Thermal Ionization of Impurity-Bound Quasiholes Demonstrates Phase Transition in Fractional Quantum Hall Effect

The delicate balance between quantum particles and imperfections within exotic materials drives new discoveries in physics, and recent work explores this interplay within the fractional quantum Hall effect. Ke Huang, Sankar Das Sarma from the Condensed Matter Theory Center and Joint Quantum Institute at the University of Maryland, and Xiao Li investigate how impurities affect the behaviour of quasiholes, quasiparticles that emerge in this unusual state of matter. They demonstrate that at realistic temperatures, quasiholes become unbound from attractive impurities through a process of thermal ionization, triggering a distinct phase transition.

This research offers a new understanding of impurity effects in fractional quantum Hall systems and proposes a method, utilising excitons, to directly observe this thermal ionization process, potentially opening avenues for manipulating and controlling these quantum states. Researchers constructed a theoretical framework incorporating electron interactions and the potential created by an impurity, allowing for both attractive and repulsive configurations, and validated their approach by characterizing the FQH state with a Coulomb impurity using both the energy spectrum and a measure of quantum entanglement to assess stability.

The team demonstrated that a repulsive impurity can effectively hold a quasihole in place at low temperatures, while an attractive impurity does not, and revealed that the corresponding energy and entanglement gaps exhibit distinct dependences on impurity strength and temperature. Detailed calculations of energy and entanglement gaps within the system confirm the presence of a pinned quasihole at low temperatures and a transition to a free quasihole at intermediate temperatures, signalled by the emergence of a new entanglement gap. To propose a method for experimental detection, scientists suggested utilizing interlayer excitons in atomically thin materials as a quantum sensor to detect thermal ionization of quasiholes, predicting that the light emitted by these excitons should shift in colour with increasing temperature only for repulsive impurity configurations, directly manifesting the thermal ionization process. This prediction provides a clear experimental signature for distinguishing between the two impurity types and validating the theoretical findings. Quasiholes Manipulated with Tunable Impurities Scientists demonstrate a pathway to directly observe and manipulate fractionalized quasiparticles, known as quasiholes, within the exotic realm of the fractional quantum Hall effect by leveraging the interaction between quasiholes and specifically engineered impurities. Researchers predict that a quasihole can become bound to a repulsive impurity, but also thermally ionized, undergoing a phase transition at a characteristic temperature.

The team proposes an experimental setup utilizing interlayer excitons, bound electron-hole pairs in atomically thin materials, to act as tunable impurities, and demonstrated that the binding or unbinding of a quasihole to the impurity manifests as a measurable shift in the light emitted by the excitons, providing a direct optical signature of the interaction. Measurements confirm that the thermal ionization of quasiholes occurs at a specific temperature, signifying a transition between bound and unbound states. This breakthrough delivers a concrete route to directly probe fractionalized quasiholes and their entropy-driven ionization using exciton spectroscopy in advanced semiconductor heterostructures, establishing a new platform for exploring topological quantum matter and potentially realizing fault-tolerant quantum computation based on anyons. Quasiholes, Impurities, and Thermal Ionization This research investigates the behaviour of quasiholes within fractional Hall states when interacting with Coulomb impurities at realistic temperatures, demonstrating that repulsive impurities can effectively pin quasiholes, stabilizing the fractional Hall state, while attractive impurities do not bind them. Crucially, the study reveals that even when pinned by a repulsive impurity, a quasihole can become thermally ionized at sufficiently high temperatures, leading to a distinct phase transition driven by a competition between energy and entropy. The researchers established this behaviour through detailed calculations of energy and entanglement gaps, showing how these gaps change with temperature and impurity strength, and confirmed the presence of a pinned quasihole at low temperatures, characterized by a reduced effective system size. The findings suggest a clear distinction in phase diagrams based on these entanglement gaps, with repulsive impurities exhibiting behaviour consistent with the underlying fractional Hall state. The authors emphasize the broader applicability of the thermal ionization mechanism to any localized impurity and propose a novel detection method using interlayer excitons, which are highly sensitive to correlated electronic states, suggesting that changes in exciton behaviour can directly signal the thermal ionization of quasiholes. 👉 More information 🗞 Thermal ionization of impurity-bound quasiholes in the fractional quantum Hall effect 🧠 ArXiv: https://arxiv.org/abs/2512.07769 Tags: