Experimental physicists discover new quantum state of a superconductor in which the material becomes a source of a magnetic field. The achieved result is important both from the point of view of fundamental science, and for the development of superconducting devices. Article published in the journal Nature Physics.
Superconductivity is a phenomenon in which electrical resistance of the material becomes strictly zero. The transition of the sample in such a state occurs when cooling below the critical temperature, it is determined by the properties of the substance. Currently, superconductors are widely used in engineering, however, a full theoretical description of this phenomenon scientists are still not developed (for more details on superconductivity and existing explanations can be read in our material).
Quantum properties of the superconductor make it a perfect diamagnetic material, which is energetically advantageous to have a zero internal magnetic field. As a result, the superconductivity and magnetism are competitors: normally they appear only separately and for their joint occurrence, we need to support special conditions.
Scientists from six countries under the leadership of Vadim Grinenko (Vadim Grinenko) from the Institute of solid state physics and materials research Leibniz Association in Dresden experimentally studied the superconductivity in the crystal of Ba1−xKxFe2As2. The authors investigated the samples with different content of impurities of potassium and barium (in the chemical formula of they are determined by the parameter x), and watched as the composition of the material affects its superconducting and magnetic characteristics. To analyze these properties, the physics of irradiated crystals polarized (that is, having a given orientation of the magnetic moments) of the beam of positively charged muons were detected and particles that were born in the interaction of this beam with the sample. Such measurements allowed the researchers to understand how the material influence the magnetic moments of the particles, and thus to determine its magnetic structure.
In the result, the physicists found that at sufficiently high relative potassium content (x>0.7) and low temperature (about 10 K) the material goes into a special quantum state in which starts to generate its own magnetic field. Thus, scientists have discovered a previously unknown mechanism of the coexistence of magnetism and superconductivity. This discovery creates a new direction for experimental and theoretical studies in the future may find application in the development of superconducting devices. In addition, the authors found a correlation between the conditions that resulted in the detected condition, and terms of the Lifshitz-transition — known quantum transformations that change the energy configuration of electrons. The latter will facilitate the search for such properties of other crystals.
Earlier we wrote about how scientists predicted the emergence of superconductivity at a temperature of 200 degrees Celsius and as muons helped to measure the differential potential storm clouds the size of a billion volts.