Enhancement of Superconducting Temperatures in Cs-based Superconductors
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O R I G I N A L PA P E R
Enhancement of Superconducting Temperatures in Cs-based Superconductors Chu W. Kwang-Hua
Received: 27 July 2012 / Accepted: 7 August 2012 © Springer Science+Business Media, LLC 2012
Abstract A material, when superconductive, has an electrical resistance of exactly zero below a critical temperature (Tc ). This is universal in superconductors. We firstly verify our approaches by comparing our preliminary calculations for resistance with previous available measurements. After the intensive computations, we illustrate the effect of activation volume and energy on the enhancement of Tc (up to 50 K) for the Csx Fe2−y Se2−z (0 ≤ x, y, z ≤ 1) superconductor by using the verified Eyring’s transition-state approach which is based on the quantum chemistry to treat the activated complex: Csx Fe2−y Se2−z . Our results suggest that tuning activation volume is the efficient way to enhance the superconducting temperature. Keywords Quantum chemistry · Defect · Transport
1 Introduction Fe (iron) itself under pressure is a superconductor, with Tc ∼ 1.8 K at 20 GPa [1]. Upon chemical doping with Se, FeSe becomes superconducting with Tc = 8 K and it has a simple PbO-type structure and a similarity to the critical FeAs4 -tetrahedra layers found in all iron-based superconductors [2]. Recently, intercalation of further layers of Cs (atoms) between the FeSe layers to try to increase Tc ∼ 29.6 K was reported via Cs0.8 (FeSe0.98 )2 [3, 4]. The question comes next: Can we increase Tc up to, say, around 50 K for this series of superconductors [3–5]? C.W. Kwang-Hua () Transfer Centre, No. 24, 260th Lane, First Section, Road Muja, Taipei 116, Taiwan ROC e-mail: [email protected]
Almost all of the iron pnictide and chalcogenide superconductors have structural and physical properties in common [3, 5]. Recently, a microscopic coexistence between the superconducting phase and a strong magnetic phase was found in single crystal Cs0.8 (FeSe0.98 )2 (iron selenide (FeSe) molecular layers intercalated by Cs spacer layer) [4]. Nevertheless, it was remarked in [5] about its unclear materials’ properties and incomplete experimental information on the superconducting state (It is the grand challenge for theory to guide the search through this terrain. [5]). At least, it is not yet clear whether the superconductivity and antiferromagnetic order coexist locally or in different regions of a sample. Thus, we also have another question. What is the extreme for an interplay between magnetism and superconductivity considering the possible occurrence of unconventional superconducting states? Note that when superconductive, a material has an electrical resistance of exactly zero [6]. Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared [7]. All superconductors have exactly zero resistivity to low applied
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