Topological superconductivity in the Kondo-Kitaev model

Abstract

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]

Soliton signature in the phonon spectrum of twisted bilayer graphene

“…Similar to previous studies [6,[9][10][11][12][13][14][15], accommodation between the layers is observed in order to minimize the AA-stacking region, which proves especially significant for small twist angles. Buckling is found to occur for certain structures with twist angles that are below some critical buckling angle θ B , defined here as the angle below which negative modes are observed for the corresponding structure after one full CG relaxation.…”

“…Unconventional superconductivity and magnetism were not typically associated with graphene until very recently with the observation of strong electronic correlation in bilayer graphene twisted roughly at the θ = 1.1°magic angle [1][2][3][4][5]. This effect is related to the emergence of flat electronic bands with narrow band width [1,[5][6][7][8], and theoretical studies have established the importance of structural relaxation in the description of these phenomena [6,[9][10][11][12][13][14][15]. The atomic relaxation in twisted bilayer graphene (tBLG) is linked to the development of strain fields that tend to minimize the unfavorable AA-stacking regionswith local buckling-and lead to the formation of triangular domain patterns in the moiré pattern.…”

“…Most of the existing theoretical studies devoted to tBLGs have focused on electronic properties. However, tBLG phonons are also expected to be affected by the formation of the moiré superlattice and its underlying strain fields, since they fundamentally correspond to excitations of the lattice [13,18,19]. Studying the large unit-cells corresponding to small values of twisting angles is computationally challenging and a fine analysis of the tBLG phonons has proven difficult, since a full treatment requires the calculations of dynamical matrices with hundreds of thousand elements for structures prepared at a minimum energy configuration.…”

Critical role of device geometry for the phase diagram of twisted bilayer graphene

“…Several groups have reported the experimental observation of correlated insulator states in both doped and undoped tBLG near the magic twist angle [1][2][3][4]. Despite much theoretical work, no consensus has yet been reached regarding the microscopic mechanism of these phases [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Superconductivity is also found at low temperatures [2][3][4], but neither the nature of the pairing interaction nor the symmetry of the superconducting order parameter have been determined.…”

Competition between Kondo physics and Kitaev physics in Kitaev clusters coupled to a fermionic bath

“…Subsequent studies, using perturbative scaling [13,14] as well as more rigorous numerical treatment using the numerical renormalization group [15], have shown the existence of an unstable fixed point that gives rise to a first-order flux transition between the weak-coupling flux-free phase and the strongcoupling impurity-flux phase, upon tuning the coupling between the impurity and the lattice. Other studies have used slave-particle mean field theories to investigate situations involving a Kondo lattice model on the honeycomb lattice with Kitaev interactions among the local moments, giving rise to fractionalized Fermi liquid behavior and exotic superconductivity [16,17]. Here, the effective hybridization of Majorana modes and conduction electrons due to the Kondo effect imprints superconductivity onto the conduction electron system.…”