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# Topic: Fermi gas

 PhysicsCentral: Energetic Degenerates A system of identical Fermions is called a “Fermi gas.” If the temperature is low enough, the Fermi gas is “degenerate,” which means the low-lying states are filled up to a well-defined maximum energy, as shown in the diagram. Following groundbreaking low-temperature experiments with a gas of Bose atoms, which resulted in a form of matter called a Bose-Einstein Condensate (BEC) [See Matters of State], other researchers cooled fermionic atoms, looking for a degenerate Fermi gas, but this proved much more difficult. In a degenerate Fermi gas, however, the low-energy states are already filled, so if two atoms collide, there are no lower-energy states available for the atoms to go to after the collision and they must stay in the original ones. www.physicscentral.com /action/2004/gas.html   (512 words)

 A Fermi gas of atoms - Physics World - physicsworld.com Once the Fermi gas had reached the quantum regime, we obtained information about it by turning the magnetic trap off, allowing the gas to expand and measuring the shadow of the gas cast by a laser. An optical image of the gas therefore reveals the momentum distribution of the atoms: those atoms with low momentum remain near the centre of the cloud, while atoms with high momentum appear at the edges. The lack of collisions in a single-component Fermi gas of atoms could be exploited for precision measurements of these atoms, while recent experiments on two-component Fermi gases have begun to study the interplay of interactions and quantum statistics in determining behaviour. physicsweb.org /articles/world/15/4/7/1   (2972 words)

 The Fermi gas model We consider a Fermi gas of nucleons confined to a nuclear volume Since neutrons and protons are distinguishable, we consider two independent gases; the particles do not interact and we neglect the Coulomb interaction in the case of protons; and we include a factor of two to account for the spin degeneracy (i.e. The gas is assumed to be degenerate, so that the lowest possible levels are fully occupied. www.phy.uct.ac.za /courses/phy300w/np/ch1/node61.html   (277 words)

 Vortices seen in Fermi gas - Physics World - physicsworld.com It is the possibility of reproducing this Cooper-pairing process in a Fermi gas, and possibly learning more about the mysterious pairing mechanism that underpins high-temperature superconductivity, that has led to intense interest in these systems. Ketterle and co-workers started with a lithium-6 gas that had been cooled to about 50 nanokelvin and then applied a magnetic field to change the strength of the interactions between the atoms. Next, the MIT team increased the strength of the magnetic field to convert the molecular condensate into a Fermi gas with strong interactions between the atoms. physicsweb.org /articles/news/9/6/15/1   (579 words)

 Superfluid Atomic Fermi Gas With a Vortex   (Site not responding. Last check: ) The best example of this is the achievement of Bose-Einstein condensation in 1995 in a gas of Bose atoms, a discovery which has invoked a confluence of ideas from condensed matter, atomic and nuclear physics. An outstanding issue is the apparent lack of a ‘smoking gun’ for superfluidity in a Fermi gas, since the bulk properties are essentially unaffected by the pairing. We propose to focus on the macroscopic coherence of the gas in the superfluid phase, in particular its ability to sustain quantized vortices. www.nist.gov /sigmaxi/Posters04/nygaard.html   (304 words)

 degenerate gas concept from the Astronomy knowledge base   (Site not responding. Last check: ) According to the classical laws of physics, the pressure of a gas is proportional to the temperature and the density. However, in 1926 Fermi and Dirac showed that if the density were high enough, departures from classical laws would occur, in that if at a given temperature the density is increased, the pressure increases more and more rapidly until it becomes independent of the temperature and is a function of the density only. For such a gas, the pressure in the nonrelativistic limit is proportional to the 5/3 power of the density. www.site.uottawa.ca:4321 /astronomy/degenerategas.html   (233 words)

 Fermi gas - Encyclopedia, History, Geography and Biography It is the quantum mechanical version of an ideal gas, for the case of fermionic particles. The energy distribution of the fermions in a Fermi gas in thermal equilibrium is determined by their density, the temperature and the set of available energy states, via Fermi-Dirac statistics. This so-called degeneracy pressure stabilizes a neutron star (a Fermi gas of neutrons) or a White Dwarf star (a Fermi gas of electrons) against the inward pull of gravity. www.arikah.com /encyclopedia/Fermi_gas   (371 words)

 Fermi gas It is therefore the quantum mechanical version of the concept of a classical ideal gas, for the case of fermionic particles. The energy-distribution of the fermions in a Fermi gas in thermal equilibrium is determined by their number (or density), the temperature and the set of available energy states, via Fermi-Dirac statistics. For the same reason, the pressure of a Fermi gas is nonzero even at zero temperature, in contrast to that of a classical ideal gas (which would be zero). www.ebroadcast.com.au /lookup/encyclopedia/fe/Fermi_gas.html   (253 words)

 SparkNotes: Gas Thermodynaics: Non-Classical Gases A Fermi gas is a gas consisting of fermions. In astrophysics, white dwarf stars are prevented from collapsing upon themselves by the pressure of the Fermi gas and the resistance it gives to having its orbitals pushed together. A Bose gas is a gas consisting of bosons. www.sparknotes.com /physics/thermodynamics/gas/section2.rhtml   (613 words)

 Ultracold atomic Fermi gases — Jyväskylän yliopisto - University of Jyväskylä Ultracold atomic Fermi gases — Jyväskylän yliopisto - University of Jyväskylä In year 2005, the final proof for the superfluidity in an atomic Fermi gas was achieved with the observation of a vortex lattice in a rotating gas. We have considered imbalanced gases in a lattice and have found that while in the literature the zero temperature phase diagram of a free imbalanced gas is dominated by the phase separated state and the FFLO area is negligibly small, in a lattice the two phases are equally visible. www.jyu.fi /science/laitokset/fysiikka/en/research/material/nanoele/research/fermigas   (714 words)

 More on Fermi Liquid The Fermi liquid is qualitatively analogous to the non-interacting Fermi-gas, in the following sense: The system's dynamics and thermodynamics at low excitation energies and temperatures may be described by substituting for the non-interacting fermions so-called quasiparticles, each of which carries the same spin, charge and momentum as the original particles. The quadratic terms correspond to a sort of "mean-field" interaction between quasiparticles, which is parameterized by so-called Landau Fermi liquid parameters and determines the behaviour of density oscillations (and spin-density oscillations) in the Fermi liquid. For a Fermi liquid, the resistance from this mechanism varies as T2, which is often taken as an experimental check for Fermi liquid behaviour (in addition to the linear temperature-dependence of the specific heat), although it only arises in combination with the lattice. www.artilifes.com /fermi-liquid.htm   (893 words)

 Enrico Fermi - Biography Enrico Fermi was born in Rome on 29th September, 1901, the son of Alberto Fermi, a Chief Inspector of the Ministry of Communications, and Ida de Gattis. In 1927, Fermi was elected Professor of Theoretical Physics at the University of Rome (a post which he retained until 1938, when he - immediately after the receipt of the Nobel Prize - emigrated to America, primarily to escape Mussolini's fascist dictatorship). Fermi was member of several academies and learned societies in Italy and abroad (he was early in his career, in 1929, chosen among the first 30 members of the Royal Academy of Italy). nobelprize.org /nobel_prizes/physics/laureates/1938/fermi-bio.html   (975 words)

 Centenario della nascita di E. Fermi Fermi was teaching mechanics and mathematics in Florence, as incaricato, a position carrying no tenure or pension privileges. Fermi and Rasetti were going to let their captured geckos loose in the dining hall for the simple pleasure of scaring the peasant girls who waited on tables. From subconscious depths came the missing factor Fermi had long sought: no two atoms of a gas can move with exactly the same velocity or, as physicists say, there can be only on atom in each of the quantum states possible for the atoms of a perfect monoatomic gas. www.fi.infn.it /fermi   (620 words)

 Ultracold Gas Shows Strange Behavior A Fermi gas is one composed of "fermions," a class of atoms constrained by a quantum mechanical property from getting too close to each other. A Fermi gas is "degenerate" when at a very low temperature, known as the Fermi temperature, its atoms approach their closeness limits. To create a strongly interacting gas of fermions, the Duke team had to fill the optical bowl with lithium atoms whose subatomic constituents are in two different states of "spin," or rotation. www.dukenews.duke.edu /2002/11/fermigas1107.html   (1468 words)

 Fermi Gas The energy-distribution of the fermions in a Fermi gas in thermal equilibrium is determined by their number (or density), the temperature and the set of available energy states, via Fermi-Dirac statistics. For the same reason, the pressure of a Fermi gas is nonzero even at zero temperature, in contrast to that of a classical ideal gas (which would be zero). Since interactions are neglected by definition, the problem of treating the equilibrium properties and dynamical behaviour of a Fermi gas reduces to the study of the behaviour of single independent particles. thermalradiation.net   (376 words)

 Extreme Impersonations: Science News Online, Sept. 18, 2004   (Site not responding. Last check: ) Fermi gases could also impersonate the hottest matter that has ever existed, which is the quark-gluon plasma. By driving down the Fermi gas' temperature to a few hundred nanokelvins, the JILA team forced its potassium atoms into a state known as degeneracy. When such a gas is permitted to swell, say, by turning off the lasers that had been confining it, the effective size of each atom grows. www.sciencenews.org /articles/20040918/bob9.asp   (2603 words)

 APS - 2006 APS March Meeting - Event - Pairing and Phase Separation in a Polarized Fermi Gas   (Site not responding. Last check: ) Pairing is qualitatively altered by the Fermi energy mismatch, and there has been considerable speculation regarding the nature and relative stability of various proposed exotic phases. We have created a two-component gas of $^6$Li atoms in which the relative Fermi energies are altered by changing the relative numbers of each component \footnote{G.B. Partridge \textit{et al.}, cond-mat/0511752.}. We also measure the universal interaction parameter $\beta$ for a strongly interacting Fermi gas to be -0.54 (5), in good agreement with recent Monte-Carlo calculations. meetings.aps.org /Meeting/MAR06/Event/42456   (250 words)

 [cond-mat/0607835] Fermi gas near unitarity around four and two spatial dimensions Near four spatial dimensions such a Fermi gas can be understood as a weakly-interacting system of fermionic and bosonic degrees of freedom. Then the phase structure of the polarized Fermi gas near the unitarity regime is studied from the epsilon expansion. We also show that the unitary Fermi gas near two spatial dimensions reduces to a weakly-interacting Fermi gas and calculate the thermodynamic quantities and the fermion quasiparticle spectrum in the expansion over \bar\epsilon=d-2. arxiv.org /abs/cond-mat/0607835   (246 words)

 Nobel laureate Cronin edits book on Fermi’s legacy Physicists speak of Fermi acceleration and Fermi liquid, Fermi pressure and Fermi gas, the Fermi paradox and Fermi questions, the Fermi-Thomas model of the atom and the Fermi-Turkevich gap. Among Fermi’s early accomplishments was to apply quantum mechanics, which explains the behavior of atoms and subatomic particles, to the physics of solids and gases, Cronin said. Fermi went on to earn the Nobel Prize in 1938 for his discovery of new radioactive elements produced by the addition of neutrons to the cores of other atoms, and for the discovery of nuclear reactions brought about by slowly moving neutrons. chronicle.uchicago.edu /041007/fermi.shtml   (750 words)

 Untitled Document At this temperature, the gas behaves more classically than quantum mechanically, and little difference between the bosons and fermions can be discerned. Fermi pressure is responsible for the minimum radius and is a dramatic manifestation of Fermi-Dirac statistics. In white dwarf and neutron stars, which are essentially “dead” due to the depletion of their nuclear fuel, it is the Fermi pressure that stabilizes the stars against gravitational collapse. atomcool.rice.edu /fermi-degeneracy.htm   (373 words)

 plasma concept from the Astronomy knowledge base   (Site not responding. Last check: ) has definition A completely ionized gas; the so-called fourth state of matter (besides solid, liquid, and gas) in which the temperature is too high for atoms as such to exist and which consists of free electrons and free atomic nuclei. When this point is reached, the gas is said to be degenerate., A gas of electrons (or, more generally, fermions) in which all the lowest quantum states are occupied. For such a gas, the pressure in the nonrelativistic limit is proportional to the 5/3 power of the density., A state of matter found in white dwarfs and other extremely dense objects, in which strong deviations from classical laws of physics occur. www.site.uottawa.ca:4321 /astronomy/plasma.html   (273 words)

 Vortices seen in Fermi gas (June 2005) - News - PhysicsWeb Although indirect evidence for superfluidity in Fermi gases has been seen before, low-temperature physicists have been searching for definitive evidence in the shape of quantized vortices in a rotating gas. It is the possibility of reproducing this Cooper-pairing process in a Fermi gas, and possibly learning more about the mysterious pairing mechanism that underpins high-temperature superconductivity, that has led to intense interest in these systems. Ketterle and co-workers started with a lithium-6 gas that had been cooled to about 50 nanokelvin and then applied a magnetic field to change the strength of the interactions between the atoms. www.physicsweb.org /articles/news/9/6/15   (606 words)

 Optical Trap Produces Degenerate Fermi Gas As the temperature of an atomic gas is reduced to ultralow levels, the behavior of the atoms can no longer be described with semiclassical rules of thermal distribution, but require fully quantum-mechanical descriptions. They subjected the gas to Doppler laser cooling, lowering the ensemble temperature to 150 µK. A ZnSe lens then focused the 10.6-µm beam from a CO laser to a diameter of 47 µm, trapping 3.5 million atoms, and the researchers applied a bias magnetic field, which interacted with the atoms remained in the trap, the Fermi temperature was 8 µK and the measured temperature was less than 4 µK. At that point, quantum effects dominated the behavior of the gas. www.photonics.com /content/spectra/2002/June/research/77366.aspx   (586 words)

 Heat Response Evidence For Superfluidity In Cold 'Fermion' Gas Although the gas was trapped by a laser beam within billionths of a degree of absolute zero, the lowest possible temperature, researchers said it behaved like a superfluid flowing at high temperatures. That change suggests the gas of lithium-6 atoms had undergone a phase change into a novel superfluid state - bolstering previous evidence for the observation of this state of frictionless flow. A Fermi gas is one composed of "fermions," a class of standoffish atoms known for keeping more of a distance from each other than the other gregarious class of atoms known as "bosons," Thomas said. www.spacedaily.com /news/physics-05d.html   (1448 words)

 More on Fermi Gas The energy distribution of the fermions in a Fermi gas in thermal equilibrium is determined by their density, the temperature and the set of available energy states, via Fermi-Dirac statistics. For this reason, the pressure of a Fermi gas is nonzero even at zero temperature, in contrast to that of a classical ideal gas. The Fermi energy surface in momentum space is known as the Fermi surface. www.artilifes.com /fermi-gas.htm   (491 words)

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