Spin and Charge Pairing Instabilities in Nanoclusters and Nanomaterials

Kocharian, Armen; Fernando, Gayanath; Yang, Cheng‐Ta

doi:10.1007/978-3-642-03535-7_15

Cited by 4 publications

(4 citation statements)

References 173 publications

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“…The magnitudes of the spin pseudogap and charge gap also differ with increasing temperature here, unlike in the BCS case. It is consistent with ARPES data that excitations in high T c superconductors (as in the exact solution) are not well defined quasiparticles as it is in the BCS theory [8].…”

Section: Spin (Pseudo)gapssupporting

confidence: 86%

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Pairing enhancement in Betts lattices with next nearest neighbor couplings: Exact results

Fang,

Fernando,

Kocharian

2011

Preprint

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Electron instabilities in the Hubbard model with the next nearest neighbor coupling are calculated by exact diagonalization in finite, two-dimensional Betts cells (lattices). A viable spin and charge coherent pairing, signaled by quantum critical points and the negative charge gap region, is found in 8-and 10-site Betts lattices at small and moderate U regions consistent with our exact results in elementary bipartite geometries [Phys. Rev. B78, 075431 (2008)]. The contour isolines for continuous temperature driven-crossover between the Mott-Hubbard insulating and coherent pairing phases are demonstrated. The criteria for smooth and abrupt phase transitions are found for systematic enhancement of coherent pairing by optimization of the next nearest neighbor coupling parameter.

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Section: Spin (Pseudo)gapssupporting

confidence: 86%

“…Strong quantum fluctuations can even dominate thermal fluctuations and affect the properties of a material well above absolute zero [4] (see Ref. [8] and also references therein). The phase separation instabilities in small (bipartite) Hubbard clusters studied in Refs.…”

Section: Introductionmentioning

confidence: 99%

Pairing enhancement in Betts lattices with next nearest neighbor couplings: Exact results

Fang,

Fernando,

Kocharian

2011

Preprint

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“…An essential element for understanding our results on pairing modulation is the formation of coherent pairing state of n electrons with a negative charge gap and positive spin gap obtained earlier in Refs. [23][24][25][26][27][28][29] and references therein. For completeness here we first briefly summarize the key results of exact diagonalization in small clusters at weak and moderate U values.…”

Section: Methodsmentioning

confidence: 99%

Phase separation instabilities and pairing modulations in $Bi_2Sr_2CaCu_2O_{8+δ}$

Kocharian¹,

Fang²,

Fernando³

et al. 2012

Preprint

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There is growing evidence that the unconventional spatial inhomogeneities in the doped high-Tc superconductors are accompanied by the pairing of electrons, subsequent quantum phase transitions (QPTs), and condensation in coherent states. We show that these superconducting states can be obtained from phase separation instabilities near the quantum critical points. We examine electron coherent and incoherent pairing instabilities using our results on exact diagonalization in pyramidal and octahedron Hubbard-like clusters under variation of chemical potential (or doping), interaction strength, temperature and magnetic field. We also evaluate the behavior of the energy gap in the vicinity of its sign change as a function of out-of-plane position of the apical oxygen atom, due to vibration of apical atom and variation of inter-site coupling. These results provide a simple microscopic explanation of (correlation induced) supermodulation of the coherent pairing gap observed recently in the scanning tunneling microscopy experiments at atomic scale in Bi 2 Sr 2 CaCu 2 O 8+δ . The existence of possible modulation of local charge density distribution in these materials is also discussed.

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“…A new guiding principle for the search of new materials with enhanced Tc is the proximity to quantum critical points (QCPs) for spontaneous first order QPTs attributed to intrinsic spatial inhomogeneities (see Ref. [6] and references therein). Strong quantum fluctuations dominate thermal fluctuations and affect the classical properties well above absolute zero temperature [7].…”

Section: Introductionmentioning

confidence: 99%

Exact quantum critical points and phase separation instabilities in Betts Hubbard nanoclusters

Kocharian

Fang

Fernando

2012

Journal of Magnetism and Magnetic Materials

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a b s t r a c tSpontaneous phase separation instabilities with the formation of various types of charge and spin pairing (pseudo)gaps in U40 Hubbard model including the next nearest neighbor coupling are calculated with the emphasis on the two-dimensional (square) lattices generated by 8-and 10-site Betts unit cells. The exact theory yields insights into the nature of quantum critical points, continuous transitions, dramatic phase separation instabilities and electron condensation in spatially inhomogeneous systems. The picture of coupled antiparallel (singlet) spins and paired charged holes suggests full Bose condensation and coherent pairing in real space at zero temperature of electrons complied with the Bose-Einstein statistics. Separate pairing of charge and spin degrees at distinct condensation temperatures offers a new route to superconductivity different from the BCS scenario. The conditions for spin liquid behavior coexisting with unsaturated and saturated Nagaoka ferromagnetism due to spin-charge separation are established. The phase separation critical points and classical criticalities found at zero and finite temperatures resemble a number of inhomogeneous, coherent and incoherent nanoscale phases seen near optimally doped high-T c cuprates, pnictides and CMR nanomaterials.

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Spin and Charge Pairing Instabilities in Nanoclusters and Nanomaterials

Cited by 4 publications

References 173 publications

Pairing enhancement in Betts lattices with next nearest neighbor couplings: Exact results

Pairing enhancement in Betts lattices with next nearest neighbor couplings: Exact results

Phase separation instabilities and pairing modulations in $Bi_2Sr_2CaCu_2O_{8+δ}$

Exact quantum critical points and phase separation instabilities in Betts Hubbard nanoclusters

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