SUPERCONDUCTIVITY

About: 

• Meaning: Materials are said to be exhibiting superconductivity when they exhibit the following two characteristics after being cooled below their critical temperature - 
  1. zero electrical resistance and
     
     
  2. expulsion of magnetic fields (Meissner effect)
     
     
  
  
  
• Superconductor materials: Property of superconductivity is inherent to variety of materials –
  • Chemical elements(e.g. mercury or lead), 
    
    
  • Alloys(such as niobium-titanium, germanium-niobium, and niobium nitride), 
    
    
  • Ceramics(YBCO and magnesium diboride) and
    
    
  • Organic superconductors(fullerenes and carbon nanotubes);
    
    
  
  
  
• Properties:
  • Phase Transition (at critical temp): In superconducting materials, the characteristics of superconductivity appear when the temperatureT is lowered below a critical temperature T_c.
    
    
  • Zero resistance to current: When the superconductor material is cooled below its critical temperature then it shows zero resistance to electric current.
    
    
  • Meissner effect: This means expulsion of a magnetic fieldfrom a superconductor when it is cooled below its critical temperature. This property is used for making high speed, magnetically-levitated trains (MAGLEV).
    
    
  • London moment: It is a phenomenonwhereby a ‘spinning’ superconductor generates a ‘magnetic field’ whose ‘axis’ lines up exactly with the ‘spin axis’.
    
    
  
  
  
• High-temperature superconductors (HTS): These are materials that behave as superconductors at unusually high temperatures.