Wilks (1970). The peculiar behaviour of helium is due to the quantum nature of this fluid. The atoms are so light that their zero-point motion is comparable to the thermal motion at low temperatures. This prevents helium from solidifying at normal pressure. In fact there is an important difference between the two isotopes of helium: 3He and 4He. The former is a Fermi liquid and does not become superfluid until the temperature has reached much lower values; the critical temperature for the superfluid transition is 2.6 mK. We shall consider 4He in more detail in chapter 34.
Introduction to Energy, Heat and Thermodynamics
Published in S. Bobby Rauf, Thermodynamics Made Simple for Energy Engineers, 2021
Scientists, under laboratory conditions, have achieved temperatures approaching absolute zero. As temperature approaches absolute zero, matter exhibits quantum effects such as superconductivity and superfluidity. A substance in a state of superconductivity has electrical resistance approaching zero. In superfluidity state, viscosity of a fluid approaches zero.
Background
Published in L. Piccirillo, G. Coppi, A. May, Miniature Sorption Coolers, 2018
L. Piccirillo, G. Coppi, A. May
The field of low-temperature physics has the “privilege” to observe quantum phenomena at macroscopic scale. In particular, we have superconductivity and superfluidity that are both described by quantum mechanics. A complete thorough treatment of superfluids and superconductors is beyond the scope of this book and we suggest the interested reader to consult various excellent books (see Further Reading at the end of the chapter).
Solution of the ‘sign problem’ in the path integral Monte Carlo simulations of strongly correlated Fermi systems: thermodynamic properties of helium-3
Published in Molecular Physics, 2022
V. S. Filinov, R. S. Syrovatka, P. R. Levashov
Theoretical studies of correlated fermions are a subject of general interest in many fields of physics as respective approaches can be generalised to other quantum many-body problems including, for instance, plasma under extreme conditions [1], uniform electron gas [2], quantum liquids such as and [3] and so on. Since the time when liquid helium became available, a lot of effort has been spent on numerous phenomena in liquid helium, including the vapour–liquid phase transition, processes in the supercritical fluid, superfluidity, the structure and density of bulk liquid and so on. Liquid helium, a simple atomic liquid with a well-known interaction potential, is a good model system for theoretical studies [4–8]. On the other hand, cryogenic helium is increasingly being used in low-temperature refrigeration equipment. Designing cryogenic experimental facilities generally requires knowledge of the properties of liquid helium [9–13].
Bose–Einstein condensation in a mixture of interacting Bose and Fermi particles
Published in Phase Transitions, 2020
Yu. M. Poluektov, A. A. Soroka
The phenomenon of Bose–Einstein condensation [1,2] was used by London [3] and Tisza [4] to explain the phenomenon of superfluidity of liquid helium discovered by Kapitsa [5] and Allen [6]. Yet the model of an ideal gas is too simple to explain properties of dense systems in which the interparticle interaction plays a substantial role, the fact that was pointed out by Landau [7]. But, as was demonstrated in experiments on neutron scattering in the superfluid He [8,9], Bose–Einstein condensate exists also in the presence of the interparticle interaction. A new splash of interest to the phenomenon of superfluidity and its relationship to condensation is associated with the discovery about 20 years ago of Bose–Einstein condensation in atomic gases of alkali metals confined in magnetic [10,11] and laser traps [12].
Magnetic dipolar modes in magnon-polariton condensates
Published in Journal of Modern Optics, 2021
Polaritons are bosonic quasiparticles. In a case of exciton polaritons, one observes strong coupling of the exciton with the optical-cavity photon. The spectral response displays mode splittings when the quantum wells and the optical cavity are in resonance. A number of quantum-well resonances were shown experimentally. Classically, the effect can be seen as the normal-mode split of coupled oscillators, the excitons and the electromagnetic field of the microcavity. Quantum mechanically, this is the Rabi vacuum-field splitting of the quantum-well excitons. Due to Bose–Einstein condensation of exciton-polaritons in semiconductor optics, one observes spontaneous phase transitions to quantum condensed phases with superfluidity and vortex formation. A quantized vortex is considered as a topological defect with zero density at its core. Quantization of a vortex in a BEC originates from the single-valuedness of the macroscopic wave function, that is, a change in the phase along an arbitrary close path must be an integral multiple of . At the same time, the -rotation effects can be observed. There are the spinor exciton-polariton condensates with half-integer vortices. It is worth noting also that excitons, by virtue of being composite particles made of two fermions, obey bosonic statistics as long as their density is low enough such that they do not overlap. In a small quantum dot, the excitons behave as fermions: we cannot put more than one in the same state. In this limit, we perceive the fermionic nature of the constituents [9–14].