Regensburg 2025 – scientific programme

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MA: Fachverband Magnetismus

MA 34: Molecular Magnetism

MA 34.3: Talk

Thursday, March 20, 2025, 10:00–10:15, H18

Effects of Boundary Condition on Quantization in the Spin-1/2 Heisenberg Chain — •Saketh Ravuri¹, Chenxiao Zhao¹, Pascal Ruffieux¹, and Roman Fasel^1,2 — ¹Empa, Dübendorf, Switzerland — ²University of Bern, Bern, Switzerland

The spin-1/2 antiferromagnetic Heisenberg chain resides in a gapless spin liquid phase in the thermodynamic limit. In finite-length systems, however, quantization introduces a length-dependent excitation gap, which is further influenced by the boundary conditions. In this work, we investigate how open and periodic boundary conditions affect the quantization and gap behavior in spin-1/2 antiferromagnetic Heisenberg chains constructed by covalently linking magnetic nanographene units. For chains of fixed length, we demonstrate that open boundary conditions result in a smaller gap compared to periodic boundary conditions, as clearly evidenced by the inelastic electron tunneling spectra. This impact of boundary conditions diminishes with increasing chain length and vanishes in the thermodynamic limit. Moreover, in periodic rings with odd-numbered units, we investigated the scattering of a single spinon caused by J-fluctuations. These findings illuminate the role of boundary effects in finite-size quantum spin systems and contribute to the fundamental understanding of quantum magnetism and excitations in spin chains.

Keywords: Magnetic Nanographene; STM; Heisenberg chain; quantum spins