arXiv subjects

Martin HvE Groves

Publications and source records attributed to Martin HvE Groves.

4 recordsLinked to original sources

arXiv2026

Fundamental Work Scaling and Non-Extensivity in Critical Engines

We present a general analytical framework for critical two-isothermal engines that emerge operationally from quasi-static quantum Stirling cycles across ground-state level crossings (GLCs) in the low-temperature regime, where reversible heat exchange is governed by the structural entropy change while the internal energy remains constant. Within this ideal-reservoir, low-temperature equilibrium model, the Primarch Formula gives an exact quasistatic ensemble-average expression linking extracted work and efficiency directly to macroscopic ground-state degeneracies. In this reversible setting, the engines reach Carnot efficiency without a classical regenerator. For the perturbative population pattern analyzed here, thermal excitations reduce the ideal work and efficiency. Validated against exact numerical simulations of generalized \textit{N}-th spin-s Heisenberg models with nontrivial interactions, the framework is applied to the one-dimensional antiferromagnetic Ising model, revealing a profound connection to number theory. Governed by Fibonacci-Lucas and parity-dependent critical degeneracies, the engine exhibits three distinct work-scaling regimes: persistent logarithmic non-extensivity, recovery of extensivity in the thermodynamic limit, and asymptotic extensivity with a logarithmic finite-size correction. In all three regimes, Carnot efficiency is attained within the reversible equilibrium model.

cond-mat.stat-mech↗

arXiv2026

Exact Combinatorial Density of States for the Critical 1D Ising Model

This work presents an exact microcanonical combinatorial analysis of the one-dimensional antiferromagnetic Ising model. At the primary ground-state level crossing $B/J=2$, degeneracies follow the Fibonacci and Lucas sequences for open chains and periodic rings, respectively. We extend this framework to the complete excitation spectrum, demonstrating that the density of states is constructed from topological defects governed by linear Diophantine equations and $p$-fold Fibonacci convolutions. Open boundaries act as fractional defects, densifying the chain spectrum into energy steps of $2J$, whereas the closed ring remains quantized in units of $4J$. Notably, this exact topological counting exposes non-trivial spectral gaps near the fully polarized limit, strictly forbidding the penultimate macroscopic energy levels in both topologies. Through the transfer matrix formalism, we derive exact closed-form expressions for the critical degeneracies at all energy levels. These results provide a rigorous analytical foundation for extracting exact residual entropies and exposing the intrinsic number-theoretic architecture of quantum critical manifolds.

cond-mat.stat-mech↗

arXiv2026

Reaching maximum efficiency in quantum Stirling engines using multilayer graphene

In this work, quantum Stirling engines based on monolayer, AB-stacked bilayer, and ABC-stacked trilayer graphene under perpendicular magnetic fields are analyzed. Performance maps of the useful work $(ηW)$ reveal a robust optimum at low magnetic fields and moderately low temperatures, with all stackings capable of reaching Carnot efficiency under suitable configurations. The AB bilayer achieves this across the broadest parameter window while sustaining finite work, the monolayer exhibits highly constrained regimes, and the trilayer shows smoother trends with sizable $ηW$. These results identify multilayer graphene, particularly the AB bilayer, as a promising platform for efficient Stirling engines, while also highlighting the versatility of the monolayer in realizing all four operational regimes of the Stirling cycle.

cond-mat.stat-mech↗

arXiv2026

Caloric Phenomena and Stirling-Cycle Performance in Heisenberg- Kitaev Magnon Systems

We investigate the Stirling-cycle performance of a Heisenberg--Kitaev magnonic medium with Dzyaloshinskii--Moriya (DM) interactions. Using linear spin-wave theory, we show the DM interaction preserves spectral symmetry, yielding even caloric responses and symmetric Stirling engine efficiency. In contrast, bond-dependent Kitaev exchange asymmetrically distorts the magnonic density of states, enabling distinct direct and inverse caloric effects. Consequently, Kitaev-driven cycles achieve significantly higher efficiencies than DM-driven protocols, approaching a high-performance saturation regime for negative couplings. This establishes exchange-anisotropic magnets as highly tunable platforms for nanoscale solid-state energy conversion.

cond-mat.stat-mech↗