Exceptional topology in Non-Hermitian Twisted Bilayer Graphene

• URL: http://arxiv.org/abs/2409.03145v2
• Date: Sun, 15 Sep 2024 02:24:42 GMT
• Title: Exceptional topology in Non-Hermitian Twisted Bilayer Graphene
• Authors: Yingyi Huang,
• Abstract summary: We study a non-Hermitian TBG formed by one-layer graphene twisted relative to another layer with gain and loss. We find Dirac cones centered at only $K_M$ ($K'_M$) corner of the moir'e Brillouin zone at $K'$ ($K'_M$) valley deformed in the presence of non-Hermiticity. This is different from single layer graphene with gain and loss, where rings of exceptional points appear in both $K$ and $K'$ corners of the Brillouin zone.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Twisted bilayer graphene has extraordinary electronic properties at the magic angle along with an isolated flat band at magic angle. However, the non-Hermitian phenomena in twisted bilayer graphene remain unexplored. In this work, we study a non-Hermitian TBG formed by one-layer graphene twisted relative to another layer with gain and loss. Using a non-Hermitian generalization of Bistritzer-MacDonald model, we find Dirac cones centered at only $K_M$ ($K'_M$) corner of the moir\'e Brillouin zone at $K'$ ($K$) valley deformed in the presence of non-Hermiticity. This is different from single layer graphene with gain and loss, where rings of exceptional points appear in both $K$ and $K'$ corners of the Brillouin zone.The coincident of exceptional rings at $\Gamma_M$ point characterizes an ``exceptional magic angle", at which the system hosts flat bands with zero energy and finite lifetime. More interestingly, we find that the topological charge in the moir\'e Brillouin zone is conserved during the expansion and fusion of the exceptional ring, which is absent in two-dimensional systems constraining by Nielsen-Ninomiya theorem.These findings can be demonstrated in realistic cold atom and metamaterial systems and will stimulate further study on non-Hermitian phenomena in twistronic.

Related papers

• Geometric bound on structure factor [44.99833362998488]
  We show that a quadratic form of quantum geometric tensor in $k$-space sets a bound on the $q4$ term in the static structure factor $S(q)$ at small $vecq$. Bands that saturate this bound satisfy a condition similar to Laplace's equation, leading us to refer to them as $textitharmonic bands$.
  arXiv  Detail & Related papers  (2024-12-03T18:30:36Z)
• Gapless Floquet topology [40.2428948628001]
  We study the existence of topological edge zero- and pi-modes despite the lack of bulk gaps in the quasienergy spectrum. We numerically study the effect of interactions, which give a finite lifetime to the edge modes in the thermodynamic limit with the decay rate consistent with Fermi's Golden Rule.
  arXiv  Detail & Related papers  (2024-11-04T19:05:28Z)
• Topological Order in the Spectral Riemann Surfaces of Non-Hermitian Systems [44.99833362998488]
  We show topologically ordered states in the complex-valued spectra of non-Hermitian systems. These arise when the distinctive exceptional points in the energy surfaces of such models are annihilated. We illustrate the characteristics of the topologically protected states in a non-Hermitian two-band model.
  arXiv  Detail & Related papers  (2024-10-24T10:16:47Z)
• Flux-Tunable Regimes and Supersymmetry in Twisted Cuprate Heterostructures [39.58317527488534]
  Two Josephson junctions are integrated in a SQuID circuit threaded by a magnetic flux. We show that the flowermon qubit regime is maintained up to a finite critical value of the magnetic field. The interplay between the inherent twisted d-wave nature of the order parameter and the external magnetic flux enables the implementation of different artificial atoms.
  arXiv  Detail & Related papers  (2024-05-06T13:27:19Z)
• Information-Theoretic Thresholds for Planted Dense Cycles [52.076657911275525]
  We study a random graph model for small-world networks which are ubiquitous in social and biological sciences. For both detection and recovery of the planted dense cycle, we characterize the information-theoretic thresholds in terms of $n$, $tau$, and an edge-wise signal-to-noise ratio $lambda$.
  arXiv  Detail & Related papers  (2024-02-01T03:39:01Z)
• Topological Floquet Flat Bands in Irradiated Alternating Twist Multilayer Graphene [0.0]
  We study the appearance of topological Floquet flat bands in alternating-twist multilayer graphene. Laser beam can open a gap at the Moir'e $K$ point and create Floquet flat bands carrying nonzero Chern numbers.
  arXiv  Detail & Related papers  (2023-09-20T23:38:04Z)
• Uncovering Exceptional Contours in non-Hermitian Hyperbolic Matter [0.0]
  We introduce non-Hermitian hyperbolic matter and elucidate its exceptional properties in depth. We use hyperbolic Bloch theory to investigate band structures of hyperbolic lattices in the presence of non-Hermitian on-site gain and loss. Our results unveil an abundance of exceptional degeneracies in hyperbolic non-Hermitian matter.
  arXiv  Detail & Related papers  (2023-06-28T05:31:24Z)
• Flat Bands and High Chern Numbers in Twisted Multilayer Graphene [0.0]
  We study Tarnopolsky-Kruchkov-Vishwanath chiral model of two sheets of $n$-layer Bernal stacked graphene twisted by a small angle. We show that magic angles of this model are exactly the same as magic angles of chiral twisted bilayer graphene with multiplicity.
  arXiv  Detail & Related papers  (2023-02-28T22:04:15Z)
• A Generic Topological Criterion for Flat Bands in Two Dimensions [0.0]
  We show that the continuum limit of moir'e graphene is described by a $(2+1)$-dimensional field theory of Dirac fermions coupled to two classical vector fields. We present the Abelianization of the theory where the Abelianized flat band can be mapped to that of the lowest Landau level.
  arXiv  Detail & Related papers  (2023-01-02T19:00:02Z)
• Aharonov-Bohm cages, flat bands, and gap labeling in hyperbolic tilings [0.0]
  We show that Aharonov-Bohm cages are also found in an infinite set of hyperbolic dice tilings defined on a negatively curved hyperbolic plane. We also consider the energy spectrum of hyperbolic kagome tilings, which displays interesting features.
  arXiv  Detail & Related papers  (2022-06-08T16:56:27Z)
• Non-Hermitian $C_{NH} = 2$ Chern insulator protected by generalized rotational symmetry [85.36456486475119]
  A non-Hermitian system is protected by the generalized rotational symmetry $H+=UHU+$ of the system. Our finding paves the way towards novel non-Hermitian topological systems characterized by large values of topological invariants.
  arXiv  Detail & Related papers  (2021-11-24T15:50:22Z)
• Non-Hermitian Edge Burst [1.6033520575204165]
  We unveil an unexpected non-Hermitian phenomenon, dubbed edge burst, in non-Hermitian quantum dynamics. Our predictions are experimentally accessible in various non-Hermitian systems including quantum-optical and cold-atom platforms.
  arXiv  Detail & Related papers  (2021-09-29T18:00:03Z)
• Non-Hermitian Higher-Order Dirac Semimetals [0.0]
  We study 3D non-Hermitian higher-order Dirac semimetals (NHHODSMs) We show that they exhibit the striking property that the bulk and surfaces are anti-PT and PT symmetric, respectively. We also find real hinge-arcs connecting the surface EFRs.
  arXiv  Detail & Related papers  (2021-06-28T18:01:02Z)
• Non-Hermitian Pseudo-Gaps [3.787008621816909]
  A new non-Hermitian mechanism induces pseudo-gaps when boundaries are introduced in a lattice. A non-Hermitian pseudo-gap can host symmetry-protected mid-gap modes like ordinary topological gaps. Surprisingly, pseudo-gaps can also host an integer number of edge modes.
  arXiv  Detail & Related papers  (2021-06-06T00:39:49Z)
• Long-lived period-doubled edge modes of interacting and disorder-free Floquet spin chains [68.8204255655161]
  We show that even in the absence of disorder, and in the presence of bulk heating, $pi$ edge modes are long lived. A tunneling estimate for the lifetime is obtained by mapping the stroboscopic time-evolution to dynamics of a single particle in Krylov subspace.
  arXiv  Detail & Related papers  (2021-05-28T12:13:14Z)
• Existence of the first magic angle for the chiral model of bilayer graphene [77.34726150561087]
  Tarnopolsky-Kruchkov-Vishwanath (TKV) have proved that for inverse twist angles $alpha$ the effective Fermi velocity at the moir'e $K$ point vanishes. We give a proof that the Fermi velocity vanishes for at least one $alpha$ between $alpha approx.586$.
  arXiv  Detail & Related papers  (2021-04-13T20:37:00Z)
• Quantum anomalous Hall phase in synthetic bilayers via twistless twistronics [58.720142291102135]
  We propose quantum simulators of "twistronic-like" physics based on ultracold atoms and syntheticdimensions. We show that our system exhibits topologicalband structures under appropriate conditions.
  arXiv  Detail & Related papers  (2020-08-06T19:58:05Z)
• Observation of Hermitian and Non-Hermitian Diabolic Points and Exceptional Rings in Parity-Time symmetric ZRC and RLC Dimers [62.997667081978825]
  We show how appears non-Hermitian degeneracy points in the spectrum and how they are protected against a Hermitian perturbation. This work opens a gold road for investigations on topological electrical circuits for robust transport of information at room temperature.
  arXiv  Detail & Related papers  (2020-04-17T15:51:49Z)
• Kane-Mele with a twist: Quasicrystalline higher-order topological insulators with fractional mass kinks [0.0]
  We show that localized modes at corners, characteristic of a HOTI, are not associated with conventional mass inversions. We also derive a relationship between corner modes in a bilayer and disclination modes in a single layer.
  arXiv  Detail & Related papers  (2020-01-15T19:00:12Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.