Phonon-drag thermopower in 3D Dirac semimetals

Kubakaddi, S. S.

doi:10.1088/0953-8984/27/45/455801

Cited by 7 publications

(12 citation statements)

References 51 publications

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“…Our predictions of T e and n e dependence of P , at low T e , may be used as better tool for determination of precise value of D , in Cd 3 As 2 Dirac semimetal, by comparing with the experimental results as done in graphene and conventional 2DEG . We feel there is need for more low T e experimental data of transport properties, that depend upon only electron–acoustic phonon interaction, to determine D which may set ultimate upper limit on intrinsic mobility of Cd 3 As 2 Dirac semimet al Phonon‐drag thermopower S g is another such transport property which purely depends upon electron–acoustic phonon coupling and been studied by us in this system very recently . The expression for F ( T ) and S g (derived in Ref.…”

Section: Resultsmentioning

confidence: 79%

Electron cooling in three-dimensional Dirac fermion systems at low temperature: Effect of screening

Bhargavi

Kubakaddi

2016

Phys. Status Solidi RRL

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Hot electron cooling rate P, due to acoustic phonons, is investigated in three‐dimensional Dirac fermion systems at low temperature taking account of the screening of electron–acoustic phonon interaction. P is studied as a function of electron temperature Te and electron concentration ne. Screening is found to suppress P very significantly for about Te < 0.5 K and its effect reduces considerably for about Te > 1 K in Cd3As2. In Bloch–Grüneisen (BG) regime, for screened (unscreened) case the Te dependence is P ∼ Te9(Te5) and the ne dependence gives P ∼ ne–5/3 (ne–1/3). The Te dependence is characteristic of 3D phonons and ne dependence is characteristics of 3D Dirac fermions. The plot of P /Te4 vs. Te shows a maximum at temperature Tem which shifts to higher values for larger ne. Interestingly, the maximum is nearly same for different ne and Tem/ne1/3 being nearly constant. More importantly, we propose, the ne dependent measurements of P would provide a clearer signature to identify 3D Dirac semimetal phase. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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Section: Resultsmentioning

confidence: 79%

Electron cooling in three-dimensional Dirac fermion systems at low temperature: Effect of screening

Bhargavi

Kubakaddi

2016

Phys. Status Solidi RRL

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“…Since the underlying mechanism for phonon limited mobility µ p , phonondrag thermopower S g and the hot electron power loss F e (T ) is the same, a relation between them is expected. They are established in conventional 2DEG and 3DEG [19,20,[42][43][44] and 2D and 3D Dirac fermions [23,45,46]. The relation between µ p and S g is a well known Herring's law S g µ p = −(Λν s /T ) [42].…”

Section: Resultsmentioning

confidence: 99%

“…For conventional 2DEG in Si-MOSFET and GaAs heterojucntions, the value of C is shown to be ∼ 5 [19,20]. By revisiting the S g / T 2 vs T curves in MLG [23], monolayer of molybdenum disulphide (MoS 2 ) [48] and threedimensional Dirac semimetals (3DDS) [45], from the position of maximum in each of these systems, we determine C = 7.0, 5.6 and 8.6, respectively.…”

Section: Resultsmentioning

confidence: 99%

Giant thermopower and power factor in magic angle twisted bilayer graphene at low temperature

Kubakaddi

2020

Preprint

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The phonon-drag thermopower S g , diffusion thermopower S d and the power factor P F are theoretically investigated in twisted bilayer graphene (tBLG) as a function of twist angle θ, temperature T and electron density ns. As θ approaches magic angle θm, the S g and S d are found to be highly enhanced, which is manifestation of great suppression of Fermi velocity νF * of electrons in moire flat band near θm. In the Bloch-Gruneisen (BG) regime, it is found that S g ∼ νF * −2 , T 3 and ns −1/2 . The T 3 and ns −1/2 dependencies are, respectively, signatures of 2D phonons and the Dirac fermions. An enhancement of S g up to ∼ 500 times that of monolayer graphene (MLG) is predicted at ∼ 1 K. This enhancement decreases with increasing θ and T . As T increases, the power δ in S g ∼ T δ , changes from 3 to nearly zero and a maximum S g value of the order of ∼ 10 mV/K at ∼ 20 K is estimated. Simple relations of 'Kohn anomaly temperature' TKA with θ and ns are obtained. S g is larger (smaller) for smaller ns in low (high) temperature region. On the other hand, S d , taken to be governed by Mott formula, ∼ νF * −1 , T and ns −1/2 and is much greater than that in MLG. S g dominates S d very significantly for T >∼ 2 K. In tBLG, θ acts as a strong tuning parameter of both S g and S d , in addition to T and ns. Moreover, in the BG regime Herring's law is found to be satisfied in tBLG. The power factor P F is also found to be strongly θ dependent and is very much larger than that in MLG. P F as a function of T is found to exhibit a broad maximum, which is, for example, ∼75 W/m-K 2 for θ = 1.2 • . Consequently, possibility of a giant figure of merit is discussed.I.

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“…These T 4 and T 3 dependences are, respectively, attributed to the 3D and 2D nature of phonons with linear dispersion, in the respective systems. We also point out that in 3D Dirac-fermion systems, in which phonons are 3D, S g DABG ~ T 4 [46]. For the unscreened piezoelectric coupling S g PABG ~ T 2 for both a conventional 2DEG [23] and a 2DEG in graphene on a GaAs substrate.…”

Section: A Temperature Dependence Of S Gmentioning

confidence: 93%

Effects of a piezoelectric substrate on phonon-drag thermopower in monolayer graphene

Bhargavi

Kubakaddi

Ford

2017

J. Phys.: Condens. Matter

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The phonon-drag thermopower is studied in monolayer graphene on a piezoelectric substrate. The phonon-drag contribution S g PA from the extrinsic potential of piezoelectric surface acoustic (PA) phonons of a piezoelectric substrate (GaAs) is calculated as a function of temperature T and electron concentration ns. At very low temperature, S g PA is found to be much greater than S g DA of the intrinsic deformation potential of acoustic (DA) phonons of the graphene. There is a crossover of S g PA and S g DA at around ~ 5 K. In graphene samples of about >10 μm size, we predict S g ~ 20 μV at 10 K, which is much greater than the diffusion component of the thermopower and can be experimentally observed. In the Bloch-Gruneisen (BG) regime T and ns dependence are, respectively, given by the power laws S g PA (S g DA) ~ T 2 (T 3 ) and S g PA, S g DA ~ ns -1/2 . The T (ns ) dependence is the manifestation of the two-dimensional phonons (Dirac phase of the electrons). The effect of the screening is discussed. Analogous to Herring's law (S g μp ~ T -1 ), we predict a new relation S g μp ~ ns 0 , where μp is the phonon-limited mobility. We suggest that ns-dependent measurements will play a more significant role in identifying the Dirac phase and the effect of screening.

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Phonon-drag thermopower in 3D Dirac semimetals

Cited by 7 publications

References 51 publications

Electron cooling in three-dimensional Dirac fermion systems at low temperature: Effect of screening

Electron cooling in three-dimensional Dirac fermion systems at low temperature: Effect of screening

Giant thermopower and power factor in magic angle twisted bilayer graphene at low temperature

Effects of a piezoelectric substrate on phonon-drag thermopower in monolayer graphene

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