15 research outputs found
Control of resonant frequency by currents in graphene: Effect of Dirac field on deflection
To construct Lagrangian based on plate theory and tight-binding model,
deflection-field coupling to Dirac fermions in graphene can be investigated. As
have been known, deflection-induced strain may cause an effect on the motion of
the electron, like a pseudo gauge field. In the present work, we will
investigate the effect of the Dirac field on the motion of the deflection-field
in graphene derived from Lagrangian density. Due to the interaction of the
deflection- and Dirac-fields, the current-induced surface-tension up to about
N/m in graphene membrane is predicted. This result may lead to controllable
resonant frequency by currents in graphene. The high resonant frequency is
found to be perfectly linearly controlled by both charge and valley currents.
Our work reveals the potential of graphene for application of
nano-electro-mechanical device and the physics of interaction of electron and
deflection-filed in graphene system is investigated.Comment: eq.(10) and references were corrected, some condition for eq.(11) and
(12) was added (accepted in Journal of applied physics
Possible strain-induced directional superconductivity in graphene
Applying large strain in zigzag direction, gapless graphene may turns into
gapped graphene at the critical strain. The energy gap between valence and
conduction bands is created above the critical deformation. We theoretically
predict that, using the Landauer formalism to study conductance in ballistic
limit, the strain dependence of ballistic conductance, related to
tight-binding-based carriers, evolves into a tremendously large conductance at
the critical strain, found only for the conductance of current along armchair
direction. This directional superconductance may lead graphene to resemble a
superconductor. The strain-induced energy gap plays the role of the
superconducting gap. This behavior is due to the fact that strain-induced
change of electronic properties leads to highly anisotropic fermions to cause
this tremendously large conductance.Comment: 7 pages; 4 figure
Semi-massless fermions tunneling through a gate barrier in graphene
In the case of the strongly deformed graphene, gapless graphene may turn to
gapped graphene at the critical deformation. We find that, like semi-massless
fermions, electrons in the deformed graphene, at the critical point, mimic the
dispersions of the massless fermions in one direction and the massive fermions
in the other. Our predicted dispersion formula is the generalization of the
previously predicted formula. The behavior of the particle-like semi-massless
fermions tunneling through a gate barrier is contrasted with that of the (pure)
massless fermions tunneling through a gate barrier in the original graphene.
This is due to the effect of the combination between the massless and the
massive particle dispersions at the critical deformation.Comment: 13 pages,3 figure
Specular Andreev reflection of asymmetric fermions in graphene under strain
This work investigates the effect of the uniaxial strain on the tunneling
conductance in a strained graphene superconductor where strain is applied in
the armchair direction. Based on the Tight-Binding model, applying strain in
the armchair direction gives rise to the asymmetric massless fermions as the
carriers. Their velocities depend on their directions controlled by strain.
Using the BTK theory, the conductances of strained graphene N/S junctions can
be determined. As a result, we find that the current flowing perpendicular to
the direction of strain depends linearly on strain, with the positive slope.
But the current flowing parallel to the direction of strain depends linearly on
strain, with the negative slope. This linear behavior is significant for
applications of superconductor-based nanomechanical electronic devices.Comment: 15 pages,4 figure
Electron with arbitrary pseudo spins in multilayer graphene
Using the low-energy effective Hamiltonian of the ABC-stacked multilayer
graphene, pseudo spin coupling to real orbital angular momentum of electron in
multilayer graphene is investigated. We show that electron wave function in
N-layer graphene mimics behavior of particle with spin of N/2. It is said that
for N greater than 1 the low-energy effective Hamiltonian for ABC-stacked
graphene is no longer used to describe pseudo spin 1/2-particle wave function.
The wave function of electron in multilayer graphene may behave like fermionic
(or bosonic) particle when N is odd (or even). This work proposes a theory of
graphene as a host material of electron with arbitrary pseudo spins, tunable by
changing number of graphene layers.Comment: 15 pages; 1 Figure; eq 5 was correcte
Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene
Spin-valley transport and magnetoresistance are investigated in
silicene-based N/TB/N/TB/N junction where N and TB are normal silicene and
topological barriers. The topological phase transitions in TB's are controlled
by electric, exchange fields and circularly polarized light. As a result, we
find that by applying electric and exchange fields, four groups of spin-valley
currents are perfectly filtered, directly induced by topological phase
transitions. Control of currents, carried by single, double and triple channels
of spin-valley electrons in silicene junction, may be achievable by adjusting
magnitudes of electric, exchange fields and circularly polarized light. We may
identify that the key factor behind the spin-valley current filtered at the
transition points may be due to zero and non-zero Chern numbers. Electrons that
are allowed to transport at the transition points must obey zero-Chern number
which is equivalent to zero mass and zero-Berry's curvature, while electrons
with non-zero Chern number are perfectly suppressed. Very large
magnetoresistance dips are found directly induced by topological phase
transition points. Our study also discusses the effect of spin-valley dependent
Hall conductivity at the transition points on ballistic transport and reveals
the potential of silicene as a topological material for spin-valleytronics.Comment: 25 pages, 6 Figure
Nearly pure spin-valley sideband tunneling in silicene: effect of interplay of time periodic potential barrier and spin-valley-dependent Dirac mass
We study massive Dirac fermion tunneling through time periodic potential in a
silicene-based N-TP-N junction, where Ns are normal silicene regions and TP is
the time periodic potential barrier. The fermions would absorb or emit photons
due to the presence of the Floquet sidebands created in the TP. The nearly
perfect spin-valley-sideband filtering is predicted. Applying only the exchange
field leads to just only the electron absorbing a single photon almost purely
allowed to tunnel through the junction for the large electric field. Reversing
direction of electric field can select spin of the allowed electron. In the
case of applying only off-resonant circularly polarized light, just only the
electron absorbing a single photon with spin up, is almost purely allowed to
tunnel through the junction. The valley is also selected by reversing direction
of the electric field. The controllable sideband channel may be applicable for
sideband-based spin-valleytronics.Comment: 18 pages,6 Figure
Gate control of lattice-pseudospin currents in graphene on WS2: Effect of sublattice symmetry breaking and spin-orbit interaction
Strong spin-orbit interaction (SOI) in graphene grown on tungsten disulfide
(WS2) has been recently observed, leading to energy gap opening by SOI. Energy
gap in graphene may also be induced by sublattice symmetry breaking (SSB) where
energy level in A-sublattice is not equal to that in B-sublattice. SSB-gap may
be produced by growing graphene on hexagonal boron nitride or silicon carbide.
In this work, we investigate transport property in a SOI/SSB/SOI gapped
graphene junction, focusing the effect of interplay of SOI and SSB. We find
that, lattice-pseudospin polarization (L-PSP) can be controlled perfectly from
+100% to -100% by gate voltage. This is due to the fact that in graphene grown
on WS2, the carriers carry lattice-pseudo spin degree of freedom "up and down".
The SSB-gapped graphene exhibits pseudo-ferromagnetism to play the role of
lattice-pseudospin filtering barrier. It is also found that the SOI and
SSB-gaps in graphene may be measured by characteristic of L-PSP in the
junction. The proposed controllable-lattice-pseudospin currents may be
applicable for graphene-based pseudospintronics.Comment: 17 pages, 4 figures, typos"SW2" were replaced by"WS2
Strain control of real-and lattice-spin currents in a silicene junction
We investigate real- and lattice-spin currents controlled by strain in a
silicene-based junction, where chemical potential, perpendicular electric field
and circularly polarized light are applied into the strained barrier. We find
that the junction yields strain filtering effect with perfect strain control of
real- (or lattice-) spin currents. (i) By applying electric field without
circularly polarized light we show that total current is carried by pure
lattice-spin up (or down) electrons tunable by strain. (ii) When circularly
polarized light is irradiated onto silicene sheet without applying electric
field, total current is carried by pure real-spin up (or down) electrons
tunable by strain. High conductance peaks associated with pure real-(or
lattice-) spin currents in case ii(or i) occur at specific magnitude of strain,
yielding strain filtering effect. Magnitudes of filtered strain due to pure
real- (or lattice-) spin currents may be tunable by varying chemical potential.
Sensitivity may be enhanced by increasing thickness of strained barrier.
Significantly, (iii) when both perpendicular electric field and circularly
polarized light are applied, the total current is carried by three species of
electron groups tunable by strain. This may lead to controllable numbers of
electron species to transport. This result shows that strain filtering effect
in a silicene-based junction is quite different from that in graphene junction.
Our work reveals potential of silicene as a nano-electro-mechanical device and
spin-valleytronic applications.Comment: 25 pages, 8 Figures, 1 table (accepted in physics letters A
Lattice-pseudospin and spin-valley polarizations in dual ferromagnetic-gated silicene junction
We study spin-valley and lattice-pseudo spin currents in a dual
ferromagnetic-gated silicene-based junction. Silicene has buckled atomic
structure which allows us to take sublattice-dependent ferromagnetism into
account in the investigation. One of the study results show that transmission
at the junctions exhibits anisotropic property only in anti-parallel cases.
Interestingly, the studied junctions can be switched from a pure spin-polarizer
to a pure valley-polarizer by reversing directions of exchange fields in the
parallel junctions. The perfect control of spin-valley currents can be done
only in the parallel cases and its resolution can be enhanced by increasing
gate potential between the ferromagnetic barriers. The asymmetric barriers of
anti-parallel junction is found to destroy both spin and valley filtering
effects and yield a novel result, pure sub-lattice pseudo-spin polarization.
The current in the anti-parallel junctions can be controlled to flow solely in
either A or B sub-lattice, saying that the controllable lattice current in
silicene is created in double ferromagnetic-gated junction. Our work reveals
the potential of dual ferromagnetic-gated silicene junction which may be
possible for applications in spin-valleytronics and lattice-pseudospintronics.Comment: 24 pages, 9 figure