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First observation of non-reciprocal Coulomb drag in Chern insulators reported

He Qinglin's group at the Center for Quantum Materials Science, School of Â鶹ÒùÔºics, has reported the first observation of non-reciprocal Coulomb drag in Chern insulators. This breakthrough opens new pathways for exploring Coulomb interactions in magnetic topological systems and enhances our understanding of quantum states in such materials. The work was in Nature Communications.

Coulomb drag arises when a current in one conductor induces a measurable voltage in a nearby, electrically insulated conductor via long-range Coulomb interactions.

Chern insulators are magnetic topological materials that show a quantized Hall effect without external magnetic fields, due to intrinsic magnetization and chiral edge states.

The research marks the first foray into non-reciprocal Coulomb drag in a magnetic Chern insulator, which has long remained uncharted territory. It offers insights into topological quantum materials, revealing new aspects of quantum fluctuations and interactions. The study also advances topological quantum computing by providing a non-contact detection method for quantum states (relevant for qubits).

The researchers used a Molecular Beam Epitaxy (MBE) grown V-doped (Bi,Sb)₂Te₃ optimized for the high-temperature quantum anomalous Hall (QAH) effect, along with a Dual Hall bar with nanoscale vacuum gap to ensure pure Coulomb coupling (no tunneling). Ultra-low temperature (20 mK) and perpendicular magnetic fields were used to explore quantum anomalous Hall effect (QAH) transitions.

The researchers measured longitudinal (Vₓₓ) and transverse (Vₓᵧ) drag voltages; I-V curves (to distinguish shot noise vs. fluctuation regimes); and temperature/power-law scaling (to confirm mesoscopic origin).

Key findings include:

• Longitudinal drag: Fixed polarity regardless of current/magnetic field direction suggests rectification behavior.
• Transverse drag: Depends on magnetization direction; arises via chiral edge state coupling.
• Mechanism: Mesoscopic fluctuations dominate at low T (T² scaling) while shot noise appears at higher bias and contributes to nonlinear behavior.

Chern insulators can serve as promising platforms for non-reciprocal quantum transport phenomena. The findings support the development of Majorana-based qubit interferometry, a key component in topological quantum computing. This research enables non-contact detection of quantum states, which is critical for building scalable and robust quantum devices. It also offers new insights into magnetization dynamics, potentially contributing to the design of low-power, chiral electronic devices.