Dynamics of a j=32 quantum spin liquid

Abstract

We study a spin-orbital model for 4d 1 or 5d 1 Mott insulators in ordered double perovskites with strong spin-orbit coupling. This model is conveniently written in terms of pseudospin and pseudoorbital operators representing multipoles of the effective j = 3/2 angular momentum. Similarities between this model and the effective theories of Kitaev materials motivate the proposal of a chiral spin-orbital liquid with Majorana fermion excitations. The thermodynamic and spectroscopic properties of this quantum spin liquid are characterized using parton mean-field theory. The heat capacity, spin-lattice relaxation rate, and dynamic structure factor for inelastic neutron scattering are calculated and compared with the experimental data for the spin liquid candidate Ba2YMoO6. Moreover, based on a symmetry analysis, we discuss the operators involved in resonant inelastic X-ray scattering (RIXS) amplitudes for double perovskite compounds. In general, the RIXS cross sections allow one to selectively probe pseudospin and pseudo-orbital degrees of freedom. For the chiral spin-orbital liquid in particular, these cross sections provide information about the spectrum for different flavors of Majorana fermions. arXiv:1704.06134v3 [cond-mat.str-el]

SU(4)-symmetric spin-orbital liquids on the hyperhoneycomb lattice

“…The convention is such that states with the same τ z are conjugated by time reversal and share the same electronic density distribution [35,48].…”

“…The vector M can be identified with the dipole moment M = J of the j = 3/2 multiplet [32,35]. Similarly, T γ a is an octupole forming a Γ 4 irreducible representation of the octahedral group.…”

<i>j</i> = 3/2 Quantum spin-orbital liquids

“…My original results are presented and discussed in chapters 3, 4 and 5. Chapter 3 starts with a presentation of the local physics of 4/5d 1 Mott insulators. One result of this doctoral work was the development of s = 1/2 pseudospin s and pseudo-orbital τ operators that faithfully describe the physics inside the j = 3/2 manifold.…”

“…One result of this doctoral work was the development of s = 1/2 pseudospin s and pseudo-orbital τ operators that faithfully describe the physics inside the j = 3/2 manifold. (1,4) After developing the necessary technology to understand the electronic degrees of freedom, the chapter gives a general algorithm to derive effective models for the studied compounds. These models resemble the Kugel-Khomskii models that describe the physics of Mott insulators retaining twofold orbital degeneracy.…”

“…Chapter 6 summarizes the results and gives my conclusions regarding this work. Overall, this thesis shows how 4/5d 1 Mott insulators can be modeled and how possible QSOL ground states in this compounds are investigated, both theoretically and experimentally. I close the thesis with open questions and promising extensions of the present work.…”