共查询到20条相似文献,搜索用时 31 毫秒
1.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):65-74
A precursor effect on the Fermi surface in the two-dimensional Hubbard model at finite temperatures near the antiferromagnetic
instability is studied using three different itinerant approaches: the second order perturbation theory, the paramagnon theory
(PT), and the two-particle self-consistent (TPSC) approach. In general, at finite temperature, the Fermi surface of the interacting
electron systems is not sharply defined due to the broadening effects of the self-energy. In order to take account of those
effects we consider the single-particle spectral function A(, 0) at the Fermi level, to describe the counterpart of the Fermi surface at T = 0. We find that the Fermi surface is destroyed close to the pseudogap regime due to the spin-fluctuation effects in both
PT and TPSC approaches. Moreover, the top of the effective valence band is located around = (π/2,π/2) in agreement with earlier investigations on the single-hole motion in the antiferromagnetic background. A crossover
behavior from the Fermi-liquid regime to the pseudogap regime is observed in the electron concentration dependence of the
spectral function and the self-energy.
Received 8 September 2000 and Received in final form 20 December 2000 相似文献
2.
Takao Morinari Eiji Kaneshita Tohyama Tohyama 《Physica C: Superconductivity and its Applications》2010,470(2):95-97
We propose interlayer magnetoresistance experiments which provide information about Fermi surface topology in layered multi-band systems. The interlayer magnetoresistance shows an oscillating behavior with respect to the azimuthal angle of the applied in-plane magnetic field if the Fermi surface is anisotropic. We discuss applications to LaFeAsO, a parent compound of FeAs-based superconductors. We show the results on the paramagnetic state and the antiferromagnetic state based on a mean field calculation. 相似文献
3.
Karolina Szamota-Leandersson Mats Leandersson Pål Palmgren Mats Göthelid Ulf O. Karlsson 《Surface science》2009,603(1):190-196
Deposition of Bi onto (4 × 2)/c(8 × 2)-InAs(1 0 0) and subsequent annealing results in a (2 × 6) surface reconstruction as seen by low electron energy diffraction. The Bi condensation eliminates the original (4 × 2) surface reconstruction and creates a new structure including Bi-dimers. This surface is metallic and hosts a charge accumulation layer seen through photoemission intensity near the Fermi level. The accumulation layer is located in the bulk region below the surface, but the intensity of the Fermi level structure is strongly dependent on the surface order. 相似文献
4.
A. A. Ovchinnikov M. Ya. Ovchinnikova E. A. Plekhanov 《Journal of Experimental and Theoretical Physics》1999,88(2):356-369
The phase diagram, nature of the normal state pseudogap, type of the Fermi surface, and behavior of the superconducting gap
in various cuprates are discussed in terms of a correlated state with valence bonds. The variational correlated state, which
is a band analogue of the Anderson (RVB) states, is constructed using local unitary transformations. Formation of valence
bonds causes attraction between holes in the d-channel and corresponding superconductivity compatible with antiferromagnetic spin order. Our calculations indicate that
there is a fairly wide range of doping with antiferromagnetic order in isolated CuO2 planes. The shape of the Fermi surface and phase transition curve are sensitive to the value and sign of the hopping interaction
t′ between diagonal neighboring sites. In underdoped samples, the dielectrization of various sections of the Fermi boundary,
depending on the sign of t′, gives rise to a pseudogap detected in photoemission spectra for various quasimomentum directions. In particular, in bismuth-and
yttrium-based ceramics (t′>0), the transition from the normal state of overdoped samples to the pseudogap state of underdoped samples corresponds to
the onset of dielectrization on the Brillouin zone boundary near k=(0,π) and transition from “large” to “small” Fermi surfaces. The hypothesis about s-wave superconductivity of La-and Nd-based ceramics has been revised: a situation is predicted when, notwithstanding the d-wave symmetry of the superconducting order parameter, the excitation energy on the Fermi surface does not vanish at all points
of the phase space owing to the dielectrization of the Fermi boundary at k
x=±
k
y. The model with orthorhombic distortions and two peaks on the curve of T
c versus doping is discussed in connection with experimental data for the yttrium-based ceramic.
Zh. éksp. Teor. Fiz. 115, 649–674 (February 1999) 相似文献
5.
A. Ya. Mal’tsev 《Journal of Experimental and Theoretical Physics》1997,85(5):934-942
The behavior of the electrical conductivity tensor in strong magnetic fields in the presence of unclosed quasiclassical electron
trajectories of complex form near the Fermi surface is considered. It is shown that the asymptotic behavior of the conductivity
tensor in the limit B→∞ differs in this case from the picture previously described for trajectories of simpler form. The possibility of blocking
the longitudinal conductivity in strong magnetic fields at low temperatures in the case of a Fermi surface of special form
is also treated theoretically.
Zh. éksp. Teor. Fiz. 112, 1710–1726 (November 1997) 相似文献
6.
7.
G. Seibold F. Becca F. Bucci C. Castellani C. Di Castro M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):87-97
The concept of frustrated phase separation is applied to investigate its consequences for the electronic structure of the
high T
c
cuprates. The resulting incommensurate charge density wave (CDW) scattering is most effective in creating local gaps in k-space when the scattering vector connects states with equal energy. Starting from an open Fermi surface we find that the
resulting CDW is oriented along the (10)- and (or) (01)-direction which allows for a purely one-dimensional or a two-dimensional
“eggbox type” charge modulation. In both cases the van Hove singularities are substantially enhanced, and the spectral weight
of Fermi surface states near the M-points, tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the eggbox case, leaves
finite arcs of the Fermi surface gapless. We discuss our results with repect to possible consequences for photoemission experiments.
Received 14 June 1999 相似文献
8.
V. D. Borman M. A. Pushkin V. N. Tronin V. I. Troyan 《Journal of Experimental and Theoretical Physics》2010,110(6):1005-1025
The electronic properties of nanoclusters of transition (Ni, Co, Cr) and noble (Au, Cu) metals deposited on the surface of
highly oriented pyrolytic graphite (HOPG) are studied using the method of X-ray photoelectron spectroscopy. The laws of variation
of a change ΔE
b in the binding energies of core-level electrons in the initial (ΔE
i) and final (ΔE
f) states of atoms in nanoclusters, the intrinsic widths γ of photoelectron lines, and their singularity indices α as functions
of the metal cluster size d are determined. A qualitative difference in behavior of the ΔE
i(d) and α(d) values in metals of the two groups (Ni, Cr versus Co, Cu) is found. The values of the final-state energy (ΔE
f < 0) and the line width (Δγ > 0) in the clusters of all metals studied vary in a similar manner. It is shown that a significant
contribution to E
i is due to a transfer of the valence-shell electrons at the cluster-substrate interface, which is caused by the contact potential
difference. The value of an uncompensated charge per nanocluster is determined as a function of the cluster size and the number
of atoms in the cluster. The behavior of ΔE
f(d) is controlled by the Coulomb energy of a charged cluster and by a decrease in the efficiency of electron screening, which
is different in the metals studied. The broadening of photoelectron lines is determined by a spread of the cluster sizes and
by lower electron screening in the final Fermi system. An asymmetry of the core-level electron spectra of nanoclusters can
be explained using notions about the electron-hole pair excitation near the Fermi level. The effect of the structure of the
density of electron states in the d band of transition metals on the asymmetry of photoelectron lines is considered and it is concluded that this structure near
the Fermi level qualitatively changes with a decrease in the nanocluster size. The obtained results indicate that the behavior
of the electron subsystem of clusters of the d-metals in a size range of 2–10 nm under consideration is close to the behavior of a normal Fermi system. 相似文献
9.
This paper reports on a study by angle-resolved photoelectron and low-energy electron energy loss spectroscopy of graphene
monolayers, which are produced by propylene cracking on the Ni(111) surface, followed by intercalation of Cu, Ag, and Au atoms
between the graphene monolayer and the substrate, for various thicknesses of deposited metal layers and annealing temperatures.
It has been shown that the spectra of valence-band π states and of phonon vibrational modes measured after intercalation become
similar to those characteristic of single-crystal graphite with weak interlayer coupling. Despite the strong coupling of the
graphene monolayer to the substrate becoming suppressed by intercalation of Cu and Ag atoms, the π state branch does not reach
at the K point of the Brillouin zone the Fermi level, with the graphene coating itself breaking up partially to form graphene domains.
At the same time after intercalation of Au atoms, the electronic band structure approaches the closest to that of isolated
graphene, with linear π-state dispersion near the K point of the Brillouin zone, and the point of crossing of the filled, (π), with empty, (π*), states lying in the region of
the Fermi level, which makes this system a promising experimental model of the quasi-free graphene monolayer. 相似文献
10.
S. V. Nikolaev S. G. Ovchinnikov 《Journal of Experimental and Theoretical Physics》2012,114(1):118-131
The concentration dependences of the band structure, spectral weight, density of states, and Fermi surface in the paramagnetic
state are studied in the Hubbard model within cluster pertubation theory with 2 × 2 clusters. Representation of the Hubbard
X operators makes it possible to control conservation of the spectral weight in constructing cluster perturbation theory. The
calculated value of the ground-state energy is in good agreement with the results obtained using nonperturbative methods such
as the quantum Monte Carlo method, exact diagonalization of a 4 × 4 cluster, and the variational Monte Carlo method. It is
shown that in the case of hole doping, the states in the band gap (in-gap states) lie near the top of the lower Hubbard band
for large values of U and near the bottom of the upper band for small U. The concentration dependence of the Fermi surface strongly depends on hopping to second (t′) and third (t″) neighbors. For parameter values typical of HTSC cuprates, the existence of three concentration regions with different Fermi
surfaces is demonstrated. It is shown that broadening of the spectral electron density with an energy resolution typical of
contemporary ARPES leads to a pattern of arcs with a length depending on the concentration. Only an order-of-magnitude decrease
in the linewidth makes it possible to obtain the true Fermi surface from the spectral density. The kinks associated with strong
electron correlations are detected in the dispersion relation below the Fermi level. 相似文献
11.
Using the first-principles calculations within density functional theory (DFT), we have studied the behavior of Friedel oscillations near Al (1 0 0), (1 1 0), and (1 1 1) surfaces. The results show that for the most open Al (1 1 0) surface, the Friedel oscillation exhibits smaller oscillation amplitude, bigger wavelength and deeper depth of penetration compared to the oscillations of the more close-packed Al (1 1 1) and (1 0 0) surfaces. The characteristics of the Friedel oscillations of the Al surfaces are dominated by the charge density of Al 3p electrons near the Fermi level. We further calculate relaxations of the three surfaces, and find that the multilayer relaxations of the surfaces can be well explained by the Friedel oscillations qualitatively. In turn, we have shown that by altering interlayer spacing slightly the oscillation amplitude can be tuned, but the change near the surface is in contrary to the prediction based on the jellium model, indicating that the real lattice structure will plays a key role in the Friedel oscillations near the metal surface. 相似文献
12.
I. A. Nekrasov E. E. Kokorina E. Z. Kuchinskii M. V. Sadovskii S. Kasai A. Sekiyama S. Suga 《Journal of Experimental and Theoretical Physics》2010,110(6):989-994
The slightly underdoped high-temperature system La1.86Sr0.14CuO4 (LSCO) is studied by means of high-energy high-resolution angular resolved photoemission spectroscopy (ARPES) and the combined
LDA + DMFT + Σ
k
computational scheme. The corresponding one-band Hubbard model is solved via dynamical mean field theory (DMFT), and the
model parameters needed are obtained from first principles in the local density approximation (LDA). An “external” k-dependent self-energy Σ
k
describes the interaction of correlated electrons with antiferromagnetic (AFM) pseudogap fluctuations. Experimental and theoretical
data clearly show a “destruction” of the LSCO Fermi surface in the vicinity of the (π, 0) point and formation of “Fermi arcs”
in the nodal directions. ARPES energy distribution curves as well as momentum distribution curves demonstrate a deviation
of the quasiparticle band from the Fermi level around the (π, 0) point. The same behavior of spectral functions follows from
theoretical calculations suggesting the AFM origin of the pseudogap state. 相似文献
13.
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
14.
Reconstruction of the Fermi surface of high-temperature superconducting cuprates in the pseudogap state is analyzed within
a nearly exactly solvable model of the pseudogap state, induced by short-range order fluctuations of the antiferromagnetic
(AFM), spin-density wave (SDW), or a similar charge-density wave (CDW) order parameter, competing with the superconductivity.
We explicitly demonstrate the evolution from “Fermi arcs” (on the “large” Fermi surface) observed in the ARPES experiments
at relatively high temperatures (when both the amplitude and phase of the density waves fluctuate randomly) towards the formation
of typical “small” electron and hole “pockets,” which are apparently observed in the de Haas-van Alphen and Hall resistance
oscillation experiments at low temperatures (when only the phase of the density waves fluctuate and the correlation length
of the short-range order is large enough). A qualitative criterion for the quantum oscillations in high magnetic fields to
be observable in the pseudogap state is formulated in terms of the cyclotron frequency, the correlation length of fluctuations,
and the Fermi velocity.
The text was submitted by the authors in English. 相似文献
15.
The possibilities of graphic STM image simulation of a clean Si(1 1 1) 7 × 7 surface at atomic level are indicated. The presented procedure takes into account various types of deformation on the surface near the Fermi level in order to classify them and explain their origin. It also gives a clear hint to insert relevant physical phenomena in a suggested analysis. This goal is achieved exploiting the results of DAS (dimmer adatom stacing fault) model by means of standard mathematical programmes. A clean Si(1 1 1) 7 × 7 surface is considered as the representative example, but similar evaluation is possible for another non-metal and metal surfaces. 相似文献
16.
P. Schwaller T. Greber P. Aebi J.M. Singer H. Berger L. Forró J. Osterwalder 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):215-225
Full k
-maps of the electronic structure near the Fermi level of differently doped cuprates measured with angle-scanned photoelectron
spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped
Bi2Sr2CaCu2O8+δ high-temperature superconductors are mapped in the normal state. The results confirm the existence of large Luttinger Fermi
surfaces at high doping with a Fermi surface volume proportional to (1+x), where x is the hole concentration. At very low doping, however, we find that this assumption based on Luttinger's theorem is not
fulfilled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+δ as a function of the doping is discussed.
Received 12 October 1999 and Received in final form 12 April 2000 相似文献
17.
Shailendra Kumar C. MukherjeeV.K. Dixit S.D. SinghS.N. Jha 《Applied Surface Science》2011,258(1):143-146
Plasmon peaks along with Auger PLVV peak have been observed in the ultraviolet photoelectron spectra (UPSs) of InP after 5 min of sputtering with 0.5 kV Ar+ ions. Plasmon and Auger peaks are not observed in UPS of un-sputtered InP surface with native oxides of In and P. Filled electron energy levels are not observed near the Fermi level from 5 min sputtered InP surface due to increase of ionization potential of nano In clusters. 相似文献
18.
M. Vojta R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):283-287
We consider a Kondo impurity coupled to a fermionic host with a power-law density of states near the Fermi level, ρ(ε) ∼ |ε|r, with exponent r < 0. Using both perturbative renormalization group (poor man's scaling) and numerical renormalization group methods, we analyze
the phase diagram of this model for ferromagnetic and antiferromagnetic Kondo coupling. Both sectors display non-trivial behavior
with several stable phases separated by continuous transitions. In particular, on the ferromagnetic side there is a stable
intermediate-coupling fixed point with universal properties corresponding to a fractional ground-state spin.
Received 18 February 2002 Published online 31 July 2002 相似文献
19.
P.J. Kowalczyk M. Puchalski W. Koz?owski P. D?browski Z. Klusek W. Olejniczak 《Applied Surface Science》2008,254(15):4572-4576
Scanning tunneling microscopy (STM) and spectroscopy (STS) carried out in vacuum and air were used to study the electronic structure of the Au (1 1 1) surface in the range of 0.0-0.7 eV below the Fermi level. The STS experiment carried out in UHV showed the existence of the Shockley surface state (SS) located 0.48 eV below the Fermi level. STS carried out in air showed strong local maximum located 0.35 eV below the Fermi level. This maximum was ascribed to the SS shifted toward lower energy due to carbon and oxygen overlayer. To confirm that the SS could exist on the sample exposed to air we did ultraviolet photoemission spectroscopy (UPS) experiment on air-treated and clean Au (1 1 1). Our results suggest that the SS position initially measured at 0.38 eV below the Fermi level was shifted to 0.27 eV after air treatment. Additionally, the level of contamination was measured using X-ray photoelectron spectroscopy (XPS). 相似文献
20.
E. Frantzeskakis A. Crepaldi K. Kern M. Grioni 《Journal of Electron Spectroscopy and Related Phenomena》2010,181(1):88-95
We discuss two different approaches for tuning the giant spin-orbit splitting of a BiAg2 surface alloy. The first approach consists of electron doping by alkaline metal deposition in order to shift the energy position of the spin-split surface states, while the second is based on the novel Si(1 1 1)-Ag-BiAg2 trilayer system. In both cases the spin-polarized structure near the Fermi level can be controlled by an external parameter, while the second approach permits coupling the concept of giant spin-splitting with a semiconducting substrate. 相似文献