Penetration depth measurements in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>:</mml:mo></mml:math>Evidence for unconventional superconductivity

Panagopoulos, C.; Rainford, B.D.; Xiang, Tao; Scott, Christopher A.; Kambara, Makoto; Inoue, Isao

doi:10.1103/physrevb.64.094514

Cited by 68 publications

(64 citation statements)

References 17 publications

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“…The dc magnetization data shows a small ferromagnetic component that is temperature-independent for temperatures less than 300 K. This is likely to be due to the Fe impurity clusters in this sample. Similar observations were reported by other researchers [21,28,44]. We estimate the Fe clusters fraction to be no more that 0.02 % of the total sample mass from the saturation magnetization of the ferromagnetic impurity.…”

Section: Methodssupporting

confidence: 91%

“…The observation that λ could not be fitted to the isotropic s-wave BCS model was also reported in a muon spin rotation study where it was suggested that there exist nodes in the superconducting gap [21].…”

Section: Introductionmentioning

confidence: 64%

“…It was found that σ 2 could be fitted to an isotropic s-wave superconducting gap when σ 2 at 3 meV was plotted against temperature. However, this σ 2 yields a very high value of the penetration depth (300 nm), much larger than that found by the muon spin rotation study (85 nm [21]) and greater than that determined from the magnetization data (140 nm [30], 180 nm [40]). A higher frequency far infrared study provided evidence that MgB 2 is in the dirty limit [41].…”

Section: Introductionmentioning

confidence: 66%

“…Other studies report the existence of two superconducting gaps [17][18][19][20] or nodes in the superconducting gap [21]. Early 11 B nuclear magnetic resonance measurements supported the s-wave superconducting order parameter model and a small coherence peak was reported [16].…”

Section: Introductionmentioning

confidence: 99%

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Magnetization and microwave study of superconductingMgB2

et al. 2002

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We report magnetic field dependent magnetization and microwave impedance measurements on a MgB 2 superconductor prepared by high pressure synthesis. We find that the upper critical field is linearly dependent on temperature near T c and the dc irreversibility field exponent is ~1.4. The microwave data display an excess surface resistance below T c which is neither observed in low T c nor in high temperature superconductors (HTSC). The real part of the complex conductivity, σ 1 , shows a huge maximum below T c and the imaginary part, σ 2 , is linear for temperatures less than 20 K, which can not be simply accounted for by the weak coupling BCS model with an s-wave superconducting order parameter. We speculate that this may be due to the two gaps reported by other studies.Unlike measurements on the high temperature superconducting cuprates, we find no evidence of weak-links in the superconducting state. By inverting the magnetic field dependent impedance data, we find a vortex depinning frequency that decreases with increasing magnetic field and evidence for an anisotropic upper critical magnetic field.

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Section: Methodssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

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Magnetization and microwave study of superconductingMgB2

et al. 2002

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“…Moreover, in the case of a thin film this would correspond to probe the true "bulk" properties of the superconductor. First experiments performed on MgB 2 pellets using muon spin resonance (µSR) [25] and ac susceptibility [25,26] reported a quadratic behavior of ∆λ at low temperatures, that the authors interpreted as the signature of the presence of nodes in the gap. Very recently, however, a more careful analysis of µSR data showed [27] results consistent with a twogap model, while the peculiar exponential behavior expected for a s-wave superconductor was indeed observed in polycrystalline samples [28], in wires [29], and recently in single crystals [30].…”

Section: Iii1 Radiofrequency Magnetic Penetration Depth Measurementsmentioning

confidence: 99%

STUDY OF THE ELECTRODYNAMIC RESPONSE OF MgB₂ SINTERED PELLETS AND THIN FILMS

Andreone

Gennaro

Lamura

et al. 2002

Int. J. Mod. Phys. B

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We present a number of experimental results on the temperature dependence of the magnetic penetration depth λ and on the temperature and field dependence of the microwave surface impedance Z s =R s +iX s in both pellets and thin films of MgB2 , exhibiting critical temperatures ranging between 26 and 38 K. Accurate measurements of Z s (H,T) were performed by means of a sapphire dielectrically loaded cavity operating in the microwave region (20 GHz). The study of λ(T) was carried out employing a single coil mutual inductance technique in the MHz region. An anisotropic s-wave BCS model can account for the temperature dependence experimentally observed in the penetration depth data of the best films, confirming previous reports on the conventional nature of superconductivity in diborides. On the contrary, films having a reduced value of the critical temperature and pellets show no evidence of saturation, and the experimental results strictly follow a quadratic dependence down to the lowest temperatures. We explain this behavior with the presence of metallic Mg inclusions that may locally depress the gap. The study of the surface impedance versus temperature and field shows also that the source of microwave loss can be markedly different, depending on the structural and transport properties of the samples.

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Thermodynamic Parameters of Single‐ or Multi‐Band Superconductors Derived from Self‐Field Critical Currents

2017

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Key questions for any superconductor include: what is its maximum dissipation-free electrical current (its 'critical current') and can this be used to extract fundamental thermodynamic parameters? Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self-field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here we generalise this observation to include thin films, wires or nanowires of singleor multi-band s-wave and d-wave superconductors. Using extended BCS equations we consider dissipation-free self-field transport currents as London-Meissner currents, avoiding the concept of pinning altogether. We find quite generally, for type I or type II superconductors, the current is limited by the relevant critical field divided by the penetration depth. Our fits to 64 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent. Extracted London penetration depths, superconducting energy gaps and specific heat jumps agree well with reported bulk values. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions.

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Penetration depth measurements inMgB2:Evidence for unconventional superconductivity

Cited by 68 publications

References 17 publications

Magnetization and microwave study of superconductingMgB2

Magnetization and microwave study of superconductingMgB2

STUDY OF THE ELECTRODYNAMIC RESPONSE OF MgB₂ SINTERED PELLETS AND THIN FILMS

Thermodynamic Parameters of Single‐ or Multi‐Band Superconductors Derived from Self‐Field Critical Currents

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Penetration depth measurements inMgB2:Evidence for unconventional superconductivity

Cited by 68 publications

References 17 publications

Magnetization and microwave study of superconductingMgB2

Magnetization and microwave study of superconductingMgB2

STUDY OF THE ELECTRODYNAMIC RESPONSE OF MgB2 SINTERED PELLETS AND THIN FILMS

Thermodynamic Parameters of Single‐ or Multi‐Band Superconductors Derived from Self‐Field Critical Currents

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STUDY OF THE ELECTRODYNAMIC RESPONSE OF MgB₂ SINTERED PELLETS AND THIN FILMS