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

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...

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Autores principales:	Nick Bultinck, Eslam Khalaf, Shang Liu, Shubhayu Chatterjee, Ashvin Vishwanath, Michael P. Zaletel
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2020
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/4c0d6ad9601d49f6adf80f196d57a9ff
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spelling	oai:doaj.org-article:4c0d6ad9601d49f6adf80f196d57a9ff2021-12-02T14:10:46ZGround State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling10.1103/PhysRevX.10.0310342160-3308https://doaj.org/article/4c0d6ad9601d49f6adf80f196d57a9ff2020-08-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.10.031034http://doi.org/10.1103/PhysRevX.10.031034https://doaj.org/toc/2160-3308In 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” time-reversal symmetry is preserved. Our analytic arguments are built on first identifying an approximate U(4)×U(4) 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.Nick BultinckEslam KhalafShang LiuShubhayu ChatterjeeAshvin VishwanathMichael P. ZaletelAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 10, Iss 3, p 031034 (2020)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 Nick Bultinck Eslam Khalaf Shang Liu Shubhayu Chatterjee Ashvin Vishwanath Michael P. Zaletel Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
description	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” time-reversal symmetry is preserved. Our analytic arguments are built on first identifying an approximate U(4)×U(4) 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.
format	article
author	Nick Bultinck Eslam Khalaf Shang Liu Shubhayu Chatterjee Ashvin Vishwanath Michael P. Zaletel
author_facet	Nick Bultinck Eslam Khalaf Shang Liu Shubhayu Chatterjee Ashvin Vishwanath Michael P. Zaletel
author_sort	Nick Bultinck
title	Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
title_short	Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
title_full	Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
title_fullStr	Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
title_full_unstemmed	Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
title_sort	ground state and hidden symmetry of magic-angle graphene at even integer filling
publisher	American Physical Society
publishDate	2020
url	https://doaj.org/article/4c0d6ad9601d49f6adf80f196d57a9ff
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Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling

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