We present studies of thermal entanglement of a three-spin system intriangular symmetry. Spin correlations are described within an effectiveHeisenberg Hamiltonian, derived from the Hubbard Hamiltonian, withsuper-exchange couplings modulated by an effective electric field. Additionallya homogenous magnetic field is applied to completely break the degeneracy ofthe system. We show that entanglement is generated in the subspace of doubletstates with different pairwise spin correlations for the ground and excitedstates. At low temperatures thermal mixing between the doublets with the samespin destroys entanglement, however one can observe its restoration at highertemperatures due to the mixing of the states with an opposite spin orientationor with quadruplets (unentangled states) always destroys entanglement. Pairwiseentanglement is quantified using concurrence for which analytical formulae arederived in various thermal mixing scenarios. The electric field plays aspecific role -- it breaks the symmetry of the system and changes spincorrelations. Rotating the electric field can create maximally entangled qubitpairs together with a separate spin (monogamy) that survives in a relativelywide temperature range providing robust pairwise entanglement generation atelevated temperatures.
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