Large magnetic thermal conductivity induced by frustration in low-dimensional quantum magnets

: We study the magnetic field-dependence of the thermal conductivity due to magnetic excitations in frustrated spin-1/2 Heisenberg chains. Near the saturation field, the system is described by a dilute gas of weakly-interacting fermions (free-fermion fixed point). We show that in this regime the thermal conductivity exhibits a non-monotonic behavior as a function of the ratio α=J2/J1 between second and first nearest-neighbor antiferromagnetic exchange interactions. This result is a direct consequence of the splitting of the single-particle dispersion minimum into two minima that takes place at the Lifshitz point α=1/4. Upon increasing α from zero, the inverse mass vanishes at α=1/4 and it increases monotonically from zero for α≥1/4. By deriving an effective low-energy theory of the dilute gas of fermions, we demonstrate that the Drude weight Kth of the thermal conductivity exhibits a similar dependence on α near the saturation field. Moreover, this theory predicts a transition between a two-component Tomonaga-Luttinger liquid and a vector-chiral phase at a critical value α=αc that agrees very well with previous density matrix renormalization group results. We also show that the resulting curve Kth(α) is in excellent agreement with exact diagonalization (ED) results. Our ED results also show that Kth(α) has a pronounced minimum at α≃0.7 and it decreases for sufficiently large α at lower magnetic field values. We also demonstrate that the thermal conductivity is significantly affected by the presence of magnetothermal coupling