Symmetry breaking and skyrmionic transport in twisted bilayer graphene

Chatterjee, Shubhayu; Bultinck, Nick; Zaletel, Michael P.

doi:10.1103/physrevb.101.165141

Cited by 73 publications

(49 citation statements)

References 126 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Finally, we conclude by posing a few questions for future investigations. The DWs may provide an interesting platform to understand and manipulate various topological phases observed [70,71] or proposed [72][73][74] in TBG based systems the TBG system. It would also be interesting to understand the transport characteristics of a sample containing many (randomly distributed) domain walls [75,76] or a random distribution of Fermi velocities [77].…”

Section: Discussionmentioning

confidence: 99%

Transport across twist angle domains in moiré graphene

Padhi

Tiwari

Neupert

et al. 2020

Phys. Rev. Research

View full text Add to dashboard Cite

Many experiments in twisted bilayer graphene (TBG) differ from each other in terms of the details of their phase diagrams. Few controllable aspects aside, this discrepancy is largely believed to arise from the presence of a varying degree of twist angle inhomogeneity across different samples. Real-space maps indeed reveal TBG devices splitting into several large domains of different twist angles. Motivated by these observations, we study the quantum mechanical tunneling across a domain wall (DW) that separates two such regions. We show that the tunneling of the moiré particles can be understood by the formation of an effective step potential at the DW. The height of this step potential is simply a measure of the difference in twist angles. These computations lead us to identify the global transport signatures for detecting and quantifying the local twist angle variations. In particular, using Landauer-Büttiker formalism, we compute single-channel conductance (dI/dV) and Fano factor for shot noise (ratio of noise power and mean current). A reduction in the low-energy conductance and a zero-bias sub-meV gap in the conductance are observed which scale with the twist angle difference. One of the key findings of our work is that transport in presence of twist angle inhomogeneity is "noisy," though sub-Poissonian. In particular, the differential Fano factor peaks near the van Hove energies corresponding to the domains in the sample. The location and the strength of the peak are simply a measure of the degree of twist angle inhomogeneity.

show abstract

Section: Discussionmentioning

confidence: 99%

Transport across twist angle domains in moiré graphene

Padhi

Tiwari

Neupert

et al. 2020

Phys. Rev. Research

View full text Add to dashboard Cite

show abstract

“…The intervalley-Hunds coupling fixes the value of the relative phase θ between the K-IVC states for up and down spins. An antiferromagnetic coupling, perhaps driven by phonons [47], leads to θ ¼ 0. As expected, this is the spin-singlet K-IVC state, where the orbital currents from opposite spins are added.…”

Section: A Energetics and Ground State Of The Spinless Modelmentioning

confidence: 99%

“…Finally, let us comment briefly on the effect of magnetic field. The Zeeman coupling depends on the spin structure, and its effect on the gap depends nontrivially on the type of low-lying excitations [47]. On the other hand, the orbital effect of the magnetic field can be understood as follows.…”

Section: B Effect Of Single-particle Perturbationsmentioning

confidence: 99%

Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling

et al. 2020

Self Cite

View full text Add to dashboard Cite

In magic angle twisted bilayer graphene (TBG), electron-electron interactions play a central role, resulting in correlated insulating states at certain integer fillings. Identifying the nature of these insulators is a central question, and it is potentially linked to the relatively high-temperature superconductivity observed in the same devices. Here, we address this question using a combination of analytical strong-coupling arguments and a comprehensive Hartree-Fock numerical calculation, which includes the effect of remote bands. The ground state we obtain at charge neutrality is an unusual ordered state, which we call the Kramers intervalley-coherent (K-IVC) insulator. In its simplest form, the K-IVC order exhibits a pattern of alternating circulating currents that triples the graphene unit cell, leading to an "orbital magnetization density wave." Although translation and time-reversal symmetry are broken, a combined "Kramers" timereversal symmetry is preserved. Our analytic arguments are built on first identifying an approximate Uð4Þ × Uð4Þ symmetry, resulting from the remarkable properties of the TBG band structure, which helps select a low-energy manifold of states that are further split to favor the K-IVC state. This low-energy manifold is also found in the Hartree-Fock numerical calculation. We show that symmetry-lowering perturbations can stabilize other insulators and the semimetallic state, and we discuss the ground state at half-filling and give a comparison with experiments.

show abstract

“…A natural possibility are states with broken translational symmetry which have been considered in Refs. [43,49]. Here we would like to discuss another possibility, namely the appearance of excitonic Laughlin-type states.…”

Section: Exciton Interactions and Excitonic Laughlin Statesmentioning

confidence: 99%

“…In fact, experiments have observed hysteretic [7] and quantized anomalous Hall effect in twisted bilayer graphene [14] and trilayer graphene [22] moiré superlattices on hBN substrates. These states have been theoretically rationalized as spontaneously valley polarized magnetic Chern insulators [40,43,[47][48][49][50][51][52][53].…”

Section: Introductionmentioning

confidence: 99%

Excitonic Laughlin states in ideal topological insulator flat bands and their possible presence in moiré superlattice materials

Stefanidis

Sodemann

2020

Phys. Rev. B

View full text Add to dashboard Cite

We investigate few-and many-body states in half-filled ideal topological insulator flat bands realized by two degenerate Landau levels which experience opposite magnetic fields. This serves as a toy model of flat bands in moiré materials in which valleys have Chern numbers C = ±1. We argue that although the spontaneously polarized Ising Chern magnet is a natural ground state for repulsive Coulomb interactions, it can be in reasonable energetic competition with correlated Laughlin states of excitons when short-distance corrections to interactions are included. This is because charge neutral excitons in these bands behave effectively as charged particles in ordinary Landau levels. In particular, the Ising Chern magnet is no longer the ground state once the strength of a short-range intravalley repulsion is about 30% larger than the intervalley repulsion. Remarkably, these excitonic Laughlin states feature valley number fractionalization but no charge fractionalization and a quantized charge Hall conductivity identical to the Ising magnet, σ xy = ±e 2 /h, and thus cannot be distinguished from it by ordinary charge transport measurements. The Laughlin state with the highest density of excitons that can be constructed in these bands is an analog of ν = 1/4 bosonic Laughlin state and has no valley polarization even though it spontaneously breaks time reversal symmetry.

show abstract

Symmetry breaking and skyrmionic transport in twisted bilayer graphene

Cited by 73 publications

References 126 publications

Transport across twist angle domains in moiré graphene

Transport across twist angle domains in moiré graphene

Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling

Excitonic Laughlin states in ideal topological insulator flat bands and their possible presence in moiré superlattice materials

Contact Info

Product

Resources

About