Nonclassical dipoles in cold niobium clusters

Xu, Xiaoshan; Yin, Shuangye; Moro, Ramiro; Liang, Anthony; Bowlan, John; Heer, Walt A. de

doi:10.1103/physrevb.75.085429

Cited by 34 publications

(42 citation statements)

References 22 publications

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“…36 At cryogenic temperature neutral niobium clusters show a permanent electric dipole moment implying that they are ferroelectric, but that vanishes at higher temperature or upon laser heating. 37,38 This behavior is explained by a two component model that assumes a low-energy transition between two electronically very different states of the cluster, but the nature of these states is not understood.…”

Section: Introductionmentioning

confidence: 99%

The far-infrared spectra of neutral and cationic niobium clusters: Nb5∕+ to Nb9∕+

Fielicke

Rätsch

Helden

et al. 2007

The Journal of Chemical Physics

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Far-infrared absorption spectra of small neutral and cationic niobium clusters containing five to nine Nb atoms have been obtained by multiple photon dissociation spectroscopy of their argon complexes. The experimental far-IR spectra are recorded in the 85-600 cm −1 region and cover the range of the structure-specific vibrational fundamentals, i.e., the finger-print range, for these metal clusters. The experiments are accompanied by quantum chemical calculations employing the density-functional theory. A comparison of the experimental and calculated far-IR spectra allows to identify the cluster structures. Although the experimental spectra for clusters containing five, six, eight, and nine Nb atoms are very different for cationic and neutral clusters, the comparison with theory reveals that, nevertheless, the overall geometries for cations and neutrals are very similar, except for Nb 6 0/+ .

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Section: Introductionmentioning

confidence: 99%

The far-infrared spectra of neutral and cationic niobium clusters: Nb5∕+ to Nb9∕+

Fielicke

Rätsch

Helden

et al. 2007

The Journal of Chemical Physics

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“…[1][2][3][4][5][6][7][8] The ability to obtain desired nanocluster sizes and distribution is an important step in effectively utilizing these materials. [1][2][3][4][5][6]16,17 The low temperature, ferroelectric properties of niobium make Nb clusters of even greater interest. 10 Nanoclusters have been deposited onto substrates 2,5,7,8,11,12 and codeposited to form nanocomposite films using PGC processes.…”

Section: Introductionmentioning

confidence: 99%

“…9 Nanoclusters have been synthesized from a variety of techniques including laser vaporization, plasma gas condensation (PGC), pulsed arc vaporization, and supersonic expansion. 16,17 In this study, PGC is utilized to produce Nb nanoclusters using a Nanogen 50 nanoparticle source from Mantis Deposition, Ltd. (Fig. [13][14][15] A wide range of possible uses makes transition metal clusters of great interest.…”

Section: Introductionmentioning

confidence: 99%

Influence of carrier gas on the nucleation and growth of Nb nanoclusters formed through plasma gas condensation

Bray

Jiao

DeCerbo

2014

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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Fabrication and optical properties of Ti-doped W 18 O 49 nanorods using a modified plasma-arc gascondensation techniquea)Niobium nanoclusters with an average diameter from 2 nm to 10 nm were produced using a plasma gas condensation process. Cluster size and concentration can be tuned by controlling the sputter source current, aggregation length, and gas flow rate. In this paper, the effects of the addition of helium to the cluster growth process will be examined. Process parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. The results from the helium flow rate dependence study emphasize the competing mechanism present during these processes. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

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“…2 Theoretical investigations of mechanisms of FE-SC interaction go back at least to the conjecture of Matthias 3 that SC and FE are at least as mutually forbidden as superconductivity and ferromagnetism. Regarding the soft-mode type, the early observation of superconductivity in alkali-metal doped titanates led to the investigation of models based on electron-phonon interactions.…”

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confidence: 99%

Theory of coexistence of superconductivity and ferroelectricity

2007

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A new investigation of the coexistence and competition of ferroelectricity and superconductivity is reported. In particular we show that the starting Hamiltonian of a previous study by Birman and Weger (2001) can be exactly diagonalized. The result differs significantly from mean-field theory. A Hamiltonian with a different realization of the coupling between ferroelectricity and superconductivity is proposed. We report the results for mean-field theory applied to this Hamiltonian. We find that the order parameters are strongly affected by this coupling.PACS numbers: 74.20.-z, 77.80.-e, 64.90.+b, 77.90.+k In the present paper we report two related results from a reexamination of previous work on nearly ferroelectric superconductors 1 . In that paper a coupling term was introduced into the original Hamiltonian (Eq. 27 of Ref. 1). An investigation of that coupling term shows that it only gives a squeezing of the phonons and no coupling to the electronic pairs, and therefore the Hamiltonian can be diagonalized exactly. However, the double mean-field approximation does result in an effective coupling between the two subsystems. (Eq. 34 of Ref. 1). Therefore the results of the analysis of that equation remain valid. Our second result follows from introducing a different biquadratic coupling term in the Hamiltonian of Eq. 27 of Ref. 1, which satisfies gauge and inversion symmetries. This term does couple the two subsystems. We will treat this new Hamiltonian in mean-field approximation.We start with the model of coexistence of superconductivity and ferroelectricity proposed by Birman and Weger 1 . For convenience we include its main features here. Birman and Weger start with two separate Hamiltonians for the superconducting and ferroelectric sectors. The superconducting sector is a mean-field reduced BCS pseudo-spin model (we corrected a misprint in Ref. 1)where ε k is the single-electron energy and ∆ k is the pairing interaction energy. The pseudo-spin operators pk obey SU (2) commutation relations and are defined aŝandâ k↑ andâ † k↑ are the electron annihilation and creation operators for wave vector k, spin (↑) , etc.The Hamiltonian of the ferroelectric sector of the model is simply a Hamiltonian of a displaced harmonic oscillator If a single k mode is isolatedHere we notice that the structure of the pseudo-spin operators in terms of the pair operators implieŝ

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Nonclassical dipoles in cold niobium clusters

Cited by 34 publications

References 22 publications

The far-infrared spectra of neutral and cationic niobium clusters: Nb5∕+ to Nb9∕+

The far-infrared spectra of neutral and cationic niobium clusters: Nb5∕+ to Nb9∕+

Influence of carrier gas on the nucleation and growth of Nb nanoclusters formed through plasma gas condensation

Theory of coexistence of superconductivity and ferroelectricity

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