24 November 2021 Wed 5 pm

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Localized magnon states and one-magnon flat bands have been is the focus of intensive researches during last years. A number of geometrically frustrated quantum spin models have been considered in the context of localized magnon states. They share general features of a low-temperature magneto-thermal behavior, e.g. magnetization jumps, enhanced magnetocaloric effect, low-temperature thermodynamics in terms of hard-core object arrangements on the corresponding auxiliary lattice, etc. Usually, the localized states are possible only at the certain strict relations between the lattice exchange coupling constants. In the present talk we consider an extension of the flat-band scenario in one-dimensional frustrates S=1/2 spin model, which becomes possible due to additional antisymmetric exchange (Dzyaloshinskii-Moriya interaction) in general and in its particular case, magnetoelectric coupling due to Katsura-Nagaosa-Baladsky (KNB) mechanism. Thus, in the context of KNB mechanism one can have an electric field induced flat bands. We will present in detail the case of S=1/2 XXZ sawtooth chain. Electric field acting on the spin configurations due to KNB mechanism can induce a localized one- magnon states even if the parameters of symmetric exchange interaction do not satisfy the flat band condition. Tuning the magnitude and the direction of the electric field, it is possible to obtain several flat-bands. Interestingly, if the direction of the electric field coincides with the basal line of the chain, the value of the saturation magnetic field can be lowered. The mechanism is quite general, some preliminary result for other frustrated one-dimensional quantum spin model will be also presented.

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