Lack of quenching for the resonant transmission through an inhomogeneously oscillating quantum well

The spectral weights of the wave-function sidebands for a quantum well in the presence of an inhomogeneous electromagnetic (EM) field are studied by introducing a wave function with the form of a Floquet state and then solving the time-dependent Schrödinger equation approximately. The two cases of radiation direction of the EM field parallel and perpendicular to the well axis are considered. We find that the inhomogeneity of the EM field may eliminate the sideband quenching. Based on the spectral weight, the transmission probability through the well is investigated. The energy-level splitting for a special case, the averaged vector potential equal to zero, is also studied.published_or_final_versio

Effect of magnetic field on electron transport in HgTe/CdTe quantum wells: numerical analysis

The effect of magnetic field on electron transport in the inverted band structure of HgTe/CdTe quantum well is investigated. Although magnetic field breaks the time-reversal symmetry, the quantum spin Hall effect can still survive at large magnetic field up to 10 T. Moreover, two quantum anomalous Hall-like phases emerge, in which the system only has a spin-up or spin-down edge state at a given sample edge and the edge current is spin polarized. By tuning the Fermi energy, the system can transit between the quantum spin Hall phase and two quantum anomalous Hall-like phases, so the polarized direction of the edge current is well controllable. Thus the spin selectivity can be realized for potential applications of spintronics. Due to the quantum spin and anomalous Hall-like effects, the longitudinal and Hall resistances exhibit quantum plateaus. In addition, at certain magnetic field, some exotic plateaus like 23 fractional quantum Hall effect are also observed, where edge states with the same spin counterpropagate at the one edge. At last, these plateaus are hardly affected by Rashba spin-orbit interaction, Zeeman effect, and Anderson disorder. © 2012 American Physical Society.published_or_final_versio

Theoretical study for a quantum-dot molecule irradiated by a microwave field

Motivated by the recent experiment by Oosterkamp et al. [Nature 395, 873 (1998)] we have developed a theory to describe electron tunneling through two coupled quantum dots irradiated by a microwave field. Our results for both the weak- and strong-coupling regimes are in excellent agreement with experiment. In addition, our theory suggests several unique features in the strong-coupling regime, including Rabi oscillations, which can be verified experimentally. The main resonance and the sideband resonance of the molecular level are also calculated for the entire range of the coupling strength, and show interesting crossover behavior.published_or_final_versio

Theory of excess noise of a quantum dot in the presence of a microwave field

The power spectrum of excess noise of a quantum dot coupled to two leads and irradiated by a microwave field of frequency Ω is derived exactly by directly solving the Heisenberg equation. We found that for Γ<ħΩ, where Γ is the linewidth of the intradot energy level, the power spectrum can be nonzero even if the averaged current is zero. This property originates from photon-assisted tunneling and is very different from the shot noise in steady state. For Γ≫ħΩ, our results are consistent with the recent experiment by Schoelkopf et al. and previous theory.published_or_final_versio

Electron transport through a mesoscopic hybrid multiterminal resonant-tunneling system

For a mesoscopic hybrid system which contains a normal central region coupled to multiple superconducting leads, a general expression of the current is derived by using nonequilibrium-Green-function method. This current formula can be used to describe the case with time-dependent external fields applied to any parts of the system, arbitrarily finite voltages, and any kinds of interactions in the central region. For a normal two-terminal interacting electron system, this expression reduces to the general time-dependent current formula previously obtained by Wingreen et al. [Phys. Rev. B 98, 8487 (1993)]. As an application, we use this current formula to study a special case of a noninteracting single-level central region coupled to two or three superconducting leads, respectively.published_or_final_versio

Spin-polarized transport through a quantum dot: Anderson model with on-site Coulomb repulsion

We report on a theoretical analysis of transport characteristics of a spin-valve system formed by a quantum dot connecting to two ferromagnetic electrodes whose magnetic moments are oriented at an angle θ with respect to each other. We pay special attention to the effects of a finite on-site Coulomb repulsion U. Using the Keldysh nonequilibrium Green’s functions we derived a formula for the current in general terms of bias, temperature, and the parameters θ,U. We have studied the local density of states and nonlinear conductance of this device in the Kondo regime at different polarization angle θ. Our results suggest that the Kondo peaks in the local density of states and in the conductance can be modulated by θ.published_or_final_versio

Regional difference of the start time of the recent warming in Eastern China: prompted by a 165-year temperature record deduced from tree rings in the Dabie Mountains

Tree-ring studies from tropical to subtropical regions are rarer than that from extratropical regions, which greatly limit our understanding of some critical climate change issues. Based on the tree-ring-width chronology of samples collected from the Dabie Mountains, we reconstructed the April-June mean temperature for this region with an explained variance of 46.8%. Five cold (1861-1869, 1889-1899, 1913-1920, 1936-1942 and 1952-1990) and three warm (1870-1888, 1922-1934 and 2000-2005) periods were identified in the reconstruction. The reconstruction not only agreed well with the instrumental records in and around the study area, but also showed good resemblance to previous temperature reconstructions from nearby regions, indicating its spatial and temporal representativeness of the temperature variation in the central part of eastern China. Although no secular warming trend was found, the warming trend since 1970 was unambiguous in the Dabie Mountains (0.064 A degrees C/year). Further temperature comparison indicated that the start time of the recent warming in eastern China was regional different. It delayed gradually from north to south, starting at least around 1940 AD in the north part, around 1970 AD in the central part and around 1980s in the south part. This work enriches the high-resolution temperature reconstructions in eastern China. We expect that climate warming in the future would promote the radial growth of alpine Pinus taiwanensis in the subtropical areas of China, therefore promote the carbon capture and carbon storage in the Pinus taiwanensis forest. It also helps to clarify the regional characteristic of recent warming in eastern China.</p

Effect of hypoxia-inducible factor 1-alpha (HIF-1α) on proliferation and apoptosis of adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma cells

To understand whether hypoxia-inducible factor 1-alpha (HIF-1α) could protect AtT-20 cells from hypoxia induced apoptosis, we investigated the effects of HIF-1α on proliferation and apoptosis of adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma cells (AtT-20 cells). AtT-20 cells were treated with various concentrations of CoCl2 to induce hypoxia. 3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide, a yellow tetrazole (MTT) was applied to detect the proliferation of these cells. Western blot assay and real time polymerase chain reaction (PCR) were used to determine the protein and mRNA expressions of HIF-1α, respectively. In addition, AtT-20 cells were transfected with siRNA targeting HIF-1α and treated with different concentrations of CoCl2. The transfection efficacy was assessed by real-time PCR and western blot assay. Apoptosis was measured by fluorescein isothiocyanate (FITC)-annexin V/ propidium iodide (PI) staining and TUNEL staining. The effect of CoCl2 on the proliferation of AtT-20 cells was in a concentration and time dependent manner. When the concentration of CoCl2 was ≤100 μM and/or duration of CoCl2 treatment was ≤48 h, CoCl2 triggered the proliferation of AtT-20 cells. Nevertheless, the apoptosis rate of cells transfected with HIF-1α-siRNA was markedly increased after CoCl2 treatment. These findings suggest that, HIF-1α can promote the proliferation of AtT-20 cells and exert anti-apoptotic effect under hypoxic condition.Key words: Hypoxia inducible factor–1α, cobalt chloride, apoptosis, pituitary adenom

The universal definition of spin current

The spin current, orbit angular momentum current and total angular momentum current in a tensor form have been universally defined according to the quantum electrodynamics. Their conservation quantities and the continuity equations have been discussed in different cases. Non-relativistic approximation forms are deduced in order to explain their physical meanings, and to analyze some experimental results. The spin current of helical edge states in HgTe/CdTe quantum wells is calculated to demonstrate the properties of the spin current of the two dimensional quantum spin-Hall system. A generalized spin-orbit coupling term in the semiconducting media is deduced based on the theory of the electrodynamics in the moving media. It is recommended to use the effective total angular momentum current instead of the pure spin current to describe the distribution of polarization and the transport properties in spintronics

Influence of magnetic disorders on quantum anomalous Hall effect in magnetic topological insulator films beyond the two-dimensional limit

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