共查询到20条相似文献,搜索用时 15 毫秒
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Putti M Affronte M Ferdeghini C Manfrinetti P Tarantini C Lehmann E 《Physical review letters》2006,96(7):077003
We report specific heat measurements on neutron-irradiated MgB2 samples, for which the critical temperature is lowered to 8.7 K, but the superconducting transition remains extremely sharp, indicative of a defect structure extremely homogeneous. Our results evidence the presence of two superconducting gaps in the temperature range above 21 K, while single-gap superconductivity is well established as a bulk property, not associated with local disorder fluctuations, when Tc decreases to 11 K. 相似文献
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新型超导体二硼化镁(MgB_2)基础研究及其应用展望 总被引:2,自引:0,他引:2
文章简要介绍了新型超导体二硼化镁的发现、研究进展和应用前景 .理论和实验都已经证明 ,二硼化镁的超导电性来源于电声子耦合 ,可以用具有S -波对称性波函数的BCS图像来描述 .然而在二硼化镁超导体中 ,人们发现有两个超导能隙 ,一个在 6meV ,另外一个在 2meV左右 ,它们同时在超导转变温度处打开 ,这给超导机理研究带来了一些新的内容 .在混合态物理方面 ,人们发现超导与正常态的边界线 (上临界磁场Hc2 )与磁通融化线(不可逆线Hirr)之间有很大的间隙 ,即使在绝对零度时也是如此 ,作者提出这可能是由于双能隙的结果或磁通物质的量子融化 .在应用方面 ,最有可能把它做成超导磁体 ,利用闭路循环制冷机制冷在 2 0K左右使用 ,这样极有可能取代现在医学上使用的核磁共振成像的液氦温度超导磁体 相似文献
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Szabó P Samuely P Kacmarcík J Klein T Marcus J Fruchart D Miraglia S Marcenat C Jansen AG 《Physical review letters》2001,87(13):137005
Experimental support is found for the multiband model of the superconductivity in the recently discovered system MgB(2) with the transition temperature T(c) = 39 K. By means of Andreev reflection, evidence is obtained for two distinct superconducting energy gaps. The sizes of the two gaps ( Delta(S) = 2.8 meV and Delta(L) = 7 meV) are, respectively, smaller and larger than the expected weak coupling value. Because of the temperature smearing of the spectra the two gaps are hardly distinguishable at elevated temperatures, but when a magnetic field is applied the presence of two gaps can be demonstrated close to the bulk T(c) in the raw data. 相似文献
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Singh PP 《Physical review letters》2006,97(24):247002
We study the effects of pressure on the electron-phonon interaction in MgB2 using density-functional-based methods. Our results show that the superconductivity in MgB2 vanishes by 100 GPa, and then reappears at higher pressures. In particular, we find a superconducting transition temperature Tc approximately 2 K for mu*=0.1 at a pressure of 137 GPa. 相似文献
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Floris A Profeta G Lathiotakis NN Lüders M Marques MA Franchini C Gross EK Continenza A Massidda S 《Physical review letters》2005,94(3):037004
Solid MgB(2) has rather interesting and technologically important properties, such as a very high superconducting transition temperature. Focusing on this compound, we report the first nontrivial application of a novel density-functional-type theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, we obtain the transition temperature, the gaps, and the specific heat of MgB(2) in very good agreement with experiment. Moreover, our calculations show how the Coulomb interaction acts differently on sigma and pi states, thereby stabilizing the observed superconducting phase. 相似文献
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Thermal transport measurements have been made on the Fe-based superconductor Lu2Fe3Si5 (T(c) ~ 6 K) down to a very low temperature T(c)/120. The field and temperature dependences of the thermal conductivity confirm the multigap superconductivity with fully opened gaps on the whole Fermi surfaces. In comparison to MgB2, Lu2Fe3Si5 reveals a remarkably enhanced quasiparticle heat conduction in the mixed state. The results can be interpreted as a consequence of the unequal weight of the Fe 3d-electron character among the distinct bands. 相似文献
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The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs B2). We show that hole doping of LiBC results in Fermi surfaces of B-C p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at T(c) approximately equal to 40 K in MgB2. Comparison of Li(0.5)BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2. 相似文献
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Iavarone M Karapetrov G Koshelev AE Kwok WK Crabtree GW Hinks DG Kang WN Choi EM Kim HJ Kim HJ Lee SI 《Physical review letters》2002,89(18):187002
The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV and Delta(2)=7.1 meV at 4.2 K. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multiband system. Temperature evolution of the tunneling spectra follows the BCS scenario [Phys. Rev. Lett. 3, 552 (1959)]] with both gaps vanishing at the bulk T(c). The data confirm the importance of Fermi-surface sheet dependent superconductivity in MgB2 proposed in the multigap model by Liu et al. [Phys. Rev. Lett. 87, 087005 (2001)]]. 相似文献
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We have measured the Raman spectra of polycrystalline MgB2 from 25 to 1200 cm(-1). A superconductivity-induced redistribution in the electronic Raman continuum was observed. Two pair-breaking peaks appear in the spectra, suggesting the presence of two superconducting gaps. The measured spectra were analyzed using a quasi-two-dimensional model in which two s-wave superconducting gaps open on two sheets of Fermi surface. For the gap values we have obtained Delta(1) = 22 cm(-1) ( 2.7 meV) and Delta(2) = 50 cm(-1) ( 6.2 meV). Our results suggest that a conventional phonon-mediated pairing mechanism occurs in the planar boron sigma bands and is responsible for the superconductivity of MgB2. 相似文献
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Eskildsen MR Kugler M Tanaka S Jun J Kazakov SM Karpinski J Fischer Ø 《Physical review letters》2002,89(18):187003
We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c axis, a single superconducting gap (Delta=2.2 meV) associated with the pi band is observed. The vortices in the pi band have a large core size compared to estimates based on H(c2) and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi band is, at least partially, induced by the intrinsically superconducting sigma band. 相似文献
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Bouquet F Wang Y Sheikin I Plackowski T Junod A Lee S Tajima S 《Physical review letters》2002,89(25):257001
Heat-capacity measurements of a 39 microg MgB2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence, and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the smaller gap being isotropic, that carrying the larger gap having an anisotropy of approximately 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2. 相似文献
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MgB 2 thin films and MgB 2 /Fe multilayers have been prepared by vapor deposition of the elements in vacuum. X-ray diffraction studies of the MgB 2 samples show preferred c -axis growth along the film normal direction. Superconducting transition temperatures of 18 K and 22 K have been measured before and after annealing, respectively, of an MgB 2 film of 1575 Å thickness. Atomic force microscope images show island growth of the films leading to a rough surface. Mössbauer spectroscopy on MgB 2 /Fe/MgB 2 multilayers of various Fe layer thicknesses indicates superparamagnetic behavior. Evidence is provided for the formation of interfacial amorphous (a-) Fe 3 B. The magnetic ordering of Fe and a-Fe 3 B and the size effect in MgB 2 are assumed to be the cause for the destruction of the superconductivity in the as-grown multilayers. 相似文献
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Mazin II Andersen OK Jepsen O Dolgov OV Kortus J Golubov AA Kuz'menko AB Van Der Marel D 《Physical review letters》2002,89(10):107002
A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB2. However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation has been observed. We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport. 相似文献
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Uchiyama H Shen KM Lee S Damascelli A Lu DH Feng DL Shen ZX Tajima S 《Physical review letters》2002,88(15):157002
The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching the Fermi energy. These can be assigned to the theoretically predicted sigma (B 2p(x,y)) and pi (B 2p(z)) bands. In addition, a small parabolic-like band is detected around the Gamma point, which can be attributed to a surface-derived state. The overall agreement between our results and the band calculations suggests that the electronic structure of MgB2 is of a conventional nature, thus implying that electron correlations are weak and may be of little importance to superconductivity in this system. 相似文献