Unconventional superconductors are materials that display superconductivity which does not conform to conventional BCS theory or its extensions.
High-temperature superconductors are defined as materials with critical temperature above 77 K, the boiling point of liquid nitrogen. They are only "high-temperature" relative to previously known superconductors, which function at even colder temperatures, close to absolute zero. The "high temperatures" are still far below ambient, and therefore require cooling. The first breakthrough of high-temperature superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller. Although the critical temperature is around 35.1 K, this new type of superconductor was readily modified by Ching-Wu Chu to make the first high-temperature superconductor with critical temperature 93 K. Bednorz and Müller were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". Most high-Tc materials are type-II superconductors.
Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the scanning tunneling microscope, an instrument for imaging surfaces at the atomic level. The first successful scanning tunneling microscope experiment was done by Gerd Binnig and Heinrich Rohrer. The key to their success was using a feedback loop to regulate gap distance between the sample and the probe.
In superconductivity, a semifluxon is a half integer vortex of supercurrent carrying the magnetic flux equal to the half of the magnetic flux quantum Φ0. Semifluxons exist in the 0-π long Josephson junctions at the boundary between 0 and π regions. This 0-π boundary creates a π discontinuity of the Josephson phase. The junction reacts to this discontinuity by creating a semifluxon. Vortex's supercurrent circulates around 0-π boundary. In addition to semifluxon, there exist also an antisemifluxon. It carries the flux −Φ0/2 and its supercurrent circulates in the opposite direction.
In superconductivity, a Josephson vortex is a quantum vortex of supercurrents in a Josephson junction. The supercurrents circulate around the vortex center which is situated inside the Josephson barrier, unlike Abrikosov vortices in type-II superconductors, which are located in the superconducting condensate.
A Josephson junction (JJ) is a quantum mechanical device which is made of two superconducting electrodes separated by a barrier. A π Josephson junction is a Josephson junction in which the Josephson phase φ equals π in the ground state, i.e. when no external current or magnetic field is applied.
In condensed matter physics, scanning SQUID microscopy is a technique where a superconducting quantum interference device (SQUID) is used to image surface magnetic field strength with micrometre-scale resolution. A tiny SQUID is mounted onto a tip which is then rastered near the surface of the sample to be measured. As the SQUID is the most sensitive detector of magnetic fields available and can be constructed at submicrometre widths via lithography, the scanning SQUID microscope allows magnetic fields to be measured with unparalleled resolution and sensitivity. The first scanning SQUID microscope was built in 1992 by Black et al. Since then the technique has been used to confirm unconventional superconductivity in several high-temperature superconductors including YBCO and BSCCO compounds.
Juan Carlos Campuzano is a Paraguayan American physicist. He is a Distinguished Professor of Physics at the University of Illinois at Chicago. He was a Distinguished Fellow at Argonne National Laboratory, and a he is also a 2001 American Physical Society Fellow and a recipient of the 2011 Oliver Buckley Prize in Condensed Matter Physics. He is an expert in high-temperature superconductivity.
Steven M. Girvin is an American physicist who is the Eugene Higgins Professor of Physics at Yale University and who served as deputy provost for research at Yale from 2007 to 2017. Girvin is noted for his theoretical work on quantum many body systems such as the fractional quantum Hall effect, and as co-developer of circuit QED, the application of the ideas of quantum optics to superconducting microwave circuits. Circuit QED is now the leading architecture for construction of quantum computers based on superconducting qubits.
Distrontium ruthenate, also known as strontium ruthenate, is an oxide of strontium and ruthenium with the chemical formula Sr2RuO4. It was the first reported perovskite superconductor that did not contain copper. Strontium ruthenate is structurally very similar to the high-temperature cuprate superconductors, and in particular, is almost identical to the lanthanum doped superconductor (La, Sr)2CuO4. However, the transition temperature for the superconducting phase transition is 0.93 K (about 1.5 K for the best sample), which is much lower than the corresponding value for cuprates.
Kathryn Ann Moler is an American physicist, and current dean of research at Stanford University. She received her BSc (1988) and Ph.D. (1995) from Stanford University. After working as a visiting scientist at IBM T.J. Watson Research Center in 1995, she held a postdoctoral position at Princeton University from 1995 to 1998. She joined the faculty of Stanford University in 1998, and became an Associate in CIFAR's Superconductivity Program in 2000. She became an associate professor at Stanford in 2002 and is currently a professor of applied physics and of Physics at Stanford. She currently works in the Geballe Laboratory for Advanced Materials (GLAM), and is the director of the Center for Probing the Nanoscale (CPN), a National Science Foundation-funded center where Stanford and IBM scientists continue to improve scanning probe methods for measuring, imaging, and controlling nanoscale phenomena. She lists her scientific interests and main areas of research and experimentation as:
Jochen Mannhart is a German physicist.
Xue Qikun is a Chinese physicist. He is a professor of Tsinghua University, Beijing. He has done much work in Condensed Matter Physics, especially on superconductors and topological insulators. In 2013, Xue was the first to achieve the quantum anomalous Hall effect (QAHE), an unusual orderly motion of electrons in a conductor, in his laboratory at Tsinghua University. Xue is a member of the Chinese Academy of Sciences, vice president for research of Tsinghua University, and director of State Key Lab of Quantum Physics. In 2016, he was one of the first recipients of the new Chinese Future Science Prize for experimental discovery of high-temperature superconductivity at material interfaces and the QAHE. This award has been described as "China's Nobel Prize".
Gerald J. Dolan was an American solid state physicist.
Elihu Abrahams was a theoretical physicist, specializing in condensed matter physics.
Zhi-Xun Shen is a Chinese-American experimental and solid state physicist who is a professor at Stanford University. He is particularly noted for his ARPES studies on high-temperature superconductors.
Aharon Kapitulnik is an Israeli-American experimental condensed matter physicist working at Stanford University. He is known primarily for his work on strongly correlated electron systems, low dimensional electronic systems, unconventional superconductors, topological superconductors, superconductivity and magnetism, transport in bad metals and precision measurements.
Dale J. Van Harlingen is an American condensed matter physicist.
Allen Marshall Goldman is an American experimental condensed matter physicist, known for his research on electronic transport properties of superconductors and for the eponymous Carlson-Goldman mode involving collective oscillations in superconductors.
Ali Yazdani is an American physicist who focuses on understanding new quantum phases of matter. He is currently the Class of 1909 Professor of Physics at Princeton University and the Director of the Princeton Center for Complex Materials, a material research science and technology (MRSEC) center supported by the National Science Foundation. Together with Seamus Davis, he is the recipient of the 2023 Buckley Prize from the American Physical Society.
