Thermoelectric spin voltage in graphene

Discovery of topological Weyl semimetals has revealed the opportunities to realize several extraordinary physical phenomena in condensed matter physics. Specifically, these semimetals with strong spin-orbit coupling, broken inversion symmetry and novel spin texture are predicted to exhibit a large spin Hall effect that can efficiently convert the charge current to a spin current. Here we report the direct experimental observation of a large spin Hall and inverse spin Hall effects in Weyl semimetal WTe2 at room temperature obeying Onsager reciprocity relation. We demonstrate the detection of the pure spin current generated by spin Hall phenomenon in WTe2 by making van der Waals heterostructures with graphene, taking advantage of its long spin coherence length and spin transmission at the heterostructure interface. These experimental findings well supported by ab initio calculations show a large charge-spin conversion efficiency in WTe2; which can pave the way for utilization of spin-orbit induced phenomena in spintronic memory and logic circuit architectures. Figure S1. Devices with WTe2-graphene heterostructure. (a) Optical micrograph of Device 1, with WTe2graphene heterostructure and ferromagnetic (TiO2 1 nm/Co 60 nm) contacts on graphene for detection and creation of (I)SHE in WTe2. The scale bar is 2 μm. (b) Atomic force microscope (AFM) picture of the heterostructure area (red mark in (a)). The inset is the thickness profile of WTe2 on few-layer graphene along the white dash line showing the WTe2 thickness is 27nm in Device 1. (c) AFM picture and thickness profile of Dev 3 (after the device burnout) showing WTe2 thickness to be 11 nm on monolayer CVD graphene.

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“…As shown in Fig Supplementary Fig. S5), we can rules out all the thermal related effects 41,42 . Supplementary Fig.…”

Section: Ishe Signal Data and Fitting Curve With Out-of-plane Magnetimentioning

confidence: 97%

Observation of charge to spin conversion in Weyl semimetal WTe2 at room temperature

Zhao

Khokhriakov

Zhang

et al. 2020

Phys. Rev. Research

104

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“…To find an answer to the questions raised above, we first need to classify the main effects that can contribute to photocurrent (or photovoltage) generation in waveguide-integrated graphene devices [25][26][27][28]. One can distinguish three main effects -photo-voltaic (PV) [29][30][31][32][33][34], photo-bolometric (PB) [35][36][37][38][39] and photo-thermoelectric (PTE) [40][41][42][43] effects. The choice of the effect depends on device configuration, design and operation conditions [25,28,34,40].…”

Section: Photo-thermoelectric Effectmentioning

confidence: 99%

“…Recent studies have shown that the PTE effect dominates over PV photocurrent generation in graphene devices [44,45], therefore it is the PTE devices that we consider optimizing in this work. The operational principle of most PTE detectors relies on a temperature gradient in the material's p-n junction under an electromagnetic field excitation, resulting in a net thermoelectric voltage across the material due to the Seebeck effect [16,21,26,33,[40][41][42][43]46]. Thus, the generated photocurrent is proportional to the Seebeck coefficient for the two sides of the junction.…”

Section: Photo-thermoelectric Effectmentioning

confidence: 99%

Ultrafast Plasmonic Graphene Photodetector Based on the Channel Photothermoelectric Effect

2020

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We propose an on-chip CMOS compatible graphene plasmonic photodetector based on the photothermoelectric effect (PTE) that occurs across an entire homogeneous graphene channel. The proposed photodetector incorporates the long-range dielectric-loaded surface plasmon polariton (LR-DLSPP) waveguide with a metal stripe serving simultaneously as a plasmon supporting metallic material and one of the metal electrodes. Large in-plane component of the transverse magnetic (TM) plasmonic mode can couple efficiently to the graphene causing large temperature increases across an entire graphene channel with a maximum located at the metal stripe edge. As a result, the electronic temperatures exceeding 12000K at input power of only a few tens of μW can be obtained at the telecom wavelength of 1550nm. Even with limitations such as the melting temperature of graphene (T= 4510 K), a responsivity exceeding at least 200 A/W is achievable at telecom wavelength of 1550 nm. It is also shown that under certain operation conditions, the PTE channel photocurrent can be isolated from photovoltaic and p-n junction PTE contributions providing an efficient way for optimizing the overall photodetector performance.

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“…On the other hand, due to its novel physics as well as its potential applications in environmental protection and energy conversion, spin caloritronics has attracted much recent interest [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Besides the spin Seebeck effect using magnons as carries, the spin-dependent Seebeck effect (SSE) using fermions as carries has also attracted much recent attention in two dimensional graphenelike materials, such as graphene [30][31][32] and silicene [33][34][35][36][37][38][39]. In these works thermally induced spin-polarized current [30,31], thermoelectric spin voltage [32], and spin-Seebeck diode [33] have been reported.…”

Section: Introductionmentioning

confidence: 99%

“…Besides the spin Seebeck effect using magnons as carries, the spin-dependent Seebeck effect (SSE) using fermions as carries has also attracted much recent attention in two dimensional graphenelike materials, such as graphene [30][31][32] and silicene [33][34][35][36][37][38][39]. In these works thermally induced spin-polarized current [30,31], thermoelectric spin voltage [32], and spin-Seebeck diode [33] have been reported. Due to the presence of the valley degree of the freedom, similar to SSE, valley Seebeck effect is also put forward, where the pure or valley polarized current can be induced by the temperature gradient [34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Spin-valley filter effect and Seebeck effect in a silicene based antiferromagnetic/ferromagnetic junction

Niu

2019

New J. Phys.

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The presence of the coupled spin and valley degrees of freedom makes silicene an important material for spintronics and valleytronics. Here we report a spin-valley filter effect in a silicene based antiferromagnetic/ferromagnetic junction. It is found that at zero Fermi level a valley locked bipolar spin filter effect is observed, where in a broad gate voltage range in one valley one spin (the other spin) electrons contribute to the current under the positive (negative) bias, but in the other valley the transport is forbidden. At the finite Fermi level a valley locked fully spin-polarized current can exist under both the positive and negative biases. Furthermore, at the high Fermi level by reversing the bias direction, the spin filter effect can switch to the valley filter effect. In addition, by changing the sign of the Fermi level, the spin polarization direction of the current can be reversed. If a temperature bias is applied, the spin-dependent Seebeck effect (SSE) always exists. With increasing the temperature bias, the system undergoes three regions: valley locked SSE, normal SSE and valley Seebeck effect. Moreover, by tuning the interlayer electric field, three phases: thermally induced valley locked spin filter effect, valley Seebeck effect and valley mixed Seebeck effect are observed.

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Thermoelectric spin voltage in graphene

Cited by 77 publications

References 29 publications

Observation of charge to spin conversion in Weyl semimetal WTe2 at room temperature

Observation of charge to spin conversion in Weyl semimetal WTe2 at room temperature

Ultrafast Plasmonic Graphene Photodetector Based on the Channel Photothermoelectric Effect

Spin-valley filter effect and Seebeck effect in a silicene based antiferromagnetic/ferromagnetic junction

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