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ABSTRACT: We perform a systematic quantum Monte Carlo study of the pairing correlation in the S_{4} symmetric microscopic model for iron-based superconductors. It is found that the pairing with an extensive s-wave symmetry robustly dominates over other pairings at low temperature in a reasonable parameter region regardless of the change of Fermi surface topologies. The pairing susceptibility, the effective pairing interaction, and the (π, 0) antiferromagnetic correlation strongly increase as the on-site Coulomb interaction increases, indicating the importance of the effect of electron-electron correlation. Our nonbiased numerical results provide a unified understanding of the superconducting mechanism in iron pnictides and iron chalcogenides and demonstrate that the superconductivity is driven by strong electron-electron correlation effects.
Physical Review Letters 03/2013; 110(10):107002. · 7.37 Impact Factor
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ABSTRACT: In a pristine monolayer graphene subjected to a constant electric field along
the layer, the Bloch oscillation of an electron is studied in a simple and
efficient way. By using the electronic dispersion relation, the dynamic formula
of semi-classical velocity is derived analytically, and then many aspects of
conventional Bloch oscillation, such as the frequency, amplitude, as well as
the direction of the oscillation, are investigated. It is interesting to find
that the electric field should affect the component of motion which is
non-collinear with electric field, making the particle accelerated or
oscillated in another component.
01/2013;
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ABSTRACT: In this paper, we try to establish a connection between a quantum information
concept, i.e. the mutual information, and the conventional order parameter in
condensed matter physics. We show that a non-vanishing mutual information at a
long distance means the existence of long-range order. By analyzing the
entanglement spectra of the reduced density matrix that are used to calculate
the mutual information, we show how to find the local order operator used to
identify various phases with long-rang order.
09/2012;
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ABSTRACT: We perform a systematic quantum Monte Carlo study of the pairing correlation
in the $S_4$ symmetric microscopic model for iron-based superconductors. It is
found that the pairing with an extensive s-wave symmetry robustly dominates
over other pairings at low temperature in reasonable parameter region. The
pairing susceptibility, the effective pairing interaction and the
$(\pi,0)$antiferromagnetic correlation strongly increase as the on-site Coulomb
interaction increases, indicating the importance of the effect of
electron-electron correlation. Our non-biased numerical results provide a
unified understanding of superconducting mechanism in iron-pnictides and
iron-chalcogenides and demonstrate that the superconductivity is driven by
strong electron-electron correlation effects.
06/2012;
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ABSTRACT: We have studied the electronic properties in aperiodic graphene superlattices
of Thue-Morse sequence. Although the structure is aperiodic, an unusual Dirac
point (DP) does exist and its location is exactly at the position of the
zero-averaged wave number (zero-$\bar{k})$. Furthermore, the zero-$\bar{k}$ gap
associated with the DP is robust against the lattice constants and the incident
angles, and multi-DPs can appear under the suitable conditions. A resultant
controllability of electron transport in Thue-Morse sequence is predicted,
which may facilitate the development of many graphene-based electronics.
02/2012;
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ABSTRACT: We study the quantum Zeno effect (QZE) in a many-body system, namely the Lipkin–Meshkov–Glick model, coupled to a central qubit. Our result shows that in order to observe QZE in the symmetry-broken phase of the model, the frequency of the projective measurement should be of comparable order to that of the system sizes. However, in the polarized phase of the model, the QZE can be easily observed by frequent measurements.
Journal of Physics A Mathematical and Theoretical 01/2012; 45(7):075306. · 1.56 Impact Factor
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ABSTRACT: Understanding magnetism and electron correlation in many unconventional superconductors is essential to explore mechanism of superconductivity. In this work, we perform a systematic numerical study of the magnetic and pair binding properties in recently discovered polycyclic aromatic hydrocarbon (PAH) superconductors including alkali-metal-doped picene, coronene, phenanthrene, and dibenzopentacene. The π-electrons on the carbon atoms of a single molecule are modelled by the one-orbital Hubbard model, and the energy difference [Formula: see text] between carbon atoms with and without hydrogen bonds is taking into account. We demonstrate that the spin polarized ground state is realized for charged molecules in the physical parameter regions, which provides a reasonable explanation of local spins observed in PAHs. In alkali-metal-doped dibenzopentacene, our results show that electron correlation may produce an effective attraction between electrons for the charged molecule with one or three added electrons.
Scientific Reports 01/2012; 2:922.
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ABSTRACT: With quantum Monte Carlo methods, we investigate the consequences of placing
a magnetic adatom adjacent to a vacancy in a graphene sheet. We find that
instead of the adatom properties depending on the energy of the adatom orbital,
as in a single impurity problem, they develop a dependence on the energy of the
split localized state associated with the single vacancy problem. Shifting the
chemical potential through this experimentally more accessible energy scale
reveals novel behavior in the spectral density, magnetic susceptibility, and
the correlations of the adatom spin and charge with those of the conduction
electrons. In general, the behavior of the adatom in the presence of a vacancy
differs significantly from its behavior in the absence of a vacancy.
12/2011;
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ABSTRACT: To address the issue of electron correlation driven superconductivity in
graphene, we perform a systematic quantum Monte Carlo study of the pairing
correlation in the t-U-V Hubbard model on a honeycomb lattice. For V=0 and
close to half filling, we find that pairing with d+id symmetry dominates
pairing with extended-s symmetry. However, as the system size or the on-site
Coulomb interaction increases, the long-range part of the d+id pairing
correlation decreases and tends to vanish in the thermodynamic limit. An
inclusion of nearest-neighbor interaction V, either repulsive or attractive,
has a small effect on the extended-s pairing correlation, but strongly
suppresses the d+id pairing correlation.
09/2011;
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ABSTRACT: In this paper, we study the ground state of a one-dimensional exactly
solvable model with a spiral order. While the model's energy spectra is the
same as the one-dimensional transverse field Ising model, its ground state
manifests spiral order with various periods. The quantum phase transition from
a spiral-order phase to a paramagnetic phase is investigated in perspectives of
quantum information science and mechanics. We show that the modes of the
ground-state fidelity and its susceptibility can tell the change of periodicity
around the critical point. We study also the spin torsion modulus which defines
the coefficient of the potential energy stored under a small rotation. We find
that at the critical point, it is a constant; while away from the critical
point, the spin torsion modulus tends to zero.
08/2011;
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ABSTRACT: We used a quantum Monte Carlo method to study the magnetic impurity adatoms
on graphene. We found that by tuning the chemical potential we could switch the
values of the impurity's local magnet moment between relatively large and small
values. Our computations of the impurity's spectral density found its behavior
to differ significantly from that of an impurity in a normal metal and our
computations of the charge-charge and spin-spin correlations between the
impurity and the conduction band electrons found them to be strongly
suppressed. In general our results are consistent with those from poor man's
scaling and numerical renormalization group methods.
07/2011;
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ABSTRACT: We study the quantum Zeno effect (QZE) in two many-body systems, namely the
one-dimensional transverse-field Ising model and the Lipkin-Meshkov-Glick (LMG)
model, coupled to a central qubit. Our result shows that in order to observe
QZE in the Ising model, the frequency of the projective measurement should be
of comparable order to that of the system sizes. The same criterion also holds
in the symmetry broken phase of the LMG model while in the model's polarized
phase, the QZE can be easily observed.
07/2011;
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ABSTRACT: Pairwise quantum discord (QD) and classical correlation (CC) are studied in the XY spin chain with three-spin interaction. We analyze their capability in detecting quantum phase transitions (QPTs) at both zero and finite temperatures and find that the pairwise QD of two neighboring spins is more reliable than that of any other distances in identifying QPTs. Both the QD and CC detect quantum critical points associated with first- and higher-order QPTs caused by field and three-spin interactions at finite temperatures. In addition, we find a different finite-size scaling behavior for QD from previous reports for the transverse field Ising case and show some interesting phenomena of QD and entanglement of formation for finite temperatures.
Phys. Rev. A. 05/2011; 83(5).
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Computer Physics Communications. 01/2011; 182:74-76.
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ABSTRACT: We investigate the quantum phase transitions in the half-filled ionic Hubbard model on a two-dimensional (2D) square lattice using the variational cluster approach (VCA). We present explicit evidence for the tendency toward a novel intermediate phase in this model. This phase is characterized by bond-located magnetization. For weak Coulomb repulsion U, the system is a band insulator, and then undergoes a transition to the intermediate phase at the first-phase boundary U=Uc1. As U is increased beyond the second transition point Uc2, there occurs a Mott insulator accompanied by a long-range antiferromagnetic (AF) order. The bond-located spin density wave competes with the antiferromagnetism while the charge-density modulation exists all the way due to the staggered potential Δ.
New Journal of Physics 09/2010; 12(9):093021. · 4.18 Impact Factor
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ABSTRACT: In the present paper, we study the properties of the two-dimensional quantum compass model by a mathematically rigorous approach. Based on the Perron–Fröbenius theorem and the reflection positivity method, we show that the low-energy spectrum of this model is of one-dimensional type. Furthermore, its global ground states have a directional long-range order. Our results confirm several previous conclusions obtained by either numerical or perturbation calculations
Journal of Physics A Mathematical and Theoretical 06/2010; 43(27):275001. · 1.56 Impact Factor
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ABSTRACT: We study the reduced fidelity and reduced fidelity susceptibility in the Kitaev honeycomb model. It is shown that the reduced fidelity susceptibility of two nearest site manifest itself a peak at the quantum phase transition point, although the one-site reduced fidelity susceptibility vanishes. Our results directly reveal that the reduced fidelity susceptibility can be used to characterize the quantum phase transition in the Kitaev honeycomb model, and thus suggest that the reduced fidelity susceptibility is an accurate marker of the topological phase transition when it is properly chosen, despite of its local nature. Comment: 5 pages, 9 figures
05/2010;
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ABSTRACT: In this brief report, we present a proposal to observe the classical zeno effect via the frequent measurement in optics. Comment: 2 pages, 2 figures
03/2010;
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ABSTRACT: We propose a scheme to induce transparency in one-dimensional disordered multilayers which are composed of negative permittivity and negative permeability metamaterials. First, analytical expressions for transparency condition are derived exactly, providing us a picture that complete tunneling in such kind of multiple-resonance system can be achieved if exponentially growing waves can compensate exponentially decaying waves. Second, a compensating method is used to realize this idea, and both simulations and experiments are performed in the microwave regime to confirm the theoretical analysis. Last, we have a discussion on how the coupling of resonances affects the transport properties of samples.
Optics Express 12/2009; 17(26):24371-6. · 3.59 Impact Factor
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ABSTRACT: We systematically study magnetic correlations in graphene within Hubbard model on a honeycomb lattice by using quantum Monte Carlo simulations. In the filling region below the Van Hove singularity, the system shows a short-range ferromagnetic correlation, which is slightly strengthened by the on-site Coulomb interaction and markedly by the next-nearest-neighbor hopping integral. The ferromagnetic properties depend on the electron filling strongly, which may be manipulated by the electric gate. Due to its resultant controllability of ferromagnetism, graphene-based samples may facilitate the development of many applications. Comment: Published version in Applied Physics Letters
12/2009;
