Thermodynamic properties, magnetism and Mott–Hubbard-like transitions in nanoscale clusters

Kocharian, Armen; Fernando, Gayanath; Palandage, Kalum; Davenport, J. W.

doi:10.1016/j.jmmm.2005.10.242

Cited by 23 publications

(52 citation statements)

References 32 publications

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“…We have identified the following phases in these diagrams: (I) and (II) are charge pseudogap phases separated by a phase boundary where the spin susceptibility reaches a maximum, with ∆ e−h (T ) > 0, ∆ AF (T ) = 0; at finite temperature, phase I has a higher N and coupled spin compared to phase II spin liquid phase; Phase (III) is a MH-like antiferromagnetic insulator with bound charge and spin, when ∆ e−h (T ) > 0, ∆ AF (T ) > 0; phase separation (PS) in T − µ plane for U = 4 with a vanished charge gap at N = 3, now corresponding to the opening of a pairing gap (∆ P (T ) > 0) in the electron-electron channel with ∆ c 3 (U : T ) < 0. We have also verified the well known fact that the low temperature behavior in the vicinity of half filling, with charge and spin pseudogap phases coexisting, represents an AF insulator [22]. However, away from half filling, we find very intriguing behavior in thermodynamical charge and spin degrees of freedom.…”

Section: F Phase Diagramssupporting

confidence: 82%

“…Using peaks in spin and charge susceptibilities, phase diagrams in a T vs µ plane for arbitrary U and h can be constructed. This approach also allows us to obtain quantum critical points (QCPs) and rigorous criteria for various sharp transitions, such as the Mott-Hubbard (MH), antiferromagnetic (AF) or ferromagnetic (F) transitions in the ground state [22] and charge (particle-particle) or spin condensation at finite temperatures [23] using peaks in charge or spin susceptibilities (see below).…”

Section: Charge and Spin Pseudogapsmentioning

confidence: 99%

“…Notice that µ + (T ) and µ − (T ) identify peak positions in a T − µ space for charge susceptibility χ c at finite temperature. The condition ∆ c (T ) > 0 provides electronhole (excitonic) excitations, with a positive pseudogap, ∆ e−h (T ) ≥ 0 [22]. Accordingly, the condition ∆ c (T ) < 0 with µ − (T ) > µ + (T ) gives electron-electron pairing with positive energy, ∆ P (T ) > 0 [23].…”

Section: Charge and Spin Pseudogapsmentioning

confidence: 99%

“…[22]. At zero temperature, the sharp transition at critical parameter U c (0) is defined from the condition ∆ c 3 (U c : 0) ≡ 0 which yields, U c (0) = 4.58399938.…”

Section: B Quantum Critical Pointsmentioning

confidence: 99%

“…In our opinion, thermodynamic properties of small Hubbard clusters under variation of composition, size, structure, temperature and magnetic field have not been fully explored, although there have been numerous exact calculations [20,21]. From this perspective the exact diagonalization of small Hubbard nanoclusters can give insights related to the origin of superconductivity and ferromagnetism in an ensemble of clusters, nanoparticles, and eventually, nanomaterials [22,23].…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Exact thermodynamics of pairing and charge–spin separation crossovers in small Hubbard nanoclusters

et al. 2007

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The exact numerical diagonalization and thermodynamics in an ensemble of small Hubbard clusters in the ground state and finite temperatures reveal intriguing insights into the nascent charge and spin pairings, Bose condensation and ferromagnetism in nanoclusters. The phase diagram off half filling strongly suggests the existence of subsequent transitions from electron pairing into unsaturated and saturated ferromagnetic Mott-Hubbard like insulators, driven by electron repulsion. Rigorous criteria for the existence of quantum critical points in the ground state and corresponding crossovers at finite temperatures are formulated. The phase diagram for 2 × 4-site clusters illustrates how these features are scaled with cluster size. The phase separation and electron pairing, monitored by a magnetic field and electron doping, surprisingly resemble phase diagrams in the family of doped high Tc cuprates.

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Section: F Phase Diagramssupporting

confidence: 82%

Section: Charge and Spin Pseudogapsmentioning

confidence: 99%

Section: Charge and Spin Pseudogapsmentioning

confidence: 99%

“…[22]. At zero temperature, the sharp transition at critical parameter U c (0) is defined from the condition ∆ c 3 (U c : 0) ≡ 0 which yields, U c (0) = 4.58399938.…”

Section: B Quantum Critical Pointsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exact thermodynamics of pairing and charge–spin separation crossovers in small Hubbard nanoclusters

et al. 2007

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The Hubbard model extended by nearest‐neighbor Coulomb and exchange interaction on a cubic cluster – rigorous and exact results

Schumann

Zwicker

2010

Annalen der Physik

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Key words extended Hubbard model, nearest-neighbor interaction, cubic cluster PACS 85. 80.+n, 73.22.-f, 71.27.+aThe Hubbard model on a cube was revisited and extended by both nearest-neighbor (nn) Coulomb correlation W and nearest-neighbor Heisenberg exchange J. The complete eigensystem was computed exactly for all electron occupancies and all model parameters ranging from minus infinity to plus infinity. For two electrons on the cluster the eigensystem is given in analytical form. For six electrons and infinite on-site correlation U we determinded the groundstate and the groundstate energy of the pure Hubbard model analytically. For fixed electron numbers we found a multitude of ground state level crossings. in dependence on the various model parameters. Furthermore the groundstates of the pure Hubbard model in dependence on a magnetic field h coupled to the spins are shown for the complete U − h plane. The critical magnetic field, where the zero spin groundstate breaks down is given for four and six electrons. Suprisingly we found parameter regions, where the ground state spin does not depend monotonously on J in the extended model. For the cubic cluster gas, i.e. an ensemble of clusters coupled to an electron bath, we calculated the density n(µ, T, h) and the thermodynamical density of states from the grand potential. The ground states and the various spin-spin correlation functions are studied for both attractive and repulsive values of the three interaction constants. We determined the various anomalous degeneration lines, where n(µ, T = 0, h = 0) steps more than one, since in this parameter regions exotic phenomena as phase separation are to expect in extended models. For the cases where these lines end in triple points, i.e. groundstates of three different occupation numbers are degenerated, we give the related parameter values. Regarding the influence of the nn-exchange and the nn-Coulomb correlation onto the anomalous degeneration we find both lifting and inducing of degeneracies in dependence on the parameter values.

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Spin and Charge Pairing Instabilities in Nanoclusters and Nanomaterials

Kocharian

Fernando²,

Yang³

2009

Scanning Probe Microscopy in Nanoscience and Nanotechnology

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Thermodynamic properties, magnetism and Mott–Hubbard-like transitions in nanoscale clusters

Cited by 23 publications

References 32 publications

Exact thermodynamics of pairing and charge–spin separation crossovers in small Hubbard nanoclusters

Exact thermodynamics of pairing and charge–spin separation crossovers in small Hubbard nanoclusters

The Hubbard model extended by nearest‐neighbor Coulomb and exchange interaction on a cubic cluster – rigorous and exact results

Spin and Charge Pairing Instabilities in Nanoclusters and Nanomaterials

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