Quantum Hall Antidot as a Fractional Coulombmeter

preprint, arXiv:2509.04209

Authors:

Mario Di Luca, Emily Hajigeorgiou, Zekang Zhou, Tevž Lotrič, Tengyan Feng, Kenji Watanabe, Takashi Taniguchi, Steven H. Simon, Mitali Banerjee

Abstract:

The detection of fractionally charged quasiparticles, which arise in the fractional quantum Hall regime, is of fundamental importance for probing their exotic quantum properties. While electronic interferometers have been central to probe their statistical properties, their interpretation is often complicated by bulk-edge interactions. Antidots, potential hills in the quantum Hall regime, are particularly valuable in this context, as they overcome the geometric limitations of conventional designs and act as controlled impurities within a quantum point contact. Furthermore, antidots allow for quasiparticle charge detection through straightforward conductance measurements, replacing the need for more demanding techniques. In this work, we employ a gate-defined bilayer graphene antidot operating in the Coulomb-dominated regime to study quasiparticle tunneling in both integer and fractional quantum Hall states. We show that the gate-voltage period and the oscillation slope directly reveal the charge of the tunneling quasiparticles, providing a practical method to measure fractional charge in graphene. We report direct measurements of fractional charge, finding q=e/3 at ν=4/3, 5/3 and 7/3, q=2e/3 at ν=2/3 and q=3e/5 at ν=3/5, while at ν=8/3 we observe signatures of both e/3 and 2e/3 tunneling charge. The simplicity and tunability of this design open a pathway to extend antidot-based charge measurements to other van der Waals materials, establishing antidots as a powerful and broadly applicable platform to study the quantum Hall effect.

Hydrodynamic memory and Quincke rotation

Physical Review Fluids American Physical Society (APS) 10:9 (2025) 093701

Authors:

Jason K Kabarowski, Aditya S Khair, Rahil N Valani

Active sorting to boundaries in active nematic-passive isotropic fluid mixtures.

Soft Matter (2025)

Authors:

Saraswat Bhattacharyya, Julia M Yeomans

Abstract:

We use a two-fluid model to study a confined mixture of an active nematic fluid and a passive isotropic fluid. We find that an extensile active fluid preferentially accumulates at a boundary if the anchoring is planar, whereas its boundary concentration decreases for homeotropic anchoring. These tendencies are reversed if the active fluid is contractile. We argue that the sorting results from gradients in the nematic order, and show that the behaviour can be driven by either imposed boundary anchoring or spontaneous anchoring induced by active flows. Our results can be tested by experiments on microtubule-kinesin motor networks, and may be relevant to sorting to the boundary in cell colonies or cancer spheroids.

Nonreciprocal Mixtures in Suspension: The Role of Hydrodynamic Interactions

Physical Review Letters American Physical Society (APS) 135:10 (2025) 108301

Authors:

Giulia Pisegna, Navdeep Rana, Ramin Golestanian, Suropriya Saha

Abstract:

The collective chasing dynamics of nonreciprocally coupled densities leads to stable traveling waves which can be mapped to a model for emergent flocking. In this Letter, we couple the nonreciprocal Cahn-Hilliard model to a fluid to minimally describe scalar active mixtures in a suspension, with the aim to explore the stability of the waves, i.e., the emergent flock in the presence of self-generated fluid flows. We show that the emergent polarity is linearly unstable to perturbations for a specific sign of the active stress recalling instabilities of orientational order in a fluid. Using numerical simulations, we find, however, that nonreciprocity stabilizes the waves against the linear instability in a large region of the phase space.

Classification of spin-12 fermionic quantum spin liquids on the trillium lattice

Physical Review B American Physical Society (APS) 112:10 (2025) 104429

Authors:

Ming-Hao Li, Sounak Biswas, SA Parameswaran

Abstract:

We study fermionic quantum spin liquids (QSLs) on the three-dimensional trillium lattice of corner-sharing triangles. We are motivated by recent experimental and theoretical investigations that have explored various classical and quantum spin liquid states on similar networks of triangular motifs with strong geometric frustration. Using the framework of projective symmetry groups (PSG), we obtain a classification of all symmetric Z 2 and U ( 1 ) QSLs on the trillium lattice. We find two Z 2 spin-liquids, and a single U ( 1 ) spin-liquid that is proximate to one of the Z 2 states. The small number of solutions reflects the constraints imposed by the nonsymmorphic symmetries in the space group of the trillium lattice. Using self-consistency conditions of the mean-field equations, we obtain the spinon band-structure and spin structure factors corresponding to these states. All three of our spin liquids are gapless at their saddle points: one of the two Z 2 QSLs is nodal, while the U ( 1 ) case hosts a spinon Fermi surface. One of our Z 2 spin liquids hosts a stable gapless nodal star that is protected by projective symmetries against additions of further neighbor terms in the mean-field ansatz. We comment on directions for further work.