Year: 2026
Type: preprint
Abstract: The orbital susceptibility of a small disordered grain is dominated by rare samples in which an occupied and an empty level nearly touch. In a chaotic grain such near-degeneracies are suppressed by level repulsion and must also coincide with the chemical potential, so the mean susceptibility stays finite. In a neutral honeycomb flake, chiral (sublattice) symmetry removes the second condition: It places the chemical potential in the middle of the smallest gap, in every disorder realization. Here we show that the mean orbital susceptibility then grows as $\ln(1/T)$ at low temperature $T$ if disorder can close this gap while a magnetic field still mixes the two levels, and that the hopping geometry decides whether it can: Positive nearest-neighbor hopping on a compact hexagonal flake keeps the gap open, third-neighbor hopping allows it to close. In a chiral random-matrix model with $n$ level pairs the coefficient of the logarithm is $C_n=\sqrt{2/n}\,Γ[(n+1)/2]/Γ(n/2)$, close to unity, and a detuned chemical potential cuts the logarithm off.
Source: arXiv (Cornell University)
Author: Murzaliev, B.
Institution: Thermo Fisher Scientific (Netherlands)
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223047359