Evidence for Two Superconducting Gaps in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Chen, X. K.; Konstantinović, M.J.; Irwin, J. C.; Lawrie, D. D.; Franck, J. P.

doi:10.1103/physrevlett.87.157002

Cited by 242 publications

(143 citation statements)

References 22 publications

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“…50, which compares the fieldinduced variation of κ e at temperatures well below T c for different conventional and unconventional superconductors, amended by our data for MgB 2 at T = 0.60 K. The Nb data 51 reveal the typical salient features of a clean, almost isotropic s-wave superconductor, and confirms the very weak energy transport by quasiparticles far below H c2 , in agreement with Eq. (8). A considerably faster, almost linear in H, increase of κ e is observed for a superconductor with nodes in ∆(k), here exemplified by UPt 3 .…”

Section: Thermal Conductivity In the Mixed Statementioning

confidence: 75%

Thermal conductivity of single-crystallineMgB2

et al. 2002

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The ab-plane thermal conductivity κ of single-crystalline hexagonal MgB2 has been measured as a function of magnetic field H with orientations both parallel and perpendicular to the c-axis and at temperatures between 0.5 and 300 K. In the mixed state, κ(H) measured at constant temperatures reveals features that are not typical for common type-II superconductors. The observed behavior may be associated with the field-induced reduction of two superconducting energy gaps, significantly different in magnitude. A nonlinear temperature dependence of the electronic thermal conductivity is observed in the field-induced normal state at low temperatures. This behavior is at variance with the law of Wiedemann and Franz, and suggests an unexpected instability of the electronic subsystem in the normal state at T ≈ 1 K.

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Section: Thermal Conductivity In the Mixed Statementioning

confidence: 75%

Thermal conductivity of single-crystallineMgB2

et al. 2002

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“…This two-gap scenario was confirmed experimentally by a number of investigations including heat capacity measurements [126], Raman scattering [127], and tunneling spectroscopy [128]. To understand the pressure effects in superconducting MgB 2 the pinduced changes of the microscopic parameters of the two bands as well as the coupling between the bands need to be taken into account.…”

Section: Pressure Effects In Mgb 2 and Isostructural Intermetallic Comentioning

confidence: 83%

High Pressure Effects on Superconductivity

Lorenz

Chu

2005

Frontiers in Superconducting Materials

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The review is devoted to a discussion of the effects of high pressure imposed on superconducting materials. Low-temperature superconductors, high-temperature superconducting cuprates, and some unconventional superconducting compounds are investigated. Experimental as well as theoretical results regarding the pressure effects on Tc and other interesting properties are summarized.Comment: To be published in: "Frontiers in Superconducting Materials", Edt. A. Narlikar, Springer Verla

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“…1a, the spectrum of the undoped MgB 2 sample is dominated by a band centered around 600 cm −1 , in agreement with previous Raman experiments reporting a band centered between 580 and 630 cm −1 , characterized by a large width (200-300 cm −1 ) and a relevant asymmetry. [8][9][10][11][12] A close inspection of the MgB 2 spectrum of Fig. 1a reveals two weak shoulders on the low-and the high-frequency side of the 600 cm −1 band (ν 2 ), around 400 (ν 1 ) and 750 cm −1 (ν 3 ), respectively.…”

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confidence: 99%

“…It is quite a general statement that the E 2g mode is expected to allow for the strongest e-ph coupling [5][6][7] and then to play a relevant role in superconductivity. Raman experiments [8][9][10][11][12] carried out on MgB 2 have shown that the spectrum is dominated by a quite large and asymmetric band around 600 cm −1 , ascribed to the E 2g mode. The anomalous width of this phonon peak has been interpreted as a signature of the e-ph coupling.…”

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Effect of the Al content on the optical phonon spectrum inMg1−xAlx

et al. 2001

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Raman and infrared absorption spectra of Mg1−xAlxB2 have been collected for 0 ≤ x ≤ 0.5 in the spectral range of optical phonons. The x-dependence of the peak frequency, the width and the intensity of the observed Raman lines has been carefully analized. A peculiar x-dependence of the optical modes is pointed out for two different Al doping ranges. In particular the onset of the high-doping structural phase previously observed in diffraction measurements is marked by the appearence of new spectral components at high frequencies. A connection between the whole of our results and the observed suppression of superconductivity in the high doping region is established.The recent discovery 1 of superconductivity below 39 K in MgB 2 has stimulated a great deal of effort among the scientific community and a large number of theoretical and experimental papers have been published within few months. The debate on the origin of this unexpected superconductivity is still open, although both experimental 2-4 and theoretical 5-7 works indicate that MgB 2 is a BCS-like system. In this framework, the obvious relevant interaction in the superconducting transition is the electron-phonon (e-ph) coupling. Owing to the simple hexagonal structure (space group P 6 mmm), four zone-center optical modes are predicted for MgB 2 : a silent B 1g mode, the E 2g Raman mode, and the infrared active E 2u and A 2u modes. While the doubly-degenerate E 2u and E 2g modes are ascribed to in-plane stretching modes of the boron atoms, both non-degenerate A 2u and B 1g modes involve vibrations along the perpendicular direction (c axis). It is quite a general statement that the E 2g mode is expected to allow for the strongest e-ph coupling 5-7 and then to play a relevant role in superconductivity. Raman experiments 8-12 carried out on MgB 2 have shown that the spectrum is dominated by a quite large and asymmetric band around 600 cm −1 , ascribed to the E 2g mode. The anomalous width of this phonon peak has been interpreted as a signature of the e-ph coupling.Up to now, no other isostructural boride (XB 2 ) has shown the peculiar high temperature superconductivity of MgB 2 . In particular, MgAl 2 is not superconducting. Indeed, several studies on the Mg 1−x Al x B 2 compounds have shown that superconductivity is progressively suppressed for increasing x and vanishes for x>0.5. [13][14][15] In order to achieve a deeper understanding of the effects of Al doping, we have studied the evolution of the phonon spectrum of Mg 1−x Al x B 2 in the 0 ≤ x ≤ 0.5 range by means of both Raman and infrared spectroscopy.Pure MgB 2 and Al doped polycrystalline samples have been synthesized at high temperature by direct reaction of the elements in a tantalum crucible under argon atmosphere. The samples, which show an average grain dimension around 1-2µm, have been characterized by xray diffraction and by resistivity measurements, in order to determine, in particular, the x-dependence of the superconductivity transition temperature T c . 14,16 .The Raman spectra were measure...

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Evidence for Two Superconducting Gaps inMgB2

Cited by 242 publications

References 22 publications

Thermal conductivity of single-crystallineMgB2

Thermal conductivity of single-crystallineMgB2

High Pressure Effects on Superconductivity

Effect of the Al content on the optical phonon spectrum inMg1−xAlx

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