Thermal entanglement of a coupled electronic spins system: interplay between an external magnetic field, nuclear field and spin-orbit interaction

We have studied the thermal entanglement as a function of the temperature for a two-qubits Heisenberg spins system; we have included Dzyaloshinskii-Moriya interaction (DM), an external magnetic field (EMF) and hyperfine interaction due to the nuclear field of the surrounding nuclei. A critical value for the EMF was found, around B-ext, z((c)) similar to 39 mT, which characterizes two regimes of behavior of the thermal entanglement. Our results show that the DM term acts as a facilitator for the entanglement because it prolongs the nonzero thermal entanglement for larger temperatures. We found that the concurrence as a function of the temperature has a local maximum, for values of the magnetic field larger than the critical field. We also show that the critical temperature T-c follows a polynomial growth as a function of the DM term, with characteristic behavior T-c similar to beta(2)(0), and the hyperfine field implies a critical temperature as a function of the field variance, sigma of the form T-c similar to sigma(2). We show that in this system, the entanglement measure by the concurrence and the one-spin polarization observable exhibit opposite behavior, providing a method to obtain the entanglement from the measurement of an observable.