Gapless quantum spin liquid in a honeycomb Γ magnet

Abstract

A family of spin–orbit coupled honeycomb Mott insulators offers a playground to search for quantum spin liquids (QSLs) via bond-dependent interactions. In candidate materials, a symmetric off-diagonal Γ term, close cousin of Kitaev interaction, has emerged as another source of frustration that is essential for complete understanding of these systems. However, the ground state of honeycomb Γ model remains elusive, with a suggested zigzag magnetic order. Here we attempt to resolve the puzzle by perturbing the Γ region with a staggered Heisenberg interaction which favours the zigzag ordering. Despite such favour, we find a wide disordered region inclusive of the Γ limit in the phase diagram. Further, this phase exhibits a vanishing energy gap, a collapse of excitation spectrum, and a logarithmic entanglement entropy scaling on long cylinders, indicating a gapless QSL. Other quantities such as plaquette-plaquette correlation are also discussed.

Phases and quantum phase transitions in an anisotropic ferromagnetic Kitaev-Heisenberg- Γ magnet

“…43 (≡ γ F it ) seems to show a finite value in the large Γ phase, this however is a spurious artifact of the fitting scheme as has been pointed out in [86] for stacked/cluster SPT like states. It is pertinent to point out that in the large Γ phase we often find a curvature in the behavior of S as a function of L which may suggest a logarithmic correction [51]. However, in our limited ED calculations it is hard to separate out if this due to the gapless nature of the (λ 1 , λ 2 ) point or due to a finite correlation length in the large Γ phase.…”

“…Remarkably this gapless critical point supports edge modes that do not hybridise with the bulk modes due to subsystem symmetries. Interestingly in recent studies investigating the role of pseudo-dipolar interactions in both isotropic and anisotropic Kitaev Hamiltonians [47][48][49][50] have found gapless phases [51,52] (often for ferromagnetic Kitaev exchanges). The relevance of these other gapless phases to our work is not immediately clear and needs to be further explored.…”

Honeycomb-lattice Gamma model in a magnetic field: hidden Néel order and spin-flop transition

“…Although our semiclassical analysis only applies to largespin Gamma model, it is likely that this magnetic order is stabilized at high magnetic field even for quantum spin-1/2. A related intriguing question is what happens to the ground state of spin-1/2 Gamma model, which seems to be a gapless spin liquid that is proximate to a zigzag order [74,75], in the presence of magnetic field. Also of interest is the effect of other exchange interactions on the spin-flop state of the Γ model reported here.…”

Reentrance of metal-insulator transition and magnetic competitions on a triangular lattice with second nearest-neighbor hopping

“…In sharp contrast to the 120 • noncollinear AFM, the appearance of nonmagnetic quantum spin-liquid phase in 𝜅-(BEDT-TTF) 2 Cu 2 (CN) 3 is astonishing. Many theoretical works have been devoted to this challenging problem [32][33][34][35][36][37][38][39][40][41], with the conclusions converging to the competition of geometrical frustration and electronic correlations.…”