scholarly journals Finite temperature behaviors of q-deformed Fermi gases

2019 ◽  
Vol 33 (24) ◽  
pp. 1950294 ◽  
Author(s):  
Xun Huang ◽  
Xu-Yang Hou ◽  
Yan Gong ◽  
Hao Guo
Keyword(s):  
Deformation Parameter ◽  
Fermi Gases ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Quantum Gas ◽  
Physical Systems ◽  
Quantum Particles ◽  
Fermi Statistics ◽  
Ultracold Fermi Gases ◽  
Bose Einstein

During the last three decades, nonstandard statistics for indistinguishable quantum particles has attracted wide attention and research interests from many institutions. Among these new types of statistics, the [Formula: see text]-deformed Bose and Fermi statistics, originated from the study of quantum algebra, are being applied in more and more physical systems. In this paper, we construct a [Formula: see text]-deformed generalization of the BCS-Leggett theory for ultracold Fermi gases based on our previously constructed [Formula: see text]-deformed BCS theory. Some interesting features of this [Formula: see text]-deformed interacting quantum gas are obtained by numerical analysis. For example, in the ordinary Bose–Einstein Condensation regime, the gas presents a fermionic feature instead of bosonic feature if the deformation parameter is tuned suitably, which might be referred to as the [Formula: see text]-induced “Bose–Fermi” crossover. Conversely, a weak sign of the “Fermi–Bose” crossover is also found in the ordinary weak fermionic regime.

scholarly journals Theoretical Approach to the Gauge Invariant Linear Response Theories for Ultracold Fermi Gases with Pseudogap

2015 ◽  
Vol 2015 ◽  
pp. 1-9
Author(s):  
Hao Guo ◽  
Yan He
Keyword(s):  
Linear Response ◽  
Ward Identity ◽  
Superfluid Transition ◽  
Fermi Gases ◽  
Einstein Condensation ◽  
Gauge Invariant ◽  
Ultracold Fermi Gases ◽  
Consistency Constraints ◽  
Bose Einstein ◽  
Physical Quantities

Recent experimental progress allows for exploring some important physical quantities of ultracold Fermi gases, such as the compressibility, spin susceptibility, viscosity, optical conductivity, and spin diffusivity. Theoretically, these quantities can be evaluated from suitable linear response theories. For BCS superfluid, it has been found that the gauge invariant linear response theories can be fully consistent with some stringent consistency constraints. When the theory is generalized to stronger than BCS regime, one may meet serious difficulties to satisfy the gauge invariance conditions. In this paper, we try to construct density and spin linear response theories which are formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein Condensation (BEC) crossover, especially below the superfluid transition temperatureTc. We adapt a particulart-matrix approach which is close to theG0Gformalism to incorporate noncondensed pairing in the normal state. We explicitly show that the fundamental constraints imposed by the Ward identities andQ-limit Ward identity are indeed satisfied.

SUPERFLUID REGIMES IN DEGENERATE ATOMIC FERMI GASES

2006 ◽  
Vol 20 (19) ◽  
pp. 2739-2754
Author(s):  
G. V. SHLYAPNIKOV
Keyword(s):  
Scattering Length ◽  
Fermi Gases ◽  
Einstein Condensation ◽  
Weakly Bound ◽  
Future Studies ◽  
Bose Einstein Condensation ◽  
Ultracold Fermi Gases ◽  
Fermionic Atoms ◽  
Atom Interaction ◽  
Bose Einstein

We give a brief overview of recent studies of quantum degenerate regimes in ultracold Fermi gases. The attention is focused on the regime of Bose-Einstein condensation of weakly bound molecules of fermionic atoms, formed at a large positive scattering length for the interspecies atom-atom interaction. We analyze remarkable collisional stability of these molecules and draw prospects for future studies.

Entropy and heat capacity in the generalized Bose–Einstein condensation theory of superconductors

2019 ◽  
Vol 33 (26) ◽  
pp. 1950311
Author(s):  
L. A. García ◽  
M. de Llano
Keyword(s):  
Heat Capacity ◽  
Energy Gap ◽  
Coupling Parameter ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Total Electron ◽  
Bose Einstein Condensation ◽  
Unpaired Electrons ◽  
Bose Einstein

The new generalized Bose–Einstein condensation (GBEC) quantum-statistical theory starts from a noninteracting ternary boson-fermion (BF) gas of two-hole Cooper pairs (2hCPs) along with the usual two-electron Cooper pairs (2eCPs) plus unpaired electrons. Here we obtain the entropy and heat capacity and confirm once again that GBEC contains as a special case the Bardeen–Cooper–Schrieffer (BCS) theory. The energy gap is first calculated and compared with that of BCS theory for different values of a new dimensionless coupling parameter n/n[Formula: see text] where n is the total electron number density and n[Formula: see text] that of unpaired electrons at zero absolute temperature. Then, from the entropy, the heat capacity is calculated. Results compare well with elemental-superconductor data suggesting that 2hCPs are indispensable to describe superconductors (SCs).

GENERALIZED BOSE-EINSTEIN CONDENSATION IN SUPERCONDUCTIVITY

2010 ◽  
Vol 24 (25n26) ◽  
pp. 5163-5171
Author(s):  
MANUEL de LLANO
Keyword(s):  
Spin Fluctuation ◽  
Interaction Model ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Condensation Energy ◽  
Weakly Bound ◽  
Bose Einstein Condensation ◽  
Fermi Temperature ◽  
Bose Einstein

Unification of the BCS and the Bose-Einstein condensation (BEC) theories is surveyed in detail via a generalized BEC (GBEC) finite-temperature statistical formalism. Its major difference with BCS theory is that it can be diagonalized exactly. Under specified conditions it yields the precise BCS gap equation for all temperatures as well as the precise BCS zero-temperature condensation energy for all couplings, thereby suggesting that a BCS condensate is a BE condensate in a ternary mixture of kinematically independent unpaired electrons coexisting with equally proportioned weakly-bound two-electron and two-hole Cooper pairs. Without abandoning the electron-phonon mechanism in moderately weak coupling it suffices, in principle, to reproduce the unusually high values of Tc (in units of the Fermi temperature TF) of 0.01-0.05 empirically reported in the so-called "exotic" superconductors of the Uemura plot, including cuprates, in contrast to the low values of Tc/TF ≤ 10-3 roughly reproduced by BCS theory for conventional (mostly elemental) superconductors. Replacing the characteristic phonon-exchange Debye temperature by a characteristic magnon-exchange one more than twice in size can lead to a simple interaction model associated with spin-fluctuation-mediated pairing.

INTRIGUING ROLE OF HOLE-COOPER-PAIRS IN SUPERCONDUCTORS AND SUPERFLUIDS

2008 ◽  
Vol 22 (25n26) ◽  
pp. 4367-4378 ◽  
Author(s):  
M. GRETHER ◽  
M. de LLANO ◽  
S. RAMÍREZ ◽  
O. ROJO
Keyword(s):  
Free Energy ◽  
Helmholtz Free Energy ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Superconducting Transition ◽  
Electron Phonon Interaction ◽  
Bose Einstein ◽  
Hole Cooper Pairs

The role in superconductors of hole-Cooper-pairs (CPs) are examined and contrasted with the more familiar electron-CPs, with special emphasis on their “background” effect in enhancing superconducting transition temperatures Tc — even when electron-CPs drive the transition. Both kinds of CPs are, of course, present at all temperatures. An analogy is drawn between the hole CPs in any many-fermion system with the antibosons in a relativistic ideal Bose gas that appear in substantial numbers only at higher and higher temperatures. Their indispensable role in yielding a lower Helmholtz free energy equilibrium state is established. For superconductors, the problem is viewed in terms of a generalized Bose-Einstein condensation (GBEC) theory that is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that the GBEC theory includes hole CPs as well as electron-CPs — thereby containing as well as further extending BCS theory to higher temperatures with the same weak-coupling electron-phonon interaction parameters. We show that the Helmholtz free energy of both 2e- and 2h-CP pure condensates has a positive second derivative, and are thus stable equilibrium states. Finally, it is conjectured that the role of hole pairs in ultra-cold fermionic atom gases will likely be negligible because the very low densities involved imply a “shallow” Fermi sea.

scholarly journals STATISTICAL MECHANICS OF CONFINED QUANTUM PARTICLES

2007 ◽  
Vol 22 (30) ◽  
pp. 2297-2305 ◽  
Author(s):  
VISHNU M. BANNUR ◽  
K. M. UDAYANANDAN
Keyword(s):  
Statistical Mechanics ◽  
Gluon Plasma ◽  
Compact Stars ◽  
Einstein Condensation ◽  
Quark Star ◽  
Fermi Systems ◽  
Confining Potential ◽  
Quantum Particles ◽  
Relativistic Harmonic Oscillator ◽  
Bose Einstein

We develop statistical mechanics and thermodynamics of Bose and Fermi systems in relativistic harmonic oscillator (RHO) confining potential, which is applicable in quark gluon plasma (QGP), astrophysics, Bose–Einstein condensation (BEC) etc. Detailed study of QGP system is carried out and compared with lattice results. Furthermore, as an application, our equation of state (EoS) of QGP is used to study compact stars like quark star.

scholarly journals The self-trapping of superfluid Fermi gases in the Bose-Einstein condensation regime and in unitarity

2012 ◽  
Vol 61 (10) ◽  
pp. 100301
Author(s):  
Wang Wen-Yuan ◽  
Yang Yang ◽  
Meng Hong-Juan ◽  
Ma Ying ◽  
Qi Peng-Tang ◽  
...  
Keyword(s):  
The Self ◽  
Fermi Gases ◽  
Einstein Condensation ◽  
Bose Einstein Condensation ◽  
Self Trapping ◽  
Bose Einstein ◽  
Superfluid Fermi

scholarly journals Modified Bose-Einstein condensation in an optical quantum gas

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mario Vretenar ◽  
Chris Toebes ◽  
Jan Klaers
Keyword(s):  
Radiative Decay ◽  
Open Quantum Systems ◽  
Einstein Condensate ◽  
Einstein Condensation ◽  
Destructive Interference ◽  
Quantum Gas ◽  
Bose Einstein Condensation ◽  
Open Quantum ◽  
Physical Mechanisms ◽  
Bose Einstein

AbstractOpen quantum systems can be systematically controlled by making changes to their environment. A well-known example is the spontaneous radiative decay of an electronically excited emitter, such as an atom or a molecule, which is significantly influenced by the feedback from the emitter’s environment, for example, by the presence of reflecting surfaces. A prerequisite for a deliberate control of an open quantum system is to reveal the physical mechanisms that determine its state. Here, we investigate the Bose-Einstein condensation of a photonic Bose gas in an environment with controlled dissipation and feedback. Our measurements offer a highly systematic picture of Bose-Einstein condensation under non-equilibrium conditions. We show that by adjusting their frequency Bose-Einstein condensates naturally try to avoid particle loss and destructive interference in their environment. In this way our experiments reveal physical mechanisms involved in the formation of a Bose-Einstein condensate, which typically remain hidden when the system is close to thermal equilibrium.

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