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Muon-spin rotation measurements of the penetration depth of the Mo 3 Sb 7 superconductor
| Content Provider | Semantic Scholar |
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| Author | Khasanov, R. Klamut, Piotr W. Shengelaya, Alexander Bukowski, Zbigniew Savic, Ivana M. Baines, C. Keller, Hans-W. |
| Copyright Year | 2008 |
| Abstract | Measurements of the magnetic-field penetration depth lambda in superconductor Mo3Sb7 (Tc =2.1 K) were carried out by means of muon-spin rotation. The absolute values of lambda, the Ginzburg-Landau parameter kappa, and the first Hc1 and the second Hc2 critical fields at T=0 are lambda(0)=720(100) nm, kappa(0)=55(10), μ0Hc1(0)=1.8(3) mT, and μ0Hc2(0)=1.9(2) T. The zerotemperature value of the superconducting energy gap Delta(0) was found to be 0.35(1) meV, corresponding to the ratio 2Delta(0)/kBTc=3.83(10). At low temperatures lambda−2(T) saturates and becomes constant below T =0.3Tc, in agreement with what is expected for s-wave BCS superconductors. Our results suggest that Mo3Sb7 is a superconductor with the single isotropic energy gap. DOI: https://doi.org/10.1103/PhysRevB.78.014502 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-13707 Accepted Version Originally published at: Khasanov, R; Klamut, P W; Shengelaya, A; Bukowski, Z; Savic, I M; Baines, C; Keller, H (2008). Muonspin rotation measurements of the penetration depth of the Mo3Sb7 superconductor. Physical Review. B, Condensed Matter and Materials Physics, 78(1):014502. DOI: https://doi.org/10.1103/PhysRevB.78.014502 ar X iv :0 90 5. 39 06 v1 [ co nd -m at .s up rco n] 2 4 M ay 2 00 9 PREPRINT (May 24, 2009) Muon-spin rotation measurements of the penetration depth of the Mo3Sb7 superconductor R. Khasanov, ∗ P.W. Klamut, A. Shengelaya, Z. Bukowski, 4 I.M. Savić, C. Baines, and H. Keller Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland Institute of Low Temperature and Structure Research of the Polish Academy of Sciences, Okólna 2, 50-422 Wroc law, Poland Physics Institute of Tbilisi State University, Chavchavadze 3, GE-0128 Tbilisi, Georgia Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland Faculty of Physics, University of Belgrade, 11001 Belgrade, Serbia and Montenegro Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland Measurements of the magnetic field penetration depth λ in superconductor Mo3Sb7 (Tc ≃ 2.1 K) were carried out by means of muon-spin-rotation. The absolute values of λ, the Ginzburg-Landau parameter κ, the first Hc1 and the second Hc2 critical fields at T = 0 are λ(0) = 720(100) nm, κ(0) = 55(9), μ0Hc1(0) = 1.8(3) mT, and μ0Hc2(0) = 1.9(2) T. The zero temperature value of the superconducting energy gap ∆(0) was found to be 0.35(1) meV corresponding to the ratio 2∆(0)/kBTc = 3.83(10). At low temperatures λ (T ) saturates and becomes constant below T ≃ 0.3Tc, in agreement with what is expected for s−wave BCS superconductors. Our results suggest that Mo3Sb7 is a BCS superconductor with the isotropic energy gap. PACS numbers: 74.70.Ad, 74.25.Op, 74.25.Ha, 76.75.+i Recently, the attention was devoted to Mo3Sb7. This compound was originally discovered more than forty years ago and only recently was found to become a type-II superconductor with the transition temperature Tc ≃ 2.1 K. The properties of Mo3Sb7 in a superconducting state are rather unusual. Specific heat, resistivity and magnetic susceptibility experiments of Candolfi et al. suggest that Mo3Sb7 can be classified as a coexistent superconductor – spin-fluctuating system. As discussed in Ref. 4, factoring in the effect of spin fluctuations leads to renormalized values of the electron-phonon coupling constant and the Coulomb pseudopotential, which, being substituted to the McMillan expression, lead to Tc between 1.4 K and 2.0 K. This is substantially closer to the experimentally observed Tc ≃ 2.1 K than Tc ≈ 10 K, which would be obtained without taking into account the effect of spin fluctuations. There is currently no agreement on the symmetry of the order parameter of Mo3Sb7. The recent specific heat experiments of Candolfi et al. suggest that the order parameter in Mo3Sb7 is of conventional s−wave symmetry. Tran et al., based again on the results of specific heat measurements, have reported the presence of two isotropic s−wave like gaps with 2∆1(0)/kBTc = 4.0 and 2∆2(0)/kBTc = 2.5 [∆(0) is the zero-temperature value of the superconducting energy gap]. In contrast, Andreev reflection measurements of Dmitriev et al. reveal that the superconducting gap is highly anisotropic. The maximum to the minimum gap ratio was estimated to be ∆max/∆min ≃ 40 and s + g−wave symmetry of the order parameter was proposed in a qualitative analysis. The symmetry of the superconducting order parameter can be probed by measurements of the magnetic penetration depth λ. A fully gaped, isotropic pairing state produces a thermally activated behavior leading to an almost constant value of the superfluid density ρs ∝ λ for T . 0.3Tc. 10,11 Presence of line nodes in the gap leads to a continuum of low laying excitations, which result in a linear λ(T ) at low temperatures. In two-gap superconductors with highly different gap to Tc ratios the inflection point in λ(T ) is generally present. In this paper, we report the study of the magnetic field penetration depth in superconductor Mo3Sb7 by means of muon-spin rotation. Measurements were performed down to 20 mK in a series of fields ranging from 0.02 T to 0.2 T. Our results are well explained assuming conventional superconductivity with the isotropic energy gap in agreement with the recent specific heat experiments of Candolfi et al. The zero-temperature value of the gap was found to be ∆(0) = 0.35(1) meV corresponding to the ratio 2∆(0)/kBTc = 3.83(10). The Mo3Sb7 single-crystal samples were grown through peritectic reaction between Mo metal and liquid Sb. The transverse field muon-spin rotation (TF-μSR) experiments were performed at the πM3 beam line at Paul Scherrer Institute (Villigen, Switzerland). For our experiments the ensemble of some suband millimeter size single crystals were mounted onto the silver plate to cover the area of approximately 50 mm. The silver sample holder was used because it gives a nonrelaxing muon signal and, hence, only contributes as temperature independent constant background. The crystals were oriented so that the magnetic field was preferably applied along the 001 crystallographic direction. The Mo3Sb7 samples were field cooled from above Tc down to ≃ 20 mK in magnetic fields ranging from 20 mT to 0.2 T. A full temperature scan (from 20 mK up to 2.5 K) was performed in a field of μ0H = 0.02 T. Figure 1 shows the muon-spin precession signals in μ0H = 0.02 T above (T = 2.2 K) and below (T = 0.05 K) the superconducting transition temperature of Mo3Sb7. The difference in the relaxation rate above and below Tc is due to the well-known fact that type-II superconductors exhibit a flux-line lattice leading to spatial inhomogeneity of the magnetic induction. As is shown by Brandt, the second moment of this inhomogeneous field distribution is related to the magnetic field penetration depth λ in terms of 〈∆B2〉 ∝ σ sc ∝ λ. |
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| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
