Microwave surface resistance in MgB<sub>2</sub>

Жуков, А. А.; Cohen, L. F.; Yates, K. A.; Perkins, G. K.; Bugoslavsky, Y.; Polichetti, Massimiliano; Berenov, A.; MacManus‐Driscoll, Judith L.; Caplin, A.D.; Líu, Hao; Gallop, John

doi:10.1088/0953-2048/14/5/101

Cited by 24 publications

(25 citation statements)

References 26 publications

(31 reference statements)

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“…This is especially true in the case of the novel superconducting MgB 2 material, where the procedure for thin film growth is still quite irreproducible. A comparison between our surface resistance measurements and data that have appeared in recent literature is rather encouraging: using the ordinary ω 2 law and normalizing the data at 20 GHz, one can see that while results for the pellet lie in the range of values reported for similar samples ( [49]: ~10 mΩ , [50]: ~3 mΩ), films show a surface dissipation significantly lower than previous reports ( [20]: ~3 mΩ, [31]: ~2 mΩ, [51]: ~4 mΩ). The effect of ion milling on the surface impedance was also investigated: using an Ar + beam (0.5 KV, beam current 16 mA) a nominal 60 nm layer was removed from the surface of film #1B.…”

Section: Microwave Surface Impedance: Experimental Results and Discsupporting

confidence: 82%

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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Section: Microwave Surface Impedance: Experimental Results and Discsupporting

confidence: 82%

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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“…The investigation of a longer rod is in progress and will be discussed elsewhere; nevertheless, the results we obtained in the superconducting state are consistent with those reported by Dmitriev et al at lower frequency; on the contrary, in the normal state, we obtained frequency dependence closer to the expected one with respect to the linear dependence obtained by Dmitriev et al The values of the residual surface resistance, obtained extrapolating the low temperature data to T = 0 K, are 0.5 mΩ at 2.6 GHz, 2 mΩ at 5.3 GHz, and 5 mΩ at 8.2 GHz. They are of the same order of those measured in the first MgB 2 films [35] but higher than those obtained in more recently prepared MgB 2 films [9], [36], [38], [39]. Considering that we have built the whole cavity using bulk materials of large dimensions, the values of R s we obtained at temperatures achievable with modern cryocoolers are satisfactory, although not competitive with the ones obtained in the best MgB 2 films [39].…”

Section: A Results At Low Input Powersupporting

confidence: 59%

“…The frequency dependence of the mw surface resistance of MgB 2 has not been comprehensively investigated; in the literature, there are only few papers concerning results obtained mainly in films [35], [36]. To our knowledge, R s (f ) of bulk samples has been investigated in the range of frequency 10-100 MHz by Dmitriev et al [37].…”

Section: A Results At Low Input Powermentioning

confidence: 99%

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Gallitto

Camarda

Vigni

et al. 2014

IEEE Trans. Appl. Supercond.

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Abstract-We report on the microwave properties of coaxial cavities built by using bulk MgB 2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity by using an outer MgB 2 cylinder and an inner MgB 2 rod and a hybrid cavity by using an outer copper cylinder and the same MgB 2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance R s of the MgB 2 materials as a function of the temperature and the frequency, in the absence of dc magnetic fields. At T = 4.2 K and f ≈ 2.5 GHz, by an mw pulsed technique, we have determined the quality factor of the homogeneous cavity as a function of the input power up to a maximum level of about 40 dBm (corresponding to a maximum peak magnetic field of about 100 Oe). Contrary to what occurs in many films, R s of the MgB 2 material used does not exhibit visible variations up to an input power level of about 10 dBm and varies less than a factor of 2 on further increasing the input power of 30 dB.

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“…On the other hand, we note that there are at least six low-T experiments showing or at least suggesting power-law behaviors which seem to indicate gap nodes (Panagopoulos et al 2001, Zhukov et al 2001, Pronin et al 2001, Ohishi et al 2003. [Admittedly, the lowest temperatures in some of these experiments are too high to be convincing.…”

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confidence: 77%

Strongly anisotropic s-wave gaps in exotic superconductors

Brandow

2003

Philosophical Magazine

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The exotic superconductors, defined as those which follow the phenomenological trend of Uemura (T c approximately µ l L -2 ), presently constitute the most broad and general class of superconductors which can reasonably be considered "similar to the high-T c cuprates". It is therefore of much interest to determine the forms of their pairing gap functions. We examine evidence for the gap forms in non-cuprate exotics, and demonstrate some general features. The cubic materials often have highly anisotropic gaps. The planar materials tend to have even stronger gap anisotropy, to the extent that they often have gap nodes, but nevertheless they usually have an s-wave-like gap symmetry. There is good evidence for the latter even in the controversial cases of planar organics and nickel borocarbides. Exceptions to these generalizations are also pointed out and discussed. §1. INTRODUCTIONThere are now many unusual superconductors which are recognized to share some of the novel features of the high-T c cuprate superconductors. The possibility of further similarity to the cuprates, in particular the possibility of pairing by exchange of a virtual spin fluctuation or paramagnon, has motivated suggestions of d-wave gap forms in some of these other superconductors, in cases where there is evidence for gap nodes. This argument has been applied especially to the planar organics and sometimes also to the 2 nickel borocarbides, in addition to the well known cases of heavy-fermion materials. This line of reasoning calls for a careful examination of the evidence for the gap forms in these and other unusual superconductors.In this paper we focus on the exotic superconductors of Uemura and co-workers. 1 These exotics include a number of the unusual superconductors of earlier (pre-cuprate) interest, as well as the cuprates themselves and others discovered after the cuprates, and they include most of the materials previously suggested as being similar to the cuprates. 2 As discussed below, they now constitute the most broad and general class of superconductors that can reasonably be considered similar to the cuprates. (The variety of crystal structures and material chemistries in this class of materials is remarkably extensive.2 ) It is therefore very reasonable to focus on these materials. We now examine many of the non-cuprate exotic materials and material families, those for which there is reasonable gap-form evidence, in order to establish two general conclusions about their superconducting phenomenology: (1) In the cubic and nearly-cubic materials, which are conventionally expected to have nearly isotropic gaps, there is often evidence of very strong gap anisotropy. Sometimes there even appear to be gap nodes, although the gap symmetry remains s-wave-like. (2) In the planar (quasi-two-dimensional) materials there are often gap nodes, but nevertheless they typically still have an s-wave-like gap symmetry.[Here s-wave-like means having the full point-group symmetry of the crystal structure, a condition which does allow the p...

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Microwave surface resistance in MgB₂

Cited by 24 publications

References 26 publications

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

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

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Strongly anisotropic s-wave gaps in exotic superconductors

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Microwave surface resistance in MgB2

Cited by 24 publications

References 26 publications

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

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

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Strongly anisotropic s-wave gaps in exotic superconductors

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Product

Resources

About

Microwave surface resistance in MgB₂

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

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