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Phase transitions occur when a substance changes from a solid, liquid or gaseous state to a different state—like ice melting or vapor condensing. During these phase transitions, there is a point at which the system can display properties of both states of matter simultaneously. A similar effect occurs when normal metals transition into superconductors—characteristics fluctuate and properties expected to belong to one state carry into the other.
Scientists at Harvard have developed a bismuth-based, two-dimensional superconductor that is only one nanometer thick. By studying fluctuations in this ultra-thin material as it transitions into superconductivity, the scientists gained insight into the processes that drive superconductivity more generally. Because they can carry electric currents with near-zero resistance, as they are improved, superconducting materials will have applications in virtually any technology that uses electricity.
Harvard - Scientists - Technology - Theory - Superconductors
The Harvard scientists used the new technology to experimentally confirm a 23-year-old theory of superconductors developed by scientist Valerii Vinokur from the U.S. Department of Energy's (DOE) Argonne National Laboratory.
One phenomenon of interest to scientists is the complete reversal of the well-studied Hall effect when materials transition into superconductors. When a normal, non-superconducting material carries an applied current and is subjected to a magnetic field, a voltage is induced across the material. This normal Hall effect has the voltage pointing in a specific direction depending on the orientation of the field and current.
Materials - Superconductors - Sign - Hall - Voltage
Interestingly, when materials become superconductors, the sign of the Hall voltage reverses. The "positive" end of the material becomes the "negative." This is a well-known phenomenon. But while the Hall effect has long been a major tool that scientists use to study the types of electronic properties that make a material a good superconductor, the cause of this reverse Hall effect has remained mysterious to scientists for decades, especially in regard to high-temperature superconductors for which the effect is...
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