共查询到20条相似文献,搜索用时 31 毫秒
1.
R.V. Parfeniev K.D. Moiseev N.S. Averkiev V.I. Nizhankovskii 《Journal of magnetism and magnetic materials》2009,321(7):712-715
We report a study of spin-related magnetotransport properties of a type II broken-gap heterostructure formed by InAs substrate bulky doped with Mn and δ-Mn-doped GaInAsSb epilayer. Planar and vertical quantum magnetotransport in a 2D-electron-hole system at the single type II broken-gap InAs/GaInAsSb heterointerface was investigated in high magnetic fields under the quantum Hall regime up to 15 T at low temperature (T=1.5 K). The I-V characteristics near the dielectric phase boundary show the step-like behavior that corresponds to the quantum conductance in a disordered 2D structure through the extended edge states of the nearest Landau level closest to the Fermi level. The value of these steps is determined by the orientation of the 2D-electron spin at the Landau level and the magnetic moment of Mn in the δ-layer. 相似文献
2.
Following the original analysis of Zhang and Hu for the 4-dimensional generalization of Quantum Hall effect, there has been much work from different viewpoints on the higher dimensional condensed matter systems. In this paper, we discuss three kinds of topological excitations in the SO (4) gauge field of condensed matter systems in 4-dimension—the instantons and anti-instantons, the ’t Hooft-Polyakov monopoles, and the 2-membranes. Using the ?-mapping topological theory, it is revealed that there are 4-, 3-, and 2-dimensional topological currents inhering in the SO (4) gauge field, and the above three kinds of excitations can be directly and explicitly derived from these three kinds of currents, respectively. Moreover, it is shown that the topological charges of these excitations are characterized by the Hopf indices and Brouwer degrees of ?-mapping. 相似文献
3.
Y. Hirobe Y. Ashikawa R. Kawasaki K. Noda D. Akahoshi H. Kuwahara 《Solid State Communications》2006,137(4):191-195
The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La2−2xSr1+2xMn2O7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50 K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1 mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system. 相似文献
4.
We focus attention on the particular thermodynamic relation . Using information theory concepts we show that, for a reversible process in which intensive variables change, microscopic considerations related to this thermodynamic relation make the informational contents of, respectively, and MaxEnt equivalent. The pertinent demonstration is obtained when trying to ascertain the corresponding equilibrium microscopic probability distribution. 相似文献
5.
Y. Nakajima T. Shibauchi H. Shishido K. Behnia M. Hedo T. Matsumoto Y. Onuki Y. Matsuda 《Journal of Physics and Chemistry of Solids》2008,69(12):3261-3264
We observe several non-Fermi liquid behaviors in the normal-state transport properties of CeMIn5 (M: Rh and Co) under pressure at low temperatures: (1) The dc-resistivity shows T-linear dependence, ρxx∝T. (2) The magnitude of Hall coefficient |RH| increases rapidly with decreasing temperature, and reaches a value much larger than |1/ne| at low temperatures. (3) The magnetoresistance displays T- and H-dependence that strongly violate Kohler's rule, and is well scaled by the tangent of the Hall angle, . These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. Since all of these salient features have been also reported for high-Tc cuprates, we infer that the non-Fermi liquid transport properties capture universal features of strongly correlated electron systems in the presence of strong antiferromagnetic fluctuations. 相似文献
6.
Martin Greiter 《Annals of Physics》2005,319(1):217-249
We aim to give a pedagogical introduction to those elementary aspects of superconductivity which are not treated in the classic textbooks. In particular, we emphasize that global U (1) phase rotation symmetry, and not gauge symmetry, is spontaneously violated, and show that the BCS wave function is, contrary to claims in the literature, fully gauge invariant. We discuss the nature of the order parameter, the physical origin of the many degenerate states, and the relation between formulations of superconductivity with fixed particle numbers vs. well-defined phases. We motivate and to some extend derive the effective field theory at low temperatures, explore symmetries and conservation laws, and justify the classical nature of the theory. Most importantly, we show that the entire phenomenology of superconductivity essentially follows from the single assumption of a charged order parameter field. This phenomenology includes Anderson’s characteristic equations of superfluidity, electric and magnetic screening, the Bernoulli Hall effect, the balance of the Lorentz force, as well as the quantum effects, in which Planck’s constant manifests itself through the compactness of the U (1) phase field. The latter effects include flux quantization, phase slippage, and the Josephson effect. 相似文献
7.
N.V. Agrinskaya Yu.L. IvanovP.A. Petrov V.M. Ustinov 《Solid State Communications》2003,126(7):369-372
By selective doping (Be) of the well and barrier regions of GaAs/Al0.3Ga0.7As structures we have realized the situation where the upper Hubbard band (A+ centers) has been occupied by holes in the equilibrium. We studied the temperature behavior of the Hall effect, variable range hopping (VRH) conductivity and the photoluminescence (PL) spectra of the corresponding structures. The experimental data demonstrated that the binding energy of the A+ states significantly increases with respect to 3D case and strongly depends on the well width (9 nm, 15 nm). The localization radii of the A+ states estimated from the transport data are of the order of the well widths. 相似文献
8.
W.B. Mi 《Applied Surface Science》2010,256(9):2831-2836
Fe0.5Ge0.5 nanocomposite films with different film thicknesses were fabricated using cosputtering. The films are composed of Ge, Fe and Fe3Ge2, and are ferromagnetic at room temperature. The saturation magnetization and magnetic interaction including dipolar interaction and exchange coupling increase with the increasing film thickness. The electrical conductance mechanism turns from metallic to semiconducting and the saturation Hall resistivity ρxys increases with the decreasing film thickness. At 28 nm, ρxys is ∼137 μΩ cm at 2 K, about 150 times larger than that of pure Fe film (0.9 μΩ cm) and four orders larger than that of bulk Fe. The ρxy-H curves of all the films show the same linearity character in low-field range even though the temperature-independent slope is different at different film thicknesses. At high temperatures, the skew scattering mechanism is dominant. At low temperatures, side-jump effect should be dominant at large resistivity ρxx regime for the thin films, and the skew scattering is dominant at small ρxx regime for the thick films. 相似文献
9.
10.
We reexamine the atomic spontaneous decay in a Kerr nonlinear blackbody by contrast with our previous paper [M. Yin, Z. Cheng, Phys. Rev. A 78 (2008) 063829]. In the process of deriving the atomic decay rate, we use the temperature-dependent velocity of photons to take the full nonlinearity of a KNB into account. It is found that below a transition temperature Tc, the atomic spontaneous emission in a KNB might be enhanced or inhibited compared with that in a normal blackbody whose interior is filled with a nonabsorbing linear medium. The physical origin of the enhancement and inhibition of spontaneous emission is also discussed. 相似文献
11.
In this paper, we consider the phenomenon of stochastic resonance (SR) in an asymmetric bistable system with coloured noises and periodic rectangular signal. Expression of the signal-to-noise ratio (SNR) has been obtained under the adiabatic limit. We investigate the effect of any system parameter (such as p, q, r, τ1, τ2) on the SNR. The plot of SNR-τ1 shows SR for some values of the additive noise self-correlation time τ2, but not for the whole range of τ2. The system bias r suppresses the SNR. When the intensity of additive noise q is increased, the SR phenomenon disappears in the plot of SNR-p, but the plot of SNR-q presents SR for almost all values of the multiplicative noise intensity p. 相似文献
12.
Y.D. Su 《Applied Surface Science》2009,255(18):8164-8170
We deposit ternary WCxNy thin films on Si (1 0 0) substrates at 500 °C using direct current (DC) reactive magnetron sputtering in a mixture of CH4/N2/Ar discharge, and explore the effects of substrate bias (Vb) on the intrinsic stress, preferred orientation and phase transition for the obtained films by virtue of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and selective area electron diffraction (SAED). We find that with increasing the absolute value of Vb up to 200 V the carbon (x) and nitrogen (y) atom concentrations of WCxNy films keep almost constant with the values of 0.75 and 0.25, respectively. The XPS and SAED results, combined with the density-functional theory (DFT) calculations on the electronic structure of WC0.75N0.25, show our obtained WCxNy films are single-phase of carbonitrides. Furthermore, we find that the compressive stress sharply increases with increasing the absolute value of Vb, which leads to a pronounced change in the preferred orientation and phase structure for the film, in which a phase transition from cubic β-WCxNy to hexagonal α-WCxNy occurs as Vb is in the range of −40 to −120 V. In order to reveal the relationship between the stress and phase transition as well as preferred orientation, the DFT calculations are used to obtain the elastic constants for β-WCxNy and α-WCxNy. The calculated results show that the preferred orientation is dependent on the competition between strain energy and surface energy, and the phase transition can be attributed to a decrease in the strain energy. 相似文献
13.
Soluble multi-walled carbon nanotubes (MWNTs) have been obtained by noncovalent modification with poly [2-methoxy,5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV). For the composite MWNT/MEH-PPV, there is π-π interaction between the MEH-PPV and MWNTs in addition to the wrapping of the polymer. The nonlinear optical transmittance was measured using a nanosecond optical parametric oscillator pumped with a Nd:YAG system. Excellent optical limiting performance of the composite MWNT/MEH-PPV was observed both in the visible region of 590-680 nm and at the wavelength of 1064 nm. By means of time-correlated single-photon counting fluorescence measurement, an explanation based on the nonlinear absorption of MWNT dominated by the intermolecular energy transfer was proposed. 相似文献
14.
Giuseppe Gaeta 《Annals of Physics》2004,312(2):511-540
In the Landau theory of phase transitions one considers an effective potential Φ whose symmetry group G and degree d depend on the system under consideration; generally speaking, Φ is the most general G-invariant polynomial of degree d. When such a Φ turns out to be too complicate for a direct analysis, it is essential to be able to drop unessential terms, i.e., to apply a simplifying criterion. Criteria based on singularity theory exist and have a rigorous foundation, but are often very difficult to apply in practice. Here we consider a simplifying criterion (as stated by Gufan) and rigorously justify it on the basis of classical Lie-Poincaré theory as far as one deals with fixed values of the control parameter(s) in the Landau potential; when one considers a range of values, in particular near a phase transition, the criterion has to be accordingly partially modified, as we discuss. We consider some specific cases of group G as examples, and study in detail the application to the Sergienko-Gufan-Urazhdin model for highly piezoelectric perovskites. 相似文献
15.
I Bar-JosephH Shtrikman 《Solid State Communications》2003,127(12):765-770
We study the photoluminescence (PL) spectrum of a two-dimensional electron system at the high magnetic field limit, where all electrons reside at the lowest Landau level (ν<2). Using a gated structure we tune the electron density from the dilute limit to a dense electron gas, and follow the changes in the emission spectrum. We find that the spectrum at the dilute limit consists of two bound triplets, whose behavior is consistent with that of the dark and bright triplets. We show that the spectrum undergoes critical changes at ν=1/3, from an isolated charged exciton-like spectrum at ν<1/3, to a spectrum that reflects the interactions with the surrounding electrons above this filling factor. This behavior is found to be robust, independent of the electron density and magnetic field. We compare our observations with other recent low temperature PL measurements of a two-dimensional electron gas at high magnetic field and find good agreement and consistency. 相似文献
16.
We perform three tests on our proposal to implement diffeomorphism invariance in the non-abelian D0-brane DBI action as a base-point independence constraint between matrix Riemann normal coordinate systems. First, we show that T-duality along an isometry correctly interchanges the potential and kinetic terms in the action. Second, we show that the method to impose base-point independence using an auxiliary dN2-dimensional nonlinear sigma model also works for metrics which are curved along the brane, provided a physical gauge choice is made at the end. Third, we show that without alteration this method is applicable to higher order in velocities. Testing specifically to order 4, we elucidate the range of validity of the symmetrized trace approximation to the non-abelian DBI action. 相似文献
17.
Subhash C. Kashyap K. Gopinadhan D.K. Pandya Sujeet Chaudhary 《Journal of magnetism and magnetic materials》2009,321(8):957-962
Room-temperature ferromagnetism has been observed in Co- or Mn-doped SnO2 and Co- and F-co-doped SnO2 thin films. A maximum magnetic moment of 0.80μB/Co ion has been observed for Sn0.90Co0.10O1.925−δF0.075 thin films, whereas in the case of Sn1−xMnxO2−δ it was 0.18μB/Mn ion for x=0.10. The magnetization of both Sn1−xCoxO2−δ and Sn1−xCoxO2−y−δFy thin films depends on the free carrier concentration. An anomalous Hall effect has been observed in the case of Co-doped SnO2 films. However, the same was not observed in the case of Mn-doped SnO2 thin films. Carrier-mediated interaction is convincingly proved to be the cause of ferromagnetism in the case of Co:SnO2. It is, however, proposed that no carrier-mediated interaction exists in the case of Mn:SnO2. Present studies indicate that dopants and hence electronic cloud-lattice interaction plays an important role in inducing ferromagnetism. 相似文献
18.
In this work, we present a model and a method to study integer quantum Hall (IQH) systems. Making use of the Landau levels structure we divide these two-dimensional systems into a set of interacting one-dimensional gases, one for each guiding center. We show that the so-called strong field approximation, used by Kallin and Halperin and by MacDonald, is equivalent, in first order, to a forward scattering approximation and analyze the IQH systems within this approximation. Using an appropriate variation of the Landau level bosonization method we obtain the dispersion relations for the collective excitations and the single-particle spectral functions. For the bulk states, these results evidence a behavior typical of non-normal strongly correlated systems, including the spin-charge splitting of the single-particle spectral function. We discuss the origin of this behavior in the light of the Tomonaga-Luttinger model and the bosonization of two-dimensional electron gases. 相似文献
19.
We introduce a high-dimensional symplectic map, modeling a large system, to analyze the interplay between single-particle chaotic dynamics and particles interactions in thermodynamic systems. We study the initial growth of the Boltzmann entropy, SB, as a function of the coarse-graining resolution (the late stage of the evolution is trivial, as the system is subjected to no external drivings). We show that a characteristic scale emerges, and that the behavior of SB vs t, at variance with the Gibbs entropy, does not depend on the resolution, as far as it is finer than this scale. The interaction among particles is crucial to achieve this result, while the rate of entropy growth, in its early stage, depends essentially on the single-particle chaotic dynamics. It is possible to interpret the basic features of the dynamics in terms of a suitable Markov approximation. 相似文献
20.
The single-phase diluted magnetic Fe-ion (5%) doped ZnO powders were prepared by solid-state reaction method. The powders were annealed in Ar or Ar/H2(5%) atmosphere at 1200 °C. The crystal structure, electric and magnetic properties for the Zn0.95Fe0.05O powders have been studied with X-ray diffraction (XRD) vibrating sample magnetometer, resistance and Hall measurement. All the peaks for the XRD pattern of samples belong to the hexagonal (P63mc) lattice of ZnO, and no indication of a secondary phase. The lattice parameters for the Zn0.95Fe0.05O with an annealing in Ar/H2(5%) atmosphere were a0=3.256 Å and c0=5.206 Å at room temperature. The hysteresis curve for the Zn0.95Fe0.05O at room temperature was enhanced ferromagnetic behaviour with an annealing in Ar/H2(5%) atmosphere. We give an explanation for enhanced ferromagnetic behaviour with H2 treatment by electric properties. 相似文献