Evolution of transport regimes in carbon nanotube quantum dots

We study the evolution of conductance regimes in carbon nanotubes with doubly degenerate orbitals (shells) by controlling the contact transparency within the same sample. For sufficiently open contacts, Kondo behavior is observed for 1, 2, and 3 electrons in the topmost shell. As the contacts are opened more, the sample enters the "mixed valence" regime, where different charge states are strongly hybridized by electron tunneling. Here, the conductance as a function of gate voltage shows pronounced modulations with a period of four electrons, and all single-electron features are washed away at low temperature. We successfully describe this behavior by a simple formula with no fitting parameters. Finally, we find a surprisingly small energy scale that controls the temperature evolution of conductance and the tunneling density of states in the mixed valence regime.     

Hopping domain wall induced by paired adatoms on an atomic wire: si(111)-(5 x 2)-Au

We observed an inhomogeneous fluctuation along one-dimensional atomic wires self-assembled on a Si(111) surface using scanning tunneling microscopy. The fluctuation exhibits dynamic behavior at room temperature and is observed only in a specific geometric condition; the spacing between two neighboring adatom defects is discommensurate with the wire lattice. Upon cooling, the dynamic fluctuation freezes to show the existence of an atomic-scale dislocation or domain wall induced by such "unfavorably" paired adatoms. The microscopic characteristics of the dynamic fluctuation are explained in terms of a hopping solitonic domain wall, and a local potential for this motion imposed by the adatoms is quantified.     

Nonlinear quasiparticle tunneling between fractional quantum hall edges

Remarkable nonlinearities in the differential tunneling conductance between fractional quantum Hall edge states at a constriction are observed in the weak-backscattering regime. In the nu=1/3 state a peak develops as temperature is increased and its width is determined by the fractional charge. In the range 2/3相似文献   

Effect of nuclear quadrupole interactions on the dynamics of two-level systems in glasses

The standard tunneling model describes quite satisfactorily the properties of amorphous solids at temperatures T < 1K in terms of an ensemble of two-level systems including the logarithmic temperature dependence of the dielectric constant. Yet, experiments have shown that at ultralow temperatures T< 5 mK such a temperature behavior breaks down and the dielectric constant becomes temperature independent (plateau effect). In this Letter we suggest an explanation of this behavior exploiting the effect of the nuclear quadrupole interaction on tunneling. We also predict that the application of a sufficiently large magnetic field B> 10T should restore the logarithmic dependence because of the suppression of the nuclear quadrupole interaction.     

Particles’ Tunneling in Spherically Symmetric Spacetimes with Dark Matter

Applying the Hamilton-Jacobi method, we investigate particles’ tunneling behavior in a spherically symmetric spacetime with dark matter. The tunneling rate and Hawking temperature at the event horizon are obtained. The result shows that the dark matter parameter β has an important influence on the Hawking temperature and the tunneling rate.     

Non-fermi-liquid behavior in quasi-one-dimensional Li0.9Mo6O17

We present temperature dependent scanning tunneling spectroscopy data of the quasi-one-dimensional conductor Li0.9Mo6O17. The differential tunneling current in our low-temperature spectra shows a power-law behavior around the Fermi energy, which is expected for a clean Luttinger liquid. The power-law exponent is found to be 0.6. Spectra for a temperature range of 5 to 55 K can be fitted fairly well with a model for tunneling into a Luttinger liquid at the appropriate temperature. A fit with a model based on a zero bias anomaly is significantly worse compared to the Luttinger liquid model. No signature of a phase transition at T = 24 K is observed in our temperature dependent data.     

Transient tunneling spectroscopy (TTS) study of electron tunneling from phosphorus atoms in silicon

Recently developed method of transient tunneling spectroscopy (TTS) is applied to investigate the tunneling dynamics of electrons from phosphorus atoms to the silicon conduction band. In contrast to the conventional constant-current spectroscopic tunneling techniques, in TTS one monitors the evolution of the tunneling process in time. Various difficulties, which may be encountered in the measurements of the tunneling time by TTS, are discussed and illustrated. The temperature dependence of the tunneling time for an isolated phosphorus atom is presented, and possible mechanisms responsible for the decrease of the tunneling time with the lattice temperature T, at T15 K, are discussed.     

Analytical result of the effect of spin scattering and impurity-assistance on magnetoresistance in doped magnetic tunneling junctions

An extended tunneling Hamiltonian method is proposed to study the temperature-dependent tunneling magnetoresistance (TMR) in doped magnetic tunnel junctions. It is found that for nonmagnetic dopants (Si), impurity-assisted tunneling is mainly elastic, giving rise to a weak spin polarization, thereby reduces the overall TMR, while for magnetic ions (Ni), the collective excitation of local spins in δ-doped magnetic layer contributes to the severe drop of TMR and the behavior of the variation of TMR with temperature different from that for Si-doping. The theoretical results can reproduce the main characteristic features of experiments. Received 13 January 2002 / Received in final form 30 November 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: yctao12@163.com     

Transport anomalies and marginal-fermi-liquid effects at a quantum critical point

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependencies that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.     

Scanning tunneling spectroscopy of charge effects on semiconductor surfaces and atomic clusters

We have used scanning tunneling microscopy and scanning tunneling spectroscopy at liquid helium temperature to study the electronic structure of in situ cleaved, (110) oriented surfaces of InAs single crystals. Both unperturbed, atomically flat areas and areas with an atomic-size defect cluster have been investigated. We show that the anomalous behavior of the local tunneling conductivity, which indicates a pronounced enhancement of the semiconductor band gap for the flat areas, is consistent with band bending induced by charges localized at the apex of the tip. Atomic-size defect clusters contain additional charges which modify the band bending; this explains the different behavior of the tunneling conductivity near the defect cluster. The experimentally observed oscillations of the tunneling conductivity near the band gap edges can be directly related to resonant tunneling through quantized surface states which appear because of the band bending. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 130–135 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

含红外发散的低温玻璃超声吸收理论

本文采用红外发散理论和二能级体系模型,讨论玻璃超声吸收在2K温度以下的行为,与现有的隧道二能级模型不同,我们把Bloch方程看作“磁化强度”所满足的宏观方程,方程中所有的物理量都是系综平均值。并且把缺陷态看作处在局域涨落场中的赝自旋,提出了在低温下赝自旋角扩散与温度的关系。我们不但得到与实验符合较好的理论吸收曲线,并且解释了弱照射共振吸收正比于T^-0.7和饱和吸收正比于ω²的实验规律。 关键词：     

Double point contact in quantum Hall line junctions

We show that multiple point contacts on a barrier separating two laterally coupled quantum Hall fluids induce Aharonov-Bohm (AB) oscillations in the tunneling conductance. These quantum coherence effects provide new evidence for the Luttinger liquid behavior of the edge states of quantum Hall fluids. For a two point contact, we identify coherent and incoherent regimes determined by the relative magnitude of their separation and the temperature. We analyze both regimes in the strong and weak tunneling amplitude limits as well as their temperature dependence. We find that the tunneling conductance should exhibit AB oscillations in the coherent regime, both at strong and weak tunneling amplitudes with the same period but with different functional form.     

Field-induced structural aging in glasses at ultralow temperatures

In nonequilibrium experiments on the glasses Mylar and BK7, we measured the excess dielectric response after the temporary application of a strong electric bias field at millikelvin temperatures. A model recently developed describes the observed long time decays qualitatively for Mylar [Phys. Rev. Lett. 90, 105501(2003)]], but fails for BK7. In contrast, our results on both samples can be described by including an additional mechanism to the mentioned model with temperature independent decay times of the excess dielectric response. As the origin of this novel process beyond the "tunneling model" we suggest bias field induced structural rearrangements of "tunneling states" that decay by quantum mechanical tunneling.     

多晶La0.7Sr0.3MnO3的低温输运性质和磁电阻效应

详细研究了由纳米晶粒组成的块体多晶La_0.7Sr_0.3MnO₃(LSM)的电阻率和磁电阻效应,以及它们的温度依赖性.随着温度从室温降低,电阻率(ρ)在250K附近存在一最大值,低于该温度后,样品表现为金属导电特性,随后在50K附近存在一极小值.也就是说在低于50K的温度范围内,随着温度降低ρ反而升高,表现为绝缘体性的导电特性.经研究发现,这种随温度降低ρ反而增加的现象与隧穿效应的理论模型(lnρ∝T^-1/2)符合得很好 关键词： 0.7Sr_0.3MnO₃')" href="#">多晶La_0.7Sr_0.3MnO₃ 隧道效应 隧道磁电阻效应     

Simulation of resonant tunneling devices: origin of the I–V multi-peak behavior

Multi-peak behavior of the $I$ – $V$ curves of an AlAs/GaAs/AlAs double-barrier resonant tunneling diode combined with a layer of InAs quantum dots (QDs) is simulated. Our simulation results show that the coupling between the energy level in the emitter quantum well (quantum dot) layer and that in the central quantum well is the key point in understanding the origin of the $I$ – $V$ multi-peak behavior. The embedded designed QD layer at the emitter spacer can enhance this effect. The effects of device temperature on the $I$ – $V$ characteristics are also obtained. Our results provide the physical basis for understanding and utilizing the multi-peak behavior of $I$ – $V$ curves in designing resonant tunneling devices.     

Fermions tunneling from rotating stationary Kerr black hole with electric charge and magnetic charge

In this paper, the method of semi-classical fermion tunneling is extended to explore the fermion tunneling behavior of a Kerr–Newman–Kasuya black hole. Thus, the Hamilton–Jacobi equation in Kerr–Newman–Kasuya space–time is derived by the method presented in Refs. Lin and Yang (2009) [24], [25], [26], the Hawking temperature at the horizon and the tunneling probability of spin- 1/2 fermions are finally obtained following the semi-classical quantum equation. The results indicate the common features of this black hole.     

Relevance of multiple quasiparticle tunneling between edge states at nu=p/(2np+1)

We present an explanation for the anomalous behavior in tunneling conductance and noise through a point contact between edge states in the Jain series nu=p/(2np+1), for extremely weak backscattering and low temperatures [Y. C. Chung, M. Heiblum, and V. Umansky, Phys. Rev. Lett. 91, 216804 (2003)10.1103/PhysRevLett.91.216804]. We consider edge states with neutral modes propagating at finite velocity, and we show that the activation of their dynamics causes the unexpected change in the temperature power law of the conductance. Even more importantly, we demonstrate that multiple-quasiparticle tunneling at low energies becomes the most relevant process. This result will be used to explain the experimental data on current noise where tunneling particles have a charge that can reach p times the single-quasiparticle charge. In this Letter, we analyze the conductance and the shot noise to substantiate quantitatively the proposed scenario.     

温度和电子有效质量对隧穿磁致电阻偏压依赖关系的影响

本文研究温度和势垒中的电子有效质量对铁磁隧道结中隧穿磁致电阻(TMR)的偏压依赖和变号行为的影响。所求得的TMR随温度上升明显减小的结果与实验一致。除了前文中指出的势垒高度(Ф)以外, 还发现垒中电子的有效质量(mB)是物理上控制TMR变号的另一个重要因素。相应于TMR变号的临界电压(VC)将随Ф升高而增大, 但随mB增大而减小。此外, 零偏压的TMR和临界电压VC将因温度升高而减小。作者希望上述理论结果将有助于实验研究。     

Elastic properties of several amorphous solids and disordered crystals below 100 K

We have measured the internal friction and speed of sound variation at temperatures between 60 mK and room temperature for amorphous CdGeAs₂, Polystyrene, and Stycast 2850FT epoxy, and the disordered crystals (ZrO₂)_0.89(CaO)_0.11 and (CaF₂)_0.74(LaF₃)_0.26. A comparison of our results with an extensive review of previously published data shows a remarkable similarity in the internal friction of disordered solids below ～5 K. The low temperature elastic behavior of these solids is adequately described by the standard tunneling model, from which one finds a nearly universal density of tunneling states for glasses. Internal friction above ～10 K for different materials, however, displays a wide range of magnitudes and temperature dependence that is far from universal. Attempts to directly link the tunneling states observed by internal friction at low temperatures to configurational states of localized oscillators existing at high temperatures must take into account this striking variation among disordered solids above 10 K.