Resonant Spectrum Analysis of the Conductance of Open Quantum System and Three Types of Fano Parameter
Keita Sasada, Naomichi Hatano, Gonzalo Ordonez
备注：
29 pages, 22 figures, considerably expanded from the first version, this time with corrections of references. To be published in J. Phys. Soc. Jpn. No. 10 (2011)
We explain the Fano peak (an asymmetric resonance peak) as an interference effect involving resonant states. We reveal that there are three types of Fano asymmetry according to their origins: the interference between a resonant state and an anti-resonant state, that between a resonant state and a bound state, and that between two resonant states. We show that the last two show the asymmetric energy dependence given by Fano, but the first one shows a slightly different form. In order to show the above, we analytically and microscopically derive a formula where we express the conductance purely in terms of the summation over all discrete eigenstates including resonant states and anti-resonant states, without any background integrals. We thereby obtain microscopic expressions of the Fano parameters that describe the three types of the Fano asymmetry. One of the expressions indicate that the corresponding Fano parameter becomes complex under an external magnetic field.
We describe the Fano asymmetry by expanding the transmission amplitude with respect to states with point spectra (discrete eigenstates), including not only bound states but also resonant states with complex eigenvalues. We first introduce a novel complete set that spans the Hilbert space of the central part of an open quantum-dot system. This complete set contains all states of point spectra, but does not contain any states of continuous spectra. We thereby analytically expand the conductance of the dot in terms of all discrete states without any background integrals. This expansion implies th…
Atomic clusters attached to a low-dimensional system, called Fano defects, produce rich wave interferences. In this work, we analytically found an enhanced thermoelectric figure-of-merit (ZT) in periodic atomic chains with Fano defects, compared to those without such defects. We further study self-assembled DNA-like systems with periodic and quasiperiodically placed Fano defects by using a real-space renormalization method developed for the Kubo-Greenwood formula, in which tight-binding and Born models are respectively used for the electric and lattice thermal conductivities. The results revea…
We investigate the Andreev reflection in the parallel double-quantum-dot structure, by considering one metallic lead and one $s$-wave superconductor to couple to the quantum dots simultaneously. It is found that the Fano lineshhape has opportunities to appear in the linear conductance spectrum of the Andreev reflection, which can be reversed by tuning the dot level or local magnetic flux. However, the property of the Fano effect is very complicated, in comparison with the normal electron tunnelling case. This is manifested as the special Fano form of the linear-conductance expression and the i…
In this paper, we investigate transient quantum transport in a nanoscale Aharonov-Bohm (AB) interferometer consisting of a laterally coupled double quantum dot (DQD) coupled to the source and drain electrodes. The transient linear conductance is derived at finite temperature of the leads, and is divided into three terms contributed from different transport channels. By observing the transient linear conductance and time evolution of the elements of the reduced density matrix of the DQD system, we show the nature of how Fano resonance is built up in the time domain.
Using Chebyshev polynomials, we study the electronic transport properties of massless Dirac fermions in symmetrical graphene superlattice composed of three regions. Matching wavefunctions and using transfer matrix method, we explicitly determine transmission probability as well as the conductance and Fano factor. At vertical Dirac points, we numerically find that the transmission probability shows transmission gaps, conductance has minimums and Fano factor has maximums.
Tuning Fano-type resonances in coupled quantum point contacts by applying asymmetric voltages
我们研究了双量子点接触（QPC）器件中的弹道磁输运，该器件由具有嵌入的岛状杂质蚀刻纳米孔的准一维量子线组成，如最近发表的实验[J. C. Chen，Y. Lin，K.- T. Lin，T. Ueda和S. Komiyama，Appl. Phys. Lett. 94，012105（2009）]。我们再现了零场量子化电导，耦合QPC引起的干涉现象，以及在实验中观察到的Ramsauer共振。在有限的磁场中，由于在杂质外围形成局域态和边缘间态共振耦合效应，电导中出现Fano型共振。据预测，Fano型共振可以通过QPC的非对称约束来控制。
We report a dual resonance feature in ballistic conductance through a quantum Hall graphene nanoribbon with a magnetic quantum dot. Such a magnetic quantum dot localizes Dirac fermions exhibiting anisotropic eigenenergy spectra with broken time-reversal symmetry. Interplay between the localized states and quantum Hall edge states is found to be two-fold, showing Breit-Wigner and Fano resonances, which is reminiscent of a double quantum dot system. By fitting the numerical results with the Fano-Breit-Wigner lineshape from the double quantum dot model, we demonstrate that the two-fold resonance …
We study the spin-resolved transport properties of T-shaped double quantum dots coupled to ferromagnetic leads. Using the numerical renormalization group method, we calculate the linear conductance and the spin polarization of the current for various model parameters and at different temperatures. We show that an effective exchange field due to the presence of ferromagnets results in different conditions for Fano destructive interference in each spin channel. This spin dependence of the Fano effect leads to perfect spin polarization, the sign of which can be changed by tuning the dots' levels.…
Resonant-impurity scanning tunneling spectroscopy in altermagnets: dual Fano resonance and Landau-quantization-induced nodal spin contrast
National Key Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics（计算物理国家重点实验室，应用物理与计算数学研究所）；Graduate School, China Academy of Engineering Physics（中国工程物理研究院研究生院）；School of Electronic and Information Engineering, Zhongshan Institute, University of Electronic Science and Technology of China（电子科技大学中山学院电子与信息工程学院）；School of Physics and Physical Engineering, Qufu Normal University（曲阜师范大学物理与光电工程学院）
Double barrier GaN/AlN resonant tunneling heterostructures have been grown by molecular beam epitaxy on the (0001) plane of commercially available bulk GaN substrates. Resonant tunneling diodes were fabricated; room temperature current-voltage measurements reveal the presence of a negative differential conductance region under forward bias with peak current densities of ~6.4 $kA/cm^2$ and a peak to valley current ratio of ~1.3. Reverse bias operation presents a characteristic turn-on threshold voltage intimately linked to the polarization fields present in the heterostructure. An analytic elec…
