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We report on measurements of the specific heat of the recently discovered superconductor MgB2 in the temperature range between 3 and 220 K. Based on a modified Debye-Einstein model, we have achieved a rather accurate account of the lattice contribution to the specific heat, which allows us to separate the electronic contribution from the total measured specific heat. From our result for the electronic specific heat, we estimate the electron-phonon coupling constant λ to be of the order of 2, significantly enhanced compared to common weak-coupling values ≤ 0.4. Our data also indicate that the electronic specific heat in the superconducting state of MgB2 can be accounted for by a conventional, s-wave type 74.25.Kc The recent discovery of superconductivity in MgB 2 below T c ≈ 39 K [1] has caused a remarkable excitement in the solid-state physics community. Critical temperatures of this magnitude inevitably raise the question whether mechanisms other than the common electron-phonon interaction are responsible for the transition. In their very recent work, Bud'ko et al. [2] have investigated the Boron isotope effect in superconducting MgB 2 and found that replacing 11 B by 10 B increases the critical temperature by about 1 K. This was taken as strong evidence that superconductivity in MgB 2 is of conventional nature, i.e., the electron pairing interaction is phonon-mediated. Kotagawa et al. have interpreted their 11 B NMR measurements as indicating strong coupling s-wave superconductivity [3]. Preliminary 11 B NMR measurements at low temperatures yield spectra which are consistent with the expectations for a type-II superconductor in the mixed state [4]. Evidence for sizeable electron-phonon coupling is also provided by recent band-structure calculations [5][6][7]. Various tunneling experiments have provided some evidence for conventional BCS-like superconductivity, but the values of the superconducting energy gap extracted from these measurements vary from 2 to 7 meV [8][9][10].In this letter, we report on measurements of the specific heat C p of MgB 2 and present C p (T ) data in a wide temperature range. Using a consistent model for the contribution of the lattice vibrations to C p (T ) we calculate the electronic specific heat of this material. We show that the electronic specific heat below T c is in good agreement with a conventional BCS-type interpretation.The sample has been prepared from commercially available MgB 2 -powder (Alfa Aesar) by sintering a pressed pellet at 500• C for about 72 h. Electron microprobe investigations of the sample have shown that impurities of heavy elements (Cu, Ni, W) with concentrations of the order of 10 −2 are present in the sample. The specific heat C p (T ) of the sintered MgB 2 sample has been measured using two different experimental techniques in overlapping temperature ranges. A standard relaxation technique was employed in the temperature range between 3 and 45 K. For temperatures between 20 and 220 K an adiabatic continuous heating calorimeter was used. Special car...

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In a recent letter [1], we reported the observation of giant zero-bias conductance peaks (ZBCPs) for contacts between Au wires and bulk UBe 13 , which we ascribed to the existence of low-energy Andreev surface bound-states in superconducting UBe 13 . In the comment [2]