| Description |
Low dimensional spin systems provide an excellent platform to explore, realize, and understand many body quantum physics. We have been working on naturally grown low-dimensional spin systems, ranging from spin-clusters, to 1D spin-chains, to 2D layered magnets with various lattice geometries, to explore quantum phenomena. Several emerging quantum phenomena including composite quasi-particle doublon and quarton excitations [1], Bethe-string states [2-3], spinon-confinement [4], and magnetization plateau state [1] have been experimentally realized. Currently, there is a particular focus on 2D spin systems with honeycomb geometry, especially in relation to the Kitaev quantum spin liquid state (QSL). The exactly solvable Kitaev honeycomb model [5], based on an effective spin-1/2 two-dimensional honeycomb lattice, offers a topological QSL state, which is a long-sought unconventional state of matter. Featured by long-range quantum entanglement and fractionalized Majorana fermion excitations, the Kitaev QSL is believed to be a way to realize fault-tolerant quantum computation. However, the realization of the strong bond- dependent exchange anisotropy is not straightforward in a solid-state material. Transition-metal elements with strong spin-orbit coupling, such as 5d Ir4+ and 4d Ru3+ ions with the d 5 spin configurations and in a proper crystal-field environment, are found to contribute a significant Kitaev interaction in honeycomb materials Na2IrO3 and α−RuCl3. Recent theoretical analysis [6] suggested that based on the 3d 7 Co2+ ions with a high-spin t2g5eg 2 configuration, a material realization of the Kitaev honeycomb model should also be possible. Our recent experimental efforts [7-9] to explore Kitaev physics in the Co-based layered honeycomb magnet Na2Co2TeO6 will be discussed.
References:
1. A. K. Bera et al., Emergent many-body composite excitations of interacting spin-1/2 trimers, Nature Communications 13, 6888 (2022).
2. A. K. Bera et al., Dispersions of many-body Bethe strings, Nature Physics 16, 625 (2020).
3. Z. Wang, J. Wu, W. Yang, A. K. Bera et al., Experimental observation of Bethe strings, Nature 554, 219 (2018).
4. A. K. Bera et al., Spinon confinement in a quasi-one-dimensional anisotropic Heisenberg magnet, Phys. Rev. B 96, 054423 (2017).
5. A. Kitaev, Anyons in an exactly solved model and beyond, Ann. Phys. 321, 2 (2006).
6. H. Liu et al., Kitaev spin liquid in 3d transition metal compounds, Phys. Rev. Lett. 125, 047201 (2020).
7. A. K. Bera et al., Field induced phase transitions and anisotropic magnetic properties of the Kiteav-Heisenberg compound Na2Co2TeO6, Phys. Rev. B 108, 214419 (2023).
8. P. Pilch, L. Peedu, A. K. Bera, et al., Field- and polarization-dependent quantum spin dynamics in the honeycomb magnet Na2Co2TeO6:
Magnetic excitations and continuum, Phys. Rev. B 108, L140406 (2023).
9. A. K. Bera et al., Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound Na2Co2TeO6, Phys. Rev. B 95, 094424 (2017).
|