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First Observation of Non-Reciprocal Coulomb Drag in Chern Insulators

A significant advancement has been made by He Qinglin’s team at the Center for Quantum Materials Science within the School of Physics. They have successfully documented the pioneering instance of non-reciprocal Coulomb drag in Chern insulators, a finding that paves the way for deeper inquiry into Coulomb interactions within magnetic topological systems and enriches our comprehension of quantum states present in these materials. This research was published in Nature Communications.

Coulomb drag is a phenomenon where a current flowing through one conductor induces a measurable voltage in a nearby electrically isolated conductor through long-range Coulomb interactions.

Chern insulators are notable magnetic topological materials recognized for exhibiting a quantized Hall effect without the requirement of external magnetic fields. This is largely attributable to their intrinsic magnetization and the existence of chiral edge states.

This research represents a groundbreaking exploration into non-reciprocal Coulomb drag in magnetic Chern insulators, an area that has remained largely unexplored. It offers valuable insights into topological quantum materials and highlights novel aspects of quantum fluctuations and interactions. Furthermore, this study contributes to advancements in topological quantum computing by introducing a non-contact detection mechanism for quantum states, which is essential for qubit development.

Utilizing a Molecular Beam Epitaxy (MBE) method, the researchers developed V-doped (Bi,Sb)₂Te₃ tailored for high-temperature quantum anomalous Hall (QAH) effects, accompanied by a Dual Hall bar equipped with a nanoscale vacuum gap. This setup ensured pure Coulomb coupling without tunneling. To facilitate the examination of QAH transitions, conditions such as ultra-low temperatures (20 mK) and perpendicular magnetic fields were employed.

Through their experimentation, the researchers collected data on longitudinal (Vₓₓ) and transverse (Vₓᵧ) drag voltages and examined I-V curves to differentiate between shot noise and fluctuation regimes, as well as temperature/power-law scaling to verify mesoscopic origins.

Key findings from the research include:

• Longitudinal drag: The fixed polarity regardless of current or magnetic field direction suggests a rectification behavior.
• Transverse drag: This depends on the direction of magnetization and emerges from chiral edge state coupling.
• Mechanism: At low temperatures, mesoscopic fluctuations dominate (T² scaling), while shot noise becomes evident at elevated bias levels, contributing to nonlinear dynamics.

Chern insulators present a promising avenue for non-reciprocal quantum transport phenomena. The results bolster the development of Majorana-based qubit interferometry, an essential aspect of topological quantum computing. This research facilitates the non-contact measurement of quantum states, which is vital for constructing scalable and resilient quantum devices. Additionally, it provides new perspectives on magnetization dynamics, potentially aiding in the creation of low-power, chiral electronic devices.

More information: Yu Fu et al, Non-reciprocal Coulomb drag between Chern insulators, Nature Communications (2025). DOI: 10.1038/s41467-025-58401-5

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phys.org