共查询到20条相似文献,搜索用时 31 毫秒
1.
For the first time submillimetric microwaves (λ<1 mm) are used to observe Azbel' Kaner cyclotron resonance in metals. The very high frequency used (typicallyF≅400 GHz) gives a large value ofωτ (typically 500) and therefore very sharp peaks. The fundamental resonance fieldH
c=m
*
cω/e is rather high (typically 200 KG), so subharmonicsH
c/n can be observed at many values ofH in the field region 0–27 KG. If relatively few electrons participate in the resonance and ifω
cτ≧50 (ω
c=eH/m
*
c,τ relaxation time) thenChambers has shown that the line shapes are independent of relaxation time while the fractional linewidthΔH/H varies as l/ωτ. For the belly orbit in pure copper the conditions of Chambers' theory are satisfied forH≧20 KG parallel to [111] axis.m
* is a minimum andτ=1.8×10−10 s. 相似文献
2.
B. A. Aronzon D. Yu. Kovalev A. N. Lagar’kov E. Z. Meilikhov V. V. Ryl’kov M. A. Sedova N. Negre M. Goiran J. Leotin 《JETP Letters》1999,70(2):90-96
It is established that the Hall effect in Fe/SiO2 nanocomposite films in the activational tunneling conduction range is anomalous, i.e., the Hall resistivity ρh is proportional to the magnetization and is due to the spin-orbit interaction. The parametric coupling of the Hall and longitudinal
(ρxx) resistances ρh ∝ ρ
xx
m
(with temperature as the parameter) is characterized by a much lower value of the exponent m than in a uniform ferromagnetic metal. This circumstance is attributed to the characteristic features of the Hall effect
mechanism in the hopping regime — in our case, the interference of the amplitudes of tunneling transitions in a set of three
granules.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 87–92 (25 July 1999) 相似文献
3.
A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm1.85Ce0.15CuO4 thin films around T
sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm3+ moments with the energy ħωsf = k
B
T
sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρres, electron-phonon ρe-ph(T) = AT, and electron-electron ρe-e(T) = BT
2 contributions in addition to the fluctuation-induced contribution ρsf(T) due to thermal broadening effects (of the width ωsf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi
energy are estimated as ωp = 2.1 meV, τ
0
−1
= 9.5 × 10−14 s−1, λ = 1.2, and E
F = 0.2 eV, respectively.
The text was submitted by the authors in English. 相似文献
4.
We study the effect of fluctuations on the ac conductivity of a layered superconductor for c-axis electromagnetic wave polarization. The fluctuation contributions of different physical nature and sign (paraconductivity,
Maki-Thompson anomalous contribution, one-electron density-of-states renormalization) are found to be suppressed by the external
field at different characteristic frequencies (ω
AL∼T-T
c
, ω
MT∼max{T-T
c
,τ
ϕ
−1
}, ω
DOS∼min{T, τ
−1}). As a result, the appearance of a nonmonotonic frequency dependence (pseudogap) in the infrared optical conductivity of
high-temperature superconductor is predicted.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 397–401 (25 September 1996)
Department of Theoretical Physics Moscow Institute of Steel and Alloys.
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
M. R. Galpin D. E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):129-145
We develop a non-perturbative local moment approach (LMA) for the gapped Anderson impurity model (GAIM), in which a locally
correlated orbital is coupled to a host with a gapped density of states.
Two distinct phases arise, separated by a level-crossing quantum phase transition: a screened singlet phase, adiabatically
connected to the non-interacting limit and as such a generalized Fermi liquid (GFL); and an incompletely screened, doubly
degenerate local moment (LM) phase.
On opening a gap (δ) in the host, the transition occurs at a critical gap δc, the GFL [LM] phase occurring for δ<δc [ δ>δc] . In agreement with numerical renormalization group (NRG) calculations, the critical
δc = 0 at the particle-hole symmetric point of the model, where the LM phase arises immediately on opening the gap. In the generic
case by contrast δc > 0, and the resultant LMA phase boundary is in good quantitative agreement with NRG results. Local single-particle dynamics
are considered in some detail.
The major difference between the two phases resides in bound states within the gap: the GFL phase is found to be characterised
by one bound state only, while the LM phase contains two such states straddling the chemical potential. Particular emphasis
is naturally given to the
strongly correlated, Kondo regime of the model. Here,
single-particle dynamics for both phases are found to exhibit universal scaling as a function of scaled frequency ω/ωm
0 for fixed gaps
δ/ωm
0, where ωm
0 is the characteristic Kondo scale for the gapless (metallic) AIM; at particle-hole symmetry in particular, the
scaling spectra are obtained in closed form. For frequencies
|ω|/ωm
0 ≫δ/ωm
0, the
scaling spectra are found generally to reduce to those of the gapless, metallic Anderson model;
such that for small gaps δ/ωm
0≪ 1 in particular, the Kondo resonance that is the spectral hallmark of the usual metallic Anderson model persists more or
less in its entirety in the GAIM. 相似文献
6.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):161-167
The parameters of the σ-ω-ρ model in the relativistic mean-field theory with nonlinear σ-meson self-interaction are determined
by nuclear-matter properties, which are taken as those extracted by fits to data based on nonrelativistic nuclear models.
The values of the relevant parameters are C
σ
2∼ 94, C
ω
2∼ 32, C
ρ
2∼ 26, b∼ - 0.09, c∼ 1, and the σ-meson mass m
σ∼ 370 MeV, while the value of the calculated nuclear- surface thickness is t∼ 1.4 fm. The field system is shown to be stable, since the σ-meson self-interaction energy is a lower bound in this whole
parameter region with positive c. On the other hand, the effective nucleon mass M* is larger than 0.73M, if the symmetry incompressibility Ks is assumed to be negative and the nuclear-matter incompressibility K0 is kept less than 300 MeV.
Received: 27 June 2001 / Accepted: 5 October 2001 相似文献
7.
The differential resistance r
xx
in a GaAs double quantum well with two occupied size-quantization subbands have been studied at temperatures T = 1.6–4.2 K in magnetic fields B < 0.5 T. It has been found that differential resistance r
xx
vanishes at the maxima of magneto-intersubband oscillations with an increase in the direct current I
dc. It has been shown that the discovered r
xx
≈ 0 state appears under the condition 2R
c
E
H/ħωc < 1/2, where R
c is the cyclotron radius of electrons at the Fermi level, E
H is the Hall electric field induced by the current I
dc, and ωc is the cyclotron frequency. 相似文献
8.
The paper answers a question debated by physicists for many years. It is proved that, for almost equal gradients of the magnetic
flux u at its zero-level curve ∂ω, which is the piecewise smooth boundary of a simply-connected domain ω ⋐ ℝ2, the inverse problem for the Grad-Shafranov equation of plasma equilibrium in a tokamak (in the cylindrical approximation)
admits essentially different profiles of distributions f
u
: ω ∋ (x, y) ↦ f(u(x, y)) = u
xx
(x, y) + u
yy
(x, y) ⩾ 0 in the class of third-order polynomials f(u) = Σ
m=03
a
m
u
m
. 相似文献
9.
The dependence of the differential resistance r
xx
on the dc current density J
dc in a wide GaAs quantum well with two occupied size quantization subbands has been investigated at the temperature T = 4.2 K in the magnetic fields B < 1 T. A peak, whose position is given by the relation 2R
c
eE
H = ħωc/2, where R
c is the cyclotron radius, E
H is the Hall electric field, and ωc is the cyclotron frequency, has been observed in the r
xx
(J
dc) curves at high filling factors. The experimental results are attributed to Zener tunneling of electrons between the Landau
levels of different subbands. 相似文献
10.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
11.
A. M. Satanin S. V. Khor’kov V. V. Skuzovatkin 《Journal of Experimental and Theoretical Physics》1997,85(2):351-359
We study the effect of a weak nonlinearity in media on the linear regime of current flow in two-dimensional periodic structures
with two equal component concentrations. We find that the asymptotic behavior of the electric field and current as functions
of the distance between the angles in heterogeneous media is determined by the parameter h=σ
2/σ
1 (here σ
1 and σ
2 are the linear conductivities of the cells) and the external magnetic field B. This dependence leads to divergence of the higher-order moments of field and current at certain critical values h
c and B
c and to divergence of the response functions related to the higher-order moments. For square cells the effective nonlinear
conductivity diverges at h⩽h
c, with
. For structures of general shape we find the dependence of h
c on the angles and the external magnetic field. We show that for a given structure the linear regime of current flow in the
system can be reversibly transformed into a nonlinear one by varying the magnetic field strength. The critical field B
c is approximately determined from the condition ω
c
τ∼1, where ω
c and τ
−1 are, respectively, the cyclotron frequency and the collision rate. Finally, we discuss the feasibility of detecting these
effects experimentally.
Zh. éksp. Teor. Fiz. 112, 643–660 (August 1997) 相似文献
12.
A ππ, ˉKK, and ρρ(ωω) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities
for elastic ππ scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the
meson resonance table of the Particle Data Group. As expected, the ππ inelasticity is very strongly related to the opening
of the ˉK channel near 1 GeV, and the opening of ρρ(4π) and ωω(6π) channels in the 1.5 GeV region. The predictions of this model are
compared to the various elastic ππ→ππ amplitudes, that were obtained from analyses of π− p →π−π+n data. The role of the various resonances, in particular the glueball candidate f
0(1500) and the f
J(1710) is investigated.
Received: 19 November 1997 相似文献
13.
I. L. Drichko I. Yu. Smirnov A. V. Suslov O. A. Mironov D. R. Leadley 《Journal of Experimental and Theoretical Physics》2010,111(3):495-502
Magnetoresistivity ρ
xx
and ρ
xy
and the acoustoelectronic effects are measured in p-Si/SiGe/Si with an impurity concentration p = 1.99 × 1011 cm−2 in the temperature range 0.3–2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt θ to the normal to the plane of a two-dimensional p-Si/SiGe/Si channel is determined. A first-order ferromagnet-paramagnet phase transition is observed in the magnetic fields
corresponding to a filling factor ν = 2 at θ ≈ 59°–60°. 相似文献
14.
B. Zeini A. Freimuth B. Büchner M. Galffy R. Gross A.P. Kampf M. Kläser G. Müller-Vogt L. Winkler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):189-208
Measurements of the thermal conductivity (kxx) and the thermal Hall effect (kxy) in high magnetic fields in Y- and Bi-based high-T
c
superconductors are presented. We describe the experimental technique and test measurements on a simple metal (niobium).
In the high-T
c
superconductors kxx and kxy increase below T
c
and show a maximum in their temperature dependence. kxx has contributions from phonons and quasiparticle (QP) excitations, whereas kxy is purely electronic. The strong increase of kxy below T
c
gives direct evidence for a strong enhancement of the QP contribution to the heat current and thus for a strong increase
of the QP mean free path. Using kxy and the magnetic field dependence of kxx we separate the electronic thermal conductivity ( k
xx
el
) of the CuO
2
-planes from the phononic thermal conductivity ( k
xx
ph
). In YBa2Cu3O
7 - δ
k
xx
el
shows a pronounced maximum in the superconducting state. This maximum is much weaker in Bi2Sr2CaCu2O
8 + δ
, due to stronger impurity scattering. The maximum of k
xx
el
is strongly suppressed by a magnetic field, which we attribute to the scattering of QPs on vortices. An additional magnetic
field independent contribution to the maximum of kxx occurs in YBa2Cu3O
7 - δ
, reminiscent of the contribution of the CuO-chains, as determined from the anisotropy in untwined single crystals. Our data analysis reveals that below T
c
as in the normal state a transport (τ) and a Hall (
) relaxation time must be distinguished: The inelastic (i.e. temperature dependent) contribution to τ is strongly enhanced in the superconducting state, whereas
displays the same temperature dependence as above T
c
. We determine also the electronic thermal conductivity in the normal state from kxy and the electrical Hall angle. It shows an unusual linear increase with temperature.
Received 23 August 2000 相似文献
15.
S. S. Murzin 《JETP Letters》2008,88(5):326-328
Experimental data available in the literature for peak values of the diagonal resistivity in the transitions between the fractional
quantum Hall states (ρ
xx
max ) are compared with the theoretical predictions. It is found that the majority of the peak values are close to the theoretical
values for two-dimensional systems with moderate mobilities.
The text was submitted by the author in English. 相似文献
16.
G.I. Lykasov W. Cassing A. Sibirtsev M.V. Rzjanin 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):71-81
We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction
πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which
leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in 12C +12C, 40Ca +40Ca and 58Ni +58Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative
to a general m
T-scaling (for π0 and η mesons) might be controlled experimentally by the TAPS Collaboration.
Received: 28 April 1999 / Revised version: 7 June 1999 相似文献
17.
A. Yu. Mollaev I. K. Kamilov R. K. Arslanov T. R. Arslanov U. Z. Zalibekov V. M. Novotortsev S. F. Marenkin 《JETP Letters》2010,91(9):478-480
The magnetic susceptibility χ/χ0 and the longitudinal Δρ
zz
/ρ0 and transverse Δρ
xx
/ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T
c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has
been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and
magnetoresistance. 相似文献
18.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):137-141
The σ-ω coupling is introduced phenomenologically in the linear σ-ω model to study the nuclear matter properties. It is shown
that not only the effective nucleon mass M* but also the effective σ meson mass m
σ
* and the effective ω meson mass m
ω
* are nucleon-density-dependent. When the model parameters are fitted to the nuclear saturation point, with the nuclear radius
constant r
0 = 1.14 fm and volume energy a
1 = 16.0 MeV, as well as to the effective nucleon mass M
* = 0.85M, the model yields m
σ
* = 1.09m
σ and m
ω
* = 0.90m
ω at the saturation point, and the nuclear incompressibility K
0 = 501 MeV. The lowest value of K0 given by this model by adjusting the model parameters is around 227 MeV.
Received: 23 March 2001 / Accepted: 8 June 2001 相似文献
19.
V. F. Gantmakher D. A. Pushin D. V. Shovkun G. E. Tsydynzhapov L. P. Kozeeva A. N. Lavrov 《JETP Letters》1997,65(11):870-876
A scan of the superconductor-nonsuperconductor transformation in single crystals of YBa2Cu3O6+x
(x≈0.37) is done in two alternative ways, namely, by applying a magnetic field and by reducing the hole concentration through
oxygen rearrangement. The in-plane normal-state resistivity ρab obtained in the two cases is quite similar; its temperature dependence can be fitted by a logarithmic law in a temperature
range of almost two decades. However, an alternative representation of the temperature dependence of σab=1/ ρ ab by a power law, typical for a 3D material near a metal-insulator transition, is also plausible. The vertical conductivity
σc=1/ρc followed a power law, and neither σc(T), nor ρc(T) could be fitted by log T. It follows from the ρc measurements that the transformation at T=0 is split into two transitions: superconductor-normal-metal and normal-metal-insulator. In our samples, they are separated
in oxygen content by Δx≈0.025.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 834–839 (10 June 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
20.
S. S. Murzin 《JETP Letters》1998,67(3):216-221
The conductance of doped n-GaAs films is studied experimentally as a function of magnetic field and temperature in strong magnetic fields right up to
the quantum limit (ħωc = E
F). The Hall conductance G
xy is virtually independent of temperature T until the transverse conductance G
xx is quite large compared with e
2/h. In strong fields, when G
xx becomes comparable to e
2/h, G
xy starts to depend on T. The difference between the conductances G
xx at the two temperatures 4.2 and 0.35 K depends only weakly on the magnetic field H over a wide range of magnetic fields, while the conductances G
xx themselves vary strongly. The results can be explained by quantum corrections to the conductance as a result of the electron-electron
interaction in the diffusion channel. The possibility of quantization of the Hall conductance as a result of the electron-electron
interaction is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 201–206 (10 February 1998) 相似文献