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Volumn 300, Issue 5623, 2003, Pages 1265-1269

Ferroelectricity in free niobium clusters

Author keywords

[No Author keywords available]

Indexed keywords

CRYOGENICS; MOLECULAR BEAMS; NIOBIUM; SUPERCONDUCTING TRANSITION TEMPERATURE; SUPERCONDUCTIVITY;

EID: 0038813676     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1083247     Document Type: Article
Times cited : (126)

References (37)
  • 4
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    • E. F. Weller, Ed. (Elsevier, Amsterdam)
    • B. Matthias, in Ferroelectricity, E. F. Weller, Ed. (Elsevier, Amsterdam, 1967), pp. 176-182.
    • (1967) Ferroelectricity , pp. 176-182
    • Matthias, B.1
  • 5
    • 0038741585 scopus 로고    scopus 로고
    • note
    • Whenever a symmetry is spontaneously broken, according to the Goldstone theorem there will then be a gapless excitation that tends to restore the symmetry. Well-known examples are phonons for the crystalline state and spin waves for the ferromagnetic state [see, for example (6)].
  • 13
    • 0003400233 scopus 로고
    • Oxford Univ. Press, Oxford
    • G. Scoles, Atomic and Molecular Beam Methods (Oxford Univ. Press, Oxford, 1988); W. A. de Heer, P. Milani, Rev. Sci. Instrum. 62, 670 (1991).
    • (1988) Atomic and Molecular Beam Methods
    • Scoles, G.1
  • 14
    • 0000061754 scopus 로고
    • G. Scoles, Atomic and Molecular Beam Methods (Oxford Univ. Press, Oxford, 1988); W. A. de Heer, P. Milani, Rev. Sci. Instrum. 62, 670 (1991).
    • (1991) Rev. Sci. Instrum. , vol.62 , pp. 670
    • De Heer, W.A.1    Milani, P.2
  • 15
    • 0038741584 scopus 로고    scopus 로고
    • See supporting material on Science Online
    • See supporting material on Science Online.
  • 19
    • 0038065165 scopus 로고    scopus 로고
    • note
    • The classical fixed dipole on a symmetric top model by P. Dugourd et al. (19) predicts a symmetric broadening of the beam at low fields and asymmetric broadening at high fields. The model fails both quatitativety and quantitatively to describe the observed deflections, which show essentially undeflected peaks superimposed on relatively flat, extended, single-sided tails as shown in Fig. 1. The quantum mechanical model suggested here emphasizes the importance of very weak interactions between quantum mechanical levels (leading to a dense system of small avoided crossings) for which these deflection measurements are extremely sensitive: Gaps as small as 1 HHz already produce observable effects. These are in principle absent in the classical model. Also note that the observed depletions are not due to spontaneous ionization effects in the deflection fields. This possibility (as well as others) was experimentally ruled out by applying uniform electric fields of similar magnitude to the beam, which did not cause depletion.
  • 21
    • 0037727478 scopus 로고    scopus 로고
    • note
    • This simplified rotational spectrum is intended to demonstrate the principle that the general features are preserved when a symmetric rotor spectrum (involving J and K quantum numbers) is used (17).
  • 22
    • 0037727479 scopus 로고    scopus 로고
    • note
    • 2], where G is the tunneling splitting between the aligned and antialigned states.
  • 23
    • 0038741582 scopus 로고    scopus 로고
    • note
    • The avoided crossing model also explains anomalous magnetic deflections of paramagnetic alkali clusters (23, 24).
  • 24
    • 0038403451 scopus 로고
    • Erice, G. Benedek, T. P. Martin, G. Pacchioni, Eds. (Springer-Verlag, Berlin)
    • W. A. de Heer, W. D. Knight, in Proceedings of the 13th International School, in Erice, G. Benedek, T. P. Martin, G. Pacchioni, Eds. (Springer-Verlag, Berlin, 1988), pp. 45-63.
    • (1988) Proceedings of the 13th International School , pp. 45-63
    • De Heer, W.A.1    Knight, W.D.2
  • 25
    • 0038741583 scopus 로고
    • thesis, University of California, Berkeley
    • W. A. de Heer, thesis, University of California, Berkeley (1985).
    • (1985)
    • De Heer, W.A.1
  • 26
    • 0038065167 scopus 로고    scopus 로고
    • note
    • N data, because the noise levels were too high to warrant a two-parameter fit.
  • 27
    • 0038741581 scopus 로고    scopus 로고
    • note
    • These properties already occur in trimers (but not in dimers), making them accessible for first-principles calculations.
  • 33
    • 0038065163 scopus 로고    scopus 로고
    • note
    • The Lorentz polarization catastrophe results from self-polarization of a system of mutually interacting polarizable objects (polarizability α, density n) for which the susceptibilty is χ = nα/(1 - 4πnα/3). In small systems, the effect also occurs and is geometry-dependent (P. B. Allen, in preparation).
  • 35
    • 0038065166 scopus 로고    scopus 로고
    • note
    • Our low-temperature measurements on Co, Mn, Bi, and AlCo do not exhibit any evidence for permanent dipoles (W. de Heer et al., in preparation); alkali cluster measurements at high temperatures also have not presented evidence for permanent dipoles.
  • 36
    • 0038065164 scopus 로고    scopus 로고
    • note
    • 2, which is a triplet (W. de Heer, in preparation)], indicating a nondegenerate energy level structure (1), with spacings greater than kT.
  • 37
    • 0038403453 scopus 로고    scopus 로고
    • note
    • The authors gratefully acknowledge P. Poncharal and P. Keghelian for the development of the apparatus and R. W. Whetten and U. Landman for stimulating discussions. Financial support was provided by the U.S. Department of Defense (grant no. DAAG55-970133).


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.