Evidence for strong electron-phonon coupling in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MgCNi</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

Wälte, A.; Fuchs, G.; Müller, K.‐H.; Handstein, A.; Nenkov, K.; Narozhnyi, V. N.; Drechsler, S.‐L.; Shulga, S. V.; Schultz, L.; Rösner, H.

doi:10.1103/physrevb.70.174503

Cited by 64 publications

(120 citation statements)

References 53 publications

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“…It is important to note that the spectral function can be qualitatively compared with phonon DOS. The e-p mass enhancement parameter (λ = λ qj ω(q),where ω(q) is the weight of the q th special phonon wave vector) and superconducting transition temperature (T c ) for MgCNi 3 are found to be 1.06 and 10 K respectively, which are in reasonably good agreement with the theoretical investigations 6,28 and experimental data 24 respectively. The superconducting transition temperature T c is calculated using Allen-Dynes formula.…”

Section: Frequency (Mev)supporting

confidence: 78%

“…Thus, in the recent past several attempts have been made to investigate the structural, electronic, vibrational and superconducting properties of MgCNi 3 . 1,[4][5][6][7][8][9][10][11][12][13][14] Experimental results 9,[15][16][17] have provided evidence for a medium to strong-coupling superconductivity driven by electron-phonon interactions. Further evidence for the phonon-mediated pairing mechanism is provided by theoretical estimates ranging between 0.8 to 1.5.…”

Section: Introductionmentioning

confidence: 99%

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Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3

Jha

Gupta

2012

AIP Advances

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A first principles calculation of the lattice dynamical properties of superconducting MgCNi 3 has been performed using density functional perturbation theory (DFPT). The calculated phonon dispersion curves and phonon density of states have been compared with inelastic x-ray scattering (IXS) and inelastic neutron scattering (INS) measurements. We show for the first time that phonon dispersion curves for MgCNi 3 in whole Brillouin zone are positive (stable phonon modes) and in good agreement with the experimental data. The phonon DOS shows absence of phonon density of states at zero energy unlike earlier calculations. There is a good agreement between calculated and experimental electron-phonon parameter and superconducting transition temperature. The Eliasberg function is quantitatively as well as qualitatively different from the phonon density of states. The lattice specific heat and Debye temperature do not show any anomalous behaviour.

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Section: Frequency (Mev)supporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3

Jha

Gupta

2012

AIP Advances

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“…Their calculation suggests that for M gCN i 3 , both the face-center substitutions of f.c.c N i by M g atom and the occupation of the C-site at the body-center position will make the Fermi level E F of M gCN i 3 to move away from the large DOS peak and make N (E F ) smaller than that of f.c.c N i, leading to a decrease of the Stoner factor and a disappearance of the magnetic order. Other theoretical studies show that [8,13,14], the correlation of N i 3d electrons in M gCN i 3 is not very important like in f.c.c N i due to strong hybridization between N i 3d and C 2p states.…”

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confidence: 99%

Optical properties ofMgCNi3in the normal state

et al. 2005

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We present the optical reflectance and conductivity spectra for non-oxide antiperovskite superconductor M gCN i3 at different temperatures. The reflectance drops gradually over a large energy scale up to 33,000 cm −1 , with the presence of several wiggles. The reflectance has slight temperature dependence at low frequency but becomes temperature independent at high frequency. The optical conductivity shows a Drude response at low frequencies and four broad absorption features in the frequency range from 600 cm −1 to 33,000 cm −1 . We illustrate that those features can be well understood from the intra-and interband transitions between different components of Ni 3d bands which are hybridized with C 2p bands. There is a good agreement between our experimental data and the first-principle band structure calculations. The discovery of non-oxide superconductor M gCN i 3 has attracted much attention due to the coexistence of ferromagnetic element N i and superconductivity [1]. M gCN i 3 has the cubic antiperovskite lattice structure with space group P m3m, in which eight M g atoms occupy the cubic corners, while six Ni atoms are at the face-center positions and one C atom is inserted into the body-center position. The lattice parameter a is 3.81Å , and the specific heat measurements [5] show that M gCN i 3 is a conventional superconductor. But band calculations indicate that the N i 3d electrons dominate the density of the states (DOS) near the Fermi level E F [6,7,8,9]. Then, the N i 3d electrons are usually considered to take part in the superconducting pairing in M gCN i 3 . In such a case, an s-wave pairing is unexpected because of the existence of localized moment of Ni atom which will break the s-wave superconducting pairing.The relationship between the electronic states of N i and the superconductivity in M gCN i 3 was intensively studied. All of the known substitutions at Ni-site are found to decrease the superconducting temperature and/or bulk superconducting volume [10,11,12]. Normal state 13 C NMR measurement implies the existence of spin fluctuation above 20 K[4]. The calculated Stoner exchange parameter S = 0.43 ∼ 0.64 [7,13] and the Stoner renormalization is 5 [8]. The value is at the high edge of paramagnetic region and close to the ferromagnetic region which may lead to ferromagnetic spin fluctuation. *

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“…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.…”

mentioning

confidence: 88%

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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Evidence for strong electron-phonon coupling inMgCNi3

Cited by 64 publications

References 53 publications

Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3

Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3

Optical properties ofMgCNi3in the normal state

Competition between BCS superconductivity and ferromagnetic spin fluctuations inMgCNi3

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