Abstract
Topological properties in material science have recently received tremendous attention, as exemplified by topological insulators. As for quantum spin systems, the Haldane chain with integer spins is the best known example1. The realization of a topological quantum phase in the Haldane chain is an innovative research development related to the 2016 Nobel Prize in Physics. For mixed spin chains composed of two different spins, the appearance of a topologically quantized magnetization plateau is predicted by the Lieb-Mattis theorem2 in combination with the Oshikawa-Yamanaka-Affleck criterion3. However, the actual magnetization plateau in the mixed spin chain has not yet been observed. Here, we present a model compound forming a mixed spin-(1/2, 5/2) chain. We observe a clear Lieb-Mattis plateau and well explain it quantitatively. The present results demonstrate a quantum many-body effect based on quantum topology and provide a new stage in the search for topological properties in condensed matter physics.
Highlights
The one-dimensional (1D) spin chain is the simplest quantum spin model in which spins are linearly arranged
The topological ground state of the Haldane chain can be described by a valence-bond picture[2], where each integer spin is considered as a collection of S = 1/2 and forms a singlet state between S = 1/2 spins on the different sites
The Leib-Mattis (LM) theorem explains that the ground state of the mixed spin-(1/2,S) Heisenberg chain is a ferrimagnet with a value of S − 1/23
Summary
The one-dimensional (1D) spin chain is the simplest quantum spin model in which spins are linearly arranged. The Leib-Mattis (LM) theorem explains that the ground state of the mixed spin-(1/2,S) Heisenberg chain is a ferrimagnet with a value of S − 1/23. The mixed spin-(1/2, 5/2) chain, which we present in this work, is expected to exhibit a 2/3 magnetization plateau[5,6].
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