| Abstract | Supravodljivost se većinom manifestira kao odsutnost otpora iznad neke kritične temperature. 1911. otkrio ju je nizozemski fizičar Kamerlingh Onnes u Leidenu, 3 godine nakon što je prvi put ukapljivao helij. Mjerio je električni otpor žive pri vrlo niskim temperaturama. Počeo je istraživati električna svojstva u metalima na ekstremno hladnim temperaturama. Dugi niz godina znalo se da padom temperature pada i otpor materijala, no nije bilo poznato što se događa pri ovako niskim temperaturama. Električni otpor žive potpuno je nestao ispod temperature od 4.2K. Poput feromagnetizma i spektralnih linija atoma, supravodljivost je kvantno mehanički fenomen. Najvažnija karakteristika supravodljivosti je Meissnerov efekt - metali ohlađeni do supravodljivoga stanja ponašaju kao savršeni dijamagnetici, to jest u tankom površinskom sloju induciraju se struje koje stvaraju takvo magnetno polje koje poništava vanjsko polje, te je u unutrašnjosti supravodiča magnetno polje jednako nuli. Supravodljivost ovisi o temperaturi , Magnetskom polju i gustoći struje . Ako su svi parametri ispod kritičnih vrijednosti, materijal će biti u supravodljivom stanju, u protivnom, ponašat će se kao običan metal. Kad supravodičem jednom potekne struja, ona će teći vječno, bez potrebe za strujnim izvorom, jer zbog nepostojanja otpora nema gubitka energije. Za praktičnu primjenu supravodiča važna je temperatura na kojoj oni postaju supravodljivi, Problem je što se supravodljivost pojavljuje samo na vrlo niskim temperaturama što predstavlja problem u masnovnoj primjeni supravodiča. Stoga, pronalazak i razumijevanje materijala koji bi vodili struju bez otpora na sobnim temperaturama predstavlja svojevrstan problem istraživanja u području fizike čvrstog stanja. |
| Abstract (english) | Superconductivity is mostly manifested as the absence of resistance above some critical temperature. It was discovered in 1911. by the Dutch physicist Kamerlingh Onnes in Leiden, 3 years after he first liquefied helium. He measured the resistance of mercury at extremely low temperatures. He began to investigate the electrical properties in metals at extremely cold temperatures. For many years, it was known that as the temperature dropped, so did the resistance of the material, but it was not known what happened at such low temperatures. The electrical resistance of the mercury completely disappeared below the temperature of 4.2K. Like ferromagnetism and spectral lines of atoms, superconductivity is a quantum mechanical phenomenon. The most important characteristic of superconductivity is the Meissner effect - metals cooled to the superconducting state behave like perfect diamagnetics, that is, currents are induced in a thin surface layer that create such a magnetic field that abolish the external field, and the magnetic field inside the superconductor is zero. The superconductivity depends on the temperature , the magnetic field and the current density . If all parameters are below the critical values, the material will be in a superconducting state, otherwise, it will behave like a common metal. Once a superconducting current flows, it will flow forever, without the need for a current source, because due to the lack of resistance there is no loss of energy. For the practical application of superconductors, the temperature at which they become superconductors is important. The problem is that superconductivity occurs only at exceptionally low temperatures, which is a problem in the mass application of superconductors. Therefore, the invention and understanding of materials that would conduct current without resistance at room temperatures is a kind of research problem in the field of solid-state physics. |
