Conductance, valley and spin polarizations, and tunneling magnetoresistance in ferromagnetic-normal-ferromagnetic junctions of silicene

Abstract

We investigate charge conductance and spin and valley polarization along with the tunnelling magneto-resistance (TMR) in silicene junctions composed of normal silicene and ferromagnetic silicene. We show distinct features of the conductances for parallel and anti-parallel spin configurations and the TMR, as the ferromagnetic−normal−ferromagnetic (FNF) junction is tuned by an external electric field. We analyse the behavior of the charge conductance and valley and spin polarizations in terms of the independent conductances of the different spins at the two valleys and the band structure of ferromagnetic silicene and show how the conductances are affected by the vanishing of the propagating states at one or the other valley. In particular, unlike in graphene, the band structure at the two valleys are independently affected by the spin in the ferromagnetic regions and lead to non-zero, and in certain parameter regimes, pure valley and spin polarizations, which can be tuned by the external electric field. We also investigate the oscillatory behavior of the TMR with respect to the strength of the barrier potential (both spin-independent and spin-dependent barriers) in the normal silicene region and note that in some parameter regimes, the TMR can even go from positive to negative values, as a function of the external electric field.

Piezotronic spin and valley transistors based on monolayer MoS2

“…Owing to size effect, electronic transport properties depend on the strip length and width [44,45]. According to typical normal-ferromagnetic-normal structure [46], we assume that the strip width is 40 nm and the length is 140 nm while the width of the ferromagnetic region is 20 nm. In this size, the piezoelectric potential is same order of magnitude with the energy intervals between subbands.…”

Valley–spin Seebeck effect in heavy group-IV monolayers

“…A ferromagnetic field with strength M is uniformly applied in the whole sample. From previous first-principles calculations, it is known that the low-energy electrons in heavy group-IV monolayers can be described by an effective Hamiltonian which reads [20][21][22][23], where λ (3.9 meV for silicene, 43 meV for germanene, 100 meV for stanene) represents the spin-orbit coupling, h = + -…”

“…To control the valley and spin in 2D Dirac materials, people usually adopt electric and optical methods to obtain valley-polarized or spin-polarized detectable effects [20][21][22][23][24][25][26][27][28], whereas only limited work has utilized the temperature difference to understand the valley Seebeck effect [29,30] or spin Seebeck effect [31][32][33][34], which can explore the possibility of directly converting heat into electrical power. Phenomenologically, the valley (spin) Seebeck effect indicates currents from two different valleys (spins) flowing in opposite directions.…”

Thermal conductance by Dirac fermions in a normal-insulator-superconductor junction of silicene

“…This two-dimensional (2D) material has been grown experimentally by successful deposition of silicene sheet on silver substrate [9][10][11] . Also the interest in silicene soared due to the possibility of its various future applications ranging from spintronics [13][14][15][16][17] , valleytronics [18][19][20][21][22] to silicon based transistor 23 at room temperature. Very recently, it has been reported that low energy excitations in silicene follows relativistic Dirac equation akin to graphene 7,24 .…”