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Spinon signatures in the critical phase of the (1,1/2) ferrimagnet in a magnetic field

A. K. Kolezhuk·H. -J. Mikeska·K. Maisinger·U. Schollwock
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Abstract

We propose an effective theory for the critical phase of a quantum ferrimagnetic chain with alternating spins 1 and 1/2 in an external magnetic field. With the help of the matrix product variational approach, the system is mapped to a spin-1/2 XXZ chain in an (effective) magnetic field; as a byproduct, we obtain an excellent description of the optical magnon branch in the gapped phase. Recent finite-temperature DMRG results for the low-temperature part of the specific heat are well described by the present approach, and the ``pop-up'' peaks, developing near the critical field values and in the middle of the critical phase, are identified with the contributions from two different spinon bands of the effective spin-1/2 chain. The effect should be as well observable in other spin-gap systems in an external field, particularly in spin ladders.

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A. K. Kolezhuk, H. -J. Mikeska, K. Maisinger, U. Schollwock. 1998-12-18. Spinon signatures in the critical phase of the (1,1/2) ferrimagnet in a magnetic field. https://doi.org/10.1103/physrevb.59.13565

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