In contrast to conventional materials, valence electrons in strongly correlated electron systems interact strongly with each other giving rise to correlation effects that go beyond the standard mean-field theories. Although at first sight it may seem that such complex systems would be chaotic, quite the opposite, they tend to self-organization and as a consequence a variety of broken symmetry phases with spin, charge and/or orbital ordering is thus realized. By changing the external parameters: temperature, pressure, magnetic field or chemical substitution, the ordered state can be destroyed or transformed to another ordered state leading to rich phase diagrams with various exotic phenomena such as metal-insulator transitions, high-temperature superconductivity, colossal magnetoresistance, quantum spin liquid, quantum critical points etc. Due to the strong coupling between electron charge, spin and orbital degrees of freedom the charge transport in strongly correlated electron systems often shows different anomalies which are poorly understood and yet seem to be the key for understanding the fundamental properties of those materials and for possible applications.

In this presentation I am going to show a couple of strongly correlated electron systems which were a part of my PhD thesis obtained at the Institute of Physics in Zagreb and the postdoctoral training at High Field Magnet Laboratory in Nijmegen. The special emphasis is put on the charge transport which was investigated with dc resistivity, Hall effect and magnetoresistance measurements in the temperature range 300 mK – 300 K and magnetic fields up to 35 T. The results of those studies revealed various anomalies in charge transport including hopping conductivity related to Mott-Anderson localization in organic κ-(BEDT-TTF)₂X family, parallel conductivity channels in organic conductor α-(BEDT-TTF)₂I₃, time- and history-dependent transport related to phase separation in manganites, and hot spot scattering in strange metal FeSe_1-xS_x as well as incoherent transport in overdoped cuprates both related to a putative quantum critical point inside the superconducting dome.

I am also going to present my future plans which would try to make a bridge between the two main strands of correlated electron research, namely the insulating broken symmetry phases in organic materials and transition-metal oxides, which were at the focus of my PhD thesis, and the strange metallic and superconducting phases in high-temperature superconductors which were the subject of my postdoctoral training. This would help to understand one of the most intriguing phenomena in the field; that is the transition from a (Mott) insulator to a superconductor, two states at the extremes of the (essentially infinite) conductivity spectrum which is my main scientific interest. In line with this, I am going to present the heat-pulse calorimetry suitable for extremely low temperatures and high magnetic fields, a technique I developed during the postdoctoral training which would be very helpful in the future studies of strongly correlated electron systems and would be easily implemented at the Institute of Physics. In the end I am going to discuss the key phases of my future scientific career at the Institute of Physics and propose possible collaborations and funding mechanisms.

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Dr. sc. Matija Čulo nastupno predavanje Znanstveni suradnik

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