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1.
Behnam Farid 《哲学杂志》2013,93(24):2829-2863
It has long since been argued that the metallic states of the single-band Hubbard Hamiltonian ? in two spatial dimensions (i.e. for d = 2) should be non-Fermi liquid, a possibility that would lead to the understanding of the observed anomalous behaviour of the doped copper-oxide-based superconducting compounds in their normal metallic states. Here we present a formalism which enables us to express, for arbitrary d, the behaviour of the momentum-distribution function nσ(k) pertaining to uniform metallic ground states of ? close to S F; σ (the Fermi surface of the fermions with spin index σ, σ = ↑, ↓) in terms of a small number of constant parameters which are bound to satisfy certain inequalities implied by the requirement of the stability of the ground state of the system. These inequalities restrict the range of variation in nσ(k) for k infinitesimally inside and outside the Fermi sea pertaining to fermions with spin index σ and consequently the range of variation in the zero-temperature limit of nσ(k) for k on S F; σ On the basis of some available accurate numerical results for nσ(k) pertaining to the Hubbard and the t-J Hamiltonian, we conclude that, at least in the strong-coupling regime, the metallic ground states of ? for d = 2 cannot be Fermi-liquid nor can they in general be purely Luttinger or marginal Fermi liquids. We further rigorously identify the pseudogap phenomenon, or 'truncation' of the Fermi surface, clearly observed in the normal states of underdoped copper-oxide-based superconductors, as corresponding to a line of resonance energies (i.e. these energies strictly do not relate to quasiparticles) located below the Fermi energy, with a concomitant suppression to zero of the jump in nσ(k) over the 'truncated' parts of the Fermi surface. Our analyses make explicit the singular significance of the non-interacting energy dispersion ε k underlying ? in determining the low-energy spectral and transport properties of the metallic ground states of ?. 相似文献
2.
A. P. Gerashenko K. N. Mikhalev S. V. Verkhovskii T. V. D’yachkova A. P. Tyutyunnik V. G. Zubkov 《Applied magnetic resonance》2001,21(2):157-163
Nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rateT
1−1 of11B have been measured in superconducting polycrystalline MgB2 with 7cons = 39.5 K. It is shown that (T
1T−1 and the Knight shiftK
s are independent of temperature and nearly isotropic aboveT
c. Both of these quantities are decreased gradually in going to the superconducting state. According to NMR data the density
of states near the Fermi level is flat at the scale of about 500 K. Some conclusions on the orbital content of the density
of states at the Fermi level were drawn and compared with the results of the band structure calculations. 相似文献
3.
Leonid I. Korogodsky 《Communications in Mathematical Physics》1994,163(3):433-460
A quantum analogue of the groupSU(1,1)Z
2—the normalizer ofSU(1, 1) inSL
2(C)—is introduced and studied. Although there isno correctly defined tensor product in the category of *-representations of the quantum algebraC[SU(1, 1)]
q
of regular functions, some categories of *-representations ofC[SU(1, 1)Z
2]
q
turn out to be endowed with a certainZ
2-graded structure which can be considered as a super-generalization of the monoidal category structure. This quantum effect may be considered as a step to understanding the concept of quantum topological locally compact group.In fact, there seems to be afamily of quantum groupsSU(1, 1)Z
2 parameterized by unitary characters T
1 of the fundamental group of the two-dimensional symplectic leaf ofSU(1, 1)/T, whereT is the subgroup of diagonal matrices.It is shown that thequasi-classical analogues of the results of the paper are connected with the decomposition of Schubert cells of the flag manifoldSL
2(C)R/B (whereB is the Borel subgroup of upper-triangular matrices) into symplectic leaves.Supported by the Rosenbaum Fellowship. 相似文献
4.
A Goswami B K Srivastava Alok Srivastava S B Manohar Satya Prakash M V Ramaniah 《Pramana》1986,26(3):179-189
Fractional independent yields of fission products in the thermal neutron-induced fission of233U,235U,239Pu,241Pu and in the spontaneous fission of252Cf have been correlated with the neutron-to-proton ratio of the fission products. The yields of the products from a fissioning
system, when plotted as a function of neutron-to-proton (N/Z) ratio of fission preducts, fall on two Gaussian distribution corresponding to light and heavy fission products. The centroids
of the distribution or the most probable value of neutron-to-proton ratio is found to be very close to theN/Z of the fissioning nucleus. From the most probable value ofN/Z the various parameters of charge distribution e.g. most probable massA
p, most probable chargeZ
p, the mass dispersionσ
Aand the charge dispersionσ
Zhave been obtained and are in good agreement with the experimental values ofA
pandZ
p. 相似文献
5.
ABSTRACTStopping cross sections (SCS) for protons, alphas and Li ions are calculated with a modified form of our earlier work by incorporating a different electron density distribution of target materials; this involves four parameters – two projectile dependent and the rest two remain fixed. The prosed model has been tested for three stripped ion (H+, He2 + and Li3 +) projectiles and found that it describes quite satisfactorily the experimental SCS data from low energies with projectile velocities nearing v = Z1v0 (with Z1 as the atomic number and v0 the Bohr velocity) up to 100.0 MeV over a wide range of stopping media with atomic numbers Z2 =3–100. 相似文献
6.
Electron spin resonance (ESR) of VO2+ doped into LiNaSO4 has been studied at 300 K on an X-band spectrometer. The ESR powder spectra have been analyzed and spin Hamiltonian parameters
have been evaluated. Using the crystal-field approach, a theoretical estimate of the ground state wave functions of VO2+ in LiMSO4 (M = Na, K) has been made from the ESR data. The dipolar hyperfine coupling constant P and Fermi contact parameter K have also been estimated. 相似文献
7.
E. Jordão Neves 《Journal of statistical physics》1995,80(1-2):103-123
We consider a variational problem on thed-dimensional latticeZ
d
which has applications in the study of the meatastable behavior of the stochastic Ising model. The problem, an isoperimetric one, is to find what is the smallest area a finite subset ofZ
d
can have restricted to three classes of subsets ofZ
d
. If is one of these subsets, we define its volume as the number of points in it and its area as the number of pairs of points inZ
d
which are neighbors and such that only one of them belongs to . 相似文献
8.
A. S. Hamid 《Central European Journal of Physics》2003,1(4):655-668
The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation
radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of
a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a
radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW),
linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed
a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined
via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were
argued in view of positron wave function in Cd. 相似文献
9.
M.?Asif the?HT- team 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):269-272
Multifaceted asymmetric radiation from the edge (MARFE) phenomena during
lower hybrid current drive (LHCD) Experiments on the HT-7 superconducting
tokamak are summarized in this paper. The best correlation has been found
between the total input (ohmic + LHCD) power and the product of the edge
line average density and Z eff. Studies show that the critical density
of MARFE onset is observed in the region of Z eff
1/2fGW = 0.6-0.9, where
, (here
is the
maximum line average electron density and nGW is the Greenwald
density). These MARFEs generally appear to have the same characteristics as
high fGW MARFEs and are positionally stable throughout the LHCD
pulse. Improved confinement mode induced by a MARFE is observed, and it is
maintained for about 65 ms. MARFE cools the plasma edge, and the electron
density profile is observed to become more narrow and peaked. 相似文献
10.
The ground state wave function of11Li obtained in a three-body model proposed earlier (S Kumar and V S Bhasin,Phys. Rev.
C65, 034007 (2002)) has been employed to study the probability distributions, momentum distributions and n−n correlation. Complex
scaling method has been used to find the energy positions and widths of the three resonant states of11Li above the breakup threshold. The formalism is extended further to study the β-decay of11Li to two channels. One is the β-transition of11Li into a high lying excited state of11Be at 18.3 MeV, i.e.,11Be* and the second is the decay to deuteron +9Li channel. The11Be* state has been considered as a halo analog state identified as a bound three-body (9Li + n + p) system. The n-9Li interaction incorporates both the virtual state and the p-wave resonance observed experimentally. For p-9Li interaction, a Coulomb corrected separable interaction is constructed using charge indepedendence for strong interaction
part. The n-p interaction is operative only in3S1 state corresponding to the isotopic spin Th =0. As a result the11Be* state has the same isotopic spin as that of9Li core, i.e.,T = 3/2. Using these realistic parameters as input and without invoking any other free parameter, the model has been used to
predict the strength of the Gamow-Teller β-decay of11Li to11Be*, i.e.,Bgt = 1.5 and the value of the branching ratio to9Li + deuteron channel to be 1.3 × 10-4. These results are found to be in rather good agreement with the recent experimental findings. 相似文献
11.
K. Krug K. Winzer M. Reiffers J. Kunes P. Novák F. Kayzel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):595-600
The Fermi surface of PrNi5 has been studied by the measurements of the de Haas-van Alphen (dHvA) effect at temperatures between 0.3 and in magnetic fields up to 12 T. Two dHvA frequencies have been obtained. The electronic structure of PrNi5 was calculated using the full potential linearized augmented plane wave method. Five sheets of the Fermi surface and the
multiple extremal cross sections were determined. First and second sheet have a hole-like structure. The agreement between
theory and experiment is obtained by a small downward shift ( 0.1 eV) of the Fermi energy which is probably due to an underestimation of the role of 4
f electrons.
Received 9 May 2000 and Received in final form 20 September 2000 相似文献
12.
The densities (α) and ultrasonic velocities (C) of binary mixtures of a polar liquid like acetone and toluene have been measured at different frequencies (lMHz, 3MHz and
5MHz) over the entire range of mole fraction of acetone at temperature 303.16k. The intermolecular free length (L
f
), isentropic compressibility (β), acoustic impedance (Z), excess values of isentropic compressibility (β
E
) and acoustic impedance (Z
E
) have been computed using values of ultrasonic velocity (C) and density (α). The ultrasonic velocity (C), intermolecular free length (L
f
) and excess values of isentropic compressibility are positive whereas excess values of acoustic impedance is negative for
the entire composition range which indicates the specific interaction between unlike molecules. The results are discussed
in the light of intermolecular interactions occurring in the solutions. 相似文献
13.
The ESR spectra ofZ
2(Eu)-centers in KBr and KCl are presented and correlated to the optical absorption and the electron spin resonance of the Europium vacancy complex. The fine structure of theZ
2 spectra can be described by a Spin-Hamiltonian with an axialb
2
0
-parameter only. At room temperature it amounts to 1,761 10–4 cm–1 for KBr, 1,854 10–4 cm–1 for KCl and 1,453 10–4 cm–1 for RbCl. Accordingly theZ
2(Eu)-center must posses a strict axial 100-symmetry in these crystals. 相似文献
14.
Summary A microwave coherent backscattering experiment has been carried out on Mirabelle, a weakly ionised plasma device, with the
objective of measuring the electron density fluctuation level. The experiment is a preliminary step in order to prepare the
detection system for a microwave stimulated backscattering experiment. The incident electromagnetic wave is focused in front
of a plane grid which excites ion acoustic or electron Bernstein waves inducing fluctuations in the plasma. The backscattering
signal is collected by the launching circuit and detected by homodyne mixing. The typical ratio of the scattered power to
the incident power is about 10−12 and the relative density fluctuations are of the order of δn
e/n
e=10−3 against a background electron density ofn
e=1–5·109 cm−3. The backscattering measurement is compared with Langmuir probe measurements. The spectral width of the backscattered signal
has also been studied, by taking into account effects due to the incident wave focusing and plasma wave damping.
The authors of this paper have agreed to not receive the proofs for correction 相似文献
15.
P. Sigmund A. Schinner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):39-50
Enhanced stopping of swift hydrogen diclusters has been analysed theoretically. The target has been modeled as a
gas of harmonic-oscillator atoms of variable density. This model predicts a proximity effect, i.e., enhanced
stopping at high beam energy, and an oscillatory behavior at low energy. Both features get less pronounced with
increasing target density due to increased screening of the ion-target interaction by polarization of the
medium. Static screening by electrons accompanying the cluster likewise reduces the proximity effect. The
Barkas-Andersen correction has been estimated in the Z13Z_1^3 limit. Our findings are in contrast with
measurements on SiO2 [S.M. Shubeita et al.,
Phys. Rev. B 77, 115327 (2008)] which showed a pronounced step in the energy dependence of the proximity effect. 相似文献
16.
J. M. Ferreira M. B. Maple H. Zhou R. R. Hake B. W. Lee C. L. Seaman M. V. Kuric R. P. Guertin 《Applied Physics A: Materials Science & Processing》1988,47(1):105-110
Finely ground powders ofRBa2Cu3O7 – (R=Y, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) have been mixed at dilute 3%-by-volume concentrations into epoxy matrices which were then allowed to harden in applied magnetic fieldsH
A=18 kOe. X-ray diffractometry studies and 4.3 K measurements of supercurrent-induced magnetization hysteresisM are interpreted as indicating at least partial alignment of single-crystal-grain c-axes (1) parallel toH
A forR=Y, Nd, Sm, Dy, Ho (as earlier found by Farrell et al. forR=Y), and (2) perpendicular toH
A forR=Eu, Er, Tm, Yb. With a few exceptions (Y, Sm, Eu) the alignment direction correlates with the sign of the second-order Stevens factor
J of the crystalline electric field Hamiltonian in the manner suggested by Livingston et al. For the best aligned specimens (Ho, Dy) critical current densitiesJ
c (4.3 K, 5 kOe) for individual grains are estimated fromM and the Bean model to be of order 107 A/cm2 for the measuring fieldH parallel to the original alignment fieldH
A, and of order 106 A/cm2 forH perpendicular toH
A. 相似文献
17.
We have observed a gas of Fermi atoms confined in the antinodes of a standing electromagnetic wave. The standing wave is formed
by two counter-propagating beams with the wavelength of 10.6 μm focused on the same spot. Each antinode confines a pancake-shaped
cloud of 7500 lithium-6 atoms in two equally populated spin states at the temperature T = 0.1E
F, where E
F is the Fermi energy. The system is in the regime beyond the local density approximation: Only the 3 lowest energy states
of the axial motion are populated. The system may become an instrument for the study of 2D Fermi physics and 3D effects beyond
the local density approximation. 相似文献
18.
B. Šesták 《Czechoslovak Journal of Physics》1972,22(4):243-263
On the basis of the expansion of the distribution function in a sum of the spherical harmonics, the distribution functionf(v, r, t) is expanded in a series of scalar products of two Cartesian tensors term by term, i.e.
The tensors and (l) (l=2, 3) are constructed in dependence on the spherical harmonic expansion coefficients (the tensors and (l) (l=0, 1) have been constructed by Jancel and Kahan [3]). On the basis of the knowledge of the analytic form off
2 andf
3 the equations forf
1
f
2 andf
3 for the case of the Boltzmann's equation are determined.Technická 2, Praha 6, Czechoslovakia. 相似文献
19.
Beginning with anLRC network with impedance functionZ(), a sequence of iterated networksN
k with impedance functionsZ
k(), k= 1, 2, 3,..., is introduced. The asymptotic comportment ofZ
k() and the spectra ofN
k are analyzed in terms of the Julia set ofZ. An example is given of an iterated network associated with a cascade of period-doubling bifurcations. 相似文献
20.
A value for the nuclear magnetic moment of theI=2 (80.56 keV) level of166Er has been obtained by comparing measurements made by the Mössbauer effect on166Er with NMR measurements on the ground state of167Er in the same matrix. From measurements on ErFe2, ErAl2 and ErZn we obtain the value N (166Er; 80.56 keV)=0.650±0.010 n.m. This result is slightly higher than previously proposed values. 相似文献