Breaking Symmetry

The postwar Red Scare and McCarthyism solidified Anderson’s left-of-center politics. He solidified his position at Bell Labs by using the concept of superexchange to explain neutron scattering data from transition metal oxides. He disengaged from Shockley and studied magnetism under the tutelage of Charles Kittel, Conyers Herring, and Gregory Wannier. The Heisenberg model is used to explain ferromagnetism and antiferromagnetism and Anderson’s discovery of spontaneous symmetry breaking in quantum antiferromagnets is described. He spends six months in Japan at the invitation of Ryogo Kubo, teaches magnetism, attends and, at an international conference, learns that he is a bone fide solid-state theoretician.

Study of effective coupling between charge degrees of freedom in low dimensional hole-doped quantum antiferromagnets

Expressions for generalized charge stiffness constant at zero temperature are derived corresponding to low dimensional hole doped quantum antiferromagnets, describable by the t-J-like models, with a view to understanding fermionic pairing possibilities and charge couplings in the itinerant antiferromagnetic systems. A detailed comparison between spin and charge correlations and couplings are presented in both strong and weak coupling limits. The result highlights that the charge and spin couplings show very similar behaviour in the over-doped region in both the dimensions, whereas they show a completely different trend in the lower doping regimes. A qualitative equivalence of generalized charge stiffness constant with the effective Drude weight and Coulomb interaction is established based on the comparison with other theoretical and experimental results. The fall in charge stiffness with increase in doping then implies reduction in the magnitude of effective Coulomb repulsion between the mobile carriers. This leads to an enhanced possibility of fermionic pairing with increase in doping in the possible presence of some other attraction producing mechanism from a source outside the t-J-like models. Moreover, under certain conditions in the optimal doping region, the t-J-like models themselves are able to produce attractive interaction for pairing.