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Quantum critical point in the spin glass–antiferromagnetism competition for fermionic Ising models

✍ Scribed by F.M. Zimmer; S.G. Magalhães


Publisher
Elsevier Science
Year
2006
Tongue
English
Weight
300 KB
Volume
359
Category
Article
ISSN
0378-4371

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✦ Synopsis


The competition between spin glass (SG) and antiferromagnetic order (AF) is analyzed in two-sublattice fermionic Ising models in the presence of a transverse G and a parallel H magnetic fields. The exchange interaction follows a Gaussian probability distribution with mean À4J 0 =N and standard deviation J ffiffiffiffiffiffiffiffiffiffiffi ffi 32=N p , but only spins in different sublattices can interact. The problem is formulated in a path integral formalism, where the spin operators have been expressed as bilinear combinations of Grassmann fields. The results of two fermionic models are compared. In the first one, the diagonal S z operator has four states, where two eigenvalues vanish (4S model), which are suppressed by a restriction in the two states 2S model. The replica symmetry ansatz and the static approximation have been used to obtain the free energy. The results are showing in phase diagrams T=J (T is the temperature) versus J 0 =J, G=J, and H=J. When G is increased, T f (transition temperature to a non-ergodic phase) reduces and the Neel temperature decreases towards a quantum critical point. The field H always destroys AF; however, within a certain range, it favors the frustration. Therefore, the presence of both fields, G and H, produces effects that are in competition. The critical temperatures are lower for the 4S model and it is less sensitive to the magnetic couplings than the 2S model.


📜 SIMILAR VOLUMES


Solutions for the T = 0 quantum spin gla
✍ R. Oppermann; M. Binderberger 📂 Article 📅 1994 🏛 John Wiley and Sons 🌐 English ⚖ 966 KB

We solve several low temperature problems of an infinite range metailic spin glass model. A compensation problem of T-0 divergencies is solved for the free energy which helped to extract the quantum critical behaviour of the spin glass order parameters as a function of J-J,(T= 0). The critical value