(Color online) The absolute amplitude of the eigenvalue spectra g(E) of the Heisenberg Hamiltonian as defined in
These are obtained for three different values of the external magnetic field h, namely h = 0, h = 0.75hc and h = 1.25hc , where hc is the critical field at which the ground state becomes degenerate. The shaded region highlights the location the the singlet state depicted in Fig. 1. The arrows indicate the direction of the peak shift when the simulated external field h is increased. The blue and red dots indicate the quantum states represented by the peak signals (cf. Fig. 1).