Experimental demonstration of superconducting critical temperature increase in electromagnetic metamaterials

Abstract

A recent proposal that the metamaterial approach to dielectric response engineering may increase the critical temperature of a composite superconductor-dielectric metamaterial has been tested in experiments with compressed mixtures of tin and barium titanate nanoparticles of varying composition. An increase of the critical temperature of the order of ΔT ~ 0.15 K compared to bulk tin has been observed for 40% volume fraction of barium titanate nanoparticles. Similar results were also obtained with compressed mixtures of tin and strontium titanate nanoparticles.

Metamaterial superconductors

“…In both cases  eff (q,) may become small and negative in substantial portions or the relevant fourmomentum (q,) space, leading to enhancement of electron pairing interaction. This approach has been verified in experiments with compressed mixtures of tin and barium titanate nanoparticles of varying composition [2]. An increase of the critical temperature of the order of T c ~ 0.15 K compared to bulk tin has been observed for 40% volume fraction of barium titanate nanoparticles, which corresponds to ENZ conditions.…”

“…Namely, we have demonstrated that the metamaterial approach to dielectric response engineering may increase the critical temperature of a composite superconductor-dielectric metamaterial [1,2]. Superconducting properties of a material, such as electronelectron interactions and the critical temperature of superconducting transition may be expressed via the effective dielectric response function  eff (q,) of the material [3].…”

“…A metamaterial superconductor geometry must be chosen carefully in such a way, that its fabrication requirements may be met at the current level of nanotechnology development. The two solutions suggested so far [1,2] involve either a random mixture of superconductor (tin) and ferroelectric (BaTiO 3 ) nanoparticles mixed in such a proportion that the random mixture exhibits negative ENZ behaviour, or the hyperbolic metamaterial scenario, which requires layer-by-layer fabrication of a planar multilayer superconductor-ferroelectric metamaterial. Both scenarios naturally lead to broadband small and negative  eff (q,) behavior in substantial portions of the relevant four-momentum spectrum.…”

Hyperbolic Metamaterials

“…However, this task is much more challenging than typical applications of superconducting metamaterials suggested so far [48], which only deal with metamaterial engineering on the scales which are much smaller than the microwave or RF wavelength. Nevertheless, these experimental difficulties have been overcome in two recent successful demonstrations of metamaterial superconductors [49,50]. In the case of aluminium, its superconducting temperature was more than tripled by the metamaterial engineering [50].…”

Optimal boson energy for superconductivity in the Holstein model

“…The strong enhancement of superconducting T c in the mono-layer FeAs or FeSe on SrTiO 3 substrate is deeply related to the interfacial optical phonon mode [11,[24][25][26][27]. Attempts of using Boson other than phonons, such as the plasma in meta-materials, to mediate the electron-electron attraction also appear promising [28,29].…”