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1.
2.
The rearrangement of the Fermi surface in a diluted two-dimensional electron gas beyond the topological quantum critical point has been examined within an approach based on the Landau theory of Fermi liquid and a nonperturbative functional method. The possibility of a transition of the first order in the coupling constant at zero temperature between the states with a three-sheet Fermi surface and a transition of the first order in temperature between these states at a fixed coupling constant has been shown. It has also been shown that a topological crossover, which is associated with the joining of two sheets of the Fermi surface and is characterized by the maxima of the density of states N(T) and ratio C(T)/T of the specific heat to the temperature, occurs at a very low temperature T ⋄ determined by the structure of a state with the three-sheet Fermi surface. A momentum region where the distribution n(p, T) depends slightly on the temperature, which is manifested in the maximum of the specific heat C(T) near T *, appears through a crossover at temperatures T ∼ T * > T ⋄. It has been shown that the flattening of the single-particle spectrum of the strongly correlated two-dimensional electron gas results in the crossover from the Fermi liquid behavior to a non-Fermi liquid one with the density of states N(T) ∝ T −α with the exponent α }~ 2/3. 相似文献
3.
M. Grether M. Fortes M. de Llano J.L. del Rıo F.J. Sevilla M.A. Solıs A.A. Valladares 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):117-124
We solve the problem of a Bose or Fermi gas in d-dimensions trapped by δ ⩽ d mutually perpendicular harmonic oscillator potentials. From the grand potential we derive their thermodynamic functions (internal
energy, specific heat, etc.) as well as a generalized density of states. The Bose gas exhibits Bose-Einstein condensation
at a nonzero critical temperature T
c if and only if d + δ > 2, along with a jump in the specific heat at T
c if and only if d + δ > 4. Specific heats for both gas types precisely coincide as functions of temperature when d + δ = 2. The trapped system behaves like an ideal free quantum gas in d + δ dimensions. For δ = 0 we recover all known thermodynamic properties of ideal quantum gases in d dimensions, while in 3D for δ = 1, 2 and 3 one simulates behavior reminiscent of quantum wells, wires anddots, respectively. Good agreement is found between experimental critical temperatures for the trapped boson gases 37
87Rb, 3
7Li, 37
85Rb, 2
4He, 19
41K and the known theoretical expression which is a special case for d = δ = 3, but only moderate agreement for 11
27Na and 1
1H.
Received 17 July 2002 / Received in final form 14 October 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: mdgg@hp.fciencias.unam.mx 相似文献
4.
In this article, we studied the specific heat data of iron-based superconductors LaO1? x F x FeAs (x?=?0.1) and SmO1? x F x FeAs (x?=?0.13,?0.12, and 0.1). (i) The contribution of phonons in specific heat above Tc depends exponentially on temperature. (ii) The specific heat has different contributions, and they change differently at Tc . This change must be the effect of a physical function on heat capacity. Therefore, transition temperature is defined by thermal parameters. For LaO0.9F0.1FeAs and SmO0.87F0.13FeAs, a transition point was evaluated at 22.11 and 26.32?K, respectively. This is in close agreement with the midpoint transition temperatures obtained from dc resistivity and magnetization experiments, where the modified electronic heat capacity led to the approximate value of the transition point in two samples. The jump, ΔC/γT c, and the electronic and lattice heat capacity coefficients, γ and β, respectively, were evaluated. 相似文献
5.
E. Braun G. Jackel B. Roden J. G. Sereni D. Wohlleben 《Zeitschrift für Physik B Condensed Matter》1988,72(2):169-173
We have measured the specific heat, the electrical resistance and the magnetic susceptibility of YBa2Cu3O7–x in a superconducting (sc) and in a non-superconducting (nsc) version. The latter was obtained by inducing a small loss of oxygen. In the sc sample we find a jump of the specific heat with C=3.6 J mole–1 K–1. Below the maximum nearT
c
the specific heat of the sc version drops too fast for an electronic effect alone: there is a cross-over from excess to deficiency already at 0.9T
c
. The specific heat of the nsc version shows a change of slope in the temperature range between 70 and 80 K, which indicates the existence of a second specific heat anomaly, which apparently exists independently of that due to the onset of superconductivity and explains at least partially the premature crossover.Alexander von Humboldt fellow. On leave in absence from Centro Atomico Bariloche—CNEA Argentina 相似文献
6.
Summary The specific heats of (R2O3)
x
(P2O5)1−x
glasses containing high concentrations of La3+ and Y3+ ions have been measured between 1.5K and 30K. It is shown that, in addition to the usual Debye contribution, there is an
excess specific heat arising from localized vibrational states which has been discussed in terms of two distinct models. The
first predicts a maximum in the temperature dependence of the excess specific heat associated with the crossover frequency
from phonon to fracton behaviour. The phonon-fracton density of states used to fit the excess specific heat gives rise to
model parameters having the same magnitudes as those found previously for other glasses including samarium phosphates. The
second model, formulated on the basis of soft vibrations in glasses, predicts a minimum in the excess specific heat, which
is also observed.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Capanello, Italy, July 4–8, 1994. 相似文献
7.
A Michelson-interferometer in combination with a He-Ne-laser was used to determine the gas temperature in a nitrogen low pressure gas discharge. With this method the radial temperature profile could be measured to about 96% of the tube radius. Moreover rotational temperatures were measured with a 2 m-grating spectrograph from the spectrum of N2- and N2+-bands. In the range from 4 to 10 torr and 25 to 100 mA gas temperatures between 460 and 890 K were measured with the belonging rotational temperature from 620 to 1170 K. At pressures below 10 torr a difference of the rotational temperatures from the first negative and the second positive system was found. A qualitative consideration on the mechanism of the radial heat conductivity in the positive column was added. 相似文献
8.
Frank A. Blood Jr. 《Journal of statistical physics》1970,2(4):301-304
A self-consistent molecular field approximation for the two-dimensional, square-lattice Ising model is used to calculate the energy and magnetization. Agreement with the exact calculations is good except near the critical temperature, which differs from the exact critical temperature by 4%. The specific heat has no anomalous behavior asT approachesT
c from above, and the magnetization follows the incorrect Weiss (T
c-T)1/2 law asT approachesT
c from below. 相似文献
9.
Y. Zhang Y. Xiao 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):425-430
We present results from lattice dynamics calculations on the phonon modes and specific heat of SiGe core-shell nanowires.
The results show that phonon dispersion relation of SiGe nanowires consists of four acoustic branches. The frequency of the
first optical mode at Γ point shifts to low frequency as the Ge concentration is increasing. There are three strong peaks in the spectra of density
of states. The peaks at 9.0 THz and 15.0 THz can be attributed to the high frequency Ge-Ge and Si-Si bond vibration. The broad
peak around 3.0 THz of pure silicon nanowire corresponds to the transverse acoustic branch of bulk silicon. Moreover, specific
heat of SiGe nanowires increases (decreases) with the increase of the concentration x at low (high) temperature. The specific heat at 300 K can be fitted by C
V
= x
2
C
Ge + (1 − x)C
Si, where C
Ge and C
Si are specific heat of pure germanium and silicon nanowires respectively. 相似文献
10.
Effect of heavy cation doping (Ca2+ at the A-site) on the thermal properties of perovskite LaMnO3 has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds,
the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La0.25Ca0.75MnO3 as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower
temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν
0), Debye temperature (Θ
D) and Gruneisen parameter (γ) are also discussed.
相似文献
11.
W. Felsch S. G. Kushnir K. Samwer H. Schröder R. van den Berg H. v. Löhneysen 《Zeitschrift für Physik B Condensed Matter》1982,48(2):99-107
The amorphous alloy Ce75.5Co24.5 prepared by melt spinning has been studied through measurements of the magnetic susceptibility, magnetization, electrical resistivity, thermoelectric power and specific heat. The results are interpreted in terms of a homogeneous intermediate valence state of the Ce ions. This is inferred from a temperature-independent magnetic susceptibility at low temperature and the absence of magnetic ordering, a large linear term in the specific heat, and aT
2 dependence of the electrical resistivity at low temperature followed by a steep increase with temperature up to 50 K. At this temperature, the thermoelectric power displays a maximum. The intrinsic properties are partially obscured at low temperatures by a contribution from roughly a few percent of magnetic impurities, presumably Ce3+ ions. They manifest themselves by an increase of the susceptibility towards low temperatures and by a broad Schottky-like contribution to the specific heat resulting from the excitation of magnetic clusters.Dedicated to Prof. Dr. S. Methfessel on the occasion of his 60th birthday 相似文献
12.
The temperature dependence of the thermoelectric power S(T) in polycrystalline La0.67Ba0.33MnO3 has been investigated. In the ferromagnetic regime, the phonon thermoelectric power is evaluated by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonon. The Mott expression is used to compute the electron diffusive thermoelectric power (Scdiff.) using Fermi energy as electron-free parameter. The Scdiff infers linear temperature dependence and Sphdrag increases exponentially with temperature, which is an artefact of various operating scattering mechanisms. The behaviour of the S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the La0.67Ba0.33MnO3. Numerical analysis of thermoelectric power of the present model shows similar results as those revealed from experiments. 相似文献
13.
《Solid State Communications》1987,62(4):271-274
We present measurements of the temperature dependence of the electrical resistivity, the thermopower and the specific heat of the hexagonal compound CeCu4Al. At high temperatures, the electrical resistivity is characterized by a nearly temperature independent behaviour, followed by a continuous increase below 100K. No maximum has been found down to 1.7 K. The thermopower shows a positive maximum at about 30 K. As in CeCu6 no negative values are observable in the range from 4.2 K up to a room temperature. The specific heat data between 7 and 15 K reveal a γ value around 280 mJ mol-1 K-2. Below this temperature range the specific heat cp/T shows a rapid rise and crosses the value of 1 J mol-1 K-2 at about 1.45 K. 相似文献
14.
The two-dimensional (2D) extended Falicov–Kimball model has been studied to observe the role of nonlocal Coulomb interaction
(U
nc) using an exact diagonalization technique. The f-state occupation (n
f
), the f–d intersite correlation function (c
fd), the specific heat (C), entropy (S) and the specific heat coefficient (γ) have been examined. Nonlocal Coulomb interaction-induced discontinuous insulator-to-metal transition occurs at a critical
f-level energy. More ordered state is obtained with the increase of U
nc. In the specific heat curves, two-peak structure as well as a single-peak structure appears. At low-temperature region, a
sharp rise in the specific heat coefficient γ is observed. The peak value of γ shifts to the higher temperature region with U
nc. 相似文献
15.
Crystal field parameters for ErGaG and Er3+ YAlG and used to compute the temperature dependence of Schottky specific heat, paramagnetic susceptibility, magnetic anisotropy,μ
eff and quadrupole splitting in the range 10–400 K. The hyperfine interaction parametersA andB for166Er and167Er in both the systems are also obtained and in turn used to estimate the nuclear specific heat contribution. The studied
parameters compare well with the available experimental results. 相似文献
16.
The specific heat C
total of crystalline and amorphous Eu2(MoO4)3 is measured in the temperature interval 4.5–30 K. The amorphous state is obtained by applying pressure ∼7 GPa at room temperature.
It is found that the specific heat of the crystal at T⩽7.5 K is described by a cubic function of temperature, while the specific
heat of the amorphous sample has a strongly non-Debye character in the entire experimental temperature interval. The curve
of C
total for amorphous europium molybdate is analyzed in a model of soft atomic potentials, and it is shown that it agrees well with
universal low-temperature anomalies of the specific heat of classical glasses obtained by quenching from the liquid.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 623–627 (25 October 1998) 相似文献
17.
T.H. Meen W.R. Chen L.W. Ji C.J. Huang 《Journal of Physics and Chemistry of Solids》2007,68(7):1390-1395
Polycrystalline samples of electron-doped Pr1.85Ce0.15CuO4+δ have been prepared under different annealing conditions and investigated by means of X-ray-diffraction, oxygen content analysis, electrical resistivity, magnetic susceptibility and low temperature specific heat measurements. X-ray-diffraction patterns show that samples contain a single T′ phase. The superconducting transition temperatures Tcm taken with the onset of diamagnetism in magnetic-susceptibility measurements are 20 and 19.5 K for sample annealed in flowing Ar gas and in vacuum (∼10−3 torr), respectively. The data of the samples, which are annealed in flowing Ar gas, show clear evidence for an αT2 term at zero magnetic field in superconducting electronic specific heat, and are consistent with d-wave superconductivity. However, this behavior is not observed in the other sample, which is annealed in vacuum. These results indicate that different heat treatments affect the oxygen content, homogeneity, superconducting transition temperature Tc, superconducting volume fraction, and the superconducting pairing symmetry of Pr1.85Ce0.15CuO4+δ. 相似文献
18.
By improving the evaluation of the contribution from the first order exchange graphs reported recently by Tsai and Isihara, the electronic specific heat of an electron gas is evaluated to ordere 2. It is shown that the specific heat contains a logarithmic term. 相似文献
19.
A. Poddar S. Das D. Plachke H.D. Carstanjen 《Journal of magnetism and magnetic materials》2006,300(2):263-272
We report measurements of electrical resistivity (ρ), Hall coefficient (RH), magnetization (M) and specific heat (Cp(T)) of high-quality icosahedral Al70.4Pd20.8Mn8.8 phases with different thermal treatment. An improvement in the quasi-crystallinity upon the annealing treatment caused a drastic increase in ρ up to 7000 μΩ cm accompanied by a very small electronic specific heat coefficient γ. The low temperature ρ(T) data has been analyzed in terms of weak localization and electron–electron interaction effects. The Hall resistivity (ρH) is found to be strongly temperature-dependent and varies linearly with the magnetization (M) for the same field and temperature. Magnetization measurement reveals that more conductive samples are more magnetic and vice versa. Magnetic susceptibility (χ) data of all the annealed samples agrees with the Curie–Weiss-like behavior implying the existence of localized moments. The negative Curie–Weiss temperature (θ) indicates strong antiferromagnetic coupling between individual Mn atoms. The magnetic Mn concentration is found to be small, ranging from 1.73×10-4 for the less magnetic sample studied up to 3×10-3 for the more magnetic one. The small electronic specific heat coefficient obtained for all the samples suggests a significant reduction in the electronic density of states (DOS) at the Fermi level (EF) upon thermal annealing treatment. 相似文献
20.
S. Rabinovich 《Journal of Experimental and Theoretical Physics》2011,112(4):637-641
A simple assumption of the emergence in gas of small atomic clusters consisting of c particles each leads to a phase separation (first-order transition). It reveals itself by the emergence of a “forbidden”
density range starting at a certain temperature. Defining this latter value as the critical temperature predicts the existence
of an interval with the anomalous heat capacity behavior c
p
∝ ΔT
−1/c
. The value c = 13 suggested in the literature yields the heat capacity exponent α = 0.077. 相似文献