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II INTERNATIONAL SCIENTIFIC CONFERENCE OF YOUNG RESEARCHERS 

66 

 Qafqaz University                         

          18-19 April 2014, Baku, Azerbaijan 

QUANTUM CRITICALITY AND SUPERCONDUCTIVITY IN SPIN AND CHARGE 

SYSTEMS 

 

Y. CELALEDDIN DURMAZ, Siddharth SAXENA 

Department Of Physics, Fatih University, Cavendish Laboratory, University Of Cambridge 

[e-mail] 

 TURKEY, UK   

 

Understanding behaviour of electrons in solids is an extremely complicated problem which is even impossible to be 

solved with the most advanced computers. Fortunately however, complex motions of electrons in materials are quite 

different than their individual motions and this complex motion produces qualitatively new forms of simplicity such as 

superconductivity and magnetism. These are examples of stable phases of matters and traditionally in physics the material 

research has been focused on stable phases of matter. However, this collective behaviour of matter becomes very important 

at unstable phases and in the past ten years condensed matter physicists have the opportunity to investigate unstable states of 

modern materials. These unstable states of matters are obtained through quantum phase transitions which are driven by an 

external parameter like pressure, magnetic field and chemical doping. This new behaviour occurs in precarious point which 

is called quantum critical point.  

In classical phase transitions ordered arrangement in matter cannot be sustained beyond a critical temperature because 

of thermal fluctuations, as in melting of ice. Over the last decade, a novel kind of phase transition has been discovered 

which is unlike classical phase transitions, is driven by quantum fluctuations rather than thermal fluctuations. These 

fluctuations are called quantum fluctuations because they are zero point vibrations and mainly associated with Heisenberg’s 

uncertainty principle.  

In our research we focus on experimental search and discovery of novel forms of quantum order in metallic and 

insulating magnets, intercalated compounds, ferroelectric systems and multi-ferroic materials. Particularly investigated is 

the pressure-induced superconductivity and critical phenomena in the vicinity of quantum phase transitions. In order to be 

able to observe emergent phenomena in quantum phase transitions selected and investigated materials need to be chosen 

very carefully in terms of their crystal structure, magnetic and electric properties. For that purpose our recent material scope 

ranges from perovksite oxides to pnictide oxides since their layered lattice structure and magnetic behaviours are very 

suitable for tuning them to quantum critical point by pressure.     

Materials tuned to the neighbourhood of a zero temperature phase transition often show the emergence of novel 

quantum phenomena. Much of the effort to study these new emergent effects, like the breakdown of the conventional 

Fermi-liquid theory in metals has been focused in narrow band electronic systems. Spin or charge ordered phases can be 

tuned to absolute zero using hydrostatic pressure. Close to such a zero temperature phase transition, physical quantities like 

resistivity, magnetisation and dielectric constant change into radically unconventional forms due to the fluctuations 

experienced in this region giving rise to new kind superconductivity and other possible ordered states. Extension of this 

methodology to dipole-ordered insulating materials provides an interesting departure and new opportunities for both new 

physics and applications. 

Understanding quantum criticality and quantum phase transitions now has a very crucial and fundamental place in both 

theoretical and experimental physics since, there haven’t been developed any theoretical framework yet to explain these 

phenomena completely and emergent ordered forms of materials i.e. superconductors, ferromagnets, ferroelectrics have a 

very wide range of applications in both fundamental and applied sciences.