We investigate possible topological superconductivity in the Kondo-Kitaev model on the honeycomb lattice, where the Kitaev spin liquid is coupled to conduction electrons via the Kondo coupling. We use the self-consistent Abrikosov-fermion mean-field theory to map out the phase diagram. Upon increasing the Kondo coupling, a first order transition occurs from the decoupled phase of spin liquid and conduction electrons to a ferromagnetic topological superconductor of Class D with a single chiral Majorana edge mode. This is followed by a second order transition into a paramagnetic topological superconductor of Class DIII with a single helical Majorana edge mode. These findings offer a novel route to topological superconductivity in the Kondo lattice system. We discuss the connection between topological nature of the Kitaev spin liquid and topological superconductors obtained in this model. arXiv:1804.10212v1 [cond-mat.str-el]

Unambiguous identification of fractionalized excitations in quantum spin liquids has been a longstanding issue in correlated topological phases. The conventional spectroscopic probes, such as the dynamical spin structure factor, can only detect composites of fractionalized excitations, leading to a broad continuum in energy. Lacking a clear signature in conventional probes has been the biggest obstacle in the field. In this work, we theoretically investigate what kinds of distinctive signatures of fractionalized excitations can be probed in two-dimensional nonlinear spectroscopy by considering the exactly solvable Kitaev spin liquids. We demonstrate the existence of a number of salient features of the Majorana fermions and fluxes in two-dimensional nonlinear spectroscopy, which provide crucial information about such excitations.Quantum spin liquids (QSLs) are prominent examples of correlated topological paramagnets that may arise due to frustrating spin interactions in Mott insulators [1,2]. The long-range quantum entanglement and ground state degeneracy, which comprises the quantum order, differentiate QSLs from trivial paramagnets and symmetrybroken phases [3]. Important manifestations of the quantum order are the emergent gauge fields and quasiparticles carrying fractional quantum numbers [4]. Since the quantum entanglement is not directly observable, measuring these fractionalized excitations would be an important experimental footstep to identify quantum spin liquids. One of the most powerful probes in magnetism, the dynamical spin structure factor measured in inelastic neutron scattering, however, shows only a broad continuum as the spin-flip involves a multitude of fractionalized excitations. The absence of sharp signatures has hampered the progress in the discovery of quantum spin liquids.In this paper, we consider two-dimensional nonlinear spectroscopy as a tool to detect distinctive signatures of fractionalized quasiparticles in quantum spin liquids. The current work is motivated by a previous work that shows how the domain wall excitations in the transverse field Ising model can clearly be detected in twodimensional THz spectroscopy [5]. Here we consider the exactly solvable Kitaev spin liquids on the honeycomb lattice [6] and investigate the signatures of Majorana fermions and fluxes in the two-dimensional spectroscopy. We consider two magnetic-field pulses separated by time τ 1 and measuring the nonlinear part of the induced transient magnetization at later time τ 2 + τ 1 . The twodimensional spectroscopy is represented by two frequencies corresponding to τ 1 and τ 2 . The response consists of nonlinear susceptibilities, some of which correspond to the out-of-time-order correlators of the magnetization [7]. We show that the third order nonlinear susceptibilities can give rise to clear signatures of the Majorana fermions and fluxes in the Kitaev spin liquids. We explain how one could obtain important informations about such excitations from the output of the two-dimensional spectroscopy. Our main resu...

We propose a theoretical model for a gapless spin liquid phase that may have been observed in a recent experiment on H3LiIr2O6 [1,2]. Despite the insulating and non-magnetic nature of the material, the specific heat coefficient C/T ∼ 1/ √ T in zero magnetic field and C/T ∼ T /B 3/2 with finite magnetic field B have been observed. In addition, the NMR relaxation rate shows 1/(T1T ) ∼ (C/T ) 2 . Motivated by the fact that the interlayer/in-plane lattice parameters are reduced/elongated by the hydrogen-intercalation of the parent compound Li2IrO3, we consider four layers of the Kitaev honeycomb lattice model with additional interlayer exchange interactions. It is shown that the resulting spin liquid excitations reside mostly in the top and bottom layers of such a layered structure and possess a quartic dispersion. In an applied magnetic field, each quartic mode is split into four Majorana cones with the velocity v ∼ B 3/4 . We suggest that the spin liquid phase in these "defect" layers, placed between different stacking patterns of the honeycomb layers, can explain the major phenomenology of the experiment, which can be taken as evidence that the Kitaev interaction plays the primary role in the formation of a quantum spin liquid in this material.

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The polarization of light can be rotated in materials with an absence of molecular or structural mirror symmetry. While this rotating ability is normally rather weak in naturally occurring chiral materials, artificial chiral metamaterials have demonstrated extraordinary rotational ability by engineering intra-molecular couplings. However, while in general, chiral metamaterials can exhibit strong rotatory power at or around resonances, they convert linearly polarized waves into elliptically polarized ones. Here, we demonstrate that strong inter-molecular coupling through a small gap between adjacent chiral metamolecules can lead to a broadband enhanced rotating ability with pure rotation of linearly polarized electromagnetic waves. Strong inter-molecular coupling leads to nearly identical behaviour in magnitude, but engenders substantial difference in phase between transmitted left and right-handed waves.