Inelastic cotunneling through a long diffusive wire

We show that electron transport through a long multichannel wire, connected to leads by tunnel junctions, at low temperatures T and voltages V is dominated by inelastic cotunneling. This mechanism results in experimentally observed power-law dependence of conductance on T and V, in the diffusive regime where usual Coulomb anomaly theory leads to exponentially low conductance. The power-law exponent α* is proportional to the distance between contacts L. The article is published in the original.     

Effects of electron–electron scattering in wide ballistic microcontacts

We consider effects of electron–electron scattering in wide ballistic microcontacts. Using a semiclassical Boltzmann equation, we obtain a positive correction to the Sharvin conductance that results from electron–electron collisions in the leads. The correction is linearly dependent on temperature at high temperatures T?eV$T?\mathit{eV}$ and proportional to |V|$\left|V\right|$ at high voltages eV?T$\mathit{eV}?T$. Magnetic field leads to strong suppression of this positive correction that results in a positive magnetoresistance in weak fields. As electron–electron scattering affects the conductance, it also influences the noise. At low voltages the noise is defined by the Nyquist relation and at high voltages it is related with the inelastic correction to the current by the Shottky formula δS=2eδI$\delta S=2e\delta I$.     

Noise in the Helical Edge Channel Anisotropically Coupled to a Local Spin

We calculate the frequency-dependent shot noise in the edge states of a two-dimensional topological insulator coupled to a magnetic impurity with spin S = 1/2 of arbitrary anisotropy. If the anisotropy is absent, the noise is purely thermal at low frequencies, but tends to the Poisson noise of the full current I at high frequencies. If the interaction only flips the impurity spin but conserves those of electrons, the noise at high voltages eV ≫ T is frequency-independent. Both the noise and the backscattering current I_bs saturate at voltageindependent values. Finally, if the Hamiltonian contains all types of non-spin-conserving scattering, the noise at high voltages becomes frequency-dependent again. At low frequencies, its ratio to 2eI_bs is larger than 1 and may reach 2 in the limit I_bs→0. At high frequencies, it tends to 1.

     

Analysis of inelastic scattering processes of electrons by localized electrons in quantum dots

The inelastic Coulomb scattering rate 1/τ_in of conduction electrons has been theoretically evaluated in the presence of localized states such as quantum dots. By a diagrammatical method, we have formulated 1/τ_in and its relation to the conductivity σ_loc(ω) through localized states. The dependence of τ_in on temperature T is examined in the case that σ_loc(ω) follows the Mott's model. It is found that 1/τ_in varies as T²(ln Δ/T)^d+1 where d is the dimensionality and Δ is tunneling energy between the localized states in the asymptonic T = 0 limit, in agreement with Imry's calculation. It is also found that calculated 1/τ_in deviates from T²(ln Δ/T)^d+1 as T increases, suggesting the importance of correction term at high temperature.     

Electron transport in manganite bicrystal junctions

The transport and magnetic properties of junctions created in La_0.67Sr_0.33MnO₃ thin films epitaxially grown on substrates with a bicrystal boundary have been investigated. In tilted neodymium gallate bicrystal substrates, the NdGaO₃(110) planes are inclined at angles of 12° and 38°. The temperature dependences of the electrical resistance, magnetoresistance, and differential conductance of the junctions at different voltages have been measured and analyzed. It has been found that the magnetoresistance and electrical resistance of the junction significantly increase with an increase in the misorientation angle, even though the misorientation of the easy magnetization axes remains nearly unchanged. The ratio of the spin-dependent and spin-independent contributions to the conductance of the bicrystal junction increases by almost an order of magnitude with an increase in the misorientation angle from 12° to 38°. The magnetoresistance of the junction increases with decreasing temperature, which is most likely associated with an increase of the magnetic polarization of the electrons. It has been shown that, at low (liquid-helium) temperatures, the conductance depends on the voltage V according to the law V ^1/2, which indicates the dominant contribution from the electron-electron interaction to the electrical resistance of the junction. An increase in the temperature leads to a decrease in this contribution and an increase in the contribution proportional to V ^3/2, which is characteristic of the mechanism involving inelastic spin scattering by surface antiferromagnetic magnons.     

Effect of impurities on thermoelectric power due to phonon drag in metals

The effect of inelastic impurity scattering of electrons on the thermoelectric power due to phonon drag in metals has been studied. It is shown that this is the main cause of the thermoelectric power suppression due to doping at low temperatures. The thermoelectric power in a metal with a quadratic electron spectrum has been calculated as a function of temperature and impurity concentration. In addition to the impurity concentration, the correction to the thermoelectric power due to inelastic scattering contains the large factor Θ_D/T. Zh. éksp. Teor. Fiz. 111, 2237–2242 (June 1997)     

Current noise in (111) n-channel Si-MOSFET's at T = 4.2 K

We have investigated the drain current-drain voltage characteristics and the spectral noise intensity of the drain current of (111) n-channel MOSFET's at T = 4.2 K. At T = 4.2 K the drain current-drain voltage characteristics showed a hysteresis which was not observed at T =77 K and at room temperature. A qualitative explanation of this hysteresis is given in terms of electron transfer from high mobility valleys to low mobility valleys due to hot electrons. In the spectra of the current noise three contributions could be distinguished: 1/ƒ-noise, white noise and generation-recombination noise. The 1/ƒ-noise is interpreted as number fluctuations noise. The effective trap density was found to be 2.3 × 10²² m^-3. At low drain voltages the white noise can be interpreted as diffusion noise. At higher drain voltages extra noise is observed over and above diffusion noise. This extra noise may be inter-valley noise. The generation-recombination noise was very sensitive to the gate voltage. A tentative explanation can be given if it is assumed that the traps which cause this noise have a non-uniform energy distribution.     

Temperature dependence of the inelastic scattering in a GaAs/n-AlGaAs selectively doped heterojunction with InGaAs quantum dots

Inelastic scattering processes of two-dimensional electron gas (2DEG) have been investigated in a inverted GaAs/n-AlGaAs heterojunction with self-organized InGaAs quantum dots (QDs) embedded near the 2DEG channel where the electron population in the QDs is controllable by the gate voltage V_g. By analyzing magnetoresistance, the inelastic scattering time τ_ε have been evaluated as functions of V_g at 0.6, 0.8, 1.2, and 1.7 K. It is found that τ_ε increases with V_g below 0.8 K and decreases above 1.2 K, which suggests that the dominant scattering mechanisms below 0.8 K and above 1.2 K are different. To interpret this behavior, we have calculated the inelastic scattering time theoretically. It is found that the experimental data are well explained by a theoretical model where a 2D electron is considered to be inelastically scattered both by the other 2D electrons and by the trapped electrons in QDs. It is also found that the 2DEG–2DEG scattering is dominant at low temperature, while the 2DEG-QDs scattering becomes important as the temperature increases.     

Low-temperature properties of CePd2In

We report measurements of the specific heatC _p(T), electrical resistivity ϱ(T) and magnetic susceptibility ξ(T) of hexagonal CePd₂In, at low temperatures. Anomalies inC _p(T), χ(T) and ϱ(T) atT=1.23 K, indicate a phase transition, most likely to an antiferromagnetically-ordered phase. The electronic entropy reachesR ln2 per mole Ce at 9.2K, suggesting that the phase transition involves a doublet state. The ordered phase coexists with moderately correlated itinerant electrons.     

Tunneling mechanism through the nonlinear electrical transport in Co/CoO particles with core-shell nanostructure

We investigate the nonlinear electrical transport as a function of temperature in Co/CoO nanoparticles having core-shell nanostructure. Nanoparticle was synthesized by sol-gel citrate precursor technique where core-shell nanostructure is confirmed by the high resolution Transmission Electron Microscopy. Current-voltage (I-V) characteristics are measured over the temperature range 20-295 K. I-V curve exhibits ohmic behaviour at 295 K. Nonlinear electrical transport is observed at low temperature (T) for T?275 K. Electrical transport properties have been interpreted in terms of tunneling mechanism where tunneling between ferromagnetic Co nanoparticles takes place through the antiferromagnetic CoO layer. Analysis of dynamic conductance (G=dI/dV) indicates that the inelastic tunneling via localized states of antiferromagnetic CoO layers is dominant in the transport mechanism at low temperature.     

Tunnelling current in Schottky diodes containing InAs quantum dots

Current transport mechanism in Schottky diode containing InAs quantum dots (QDs) is investigated using temperature-varying current-voltage characteristics. We found that the tunnelling emission has obvious effects on the I-V characteristics. The I-V-T measurements revealed clear effects of QDs on the overall current flow. Field emission (FE, pure tunnelling effect) was observed at low temperature and low voltages bias region. The zero-bias barrier height decreases and the ideality factor increases with decreasing temperature, and the ideality factor was found to follow the T₀-effect. When the reverse bias is varied, the ideality factors of Schottky barriers exhibit oscillations due to the tunnelling of electrons through discrete levels in quantum dots. The traps distributed within InAlAs layer can also act as a transition step for reverse bias defect-assisted tunnelling current which can phenomenologically explain the decrease of the effective barrier height with measurement temperature.     

Superconductors containing impurities with crystal-field split energy levels

We investigate theoretically the problem of a superconducting matrix containing paramagnetic rare earth impurities with crystal-field split energy levels. There are two competing mechanisms which change the superconducting transition temperatureT _c. One is inelastic charge scattering of conduction electrons from the aspherical part of the 4f charge distribution, which leads to an increase inT _c similar to that of optical phonons. The other and often predominant mechanism comes from the exchange interaction, which depressesT _c and can be very effective even among non-magnetic levels via off-diagonal matrix elements. Crystalline fields serve to alter the effectiveness of the two kinds of scattering depending upon the symmetry character of the low-lying levels, and in favorable cases one may study separately the effects of the two types of scattering by adding different impurities to a given host. We find that crystal-field levels at energies quite high compared tok _B·T_c can still have an important effect onT _c. It is shown that the crystalline-field splitting should be directly observable as structure in the tunneling characteristics.     

Theory of inelastic tunneling spectroscopy of a single molecule - Competition between elastic and inelastic current

A theory of inelastic electron tunneling spectroscopy of a single molecule with scanning tunneling microscope is presented using the Keldysh Green’s function method for an adsorbate-induced resonance coupled to the molecular vibration. It is found that the correction to the tunneling current is expressed in terms of the transmission probability; the correction is negative for the elastic part of the current and positive for the inelastic one. The differential conductance (dI/dV) exhibits an increase or decrease at the threshold corresponding to the opening of inelastic channel depending on the sign of the correction, and the size of this conductance jump is scaled with the vibrational damping due to electron-hole pair excitation. The lineshape of d²I/dV²-spectra calculated using a renormalized adsorbate Green’s function evolves from an antisymmetric dip to a peak through the derivative-like one as the position of the adsorbate resonance recedes from the Fermi level of the substrate.     

Fabrication and transport properties of multiwall carbon nanotube crossroads

A multiwall carbon nanotube crossroads has been fabricated by a manipulation technique using a glass microcapillary, and the low temperature transport properties investigated. The two-terminal conductance of an individual tube shows Tomonaga–Luttinger liquid behavior G∝T^α at high temperature and dI/dV ∝V ^α at low temperature. However, no evidence of such a power-law behavior is obtained in the four-terminal conductance at the junction, where the conductance shows an almost metallic behavior ‘corrected’ by weak localization. Weak localization would essentially appear in electron states at the junctions of MWNTs.     

Peculiarities of crystal field effects in CeInCu2 based heavy-fermion compounds

We have studied the evolution of the inelastic neutron magnetic scattering spectra of a compound with cubic symmetry, CeInCu₂, in the temperature range 10–130 K, and also their transformation with variation of the Kondo temperature T _K due to substitution of cerium ions in the system Ce_1−x (La,Y)_xInCu₂ at T=10 K. It turns out that the energy of the transition between the ground state and excited state of the 4 f electrons (Δ_CF) in the crystal electric field in CeInCu₂ increases with growth of the population of the ground state as the temperature is reduced, with a slight change in its intensity. Such behavior is inconsistent with the notion of classical one-ion effects of the crystal electric field. We have found that the scale of the observed variations in the excitation spectra of the 4f electrons depends on the Kondo temperature T _K and is insensitive to disorder in the rare-earth sublattice. Thus, despite the fact that T _K ≪Δ_CF, hybridization with states in the conduction band has a substantial effect on all parameters of the excitation spectrum of the ground multiplet of the 4f electrons at low temperatures. Zh. éksp. Teor. Fiz. 115, 2197–2206 (June 1999) A. A. Baikov Institute of Metallurgy     

高偏压金属─绝缘体─金属结的光发射

我们制作了一种可在6-11V偏压范围内均匀发射可见光的新型金属-绝缘体-金属结型发光器件,其内层结构是Al-Al₂O₃-MgF₂-An(Cu),其承受偏压、单位面积发光功率及相应的外量子效应高过迄今已知的M-O-M遂道结型发光器件.本文首次报导并论证了这一由Schottky热电子所激发的光发射及其物理图象:Schottky热电子在AO(Cu)-真空界面激发表面等离极化激元(SPP);Au(Cu)-真空界面的SPP通过表面粗糙度与外光子耦合.这一图象与该器件的电流-电压(I-V)、电流-温度(I-T)关系及其发射光谱的主要特征一致.     

Low temperature electrical conductivity and magnetoconductivity of Fe39Ni39Mo4Si6B12 and Co58Ni10Fe5Si11B16 metallic glass alloys

A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=T _m. The conductivity was observed to follow aT ^1/2 law forT<T _m andT ² law forT>T _m. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aT ^p law (p=2) at low temperatures.     

c-axis tunneling on YBCO films

We have measured I(V) characteristics of c-axis planar tunnel junctions on Y₁Ba₂Cu₃O _{7 - δ} films. Our results and their analysis provide experimental support for the importance of the two-dimensional character of the YBCO band structure, and a method to measure the ratio between the Fermi energy of YBCO and the barrier height. The analysis is based on the relation between the linear conductance background, related to the inelastic tunneling component, and the zero bias conductance, related to the elastic one. Received 24 September 2000 and Received in final form 15 November 2000     

Critical dynamics and multifractal exponents at the Anderson transition in 3d disordered systems

We investigate the dynamics of electrons in the vicinity of the Anderson transition in d = 3 dimensions. Using the exact eigenstates from a numerical diagonalization, a number of quantities related to the critical behavior of the diffusion function are obtained. The relation η = d ? D₂ between the correlation dimension D₂ of the multifractal eigenstates and the exponent η which enters into correlation functions is verified. Numerically, we have η ≈? 1.3. Implications of critical dynamics for experiments are predicted. We investigate the long-time behavior of the motion of a wave packet. Furthermore, electron-electron and electron-phonon scattering rates are calculated. For the latter, we predict a change of the temperature dependence for low T due to η. The electron-electron scattering rate is found to be linear in T and depends on the dimensionless conductance at the critical point.     

Mechanism for NonlinearI – V Behaviour and the Temperature Dependence of Threshold Switching in the Se-Te-Sn System

The nonlinearI – V behaviour and threshold switching of the bulk Se-Te-Sn system have been experimentally studied at various temperatures. It is observed that the curves are linear for low voltages and become superlinear at higher voltages. After a certain voltageV _th, the current through the material shoots to a very high value and the potential across the material drops to a low value. It is also found that there is a decrease in Vh with increase in percentage of tin and temperature. An attempt is made to explain the nonlinearI – V behaviour and threshold switching on the basis of a microcrystallite model. A study of Se-Te-Sn system reveals that our results are in concurrence with the theoretical predictions.