<p>Inducing superconducting correlations in chiral edge states is predicted to generate topologically protected zero energy modes with exotic quantum statistics<sup><CitationRef AdditionalCitationIDS="CR2 CR3 CR4 CR5" CitationID="CR1">1</CitationRef>–<CitationRef CitationID="CR6">6</CitationRef></sup>. Experimental efforts so far have focused on engineering interfaces between superconducting materials—typically amorphous metals—and semiconducting quantum Hall<sup><CitationRef AdditionalCitationIDS="CR8 CR9 CR10" CitationID="CR7">7</CitationRef>–<CitationRef CitationID="CR11">11</CitationRef></sup> or quantum anomalous Hall<sup><CitationRef CitationID="CR12">12</CitationRef>,<CitationRef CitationID="CR13">13</CitationRef></sup> systems. However, the strong interfacial disorder inherent in this approach can prevent the formation of isolated topological modes<sup><CitationRef AdditionalCitationIDS="CR15 CR16" CitationID="CR14">14</CitationRef>–<CitationRef CitationID="CR17">17</CitationRef></sup>. An appealing alternative is to use low-density flat band materials in which the ground state can be tuned between intrinsic superconducting and quantum anomalous Hall states using only the electric field effect. However, quantized transport and superconductivity have not been simultaneously achieved. Here we show that rhombohedral tetralayer graphene aligned to a hexagonal boron nitride substrate hosts a quantized anomalous Hall state at superlattice filling <i>ν</i> = −1 as well as a superconducting state at <i>ν</i> ≈ −3.5 at zero magnetic field. Gate voltage can also be used to actuate non-volatile switching of the chirality in the quantum anomalous Hall state<sup><CitationRef CitationID="CR18">18</CitationRef></sup>, allowing, in principle, arbitrarily reconfigurable networks of topological edge modes in locally gated devices. Thermodynamic compressibility measurements further show a topologically ordered fractional Chern insulator at <i>ν</i> = 2/3 (ref. <sup><CitationRef CitationID="CR19">19</CitationRef></sup>)—also stable at zero magnetic field—enabling proximity coupling between superconductivity and fractionally charged edge modes. Finally, we show that, as in rhombohedral bi- and trilayers<sup><CitationRef AdditionalCitationIDS="CR21" CitationID="CR20">20</CitationRef>–<CitationRef CitationID="CR22">22</CitationRef></sup>, integrating a transition metal dichalcogenide layer to the heterostructure nucleates a new superconducting pocket<sup><CitationRef AdditionalCitationIDS="CR21 CR22 CR23" CitationID="CR20">20</CitationRef>–<CitationRef CitationID="CR24">24</CitationRef></sup>, while leaving the topology of the <i>ν</i> = −1 quantum anomalous Hall state intact. Our results pave the way for a new generation of hybrid interfaces between superconductors and topological edge states in the low disorder limit.</p>

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Superconductivity and quantized anomalous Hall effect in rhombohedral graphene

  • Youngjoon Choi,
  • Ysun Choi,
  • Marco Valentini,
  • Caitlin L. Patterson,
  • Ludwig F. W. Holleis,
  • Owen I. Sheekey,
  • Hari Stoyanov,
  • Xiang Cheng,
  • Takashi Taniguchi,
  • Kenji Watanabe,
  • Andrea F. Young

摘要

Inducing superconducting correlations in chiral edge states is predicted to generate topologically protected zero energy modes with exotic quantum statistics16. Experimental efforts so far have focused on engineering interfaces between superconducting materials—typically amorphous metals—and semiconducting quantum Hall711 or quantum anomalous Hall12,13 systems. However, the strong interfacial disorder inherent in this approach can prevent the formation of isolated topological modes1417. An appealing alternative is to use low-density flat band materials in which the ground state can be tuned between intrinsic superconducting and quantum anomalous Hall states using only the electric field effect. However, quantized transport and superconductivity have not been simultaneously achieved. Here we show that rhombohedral tetralayer graphene aligned to a hexagonal boron nitride substrate hosts a quantized anomalous Hall state at superlattice filling ν = −1 as well as a superconducting state at ν ≈ −3.5 at zero magnetic field. Gate voltage can also be used to actuate non-volatile switching of the chirality in the quantum anomalous Hall state18, allowing, in principle, arbitrarily reconfigurable networks of topological edge modes in locally gated devices. Thermodynamic compressibility measurements further show a topologically ordered fractional Chern insulator at ν = 2/3 (ref. 19)—also stable at zero magnetic field—enabling proximity coupling between superconductivity and fractionally charged edge modes. Finally, we show that, as in rhombohedral bi- and trilayers2022, integrating a transition metal dichalcogenide layer to the heterostructure nucleates a new superconducting pocket2024, while leaving the topology of the ν = −1 quantum anomalous Hall state intact. Our results pave the way for a new generation of hybrid interfaces between superconductors and topological edge states in the low disorder limit.