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Probing superconductivity in MgB2 confined to magnetic field tuned cylinders by means of critical fluctuations


Weyeneth, S; Schneider, T; Zhigadlo, N D; Karpinski, J; Keller, H (2008). Probing superconductivity in MgB2 confined to magnetic field tuned cylinders by means of critical fluctuations. Journal of Physics: Condensed Matter, 20:135208.

Abstract

We report and analyze reversible magnetization measurements on a high quality MgB2 single crystal in the vicinity of the zero-field transition temperature, T_{\mathrm {c}}\simeq 38.83 K, at several magnetic fields up to 300 Oe, applied along the c-axis. Although MgB2 is a two-gap superconductor our scaling analysis uncovers remarkable consistency with 3D-xy critical behavior, revealing that close to criticality the order parameter is a single complex scalar as in 4He. This opens up the window onto the exploration of the magnetic field induced finite size effect, whereupon the correlation length transverse to the applied magnetic field Hi applied along the i-axis cannot grow beyond the limiting magnetic length LHi = (Φ0/(aHi))1/2 with a\simeq 3.12 , related to the average distance between vortex lines. We find unambiguous evidence for this finite size effect. It implies that in type II superconductors, such as MgB2, there is a 3D–1D crossover line Hpi(T) = (Φ0/(aξj0−ξk0−))(1−T/Tc)4/3 with i\neq j\neq k and ξi0,j0,k0 ± denotes the critical amplitudes of the correlation lengths above (+) and below (−) Tc along the respective axis. Consequently, above Hpi(T) and T<Tc superconductivity is confined to cylinders with diameter LHi (1D). In contrast, above Tc and Hpi(T) = (Φ0/(aξj0+ξk0+))(T/Tc−1)4/3 the uncondensed pairs are confined to cylinders. Accordingly, there is no continuous phase transition in the (H,T)-plane along the Hc2-lines as predicted by the mean-field treatment.

Abstract

We report and analyze reversible magnetization measurements on a high quality MgB2 single crystal in the vicinity of the zero-field transition temperature, T_{\mathrm {c}}\simeq 38.83 K, at several magnetic fields up to 300 Oe, applied along the c-axis. Although MgB2 is a two-gap superconductor our scaling analysis uncovers remarkable consistency with 3D-xy critical behavior, revealing that close to criticality the order parameter is a single complex scalar as in 4He. This opens up the window onto the exploration of the magnetic field induced finite size effect, whereupon the correlation length transverse to the applied magnetic field Hi applied along the i-axis cannot grow beyond the limiting magnetic length LHi = (Φ0/(aHi))1/2 with a\simeq 3.12 , related to the average distance between vortex lines. We find unambiguous evidence for this finite size effect. It implies that in type II superconductors, such as MgB2, there is a 3D–1D crossover line Hpi(T) = (Φ0/(aξj0−ξk0−))(1−T/Tc)4/3 with i\neq j\neq k and ξi0,j0,k0 ± denotes the critical amplitudes of the correlation lengths above (+) and below (−) Tc along the respective axis. Consequently, above Hpi(T) and T<Tc superconductivity is confined to cylinders with diameter LHi (1D). In contrast, above Tc and Hpi(T) = (Φ0/(aξj0+ξk0+))(T/Tc−1)4/3 the uncondensed pairs are confined to cylinders. Accordingly, there is no continuous phase transition in the (H,T)-plane along the Hc2-lines as predicted by the mean-field treatment.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Language:English
Date:2008
Deposited On:09 Feb 2009 15:35
Last Modified:05 Apr 2016 12:50
Publisher:Institute of Physics Publishing
ISSN:0953-8984
Additional Information:This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condensed Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at DOI: 10.1088/0953-8984/20/13/135208
Publisher DOI:https://doi.org/10.1088/0953-8984/20/13/135208
Related URLs:http://arxiv.org/abs/0705.3775

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