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ESR study of the spin ladder with uniform Dzyaloshinskii-Moriya interaction
Evolution of the ESR absorption in a strong-leg spin ladder magnet (C7H10N)2CuBr4 (abbreviated as DIMPY)
is studied from 300 K to 400 mK. Temperature dependence of the ESR relaxation follows a staircase of crossovers
between different relaxation regimes. We argue that the main mechanism of ESR line broadening in DIMPY is
uniform Dzyaloshinskii-Moriya interaction (|D| = 0.31 K) with an effective longitudinal component along an
exchange bond of Cu ions within the legs resulting from the low crystal symmetry of DIMPY and nontrivial
orbital ordering. The same Dzyaloshinskii-Moriya interaction along with other weaker anisotropic spin-spin
interactions results in the lifting of the triplet excitation degeneracy, revealed through the weak splitting of the
ESR absorption at low temperatures.