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21.
The ordinary thermodynamics corresponds to the equilibrium ground state of the system. We present a model making it possible to construct a second thermodynamics, an analogue of an equilibrium state of a superfluid, based on which we explain the effect of the appearance of a bottleneck in a thin capillary for a moving superfluid if it is heated to the critical point in the second thermodynamics. 相似文献
22.
M. Ahmad 《Il Nuovo Cimento D》1992,14(3):239-252
Summary Nucleation of vortices and strings is studied in superfluid helium in the context of phase transitions in this system. It
is shown that the formation of these structures depends on the homotopy groups of the manifold of degenerate condensed states.
The subsequent evolution of these structures is investigated and then impact on the superfluid nature of this system is analysed.
The cross-section for the scattering of quasi-particles is estimated. This is exploited to find the effect of scatterings
on the dynamics of shrinking vortex.
During the editorial procedure we came to know that this author deceased. 相似文献
23.
24.
Summary Coherent states in the roton region of superfluid He4 are studied with a view to determine the transition probability from phonon to roton states. These states are formed in such
a way that they are found to be identical to those of the angular-momentum states.
During the editorial procedure we came to know that this author deceased. 相似文献
25.
V. P. Maslov 《Theoretical and Mathematical Physics》2005,143(3):741-759
We replace the conditions on the capillary boundary with the Born-Karman periodic conditions, i. e., we consider a two-dimensional torus of radius L
2. If the velocity of a superfluid liquid exceeds 8πℏ /(mL
2), then it brakes because of the friction against the eddy formed by pairs (similar to the pairs in the Andreev reflection).__________Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 143, No. 3, pp. 307–327, June, 2005. 相似文献
26.
27.
David C. Roberts 《Contemporary Physics》2013,54(3):453-461
The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed. 相似文献
28.
This paper studies the superfluidity of ultracold spin-2
Bose atoms with weak interactions in optical lattices by calculating
the excitation energy spectrum using the Bogoliubov approach. The energy
spectra exhibit the characteristics of the superfluid-phase
explicitly and it finds the nonvanishing critical speeds of
superfluid. The obtained results display that the critical speeds of
superfluid are different for five spin components and can be
controlled by adjusting the lattice parameters in experiments.
Finally it discusses the feasibilities of implementing and measuring
superfluid. 相似文献
29.
We study the interactions among phonons and the phonon lifetime in a pair‐condensed Fermi gas in the BEC‐BCS crossover in the collisionless regime. To compute the phonon‐phonon coupling amplitudes we use a microscopic model based on a generalized BCS Ansatz including moving pairs, which allows for a systematic expansion around the mean field BCS approximation of the ground state. We show that the quantum hydrodynamic expression of the amplitudes obtained by Landau and Khalatnikov apply only on the energy shell, that is for resonant processes that conserve energy. The microscopic model yields the same excitation spectrum as the Random Phase Approximation, with a linear (phononic) start and a concavity at low wave number that changes from upwards to downwards in the BEC‐BCS crossover. When the concavity of the dispersion relation is upwards at low wave number, the leading damping mechanism at low temperature is the Beliaev‐Landau process 2 phonons ? 1 phonon while, when the concavity is downwards, it is the Landau‐Khalatnikov process 2 phonons ? 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependence on the interaction strength, we obtain a universal formula for the damping rate. This universal formula corrects and extends the original analytic results of Landau and Khalatnikov [ZhETF 19 , 637 (1949)] for the 2?2 processes in the downward concavity case. In the upward concavity case, for the Beliaev 1? 2 process for the unitary gas at zero temperature, we calculate the damping rate of an excitation with wave number q including the first correction proportional to q 7 to the q 5 hydrodynamic prediction, which was never done before in a systematic way. 相似文献
30.
We study superfluidity of paired Bosonic atoms in optical lattices. The atoms have strong repulsive on-slte energy. Single atom tunneling is severely suppressed while the atom-pair may co-tunnel by the second order quantum transition, which induces paired superfluidity as repulsive nearest-neighbor interactions are included. The mean-field phase diagram and low energy excitations are explored for a square lattice system. 相似文献