Superconductor-insulator Transition In Artificial Nanopatterned High-Tc Superconductors

Spontaneous symmetry breaking and elementary excitations are the foundations of condensed matter physics in the 20th century.The second-order phase transitions and critical phenomena on these bases are the most spectacular chapters of condensed matter physics,such as superconducting phase transitions,superfluid phase transitions,ferromagnetic phase transitions,ferroelectric phase transitions et al,which can be understood within the framework of Ginzburg–Landau theory of phase transitions.However,since the 1990s,there are two kinds of phase transitions beyond the paradigm of Landau phase transitions related to symmetry breaking,one is topological phase transitions,the other is quantum phase transitions represented by superconductor-insulator phase transitions.Besides superconducting ground state and insulating ground state,whether there exists metallic state in two-dimensional(2D)disorder system has become a long-pursuit question since Anderson localization was proposed more than 30years ago.Moreover,strange metals and Planckian dissipation near the quantum critical region in high-Tc superconductors is also an important issue in condensed mater physics.In this thesis,superconductor-anomalous metal-insulator transitions have been systematically in a nanopatterned high-Tc superconductor(HTS).For the first time,the direct evidence of the existence of quantum metallic state have been revealed.In addition,the scale-invariant behavior near the quantum critical region is also systematically studied,and we provide the first experimental evidence of strange metal in bosonic system.The main contents of this thesis include three parts:(1)Firstly,nanoporous YBCO thin films were fabriacated by reactive ion etching(RIE)by transferring periodic nano-honeycomb structure adonic aluminum oxide(AAO)templates ontop of ultra-thin YBCO films with high quality.By tuning RIE time,the system undergoes the superconductor-quantum metal-insulator phase transitions.The direct evidence for the existence of quantum metal state is the signature of resistance saturation at low temperatures.The critical temperature for resistance saturation of the YBCO porous films is up to 5 K,which is much higher than that of the conventional superconducting system,making the observed anomalous metallic state convincing.Furthermore,by tuning the degree of disorder,a complete phase diagram of the superconductor-quantum metal-insulator quantum phase transition is depicted.(2)In all quantum states,h/2e quantum oscillations related to Cooper pairs are observed,and we provide the direct evidence that this anomalous metallic state is a bosonic state.By analyzing the temperature dependence of quantum magnetic flux oscillation amplitude,we uncover the quantum coherence bosonic evolution across superconductor-anomalous metal-insulator transitions.The oscillation amplitude saturates in the quantum metallic region,indicating that the phase coherence length saturating at lower temperatures could be the origin of the quantum metallic state in 2D system due to the unknown decoherence or dissipation mechanism.In addition,the signatures of h/4e oscillations are observed in the insulating state near the quantum critical region,which may reveal a novel quantum Charge-40)state connected with pair density wave and superconducting stripe melting.(3)Moreover,the anomalous behaviors near the quantum critical region in nanoporous YBCO films are observed,which shows the resistance is linearly dependent on temperature,which is so-called bosonic strange metal.This study extends the strange metal with bounded dissipation to bosonic system,which suggests a universal principle governs transport in quantum matter without quasiparticles.Interestingly,by calculating the slope of resistance,the scattering rate of bosons 1/?reaches Planckian dissipation limit k_BT/?,reminiscent of the fermionic system,indicating Planckian dissipation is universal and transcends particle statistics.More intriguing,the magnetoresistance is also linear and scale-invariant near the quantum critical region.These results indicate that the dissipation process plays an important role in quantum phase transitions in the bosonic system.These dissipative processes lead to anomalous transport processes not only in the solid-state materials but also in cold atoms.In addition,the dissipation-induced decoherence process is also important in quantum computing.Therefore,our results provide a platform for the study of the dissipative quantum system.