Critical and Gaussian fluctuation effects in the specific heat and conductivity of high-T<sub>c</sub>, superconductors

Loram, J. W.; Cooper, J. R.; Wheatley, J. M.; Mirza, K. A.; Liu, R. S.

doi:10.1080/13642819208215108

Cited by 42 publications

(28 citation statements)

References 19 publications

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“…We observe just the opposite behavior, which we believe is related to a very small coherence volume in high-T c oxides. The coherence volume estimated from the heat capacity measurements near T c is comparable with or even less than the unit cell volume [15]. This favors a charged 2e Bose liquid as a plausible microscopic model of the ground state [16].…”

Section: (Received 26 July 1995)mentioning

confidence: 64%

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
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The upper critical field H c2 ͑T͒ of Bi 2 Sr 2 CaCu 2 O 8 crystals with T c . 92 K has been measured from the out-of-plane resistivity in magnetic fields ͑H Ќ ab͒ up to 15 T. By the use of the empirical procedure the H c2 ͑T ͒ curve has been extrapolated up to H c2 Ӎ 230 T and T ͞T c Ӎ 0.35 which is independent of the choice of the R͞R N ratio. We found that H c2 ͑T ͒ does not follow the conventional theory with or without fluctuations but is consistent with the prediction based on the Bose-Einstein condensation of charged bosons formed above T c . Our results together with the heat capacity measurements provide an evidence for the possibility of 2e Bose liquid ground state of high-T c oxides. proposed an explanation for this phenomenon based on the Bose-Einstein condensation (BEC) of charged bosons. However, in the highest T c cuprates, the inplane superconducting transition is known to display pronounced broadening in a magnetic field, with the top of the transition having a much weaker field dependence than in the region near the bottom [6][7][8]. This together with the high values of H c2 have made an experimental determination of H c2 very difficult in materials with T c . 60 K, with the consequence that widely varying values of H c2 ͑0͒ have been estimated based on different models. The out-of-plane resistive transition is known to show a different behavior in a magnetic field. An increasingly pronounced maximum (peak) developed below T c and shifted to lower temperature rather than broadened with increasing field [9]. By modeling the c-axis conduction with a stack of Josephson junctions in series, Gray and Kim [10] have obtained an unusually large energy gap with large fluctuations. Consequently, no attempts have been made so far to determine H c2 ͑T ͒ from these observations. We report in this Letter the out-of-plane resistivity of Bi 2 Sr 2 CaCu 2 O 8 (BSCCO-2212) crystals measured in perpendicular fields up to 15 T ͑H k I k c͒. We propose a procedure for extrapolating the values of the resistive upper critical field H c2 ͑T ͒ which is independent of the background normal resistance and the choice of R͞R N values over a wide temperature range. In contrast to the predictions of conventional theory, this H c2 ͑T͒ shows a negative curvature just below T c followed by a positive curvature at lower temperatures with no sign of saturation down to 0.35T c . We have also determined the irreversibility field H irr ͑T ͒ ͑k c͒. This has a qualitatively different temperature dependence. We propose a quantitative explanation of H c2 ͑T ͒ based on the theory of BEC in the magnetic field [5].BSCCO-2212 single crystals have been grown by the self-flux method during solid-state reaction and have ϳ͑7 10͒% Y substitution for Ca [11]. For the present measurements, three homogeneous single crystals have been selected with T c0 between 92 and 95 K and in-plane dimensions 870 3 270, 340 3 150, and 800 3 350 mm 2 . Figure 1(A) shows the typical out-of-plane resistive transitions in magnetic fields up to 15 T ͑H k I k c͒. In a...

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Section: (Received 26 July 1995)mentioning

confidence: 64%

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
View full text Add to dashboard Cite

show abstract

“…23 That favors a charged 2e Bose liquid of small bipolarons as a plausible microscopic model of the superconducting state. 3 The critical temperature of the superfluid phase transition in 2ϩ⑀ dimensions is proportional and the London penetration depth squared is inversely proportional to the density n 0 of delocalized bosons.…”

Section: Bipolarons and Critical Parameters Of High-t C Copper Oxmentioning

confidence: 99%

Bipolaron anisotropic flat bands, Hall mobility edge, and metal-semiconductor duality of overdoped high-Tcoxides

1996

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Hole bipolaron band structure with two flat anisotropic bands is derived for oxide superconductors. Strong anisotropy leads to one-dimensional localization in a random field which explains the metal-like value of the Hall effect and the semiconductorlike doping dependence of resistivity of overdoped oxides. Doping dependence of T c and H (0) as well as the low-temperature dependence of resistivity, of the Hall effect, H c2 (T) and robust features of angle-resolved photoemission spectroscopy of several high-T c copper oxides are explained.

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“…It has been established beyond doubt [1] that in high-T c superconductors the anomaly in the specific heat spreads to about jT 2 T c j͞T c ϳ 0.1 or larger. The estimations with the canonical Gaussian fluctuations yield an unusually small coherence volume, comparable or even less than the unit cell volume [2]. That means that the overlap of pairs is small.…”

mentioning

confidence: 99%

Contrasting Effects of Magnetic Field on Thermodynamic and Resistive Transitions in High-TcCuprates

Alexandrov¹,

Beere²,

Kabanov³

et al. 1997

Phys. Rev. Lett.

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Critical and Gaussian fluctuation effects in the specific heat and conductivity of high-T_c, superconductors

Cited by 42 publications

References 19 publications

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
View full text Add to dashboard Cite

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
View full text Add to dashboard Cite

Bipolaron anisotropic flat bands, Hall mobility edge, and metal-semiconductor duality of overdoped high-Tcoxides

Contrasting Effects of Magnetic Field on Thermodynamic and Resistive Transitions in High-TcCuprates

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Critical and Gaussian fluctuation effects in the specific heat and conductivity of high-Tc, superconductors

Cited by 42 publications

References 19 publications

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2SAlexandrov1, Zavaritsky2, Liang3 et al. 1996Phys. Rev. Lett.943632View full textAdd to dashboardCite

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2SAlexandrov1, Zavaritsky2, Liang3 et al. 1996Phys. Rev. Lett.943632View full textAdd to dashboardCite

Bipolaron anisotropic flat bands, Hall mobility edge, and metal-semiconductor duality of overdoped high-Tcoxides

Contrasting Effects of Magnetic Field on Thermodynamic and Resistive Transitions in High-TcCuprates

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Critical and Gaussian fluctuation effects in the specific heat and conductivity of high-T_c, superconductors

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
View full text Add to dashboard Cite

Resistive Upper Critical Field of High-TcSingle Crystals of Bi2S
Alexandrov
¹
,
Zavaritsky
²
,
Liang
³

et al. 1996
Phys. Rev. Lett.
94
3
63
2
View full text Add to dashboard Cite