无忧视频

Physics Research Reveals New State of Matter

The scaling theory of localization鈥攖he idea that metals cannot exist in two dimensions and that all electrons confined to a 2-D existence will eventually localize, becoming immobile and forming an insulating state鈥攈as been part of the standard model of solid state physics for the last 40 years. But recent studies by 无忧视频 physics professor Nicholas Breznay 鈥�02 have discovered an exception to this rule, finding evidence for a two-dimensional metal.

This work, published this fall in Science Advances (鈥淧article-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films鈥�) and in Physical Review B (鈥淪uperconductor to weak-insulator transitions in disordered tantalum nitride films鈥�), builds on careful fabrication and study of the electrical properties of tantalum nitride and indium oxide and related thin-film materials.

鈥淎t the boundary between the superconducting and insulating ground states, we discovered that there is phase of matter that shows saturation of the conductivity鈥攎etallic behavior鈥攁s the temperature is cooled to zero,鈥� Breznay says. 鈥淚n addition, we examined the Hall effect, the voltage difference that appears perpendicular to the current in the presence of a magnetic field. The Hall effect is zero in superconductors, and nonzero in metals; our measurements and analyses show that this exotic metallic state has zero Hall effect, suggesting a vestigial character from the nearby superconducting state, what we term a 鈥榝ailed鈥� superconductor.鈥�

Breznay, who joined the Harvey Mudd Department of Physics in the fall, is an experimental condensed matter physicist, studying emergent phenomena in quantum materials. Breznay鈥檚 lab investigates exotic states of matter鈥攕uperconductors, spin-liquid magnets, charge-ordered oxides and amorphous Anderson insulators鈥攗sing hands-on experiments. His group studies complex materials, measuring and modeling their electrical properties in extreme conditions of low temperatures, intense magnetic fields and high pressures.

The new 2-D metal that arises from a failed superconductor is only beginning to be explored. Breznay knows of one group at Johns Hopkins University that has studied the matter鈥檚 microwave properties and found similarly anomalous behavior, and researchers at the University of Illinois Urbana-Champaign have just developed a theoretical model.

Breznay is excited about the opportunity for new experiments and theoretical descriptions of this curious state of matter and believes that there will be practical applications for the material in the future. 鈥淲e do not have an immediate application in mind,鈥� he says, 鈥渂ut studies of this and others studies of quantum materials will inevitably lead to practical payoffs. Harvesting energy or manipulating information ultimately boils down to understanding the ins and outs of electrons in solids.鈥�