Misorientation-Controlled Cross-Plane Thermoelectricity in Twisted Bilayer Graphene

Mahapatra, Phanibhusan S.; Ghawri, Bhaskar; Garg, Mansi; Mandal, Shinjan; Watanabe, Kenji; Taniguchi, Takashi; Jain, Manish; Mukerjee, Subroto; Ghosh, Arindam

doi:10.1103/physrevlett.125.226802

Cited by 33 publications

(29 citation statements)

References 45 publications

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“…Evidently, S exhibits a linear dependence on T at all doping including the higher-energy dispersive band, except in the vicinity of ν = ±2, thus validating the estimation of ∆T from Mott fitting [25]. The S ∝ T behavior is expected in a degenerate weakly or non-interacting metal within the semiclassical framework, and has been verified for monolayer graphene [17] as well as tBLG at slightly larger θ (2 • θ 5 • ) [28]. Close to ν = ±2, however, we find an unexpected increase in S when temperature is decreased below ∼ 40 K, in contrast to the expectation of S ≈ 0 (inset of Fig.…”

supporting

confidence: 76%

Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

Ghawri

Mahapatra

Garg

et al. 2021

Preprint

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The planar assembly of twisted bilayer graphene (tBLG) hosts a multitude of interaction-driven phases when the relative rotation is close to the magic angle (θ = 1.1°). This includes correlation-induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as the possibility of non-Fermi liquid (NFL) excitations. However, experimentally, the manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity (ρ) and thermoelectric power (S) in tBLG for several twist angles between θ ≈ 1.0°-1.7°. We observe an emergent violation of the semiclassical Mott relation in the form of excess S close to half-filling for θ≈1.6° that vanishes for ≥ 2°. The excess S (≈2 μV/K at low temperatures T ≈10 K at θ≈1.6°) persists up to ≈ 40 K and is accompanied by metallic T-linear ρ with transport scattering rate (1/τ) of near-Planckian magnitude 1/τ ≈ k_BT/h_bar. Closer to θ_m, the excess S was also observed for fractional band-filling (ν≈ 0.5). The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.

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confidence: 76%

Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

Ghawri

Mahapatra

Garg

et al. 2021

Preprint

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“…We demonstrate the extreme sensitivity of the TEP to the band structure and that it can provide information about the electronic structure, which cannot be determined by conductance measurements alone . Earlier studies on the TEP of low or moderate mobility BLG have shown a general agreement with the semiclassical Mott formula − where Δ V is the thermoelectric voltage, G is the energy-dependent conductance of the sample, T is the sample temperature, and Δ T is the temperature gradient. Importantly, the factor d G /d n is evaluated from the experimentally obtained transfer characteristics and therefore captures the TEP contributions from energy-dependent and energy-independent scattering processes (section S12).…”

Section: Introductionmentioning

confidence: 54%

Evidence of Lifshitz Transition in the Thermoelectric Power of Ultrahigh-Mobility Bilayer Graphene

et al. 2021

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Resolving low-energy features in the density of states (DOS) holds the key to understanding a wide variety of rich novel phenomena in graphene-based 2D heterostructures. The Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on transport properties has been challenging because of its relatively low energy scale (∼1 meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observed additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of the Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as possible evidence of a Lifshitz transition.

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“…To determine the thermopower or Seebeck coefficient (S), one needs to measure the generated thermoelectric voltage and the temperature difference (ΔT = T h − T c , where T h and T c are the temperatures of the hot and cold contacts, respectively). We have utilized the well-established 2ω lock-in technique [27][28][29][30][31][32][33] for measuring the thermoelectric voltage (V 2ω ) at ω = 13 Hz. To measure ΔT, we have utilized Johnson noise thermometry [35][36][37][38] .…”

Section: Set-up and Device Responsementioning

confidence: 99%

“…Motivated by these observations, we have extensively explored the thermopower response of MATBLG and non magic-angle twisted bilayer graphene (TBLG) devices. Unlike previous work involving graphene and TBLG [27][28][29][30][31][32][33][34] , we have utilized Johnson noise thermometry [35][36][37][38] to directly measure the temperature gradient across the MATBLG device and accurately determine S across a temperature ranging from 100 mK to 10 K. Our measurements reveal an intricate dependence of S on carrier density (ν), temperature (T) and magnetic field (B). Our key observations are as follows.…”

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confidence: 99%

Interaction-driven giant thermopower in magic-angle twisted bilayer graphene

et al. 2022

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Magic-angle twisted bilayer graphene has proved to be a fascinating platform to realize and study emergent quantum phases arising from the strong correlations in its flat bands. Thermal transport phenomena, such as thermopower, are sensitive to the particle-hole asymmetry, making them a crucial tool to probe the underlying electronic structure of this material. Here we have carried out thermopower measurements of magic-angle twisted bilayer graphene as a function of carrier density, temperature and magnetic field. We report the observation of an unusually large thermopower reaching a value of the order of 100 μV K −1 at a low temperature of 1 K. The thermopower exhibits peak-like features that violate the Mott formula in close correspondence to the resistance peaks appearing around the integer filling of the moiré bands, including the Dirac point. We show that the large thermopower peaks and their associated behaviour arise from the emergent highly particle-hole-asymmetric electronic structure, due to the sequential filling of the moiré flat bands and the associated recovery of Dirac-like physics. Furthermore, the thermopower shows an anomalous peak around the superconducting transition, which points towards the possible role of superconducting fluctuations in magic-angle twisted bilayer graphene.

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Misorientation-Controlled Cross-Plane Thermoelectricity in Twisted Bilayer Graphene

Cited by 33 publications

References 45 publications

Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

Evidence of Lifshitz Transition in the Thermoelectric Power of Ultrahigh-Mobility Bilayer Graphene

Interaction-driven giant thermopower in magic-angle twisted bilayer graphene

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