paper

Unusual excitations and double-peak specific heat in a bond-alternating spin- - chain

arXiv:2104.10725 · doi:10.1103/PhysRevResearch.3.033048

Abstract

One-dimensional gapped phases that avoid any symmetry breaking have drawn enduring attention. In this paper, we study such phases in a bond-alternating spin-1 - chain built of a Kitaev () interaction and an off-diagonal term. In the case of isotropic bond strength, a Haldane phase, which resembles the ground state of a spin- Heisenberg chain, is identified in a wide region. A gapped Kitaev phase situated at dominant ferromagnetic and antiferromagnetic Kitaev limits is also found. The Kitaev phase has extremely short-range spin correlations and is characterized by finite -valued quantities on bonds. Its lowest entanglement spectrum is unique, in contrast to the Haldane phase whose entanglement spectrum is doubly degenerate. In addition, the Kitaev phase shows a double-peak structure in the specific heat at two different temperatures. In the pure Kitaev limit, the two peaks are representative of the development of short-range spin correlation at and the freezing of quantities at , respectively. By considering bond anisotropy, regions of Haldane phase and Kitaev phase are enlarged, accompanied by the emergence of dimerized phases and three distinct magnetically ordered states.

14 pages, 13 figures. For a previous spin-1/2 analogy, see arXiv:2012.03382

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