Methodology and search for superconductivity in the La–Si–C system

Abstract

In this paper we describe a methodology for the search for new superconducting materials. This consists of a parallel synthesis of a highly inhomogeneous alloy which covers large areas of the metallurgical phase diagram combined with a fast, microwave-based method which allows non-superconducting portions of the sample to be discarded. Once an inhomogeneous sample containing a minority phase superconductor is identified, we revert to well-known thorough identification methods which include standard physical and structural methods. We show how a systematic structural study helps in avoiding misidentification of new superconducting materials when there are indications from other methods of new discoveries. These ideas are applied to the La-Si-C system which exhibits promising normal state properties which are sometimes correlated with superconductivity. Although this system shows indications for the presence of a new superconducting compound, the careful analysis described here shows that the superconductivity in this system can be attributed to intermediate binary and single phases of the system.

Magnetic field modulated microwave spectroscopy across phase transitions and the search for new superconductors

“…In figure 2, microwave absorption due to the dissipation from nonsuperconducting electrons (equation ( 6)) has been subtracted from the total microwave absorption in order to illustrate the In type II superconductors, the existence of vortices and vortex movement contributes as an additional source for dissipation of electromagnetic energy. Depending on the magnetic field, temperature, and pinning strength, it is possible to identify three different regions (figure 3, [17]): Below the first critical field (h c1 ) the material is in the Meissner state and the surface resistance can be described by equation (6). Within this region, the absorption increases with the applied field and can be expressed as a function of λ.…”

“…The combination of phase spread alloy growth methods and MMMA was proposed to search for new superconducting materials [61]. Using this approach superconductivity was found in La 2 C 3−x [6]. The relationship between the superconducting transition temperature of Pr x Gd 1−x BaCu 3 O 7 estimated from microwave and dc transport measurements is shown in figure 9 [62].…”

“…Therefore, most of the new superconductors have been discovered through Edisonian-type searches, using the intuition of experimental scientists. In order to increase the chances of finding new superconducting materials, a combinatorial search can be used [6]. This method is based on the synthesis of inhomogeneous samples consisting of several phases with different stoichiometries.…”

Search for Superconductivity in Micrometeorites

“…(For an innovative alternative approach involving phase spread alloys, see ref. 14 ). In contrast, we have advanced a method for the fast detection of superconductivity with very high sensitivity, which allows broad searches.…”

Superconductivity found in meteorites

“…This sensitivity is critical in measuring possible minute phases within inhomogeneous materials (12). MFMMS has been used to search for novel superconductivity in several types of inhomogeneous samples, such as phase spread alloys (13), bulk samples (14), and even natural samples, including meteorites (15,16). However, previous searches for superconductivity in meteorites have not identified any superconducting compounds.…”