Giant room-temperature spin caloritronics in spin-semiconducting graphene nanoribbons

Chen, Xiaobin; Liu, Yizhou; Gu, Bing; Duan, Wenhui; Liu, Feng

doi:10.1103/physrevb.90.121403

Cited by 88 publications

(93 citation statements)

References 33 publications

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“…In addition, it also has an extremely high thermal conductivity. 23 We also note that Z S T is very small at the Fermi level, which stems from an extremely low spin conductance. These facts indicate that graphene is not a good candidate for thermoelectric device applications.…”

Section: Introductionmentioning

confidence: 73%

Giant spin thermoelectric effects in all-carbon nanojunctions

Yang

Wang

Chen

et al. 2015

Phys. Chem. Chem. Phys.

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We examine the thermospin properties of an all-carbon nanojunction constructed by a graphene nanoflake (GNF) and zigzag-edged graphene nanoribbons (ZGNRs), bridged by the carbon atomic chains. The first-principles calculations show that the phonon thermal conductance is much weaker than the electron thermal conductance at the Fermi level, and even the former is a few percent of the latter in the low-temperature regime. In the meantime, the carbon-based device possesses an excellent spin transport property at the Fermi level due to the appearance of half-metallic property. Furthermore, the single-spin Seebeck coefficient has a larger value at the Fermi level. These facts ultimately result in a significant enhancement of spin thermoelectric figure of merit (FOM) ZST. By controlling the carbon-chain lengths and the temperature, the maximal value of ZST can reach 30. Moreover, we also find that the room temperature ZST displays an odd-even effect with the carbon-chain lengths, and it is always larger than the charge thermoelectric FOM ZCT.

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Section: Introductionmentioning

confidence: 73%

Giant spin thermoelectric effects in all-carbon nanojunctions

Yang

Wang

Chen

et al. 2015

Phys. Chem. Chem. Phys.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

Valley–spin Seebeck effect in heavy group-IV monolayers

2017

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Akin to electron spin, the valley has become another highly valued degree of freedom in modern electronics, specifically after tremendous studies on monolayers of group-IV materials, i.e. graphene, silicene, germanene and stanene. Except for graphene, the other heavy group-IV monolayers have observable intrinsic spin-orbit interactions due to their buckled structures. Distinct from the usual electric or optical control of valley and spin, we here employ a temperature difference to drive electron motion in ferromagnetic heavy group-IV monolayers via designing a caloritronic device locally modulated by an interlayer electric (E z ) field. A unique valley-spin Seebeck (VSS) effect is discovered, with the current contributed only by one (the other) valley and one (the other) spin moving along one (the opposite) direction. This effect is suggested to be detected below the critical temperature about 18K for silicene, 200K for germanene and 400K for stanene, arising from the characteristic valleyspin nondegenerate band structures tuned by the E z field, but cannot be driven in graphene without spin-orbit interaction. Above the critical temperature, the VSS effect is broken by overlarge temperature broadening. Besides the temperature, it is also found that the E z field can drive a transition between the VSS effect and the normal spin Seebeck effect. Further calculations indicate that the VSS effect is robust against many realistic perturbations. Our research represents a conceptually but substantially major step towards the study of the Seebeck effect. These findings provide a platform for encoding information simultaneously by the valley and spin quantum numbers of electrons in future thermal-logic circuits and energy-saving devices.

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“…This provides a simple and clear demonstration of our proposal of ac modulation as a tuning knot for spin transfer torques in MTJs. As usual, CNTs can be described using the nearest-neighbor tight-binding method with the hopping integral γ = −2.6 eV, [31,32] shown as the second term in Eq. (3).…”

Section: B Cnt-based Mtjsmentioning

confidence: 99%

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

et al. 2017

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The phenomenon of spin transfer torque (STT) has attracted a great deal of interests due to its promising prospects in practical spintronic devices. In this paper, we report a theoretical investigation of STT in a noncollinear magnetic tunnel junction under ac modulation based on the nonequilibrium Green's function formalism, and derive a closed-formulation for predicting the time-averaged STT. Using this formulation, the ac STT of a carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the sin θ dependence on the noncollinear angle is maintained. By photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced significantly, about 12 and 75 times, respectively. Our analysis reveals the condition for achieving optimized STT enhancement and suggests that ac modulation is a very effective way for electrical manipulation of STT.

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Giant room-temperature spin caloritronics in spin-semiconducting graphene nanoribbons

Cited by 88 publications

References 33 publications

Giant spin thermoelectric effects in all-carbon nanojunctions

Giant spin thermoelectric effects in all-carbon nanojunctions

Valley–spin Seebeck effect in heavy group-IV monolayers

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

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