Researchers at Penn State and Saint Louis University have demonstrated a novel material that could power devices capable of unusual transport and grouping of electrical signals and quantum states. Published in Science Advances, the work combines approaches from rapidly growing fields of quantum physics to explore non-Hermitian dynamics and build a new platform for studying unusual physical phenomena. The team’s material, a quantum anomalous Hall (QAH) insulator, could lead to devices capable of transporting and grouping electrical signals in ways not traditionally achievable without optics or engineered systems. “We wanted to show that these phenomena can emerge naturally in a quantum material,” explains Morteza Kayyalha, assistant professor of electrical engineering at Penn State and corresponding author on the paper, laying the groundwork for scalable, non-Hermitian behavior.
A newly engineered quantum material exhibits concentrating quantum states at material boundaries and opening avenues for novel electronic devices. This work merges the rapidly evolving fields of quantum physics to create a platform for studying non-Hermitian dynamics, behaviors not observed in conventional physical models. The team focused on the quantum anomalous Hall (QAH) insulator, where electrical current flows along the material’s edge in a single direction, creating one-way paths. These one-way edge paths offer a natural way to build an electronic network whose effective connections are direction dependent. The QAH devices were fabricated from thin films of bismuth antimony telluride, synthesized at Penn State’s two-dimensional crystal consortium (2DCC), and magnetically doped to induce a quantum state with edge-channel current flow. Importantly, these QAH insulators do not require external magnetic fields, typically necessary for achieving non-Hermitian behavior in other quantum Hall devices during operation. By constructing ring-shaped devices and meticulously measuring electrical signal propagation, the team reconstructed the system’s conductance network and compared it to the Hatano-Nelson model, a standard for identifying non-Hermitian behavior. This realization in a topological quantum material, Kayyalha notes, “provides a new route for studying these phenomena using electronic transport.”
Our work lays the groundwork for achieving scalable, non-Hermitian behavior with a quantum material platform rather than relying only on optical or circuit-based designs.
Bismuth Antimony Telluride Synthesis & Magnetic Doping Process
The pursuit of quantum materials with tailored properties has led researchers to increasingly complex synthesis and doping techniques, with bismuth antimony telluride emerging as a promising platform for exploring non-Hermitian dynamics. The team detailed their findings in a paper published in Science Advances. A critical step in achieving the desired quantum state involves magnetic doping, the introduction of magnetic atoms into the non-magnetic base material. “A key advantage of this QAH platform is that, after the material is magnetized, the chiral edge state can be studied at zero applied magnetic field,” Kayyalha said, a significant benefit as many quantum Hall devices require constant external magnetic fields to function. The researchers then constructed ring-shaped devices from the magnetically doped QAH insulator, strategically placing electrical contacts around the perimeter to map the flow of electricity.
Measurements of the resulting conductance network were then compared against the Hatano-Nelson model, a theoretical framework for identifying non-Hermitian behavior. The team observed the non-Hermitian skin effect, a counterintuitive phenomenon where quantum states concentrate at the material’s boundaries rather than distributing evenly. “We can compare the measured conductance matrix directly with theoretical models of non-Hermitian physics,” Kayyalha said, allowing them to confirm the presence of these unusual dynamics within the material. The system’s behavior can be tuned via gate voltage, which further enhances its potential for exploration and application.
The non-Hermitian skin effect has been observed in several engineered platforms but realizing it in a topological quantum material provides a new route for studying these phenomena using electronic transport.
Published in Science Advances, the research details a material created by merging approaches from quantum physics, enabling the study of unusual electronic behaviors previously difficult to observe. These one-way edge paths offer a natural way to build an electronic network whose effective connections are direction dependent. This network was then directly compared with the predictions of the Hatano-Nelson model, revealing a close correspondence.
A key advantage of this QAH platform is that, after the material is magnetized, the chiral edge state can be studied at zero applied magnetic field.
The findings, detailed in Science Advances, stem from a material exhibiting both topological and non-Hermitian properties, a combination previously difficult to achieve. The interior of this material is insulating, stopping the flow of electricity, with electrical current instead passing along the material’s edge in a single direction via chiral edge channels. These one-way edge paths offer a natural way to build an electronic network whose effective connections are direction dependent, Kayyalha said. Crucially, the team discovered that the strength of this effect could be tuned by adjusting the gate voltage, an electrical signal akin to a transistor’s control mechanism. “From there, we can identify signatures of non-Hermitian dynamics in the quantum material,” Kayyalha noted, suggesting this tunability will allow for further exploration of the relationship between conductance and non-Hermitian dynamics.
That makes it a promising platform for exploring non-Hermitian physics in electronic quantum materials.
