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Kondo effect for electron transport through an artificial quantum dot 被引量:1
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作者 孙科伟 熊诗杰 《Chinese Physics B》 SCIE EI CAS CSCD 2006年第4期828-832,共5页
We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot... We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases, We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation. 展开更多
关键词 Kondo effect quantum dot numerical renormalization group
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Equilibrium dynamics of the sub-Ohmic spin-boson model under bias
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作者 郑大川 同宁华 《Chinese Physics B》 SCIE EI CAS CSCD 2017年第6期73-80,共8页
Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σz for the biased sub-Ohmic spin-boson model. The small-ω behavior C... Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σz for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω) ∝ ω~s is found to be universal and independent of the bias ε and the coupling strength α(except at the quantum critical point α = αc and ε = 0). Our NRG data also show C(ω) ∝ χ~2ω~s for a wide range of parameters, including the biased strong coupling regime(ε = 0 and α 〉 αc), supporting the general validity of the Shiba relation. Close to the quantum critical point αc,the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω0^*of the unbiased case. C(ω) is stable with respect to ε for ε《ε^*. For ε 》ε^*, it is suppressed by ε in the low frequency regime. We establish that ε^*∝(ω0^*)^1/θ holds for all sub-Ohmic regime 0≤s 〈 1, with θ = 2/(3s) for 0 〈 s≤1/2 and θ = 2/(1 + s) for 1/2 〈 s 〈 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α–ε plane. 展开更多
关键词 spin-boson model numerical renormalization group quantum phase transition dynamical correlation function
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Kosterlitz–Thouless transition, spectral property and magnetic moment for a two-dot structure with level difference
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作者 熊永臣 周望怀 +1 位作者 张俊 南楠 《Chinese Physics B》 SCIE EI CAS CSCD 2017年第6期378-383,共6页
By means of the numerical renormalization group method, we study the phase transition, the spectral property, and the temperature-dependent magnetic moment for a parallel double dot system with level difference, where... By means of the numerical renormalization group method, we study the phase transition, the spectral property, and the temperature-dependent magnetic moment for a parallel double dot system with level difference, where the dot energies are kept symmetric to the half-filled level. A Kosterlitz–Thouless(KT) transition between local spin triplet and singlet is found. In the triplet regime, the local spin is partially screened by the conduction leads and spin-1 Kondo effect is realized.While for the singlet, the Kondo peak is strongly suppressed and the magnetic moment decreases to 0 at a definite low temperature. We attribute this KT transition to the breaking of the reflection symmetry, resulting from the difference of the charge occupations of the two dots. To understand this KT transition and related critical phenomena, detailed scenarios are given in the transmission coefficient and the magnetic moment, and an effective Kondo model refers to the RayleighSchrdinger perturbation theory is used. 展开更多
关键词 double dot Structure Kosterlitz-Thouless transition numerical renormalization group strongly correlated effect
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Dynamical correlation functions of the quadratic coupling spin-Boson model
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作者 郑大川 同宁华 《Chinese Physics B》 SCIE EI CAS CSCD 2017年第6期81-86,共6页
The spin-boson model with quadratic coupling is studied using the bosonic numerical renormalization group method.We focus on the dynamical auto-correlation functions CO(ω), with the operator taken as σx, σz, and ... The spin-boson model with quadratic coupling is studied using the bosonic numerical renormalization group method.We focus on the dynamical auto-correlation functions CO(ω), with the operator taken as σx, σz, and X, respectively. In the weak-coupling regime α 〈 αc, these functions show power law ω-dependence in the small frequency limit, with the powers 1 + 2s, 1 + 2s, and s, respectively. At the critical point α = αc of the boson-unstable quantum phase transition, the critical exponents yO of these correlation functions are obtained as yσx= yσz= 1-2s and yX=-s, respectively. Here s is the bath index and X is the boson displacement operator. Close to the spin flip point, the high frequency peak of Cσx(ω) is broadened significantly and the line shape changes qualitatively, showing enhanced dephasing at the spin flip point. 展开更多
关键词 quadratic-coupling spin-boson model numerical renormalization group quantum phase transition dynamical correlation function
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Probing satellite galaxies in the Local Group by using FAST
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作者 Jing Li You-Gang Wang +3 位作者 Min-Zhi Kong Jie Wang Xuelei Chen Rui Guo 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2018年第1期21-30,共10页
The abundance of neutral hydrogen(HI)in satellite galaxies in the local group is important for studying the formation history of our local group.In this work,we generated mock HI satellite galaxies in the Local Grou... The abundance of neutral hydrogen(HI)in satellite galaxies in the local group is important for studying the formation history of our local group.In this work,we generated mock HI satellite galaxies in the Local Group using the high mass-resolution hydrodynamic APOSTLE simulation.The simulated HI mass function agrees with the ALFALFA survey very well above 10~6M_⊙,although there is a discrepancy below this scale because of the observed flux limit.After carefully checking various systematic elements in the observations,including fitting of line width,sky coverage,integration time and frequency drift due to uncertainty in a galaxy’s distance,we predicted the abundance of HI in galaxies in a future survey that will be conducted by FAST.FAST has a larger aperture and higher sensitivity than the Arecibo telescope.We found that the HI mass function could be estimated well around 10~5M_⊙ if the integration time is 40 minutes.Our results indicate that there are 61 HI satellites in the Local Group and 36 in the FAST field above 10~5M_⊙.This estimation is one order of magnitude better than the current data,and will put a strong constraint on the formation history of the Local Group.Also more high resolution simulated samples are needed to achieve this target. 展开更多
关键词 galaxies:Local Group galaxies:mass function methods:numerical
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Simulation of the spin-boson model with superconducting phase qubit coupled to a transmission line 被引量:6
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作者 YU LongBao TONG NingHua +2 位作者 XUE ZhengYuan WANG ZiDan ZHU ShiLiang 《Science China(Physics,Mechanics & Astronomy)》 SCIE EI CAS 2012年第9期1557-1561,共5页
Based on the rapid experimental developments of circuit QED,we propose a feasible scheme to simulate the spin-boson model with superconducting circuits,which can be used to detect quantum Kosterlitz-Thouless(KT) phase... Based on the rapid experimental developments of circuit QED,we propose a feasible scheme to simulate the spin-boson model with superconducting circuits,which can be used to detect quantum Kosterlitz-Thouless(KT) phase transition.We design the spinboson model by using a superconducting phase qubit coupled to a semi-infinite transmission line,which is regarded as a bosonic reservoir with a continuum spectrum.By tuning the bias current or the coupling capacitance,the quantum KT transition can be directly detected through tomography measurement on the states of the phase qubit.We also estimate the experimental parameters using the numerical renormalization group method. 展开更多
关键词 spin-boson model superconducting qubit quantum phase transition numerical renormalization group method
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