Abstract
We present a comprehensive study of the spin excitations- A s measured by the dynamical spin structure factor S(q,ω)-of the so-called block-magnetic state of low-dimensional orbital-selective Mott insulators. We realize this state via both a multi-orbital Hubbard model and a generalized Kondo-Heisenberg Hamiltonian. Due to various competing energy scales present in the models, the system develops periodic ferromagnetic islands of various shapes and sizes, which are antiferromagnetically coupled. The 2×2 particular case was already found experimentally in the ladder material BaFe2Se3 that becomes superconducting under pressure. Here we discuss the electronic density as well as Hubbard and Hund coupling dependence of S(q,ω) using density matrix renormalization group method. Several interesting features were identified: (1) An acoustic (dispersive spin-wave) mode develops. (2) The spin-wave bandwidth establishes a new energy scale that is strongly dependent on the size of the magnetic island and becomes abnormally small for large clusters. (3) Optical (dispersionless spin excitation) modes are present for all block states studied here. In addition, a variety of phenomenological spin Hamiltonians have been investigated but none matches entirely our results that were obtained primarily at intermediate Hubbard U strengths. Our comprehensive analysis provides theoretical guidance and motivation to crystal growers to search for appropriate candidate materials to realize the block states, and to neutron scattering experimentalists to confirm the exotic dynamical magnetic properties unveiled here, with a rich mixture of acoustic and optical features.
| Original language | English |
|---|---|
| Article number | 115134 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 11 |
| DOIs | |
| State | Published - Sep 2020 |
Funding
We acknowledge fruitful discussions with C. Batista, N. Kaushal, M. Mierzejewski, A. Nocera, and M. Środa. J. Herbrych acknowledges grant support by the Polish National Agency for Academic Exchange (NAWA) under Contract No. PPN/PPO/2018/1/00035. The work of G. Alvarez was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by the US DOE, Office of Science, Advanced Scientific Computer Research and Basic Energy Sciences, Division of Materials Science and Engineering. The development of the code by G. Alvarez was conducted at the Center for Nanophase Materials Science, sponsored by the Scientific User Facilities Division, BES, DOE, under contract with UT-Battelle. A. Moreo and E. Dagotto were supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. Part of the calculations were carried out using resources provided by the Wroclaw Centre for Networking and Supercomputing.