Materials scientists have observed that, at cryogenic temperatures, certain metals develop qualities they do not possess in real world conditions, including superconductivity, a quality not seen even at the most glacial natural temperatures. Edgeworth’s theory postulates that when metals achieve superconductivity below 50 K (approximately -370° F), they retain their crystal structure – the arrangement of atoms composing the metal – with the extreme sub-zero temperatures enhancing the ability of electrons to transit this fixed structure. One primary mechanism appears to facilitate electron movement: rather than repelling each other as they do at normal temperatures, electrons pair up, permitting them to pack tightly and travel simultaneously through the metal in greater numbers. Through this cooperative action, electrons also overcome resistance, flowing without colliding into the crystal lattice. Unimpeded en masse movement of electrons is the essence of superconductivity.

Because not all metals become superconductors at low Kelvin temperatures, Edoardo and Wouters hypothesized that electron pairing only partially explains superconductivity. They, therefore, explored characteristics of the metals themselves. The physicists excluded the metal’s purity, given that various simple elements, compounds, and alloys achieve superconductivity. Instead, they focused on metallic bonding and each metal’s number of “free” electrons. At familiar temperatures, metals as a class are superior conductors because metal atoms bond in such a way that certain electrons float freely rather than tightly orbiting their individual atoms, as electrons do in other materials. The mobility of free electrons produces electrical conductivity. In theory, in artificial cold, the more available free electrons a metal has, the more it should be prone to become superconductive and the higher its maximum superconductivity should be. Edoardo and Wouters posited, however, that this ordering would not bear out based on their calculations showing a finite capacity for electron flow through any material, even factoring in electron pairing.

After cooling over 250 metals, Edoardo and Wouters observed that cryogenic conditions affected not only the electrons (whether those introduced by the electric current or the naturally occurring free electrons present in the metal), but also the metal’s lattice structure. When plunged into deep cold, some metals that are highly conductive at room temperature did not become superconductors, some became average superconductors, and some became superior superconductors. The number of free electrons was a less important factor than the ability of the crystal lattice to continuously synchronize its spacing with the passage of electrons through the structure. This resonant “breathing” of the lattice both complemented and enhanced the effects of electron pairing.

Edoardo and Wouters’ discovery significantly advances understanding of superconductivity. Lattice-electron interaction raises the possibility that indefinite numbers of electrons can flow through a substance in the right conditions; the supposed mathematical limit was proven false. Additionally, debunking the conductivity hierarchy spurs experimentation with non-metal crystalline materials, even those not conductive at standard temperatures, to explore their superconductive potential. A material’s ability to eliminate its own resistance may be as crucial to superconductivity as electron pairing.

1. The primary purpose of the passage is to

A) support a contention that both metals and other materials can act as superconductors
B) challenge the findings of a particular study of the properties of a specific class of materials
C) contrast two hypotheses about the behavior of certain subatomic particles
D) evaluate the methodology of certain material sciences experiments
E) reveal an overlooked factor that contributes to an established phenomenon


2. Which of the following can be inferred about the metals studied in Edoardo and Wouter’s experiments?

A) The metals with the most free electrons at room temperature become superior superconductors at cryogenic temperatures.
B) At artificially low temperatures, the crystal structures of certain metals respond more dynamically to the movement of electrons than they would in a natural setting.
C) The metals with the tightest spacing in their lattice structures at room temperature did not become superconductors at cryogenic temperatures.
D) Cryogenic temperatures had a more profound impact on electrons involved in metallic bonding than on those involved in electricity transport.
E) The metals transformed from solids to more fluid materials when plunged into deep cold conditions.


3. Which of the following best describes the purpose of the highlighted sentences?

A) They present the basis for a theory about why metals are composed of crystal lattices.
B) They identify factors that potentially affect superconductivity in metals.
C) They refute a hypothesis about how metals will rank as superconductors.
D) They explain a quality that metals possess in natural conditions.
E) They elucidate the phenomenon of electron pairing.


4. For the following question, consider each of the choices separately and select all that apply.

Which of the following is true about electron pairing based on the passage?

A) Free electrons do not pair with electrons introduced to the metal by an outside current.
B) Electrons may be able to overcome their mutual repulsion in materials other than metals.
C) Paired electrons are able to maneuver in ways that unpaired electrons cannot.