Superconductivity near Ferromagnetism in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>MgCNi</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Rösner, H.; Weht, Ruben; Johannes, M. D.; Pickett, Warren E.; Tosatti, Erio

doi:10.1103/physrevlett.88.027001

Cited by 147 publications

(152 citation statements)

References 36 publications

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“…This material is close to a magnetic instability on hole doping. It was suggested that strong magnetic fluctuations may lead to unconventional pairing [180]. The current experimental situation is controversial.…”

Section: Magnetic Impuritiesmentioning

confidence: 99%

Magnetic penetration depth in unconventional superconductors

Prozorov

Giannetta

2006

Supercond. Sci. Technol.

405

438

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Abstract. This topical review summarizes various features of magnetic penetration depth in unconventional superconductors. Precise measurements of the penetration depth as a function of temperature, magnetic field and crystal orientation can provide detailed information about the pairing state. Examples are given of unconventional pairing in hole-and electron-doped cuprates, organic and heavy fermion superconductors. The ability to apply an external magnetic field adds a new dimension to penetration depth measurements. We discuss how field dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion. We also discuss how penetration depth measurements as a function of orientation can be used to explore superconductors with more than one gap and with anisotropic gaps. Details relevant to the analysis of penetration depth data in anisotropic samples are also discussed.Keywords: penetration depth, unconventional superconductivity, pairing symmetry IntroductionThe early suggestion that high temperature superconductors might exhibit unconventional, d-wave pairing, [24,11,154,8] has lead to a wide variety of new experimental probes with sensitivity sufficient to test this hypothesis. The pioneering work of Hardy and coworkers demonstrated that high resolution measurements of the London penetration depth could detect the presence of nodal quasiparticles characteristic of a d-wave pairing state [87]. Since that time, a large number of new superconductors have been discovered, many of which exhibit nontrivial departures from BCS behavior. As we show in this review, penetration depth measurements can be used to examine not only nodal quasiparticles but two-gap superconductivity, anisotropy of the energy gap, Andreev surface states, nonlinear Meissner effect, interplane transport, proximity coupled diamagnetism, vortex matter and the coexistence of magnetism and superconductivity, to name several problems of current interest.

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Section: Magnetic Impuritiesmentioning

confidence: 99%

Magnetic penetration depth in unconventional superconductors

Prozorov

Giannetta

2006

Supercond. Sci. Technol.

405

438

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“…The discovery of superconductivity in MgCNi 3 has caused much attention, 1 since the large Ni content suggests a magnetic state rather than superconductivity. Indeed, up to now a lot of experimental and theoretical publications point to a ferromagnetic instability at temperatures near and below the superconducting transition temperature T c ≈ 7 K. 2,3,4,5,6 So far there is much discussion on the carbon content in MgCNi 3 , since only samples with carbon excess of ≈ 50 % show large T c values, whereas for the stoichiometric composition a strongly reduced T c is found, 7,8 which may be triggered by enhanced pair-breaking due to increasing spin fluctuations.…”

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confidence: 99%

Role of carbon for superconductivity inMgCxNi3from specific heat

et al. 2005

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The influence of carbon deficiency on superconductivity of MgCNi 3 is investigated by specific heat measurements in the normal and superconducting state. In order to perform a detailed analysis of the normal state specific heat, a computer code is developed which allows for an instantaneous estimate of the main features of the lattice dynamics. By analyzing the evolution of the lattice vibrations within the series and simultaneously considering the visible mass enhancement, the loss in the electron-phonon coupling can be attributed to significant changes of the prominent Ni vibrations. The present data well supports the recently established picture of strong electron-phonon coupling and ferromagnetic spin fluctuations in this compound. The discovery of superconductivity in MgCNi 3 has caused much attention, 1 since the large Ni content suggests a magnetic state rather than superconductivity. Indeed, up to now a lot of experimental and theoretical publications point to a ferromagnetic instability at temperatures near and below the superconducting transition temperature T c ≈ 7 K.2,3,4,5,6 So far there is much discussion on the carbon content in MgCNi 3 , since only samples with carbon excess of ≈ 50 % show large T c values, whereas for the stoichiometric composition a strongly reduced T c is found, 7,8 which may be triggered by enhanced pair-breaking due to increasing spin fluctuations.9 However specific heat measurements indicate that this is not the case but instead the electron-phonon coupling is significantly reduced, 5 accompanied by a considerable hardening of low-energy vibrations.10 Band structure calculations predict a constant 9 or decreasing 5 electron density of states at the Fermi level (EDOS), leaving the interesting prospect of significantly changing lattice dynamics. Recent measurements of the carbon isotope effect support this picture.

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“…[15] completely vanishes. When the superconductivity in MgCNi 3 is investigated, the spin fluctuations can not be neglected because it may compete with superconductivity [5,11] or even lead to an exotic pairing mechanism other than the conventional s-wave [2]. If the phonon-mediated pairing wins in competing with the spin fluctuations and hence the effect of the spin fluctuations only suppress the electronphonon coupling ( or pairing-strength ) [11], the so-called α-model [26] based on BCS theory should be a good choice to describe the measured thermodynamic parameters.…”

Section: Figmentioning

confidence: 99%

“…Bt, 74.20.Rp, 74.70.Ad Since the discovery of the new intermetalic perovskite superconductor MgCNi 3 [1], plenty of efforts have been focused on the superconducting pairing symmetry in this material because its conduction electrons are derived predominantly from Ni which is itself a ferromagnet [2,3,4,5]. However, up to now, there is still not a consensus on this issue.…”

mentioning

confidence: 99%

Competition between BCS superconductivity and ferromagnetic spin fluctuations inMgCNi3

et al. 2005

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The low temperature specific heat of the superconductor MgCNi3 and a non-superconductor MgC0.85Ni3 is investigated in detail. An additional contribution is observed from the data of MgCNi3 but absent in MgC0.85Ni3, which is demonstrated to be insensitive to the applied magnetic field even up to 12 Tesla. A detailed discussion on its origin is then presented. By subtracting this additional contribution, the zero field specific heat of MgCNi3 can be well described by the BCS theory with the gap ratio (∆/kBTc ) determined by the previous tunneling measurements. The conventional s-wave pairing state is further proved by the magnetic field dependence of the specific heat at low temperatures and the behavior of the upper critical field.PACS numbers: 74.25. Bt, 74.20.Rp, 74.70.Ad Since the discovery of the new intermetalic perovskite superconductor MgCNi 3 [1], plenty of efforts have been focused on the superconducting pairing symmetry in this material because its conduction electrons are derived predominantly from Ni which is itself a ferromagnet [2,3,4,5]. However, up to now, there is still not a consensus on this issue. The measured penetration depth [6], critical current behavior [7] and earlier tunneling spectra [8] suggested an unconventional superconductivity, the later tunneling data [9] supported the s-wave pairing symmetry and gave a reasonable interpretation on the contradiction to the result in Ref [8]. The s-wave pairing has also been demonstrated by the 13 C NMR experiments [10] and the specific heat measurements [1,8,11,12,13,14]. To our knowledge, all the previous reports on the specific heat of MgCNi 3 [1,8,11,12,13,14] were characterized in the framework of a conventional phonon-mediated pairing. However, there is an obvious deviation of the experimental data from the prediction of BCS theory in the low temperature [8,15], i.e., the entropy conservation rule is not satisfied. Such deviation has been interpreted by the presence of unreacted Ni impurities in Refs [8,15], whereas it is still prominent in the samples without Ni impurities [14]. On the other hand, strong spin fluctuations have been observed in MgCNi 3 by NMR experiment [10], which is suggested to be able to severely affect the superconductivity in MgCNi 3 [2,5,10,11,16] or even induce some exotic paring mechanism [2]. Consequently, the behavior of the specific heat will inevitably be changed by the spin fluctuations. Therefore, before a real pairing mechanism being concluded from the specific heat data, we have to carefully investigate how the ferromagnetic spin fluctuations contribute to the specific heat of MgCNi 3 .In this work, we elaborate on the specific heat (C) of MgC x Ni 3 system both in normal state and supercon- * Electronic address: hhwen@aphy.iphy.ac.cn ducting state. A low temperature upturn is clearly distinguished in the C/T vs T 2 curves and found to be insensitive to the applied magnetic field. By doing some quantitative analysis, we present the evidence of most possible mechanisms responsible for this upturn. After s...

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Superconductivity near Ferromagnetism inMgCNi3

Cited by 147 publications

References 36 publications

Magnetic penetration depth in unconventional superconductors

Magnetic penetration depth in unconventional superconductors

Role of carbon for superconductivity inMgCxNi3from specific heat

Competition between BCS superconductivity and ferromagnetic spin fluctuations inMgCNi3

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