Vector chirality and inhomogeneous magnetization in frustrated spin tubes in high magnetic fields

The low-energy physics of three-leg frustrated antiferromagnetic spin-$S$ tubes in the vicinity of the upper critical field are studied. Utilizing the effective field theory based on the spin-wave approximation, we argue that in the intermediate-interchain-coupling regime, the ground state exhibits a vector chiral order or an inhomogeneous magnetization for the interchain (rung) direction and the low-energy excitations are described by a one-component Tomonaga-Luttinger liquid (TLL). In both chiral and inhomogeneous phases, the $Z_2$ parity symmetry along the rung direction is spontaneously broken. It is also predicted that a two-component TLL appears and all the symmetries are restored in the strong-rung-coupling case.

Figure 1

(Color online) Classical ground state of the spin tube (1).

Figure 2

(Color online) Magnon bands in Eq. (2).

Figure 3

(Color online) Schematic ground-state phase diagram of the $S=\frac{1}{2}$ spin tube (1). The area away from the saturation is discussed elsewhere (Ref. 24). See Endnotes 12 and 17.