Fermionic Heisenberg glasses with BCS pairing interaction (original) (raw)
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Antiferromagnetic Ising spin glass competing with BCS pairing interaction in a transverse field
The European Physical Journal B, 2006
The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J. The problem is formulated in the path integral formalism in which spin operators are represented by bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations affect deeply the transition lines and the tricritical point due to the presence of Γ.
Coexistence of spin-glass and ferromagnetic order in the ±J Heisenberg spin-glass model
Physical Review B, 2007
simulations of the bond-frustrated ±J Heisenberg model confirm the existence of a finite temperature spin-glass transition at T SG = 0.220͑5͒. Remarkably, this transition temperature is composition dependent, rising to T SG = 0.25͑1͒ by the ferromagnet-spin-glass boundary. Coexistence of ferromagnetic and spin-glass ordering is observed at low frustration levels for T Ͻ T xy , and the composition dependence of this transition is also followed. The behavior we observe below T xy agrees with both the mean field prediction and the experimental observations while being inconsistent with "re-entrance," which demands a loss of ferromagnetic order. The complete phase diagram is presented.
Dynamical ac study of the critical behavior in Heisenberg spin glasses
Physical Review B, 2005
We present some numerical results for the Heisenberg spin-glass model with Gaussian interactions, in a three dimensional cubic lattice. We measure the AC susceptibility as a function of temperature and determine an apparent finite temperature transition which is compatible with the chiral-glass temperature transition for this model. The relaxation time diverges like a power law τ ∼ (T − T c) −zν with T c = 0.19(4) and zν = 5.0(5). Although our data indicates that the spin-glass transition occurs at the same temperature as the chiral glass transition, we cannot exclude the possibility of a chiral-spin coupling scenario for the lowest frequencies investigated.
Quantum phase transition in spin glasses with multi-spin interactions
Physica a, 1998
We examine the phase diagram of the p-interaction spin glass model in a transverse field. We consider a spherical version of the model and compare with results obtained in the Ising case. The analysis of the spherical model, with and without quantization, reveals a phase diagram very similar to that obtained in the Ising case. In particular, using the static approximation, reentrance is observed at low temperatures in both the quantum spherical and Ising models. This is an artifact of the approximation and disappears when the imaginary time dependence of the order parameter is taken into account. The resulting phase diagram is checked by accurate numerical investigation of the phase boundaries.
Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction
2015
Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [ Phys. Rev. B 73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series 640, 012001 (2015)] reported SG ba...
Dynamical aspects of a three-dimensional Heisenberg spin glass
2000
Spin-glass and chiral-glass orderings of a three-dimensional isotropic Heisenberg spin glass are studied both by equilibrium and off-equilibrium Monte Carlo simulations with emphasis on their dynamical aspects. The model is found to exhibit a finite-temperature chiral-glass transition without the conventional spin-glass order. Although chirality is an Ising-like quantity from symmetry, universality class of the chiral-glass transition appears to be different
Dynamical solutions of a quantum Heisenberg spin glass model
The European Physical Journal B, 2004
We consider quantum-dynamical phenomena in the SU(2), S = 1/2 infinite-range quantum Heisenberg spin glass. For a fermionic generalization of the model we formulate generic dynamical selfconsistency equations. Using the Popov-Fedotov trick to eliminate contributions of the non-magnetic fermionic states we study in particular the isotropic model variant on the spin space. Two complementary approximation schemes are applied: one restricts the quantum spin dynamics to a manageable number of Matsubara frequencies while the other employs an expansion in terms of the dynamical local spin susceptibility. We accurately determine the critical temperature Tc of the spin glass to paramagnet transition. We find that the dynamical correlations cause an increase of Tc by 2% compared to the result obtained in the spin-static approximation. The specific heat C(T) exhibits a pronounced cusp at Tc. Contradictory to other reports we do not observe a maximum in the C(T)-curve above Tc.
Journal of the Physical Society of Japan, 2010
The nature of the ordering of the one-dimensional Heisenberg spin-glass model with a longrange power-law interaction is studied by extensive Monte Carlo simulations, with particular attention to the issue of the spin-chirality decoupling/coupling. Large system sizes up to L = 4096 are studied. With varying the exponent σ describing the power-law interaction, we observe three distinct types of ordering regimes. For smaller σ, the spin and the chirality order at a common finite temperature with a common correlation-length exponent, exhibiting the standard spin-chirality coupling behavior. For intermediate σ, the chirality orders at a temperature higher than the spin, exhibiting the spin-chirality decoupling behavior. For larger σ, both the spin and the chirality order at zero temperature. We construct a phase diagram in the σ versus the temperature plane, and discuss implications of the results. Critical properties associated with both the chiral-glass and the spin-glass transitions are also determined.
Spin glasses and other lattice systems with long range interactions
Communications In Mathematical Physics, 1989
We study classical lattice systems, in particular real spin glasses with Ruderman-Kittel interactions and dipole gases, with interactions of very long (non-summable) range but variable sign. Using the Kac-Siegert representation of such systems and Brascamp-Lieb inequalities we are able to establish detailed properties of the high-temperature phase, such as decay of connected correlations, for these systems.