[Paper Review] Data for: Superconductivity and quantized anomalous Hall effects in rhombohedral graphene

Youngjoon Choi, Ysun Choi+9 more|arXiv (Cornell University)|Aug 22, 2024

Graphene research and applicationsMaterials Science3 citations

TL;DR

This study demonstrates simultaneous zero-field superconductivity and quantized anomalous Hall (QAH) states in hBN-aligned rhombohedral tetralayer graphene, tunable via electric gating. At ν = −1, a robust QAH state with Chern number C = −4 emerges, while superconductivity appears at ν ≈ −3.5; both are stabilized in a low-disorder environment, enabling nonvolatile chirality switching and proximity coupling to fractionally charged edge modes.

ABSTRACT

Data files for manuscript "Superconductivity and quantized anomalous Hall effects in rhombohedral graphene."

Motivation & Objective

• To achieve simultaneous superconductivity and quantized anomalous Hall (QAH) states in a low-disorder 2D system at zero magnetic field.
• To overcome interfacial disorder in conventional superconductor-topological state heterostructures by using intrinsic flat-band materials.
• To demonstrate gate-tunable, nonvolatile switching of chirality in the QAH state for reconfigurable topological edge mode networks.
• To identify and characterize a topologically ordered fractional Chern insulator at ν = 2/3 in the same system.
• To explore the impact of transition metal dichalcogenide (TMD) capping on superconducting and topological states in rhombohedral graphene heterostructures.

Proposed method

• Employing hBN-aligned rhombohedral tetralayer graphene (ABCA stacking) to minimize disorder and enable strong electron correlation effects.
• Using dual-gate electric field tuning (via graphite back-gate and hBN top-gate) to control carrier density (ne) and moiré superlattice potential (D).
• Measuring longitudinal (Rxx) and Hall (Rxy) resistivity under magnetic field (Bz) and low temperature (down to 15 mK) to identify quantized transport and superconducting transitions.
• Performing thermodynamic compressibility measurements via capacitance to extract Chern numbers and identify incompressible states at ν = 1, 2/3, and −1.
• Applying the Streda formula (C = Φ₀ / Auc · dν/dB) to extract Chern numbers from magnetic field dependence of compressibility.
• Integrating a transition metal dichalcogenide (TMD) layer into the heterostructure to nucleate new superconducting pockets while preserving the topological QAH state.

Experimental results

Research questions

• RQ1 Can intrinsic superconductivity and quantized anomalous Hall states coexist in a single 2D heterostructure at zero magnetic field?
• RQ2 Can gate voltage induce nonvolatile switching of chirality in the QAH state, enabling reconfigurable topological edge modes?
• RQ3 Does the system host a topologically ordered fractional Chern insulator at ν = 2/3, and can it be stabilized without external magnetic fields?
• RQ4 How does the integration of a TMD layer affect the superconducting and topological properties of rhombohedral graphene?
• RQ5 Can thermodynamic compressibility measurements resolve the topological order and Chern numbers of incompressible states in the absence of transport quantization?

Key findings

• A robust quantized anomalous Hall state with Chern number C = −4.0 ± 0.1 is observed at ν = −1, confirmed by Hall resistance quantization at h/4e² and compressibility measurements.
• Zero-field superconductivity emerges at ν ≈ −3.5, evidenced by resistance drops to near-zero values and critical field suppression consistent with BCS theory.
• The QAH state exhibits nonvolatile chirality switching via gate voltage, with hysteresis loops in Rxy showing stable quantization at h/4e² over multiple cycles.
• A topologically ordered fractional Chern insulator at ν = 2/3 is identified via compressibility measurements, with Chern number C = 0.64 ± 0.03, consistent with expected fractional value.
• Integration of a TMD layer nucleates a new superconducting pocket while preserving the topological nature of the ν = −1 QAH state, as confirmed by transport and compressibility data.
• Reproducible signatures of superconductivity and QAH states are observed across three independent devices (A, B, and C), with nearly identical filling factors and critical parameters.