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Unified superconductors possible with improved materials

Wed, 05/14/2014 - 12:28pm
SISSA
Superconductors are promising materials, with applications ranging from medicine to transport.  Unfortunately, though, their use is for the time being limited to the very low temperatures (close to absolute zero) necessary for superconductivity to occur.  Some  materials, however, could be improved so as to obtain higher and  energetically  less  “costly”  critical  temperatures.  A  team  of  researchers coordinated  by  SISSA  investigated  a  class  of  conductors  at  high  critical  temperature,  adding  insight  into  the  physics  of  these  phenomena. Leading edge  imaging  and  medical  diagnostics,  but  also  magnetic  levitation  trains:  these  are  examples  of  technology relying  on  “superconductors”.  Superconductors  are  materials  in  which electrons  flow  without  dissipation  and  which  have  very  special properties  such  as  expelling  all magnetic  fields.  The  physics  underlying  the  phenomenon  has  only  been  explained  for  low temperature  superconductors,  those  exhibiting  their  properties  at  temperatures  close  to  absolute zero.  The  so called high temperature  superconductors  remain  one  of  the  major  mysteries of the physics  of  matter,  and  scientists  have  recently  been  redoubling  their efforts  to  understand  the phenomenon  and  improve  its  yield.  Among  them  are  Massimo  Capone  and  coworkers  who  have  just  published  a  paper  in  Physical  Review  Letters.  The  study  was  authored  by  Capone,  ERC  SUPERBAD  project  leader,  Gianluca  Giovannetti  of  CNRIOM  and  SISSA,  and  Luca  de’  Medici  of  the  European  Synchrotron  Radiation  Facility  in  Grenoble.  
 
“To  be  able  to  function,  classical  superconductors  have  to  reach  extremely  low  temperatures,  very  close  to  absolute  zero.  This  makes  their  use  very  costly  and uneconomical”,  explains  Capone.  “Almost  30  years  ago  scientists discovered  some  classes  of  materials  that  worked  at  temperatures  that  were  substantially  higher  though  still  quite  low in  the  order  of  200°C  below  zero.  Several  types  of  materials  exist,  with  different  characteristics  and  critical temperatures”,  continues  Capone,  “the  most  investigated  family  is  based  on  copper,  while  another,  slightly  less  efficient  one  is  based  on  iron and  that’s  precisely  the  family  we  set  out  to  investigate”.  As  Capone  explains,  there’s no  agreement  on  how  the  phenomenon  originates  in  the  different  materials,  and  according  to  some  scientists  the  explanations  could  be  different  for  the  various  families.  “We  carried  out  a  study  based  on  theory  and  simulations that  demonstrated  that  this  is  not  the  case:  the  theoretical  explanation  for  copper  and  iron  superconductors  could  be  the  same,  and  could  even  apply  to  other  materials  like  carbon,  for  example  carbon  fullerides,  which  have  been  extensively  studied  at  SISSA.  In  practice,  there  could  be  a  unified  theory  for  these  superconductors”. 
 
In  their  new  paper,  Capone  and  coworkers  demonstrate  that  the  explanation  is  the  same,  and  they  put  forward  some  hypotheses  as  to  the  theoretical  framework  for  this  explanation,  hypotheses which  paradoxically  liken superconductivity  and  very  high  impedance  phenomena.  “Clearly,  we  haven’t  yet  explained  the  physics  of  these  superconductors,  or  we  would  have  won  the  Nobel  prize”,  he  jokes.  “However,  demonstrating  that  there  is  a  single theoretical  framework  explaining  these  phenomena  could  be  an  important  step forward.

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