Publications in 2009

1. Vidar Gudmundsson, Cosmin Gainar, Chi-Shung Tang, Valeriu Moldoveanu and Andrei Manolescu.
Time-dependent transport via the generalized master equation through a finite quantum wire with an embedded subsystem.
New Journal of Physics 11, 113007 (2009).
Abstract In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system.
URL arXiv BibTeX

@article{1367-2630-11-11-113007,
author = "Vidar Gudmundsson and Cosmin Gainar and Chi-Shung Tang and Valeriu Moldoveanu and Andrei Manolescu",
title = "Time-dependent transport via the generalized master equation through a finite quantum wire with an embedded subsystem",
journal = "New Journal of Physics",
volume = 11,
number = 11,
pages = 113007,
url = "http://stacks.iop.org/1367-2630/11/i=11/a=113007",
year = 2009,
arxiv = "http://arxiv.org/abs/0903.3491",
abstract = "In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system."
}

2. Valeriu Moldoveanu, Andrei Manolescu and Vidar Gudmundsson.
Theoretical investigation of modulated currents in open nanostructures.
Phys. Rev. B 80, 205325 (November 2009).
Abstract We investigate theoretically the transport properties of a mesoscopic system driven by a sequence of rectangular pulses applied at the contact to the input (left) lead. The characteristics of the current which would be measured in the output (right) lead are discussed in relation with the spectral properties of the sample. The time-dependent currents are calculated via a generalized non-Markovian master equation scheme. We study the transient response of a quantum dot and of a narrow quantum wire. We show that the output response depends not only on the lead-sample coupling and on the length of the pulse but also on the states that propagate the input signal. We find that by increasing the bias window the new states available for transport induce additional structure in the relaxation current due to different dynamical tunneling processes. The delay of the output signal with respect to the input current in the case of the narrow quantum wire is associated to the transient time through the wire.
URL PDF, DOI BibTeX

@article{PhysRevB.80.205325,
title = "Theoretical investigation of modulated currents in open nanostructures",
author = "Moldoveanu, Valeriu and Manolescu, Andrei and Gudmundsson, Vidar",
journal = "Phys. Rev. B",
volume = 80,
issue = 20,
pages = 205325,
numpages = 10,
year = 2009,
month = "Nov",
doi = "10.1103/PhysRevB.80.205325",
publisher = "American Physical Society",
abstract = "We investigate theoretically the transport properties of a mesoscopic system driven by a sequence of rectangular pulses applied at the contact to the input (left) lead. The characteristics of the current which would be measured in the output (right) lead are discussed in relation with the spectral properties of the sample. The time-dependent currents are calculated via a generalized non-Markovian master equation scheme. We study the transient response of a quantum dot and of a narrow quantum wire. We show that the output response depends not only on the lead-sample coupling and on the length of the pulse but also on the states that propagate the input signal. We find that by increasing the bias window the new states available for transport induce additional structure in the relaxation current due to different dynamical tunneling processes. The delay of the output signal with respect to the input current in the case of the narrow quantum wire is associated to the transient time through the wire.",
pdf = "http://electronicsandbooks.com/eab1/manual/Magazine/P/Physical%20Review%20B/2009%20Volume%2080/20/PhysRevB.80.205325.pdf"
}

3. Valeriu Moldoveanu, Andrei Manolescu and Vidar Gudmundsson.
Geometrical effects and signal delay in time-dependent transport at the nanoscale.
New Journal of Physics 11, 073019 (2009).
Abstract Nonstationary and steady-state transport through a mesoscopic sample connected to particle reservoirs via time-dependent barriers is investigated by the reduced density operator method. The generalized master equation is solved via the Crank–Nicolson algorithm by taking into account the memory kernel which embodies the non-Markovian effects that are commonly disregarded. The lead–sample coupling takes into account the match between the energy of the incident electrons and the levels of the isolated sample, as well as their overlap at the contacts. Using a tight-binding description of the system, we investigate the effects induced in the transient current by the spectral structure of the sample and by the localization properties of its eigenfunctions. In strong magnetic fields, the transient currents propagate along edge states. The behavior of populations and coherences is discussed, as well as their connection to the tunneling processes that are relevant for transport.
URL arXiv BibTeX

@article{1367-2630-11-7-073019,
author = "Valeriu Moldoveanu and Andrei Manolescu and Vidar Gudmundsson",
title = "Geometrical effects and signal delay in time-dependent transport at the nanoscale",
journal = "New Journal of Physics",
volume = 11,
number = 7,
pages = 073019,
url = "http://stacks.iop.org/1367-2630/11/i=7/a=073019",
year = 2009,
arxiv = "http://arxiv.org/abs/0807.4015",
abstract = "Nonstationary and steady-state transport through a mesoscopic sample connected to particle reservoirs via time-dependent barriers is investigated by the reduced density operator method. The generalized master equation is solved via the Crank–Nicolson algorithm by taking into account the memory kernel which embodies the non-Markovian effects that are commonly disregarded. The lead–sample coupling takes into account the match between the energy of the incident electrons and the levels of the isolated sample, as well as their overlap at the contacts. Using a tight-binding description of the system, we investigate the effects induced in the transient current by the spectral structure of the sample and by the localization properties of its eigenfunctions. In strong magnetic fields, the transient currents propagate along edge states. The behavior of populations and coherences is discussed, as well as their connection to the tunneling processes that are relevant for transport."
}