Fractional quantization of the ballistic conductance in electron and hole systems

In the present article we give a brief overview of the theories of the 0.7 anomaly of the ballistic conductance. The special attantion is given to the concept of a fractional quantization of the ballistic conductance arising from exchange interaction of the Heisenberg type between the carrier localized in the region of the quantum point contact and freely propagating carriers in electron and hole systems. ----- Brotask\"ommtun skotlei{\eth}ninnar \'i einv\'i{\eth}um rafeinda og holukerfum \'I grein {\th}essari ver{\eth}ur sk\"ommtun skotlei{\eth}ninnar \'i einv\'i{\eth}um kerfum \'utsk\'yr{\eth} og fari{\eth} yfir n\'yjustu og helstu fr{\ae}{\eth}il\'ik\"on \'a svi{\eth}i \LDQ 0,7 fr\'aviksins \RDQ og tengdra fyrirbrig{\eth}a \'i einv\'i{\eth}um rafeinda og holukerfum. Vi{\eth} kynnum hugmynd okkar um a{\eth} brotask\"ommtun skotlei{\eth}ninnar lei{\eth}i af Heisenberg skiptaverkun milli sta{\eth}bundins rafbera \'i skammtapunktsnertunni og frj\'alsra lei{\eth}nirafbera og s\'ynum fram \'a a{\eth} heg{\eth}un lei{\eth}ninnar er eigindlega \'ol\'ik milli rafeinda og holukerfa.