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• 1
Article
Language: English
In: Physical review letters, 13 May 2016, Vol.116(19), pp.197201
Description: Using a specially designed Monte Carlo algorithm with directed loops, we investigate the triangular lattice Ising antiferromagnet with coupling beyond the nearest neighbors. We show that the first-order transition from the stripe state to the paramagnet can be split, giving rise to an intermediate nematic phase in which algebraic correlations coexist with a broken symmetry. Furthermore, we demonstrate the emergence of several properties of a more topological nature such as fractional edge excitations in the stripe state, the proliferation of double domain walls in the nematic phase, and the Kasteleyn transition between them. Experimental implications are briefly discussed.
Keywords: Condensed Matter - Strongly Correlated Electrons ; Condensed Matter - Statistical Mechanics;
ISSN: 00319007
E-ISSN: 1079-7114
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• 2
Article
Language: English
In: Physical Review B, 7/2012, Vol.86(1)
Description: The quantum antiferromagnetic spin-1/2 Ising model on a triangular lattice and analogous fully frustrated Ising model on a square lattice with quantum fluctuations induced by the application of the transverse magnetic field are studied at finite temperatures by constructing an exact mapping onto a purely classical model with a more complex interaction. It is shown that in weak fields the temperatures of the phase transitions separating the critical phase from the ordered and disordered phases in both models are proportional to the magnitude of the field. Comment: 5 pages, RevTex4
Keywords: Condensed Matter - Strongly Correlated Electrons;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 3
Article
Language: English
In: Physical Review B, 4/2012, Vol.85(13)
Description: The phase diagram of the fully frustrated XY model on a honeycomb lattice is shown to incorporate three different ordered phases. In the most unusual of them, a long-range order is related not to the dominance of a particular periodic vortex pattern but to the orientation of zero-energy domain walls separating domains with different orientations of vortex stripes. The phase transition leading to the destruction of this phase can be associated with the appearance of free fractional vortices and is of the first order. The stabilization of the two other ordered phases (existing at lower temperatures) relies a positive contribution to domain-wall free energy induced by the presence of spin waves. This effect has a substantial numerical smallness, in accordance with which these two phases can be observed only in the systems of really macroscopic sizes. In physical systems (like magnetically frustrated Josephson junction arrays and superconducting wire networks), the presence of additional interactions must lead to a better stabilization of the phase with the long-range order in terms of vortex pattern and improve the possibilities of its observation. Comment: 20 pages, 11 figures
Keywords: Condensed Matter - Statistical Mechanics ; Condensed Matter - Superconductivity;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 4
Article
Language: English
In: Physical Review B, 8/2015, Vol.92(6)
Description: We show that a physical realization of the phase diagram proposed by Minnhagen et al. [Phys. Rev. B 78, 184432 (2008) (http://dx.doi.org/10.1103/PhysRevB.78.184432)] for the socalled generalized fully frustrated XY model on a square lattice can be achieved in arrays of superconductor-ferromagnet-superconductor junctions near the transition of the junctions to the [pi] state. Moreover, the phase diagram with such a topology has to be reproduced twice, on both sides of the 0-[pi] transition.
Keywords: Phase Diagrams ; Topology ; Condensed Matter ; Lattices ; Arrays ; Condensed Matter Physics (General) (So) ; Physics of Metals (MD) ; Atomic Properties (Ep) ; Atomic Properties (Ed) ; Atomic Properties (EC) ; Solid-State Physics (Ah);
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 5
Article
Language: English
In: Physical Review B, 6/2011, Vol.83(23)
Description: We propose a new quantum model interpolating between the fully frustrated spin-1/2 Ising model in a transverse field and a dimer model. This model contains a resonating-valence-bond phase, including a line with an exactly solvable ground state of the Rokhsar-Kivelson type. We discuss the phase diagrams of this model on the square and triangular (in terms of the dimer representation) lattices. Comment: 9 pages, 7 figures
Keywords: Condensed Matter - Strongly Correlated Electrons;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 6
Article
Language: English
In: Physical Review B, 11/2014, Vol.90(20)
Description: We investigate the zero-temperature phase diagram of the fully frustrated transverse field Ising model on the square lattice both in the classical limit and in the presence of quantum fluctuations. At the classical level (the limit of infinite spin $S$), we find that upon decreasing the transverse field $\Gamma$ this model exhibits a phase transition from the fully polarized state into an eight-fold degenerate translational symmetry breaking state. This phase can be identified to correspond to plaquette order in the dimer language and remains the lowest-energy state in the entire range of fields below the critical one, $\Gamma_c$. The eight-fold degenerate solution which corresponds to columnar order in the dimer language is a saddle point of the classical energy. It is degenerate with the plaquette solution at $\Gamma=0$ and is only slightly higher in energy in the whole interval $0〈\Gamma〈\Gamma_c$. The effect of quantum fluctuations is investigated in the context of a large S expansion both for the plaquette and columnar structures. For this purpose we employ an approximate method allowing to estimate from above the fluctuation-induced correction to the energy of a configuration which at the classical level is a saddle point of the energy, \textit{not} a local minimum. Although the convergence of the $1/S$ expansion in the $\Gamma/J\rightarrow 0$ limit remains an open question, harmonic quantum fluctuations show a clear tendency to overcome the energy difference between the two states and to change the classical picture favoring the columnar order over the plaquette one in a wide parameter range. Comment: 14 pages, 6 figures
Keywords: Condensed Matter - Strongly Correlated Electrons;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 7
Article
Language: English
In: Physical Review B, 1/2012, Vol.85(1)
Description: We revisit the issue of the gap symmetry in KFe2As2, which is an Fe-pnictide superconductor with only hole pockets. Previous theoretical studies mostly argued for a d-wave gap in KFe2As2 since transport and thermodynamic measurements point to the presence of the gap nodes. However, a d-wave gap is inconsistent with recent laser-based angle-resolved photoemission measurements. We propose the scenario for a nodal s-wave superconductivity induced by a non-magnetic intra-band and inter-band interactions between fermions near hole pockets. The superconducting gap changes sign between the hole pockets and has cos 4\theta angular dependence and accidental nodes on one or several hole pockets. We argue that strong angle dependence is the consequence of near-degeneracy between inter-pocket and intra-pocket interaction on the hole pockets. We also analyze cos 4\theta angular dependence of the gap in other Fe-pnictides and compare theoretical results with the photoemission experiments of LiFeAs. Comment: 10 pages, 6 figs, 1 table; Uploading version revised for PRB
Keywords: Condensed Matter - Superconductivity;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 8
Article
Language: English
In: Physical Review B, 9/2013, Vol.88(9)
Description: We investigate the ground-state properties of the highly degenerate non-coplanar phase of the classical bilinear-biquadratic Heisenberg model on the triangular lattice with Monte Carlo simulations. For that purpose, we introduce an Ising pseudospin representation of the ground states, and we use a simple Metropolis algorithm with local updates, as well as a powerful cluster algorithm. At sizes that can be sampled with local updates, the presence of long-range order is surprisingly combined with an algebraic decay of correlations and the complete disordering of the chirality. It is only thanks to the investigation of unusually large systems (containing $\sim 10^8$ spins) with cluster updates that the true asymptotic regime can be reached and that the system can be proven to consist of equivalent (i.e., equally ordered) sublattices. These large-scale simulations also demonstrate that the scalar chirality exhibits long-range order at zero temperature, implying that the system has to undergo a finite-temperature phase transition. Finally, we show that the average distance in the order parameter space, which has the structure of an infinite Cayley tree, remains remarkably small between any pair of points, even in the limit when the real space distance between them tends to infinity. Comment: 15 pages, 10 figures
Keywords: Condensed Matter - Strongly Correlated Electrons;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 9
Article
Language: English
In: Physical review letters, 02 November 2012, Vol.109(18), pp.187202
Description: Using extensive classical and quantum Monte Carlo simulations, we investigate the ground-state phase diagram of the fully frustrated transverse field Ising model on the square lattice. We show that pure columnar order develops in the low-field phase above a surprisingly large length scale, below which an effective U(1) symmetry is present. The same conclusion applies to the quantum dimer model with purely kinetic energy, to which the model reduces in the zero-field limit, as well as to the stacked classical version of the model. By contrast, the 2D classical version of the model is shown to develop plaquette order. Semiclassical arguments show that the transition from plaquette to columnar order is a consequence of quantum fluctuations.
Keywords: Condensed Matter - Strongly Correlated Electrons;
ISSN: 00319007
E-ISSN: 1079-7114
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• 10
Article
Language: English
In: Journal of Physics: Condensed Matter, 2011, Vol.23(4), p.045701 (6pp)
Description: Several experimental and theoretical studies indicate the existence of a critical point separating the underdoped and overdoped regions of the high- T c cuprates phase diagram. There are at least two distinct proposals on the critical concentration and its physical origin. The first one is associated with the pseudogap formation for p 〈 p * , with p * 0.2. The other relies on the Hall effect measurements and suggests that the critical point and the quantum phase transition (QPT) take place at optimal doping, p opt 0.16. Here we have performed a precise density of states calculation and found that there are two QPTs and the corresponding critical concentrations associated with the change of the Fermi surface topology upon doping.
Keywords: Phases ; Phase Transformations ; Cuprates ; Mathematical Analysis ; Doping ; Mathematical Analysis ; Doping ; Phase Diagrams ; Copper Oxide ; Condensed Matter ; Phase Diagrams ; Phase Transformations ; Optimization ; Critical Point ; Condensed Matter Physics (General) (So) ; General and Nonclassified (Ep) ; General and Nonclassified (Ed) ; General and Nonclassified (EC) ; Physical Metallurgy (CD);
ISSN: 0953-8984
E-ISSN: 1361-648X
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