1,930 research outputs found
Topological states and quantized current in helical molecules
We report a theoretical study of electron transport along helical molecules
under an external electric field, which is perpendicular to the helix axis of
the molecule. Our results reveal that the topological states could appear in
single-helical molecule and double-stranded DNA in the presence of the
perpendicular electric field. And these topological states guarantee adiabatic
charge pumping across the helical molecules by rotating the electric field in
the transverse plane and the pumped current at zero bias voltage is quantized.
In addition, the quantized current constitutes multiple plateaus by scanning
the Fermi energy as well as the bias voltage, and hold for various model
parameters, since they are topologically protected against perturbations. These
results could motivate further experimental and theoretical studies in the
electron transport through helical molecules, and pave the way to detect
topological states and quantized current in the biological systems.Comment: 5 pages, 5 figure
Optimization Of Growth Conditions And Characterization Of Properties On Christensenella Minuta
Currently, increasing numbers of people are suffering from obesity. The gut microbiome becomes a useful approach to control the mechanisms associated with obesity. A novel bacterium, Christensenella minuta, which was discovered in 2012, triggers body weight loss. Our purpose in this study is to further realize characteristics of C. Minuta as a potential probiotic supplement for future obesity studies. This study determines the following characteristics of C. Minuta: DNA identification, turbidity verification, generation time, as well as optimization of pH and temperature. To test the tolerance of C. Minuta as a gastrointestinal treatment, the pH and bile salts concentration in the gastrointestinal tract were mimicked. In this study, the Hungate tube method was involved for anaerobic culture; turbidity absorbance was used to detect bacterial growth; plate-counting method was applied to measure CFU (colony-forming unit). From our findings, the optimal conditions of C. Minuta were found at 37 ºC under pH 7. The generation time of C. Minuta was found to be around 70 min. C. Minuta is sensitive to pH and bile salt, with survivability found at 0.1g/L bile salts and pH 5. In conclusion, encapsulation or another protection is needed when consuming C. Minuta in future animal or human studies
Spin-Selective Transport of Electron in DNA Double Helix
The experiment that the high spin selectivity and the length-dependent spin
polarization are observed in double-stranded DNA [Science , 894
(2011)], is elucidated by considering the combination of the spin-orbit
coupling, the environment-induced dephasing, and the helical symmetry. We show
that the spin polarization in double-stranded DNA is significant even in the
case of weak spin-orbit coupling, while no spin polarization appears in
single-stranded DNA. Furthermore, the underlying physical mechanism and the
parameters-dependence of the spin polarization are studied.Comment: 5 pages; 4 figure
Effect of gate voltage on spin transport along -helical protein
Recently, the chiral-induced spin selectivity in molecular systems has
attracted extensive interest among the scientific communities. Here, we
investigate the effect of the gate voltage on spin-selective electron transport
through the -helical peptide/protein molecule contacted by two
nonmagnetic electrodes. Based on an effective model Hamiltonian and the
Landauer-B\"uttiker formula, we calculate the conductance and the spin
polarization under an external electric field which is perpendicular to the
helix axis of the -helical peptide/protein molecule. Our results
indicate that both the magnitude and the direction of the gate field have a
significant effect on the conductance and the spin polarization. The spin
filtration efficiency can be improved by properly tuning the gate voltage,
especially in the case of strong dephasing regime. And the spin polarization
increases monotonically with the molecular length without the gate voltage,
which is consistent with the recent experiment, and presents oscillating
behavior in the presence of the gate voltage. In addition, the spin selectivity
is robust against the dephasing, the on-site energy disorder, and the space
angle disorder under the gate voltage. Our results could motivate further
experimental and theoretical works on the chiral-based spin selectivity in
molecular systems.Comment: 8 pages, 7 figure
Orbital Kondo effect in a parallel double quantum dot
We construct a theoretical model to study the orbital Kondo effect in a
parallel double quantum dot (DQD). Recently, pseudospin-resolved transport
spectroscopy of the orbital Kondo effect in a DQD has been experimentally
reported. The experiment revealed that when interdot tunneling is ignored,
there exist two and one Kondo peaks in the conductance-bias curve for the
pseudospin-non-resolved and pseudospin-resolved cases, respectively. Our
theoretical studies reproduce this experimental result. We also investigate the
situation of all lead voltages being non-equal (the complete
pseudospin-resolved case), and find that there are four Kondo peaks at most in
the curve of the conductance versus the pseudospin splitting energy. When the
interdot tunneling is introduced, some new Kondo peaks and dips can emerge.
Besides, the pseudospin transport and the pseudospin flipping current are also
studied in the DQD system. Since the pseudospin transport is much easier to be
controlled and measured than the real spin transport, it can be used to study
the physical phenomenon related to the spin transport.Comment: 18 pages, 7 figures, accepted by J. Phys.: Condens. Matter in
September 201
Delocalization and scaling properties of low-dimensional quasiperiodic systems
In this paper, we explore the localization transition and the scaling
properties of both quasi-one-dimensional and two-dimensional quasiperiodic
systems, which are constituted from coupling several Aubry-Andr\'{e} (AA)
chains along the transverse direction, in the presence of next-nearest-neighbor
(NNN) hopping. The localization length, two-terminal conductance, and
participation ratio are calculated within the tight-binding Hamiltonian. Our
results reveal that a metal-insulator transition could be driven in these
systems not only by changing the NNN hopping integral but also by the
dimensionality effects. These results are general and hold by coupling distinct
AA chains with various model parameters. Furthermore, we show from finite-size
scaling that the transport properties of the two-dimensional quasiperiodic
system can be described by a single parameter and the scaling function can
reach the value 1, contrary to the scaling theory of localization of disordered
systems. The underlying physical mechanism is discussed.Comment: 9 pages, 8 figure
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