Strange metallicity of moiré twisted bilayer graphene

Sarma, Sankar Das; Wu, Fangming

doi:10.48550/arxiv.2201.10270

Cited by 2 publications

(3 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2e-g. A linear temperature dependence of the resistivity can be due to electron-phonon scattering, at least at higher temperatures (above 5-10K) [24][25][26] . Alternatively, this dependence has also been associated with strange metal behavior due to its onset at low temperatures and its strength near the |ν| = 2 correlated phases 8,27 .…”

mentioning

confidence: 99%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

View full text Add to dashboard Cite

Twisted bilayer graphene (TBG) near the magic twist angle of ∼1.1°exhibits a rich phase diagram.However, the interplay between different phases and their dependence on twist angle is still elusive.Here, we explore the stability of various TBG phases and demonstrate that superconductivity near filling of two electrons per moiré unit cell alongside Fermi surface reconstructions, as well as entropydriven high-temperature phase transitions and linear-in-T resistance occur over a range of twist angles which extends far beyond those exhibiting correlated insulating phases. In the vicinity of the magic angle, we also find a metallic phase that displays a hysteretic anomalous Hall effect and incipient Chern insulating behaviour. Such a metallic phase can be rationalized in terms of the interplay between interaction-driven deformations of TBG bands leading to Berry curvature redistribution and Fermi surface reconstruction. Our results provide an extensive perspective on the hierarchy of correlated phases in TBG as classified by their robustness against deviations from the magic angle or, equivalently, their electronic interaction requirements. TBG is a highly tunable platform for exploring the effects of strong electronic interactions and topological bands [1][2][3][4][5][6][7][8][9] . At the magic angle, i.e., when the strength of the interactions among electrons is maximized relative to their kinetic energy, pronounced signatures of correlated phases emerge 1,2,10 . Away from the magic angle, the effective interaction strength is reduced and the correlated phases are believed to disappear rapidly. However, despite the strong impact of the twist angle on the phase diagram of nearly-magic TBG, this dependence is still experimentally under-explored. Here we report systematic measurements on multiple devices covering a wide range of twist angles between 0.79°and 1.23°(see Supplementary Table I for an overview) and examine the overall impact of twist angle, and thus strength of interactions, on the phase

show abstract

mentioning

confidence: 99%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…III through a detailed theory. We conclude by mentioning that we have also investigated the experimentally reported finite temperature transport properties of 2D graphene related systems [5,57,58,[71][72][73][74][75][76] and 3D doped semiconductors [77] (at high temperatures, so that elastic scattering effects from the impurities are not particularly quantitatively important), finding to our surprise that the Planckian hypothesis is always approximately empirically valid. This is true for 3D semiconductors even at very high temperatures (∼ 1000K) where the resistive scattering arises entirely from inelastic optical phonon scattering, and the resistivity is essentially exponential in temperature.…”

Section: Discussionmentioning

confidence: 99%

“…Even after accepting this somewhat ill-defined uncertainty argument, it is unclear why the dimensionless coupling constant α, which should be sitting in front of k B T in such dimensional reasoning, should be of order unity since no theory constrains it and in principle, it could be anything. But the two theoretical examples where detailed transport calculations are possible, namely the well-understood linear-in-T metallic resistivity due to acoustic phonon scattering [15,55,58,71] and low-temperature approximately linear-in-T resistivity in 2D doped semiconductors (as well as the inelastic scattering in an electron liquid) in the current work, seem to obey the Planckian hypothesis unreasonably well (within a factor of 10, α < 10), indicating that the effective coupling constant α entering the Planckian bound multiplying the temperature (in a strictly qualitative dimensional analysis) is indeed of order unity. Why it is so remains a mystery, and the possibility that this is merely a coincidence and that future experiments will discover strong violations of the Planckian hypothesis should not be ruled out.…”

Section: Discussionmentioning

confidence: 99%

Planckian properties of 2D semiconductor systems

Ahn¹,

Sarma²

2022

Preprint

Self Cite

View full text Add to dashboard Cite

We describe and discuss the low-temperature resistivity (and the temperature-dependent inelastic scattering rate) of several different doped 2D semiconductor systems from the perspective of the Planckian hypothesis asserting that /τ = kBT provides a scattering bound, where τ is the appropriate relaxation time. The regime of transport considered here is well-below the Bloch-Gruneisen regime so that phonon scattering is negligible. The temperature-dependent part of the resistivity is almost linear-in-T down to arbitrarily low temperatures, with the linearity arising from an interplay between screening and disorder, connected with carrier scattering from impurity-induced Friedel oscillations. The temperature dependence disappears if the Coulomb interaction between electrons is suppressed. The temperature coefficient of the resistivity is enhanced at lower densities, enabling a detailed study of the Planckian behavior both as a function of the materials system and carrier density. Although the precise Planckian bound never holds, we find somewhat surprisingly that the bound seems to apply approximately with the scattering rate never exceeding kBT by more than an order of magnitude either in the experiment or in the theory. In addition, we calculate the temperature-dependent electron-electron inelastic scattering rate by obtaining the temperaturedependent self-energy arising from Coulomb interaction, also finding it to obey the Planckian bound within an order of magnitude at all densities and temperatures. We introduce the concept of a generalized Planckian bound where /τ is bounded by αkBT with α ∼ 10 or so in the super-Planckian regime with the strict Planckian bound of α = 1 being a nongeneric finetuned situation.

show abstract

Strange metallicity of moiré twisted bilayer graphene

Cited by 2 publications

References 33 publications

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Planckian properties of 2D semiconductor systems

Contact Info

Product

Resources

About