Effects of Strong Correlations in Complex Oxides Investigated by Raman Spectroscopy

Our global environment is under excessive strain and we are facing a possible global climate change. There is a urgent need today for finding both alternative energy sources and new techniques for the transport and storage of energy in order to save our planet in its present status. One important route to improve our environment is to find a superconductor that works at room temperature. During the last decades a huge effort in science has been put on the high temperature superconducting complex oxides since they for a long time have been regarded to have the best potential to achieve superconductivity at room temperature. This thesis focus is on complex oxides, including superconductivity and related phases in the sense of structure, magnetism and charge dynamics. The main tool of investigation is Raman scattering spectroscopy. From doping and temperature dependent investigations of a quasi one-dimensional spin ladder I show the emergence and fall of a charge density wave phase. The magnetism and its relation to superconductivity has been studied in artificial superlattices of alternating superconducting and isolating layers, the results support a picture of possible coexisting antiferromagnetic and superconducting order parameters. Further, our investigations of the magnetic excitation in a oxychloride compound reveal a delicate interplay between the spin coupling parameters stemming from the two interpenetrating magnetic substructures. In an isotropic superconducting pyrochlore I follow the structural transitions that precurse the superconducting state, a refined picture for the course of events upon lowering the temperature and an order-disorder-order picture emerge from the results. Another related complex oxide that has been studied is a Fe-Cr solid solution with perovskite structure. Here, the exceptional higher order Raman scattering is assigned to a Franck-Condon type of resonance

Effects of Strong Correlations in Complex Oxides Investigated by Raman Spectroscopy

Our global environment is under excessive strain and we are facing a possible global climate change. There is a urgent need today for finding both alternative energy sources and new techniques for the transport and storage of energy in order to save our planet in its present status. One important route to improve our environment is to find a superconductor that works at room temperature. During the last decades a huge effort in science has been put on the high temperature superconducting complex oxides since they for a long time have been regarded to have the best potential to achieve superconductivity at room temperature. This thesis focus is on complex oxides, including superconductivity and related phases in the sense of structure, magnetism and charge dynamics. The main tool of investigation is Raman scattering spectroscopy. From doping and temperature dependent investigations of a quasi one-dimensional spin ladder I show the emergence and fall of a charge density wave phase. The magnetism and its relation to superconductivity has been studied in artificial superlattices of alternating superconducting and isolating layers, the results support a picture of possible coexisting antiferromagnetic and superconducting order parameters. Further, our investigations of the magnetic excitation in a oxychloride compound reveal a delicate interplay between the spin coupling parameters stemming from the two interpenetrating magnetic substructures. In an isotropic superconducting pyrochlore I follow the structural transitions that precurse the superconducting state, a refined picture for the course of events upon lowering the temperature and an order-disorder-order picture emerge from the results. Another related complex oxide that has been studied is a Fe-Cr solid solution with perovskite structure. Here, the exceptional higher order Raman scattering is assigned to a Franck-Condon type of resonance

IP block signalbehandling

The thesis aims to implement different digital filters such as finite impulse response (FIR), infinite impulse response (IIR) and cascade integrator comb (CIC) on the field-programmable gate array (FPGA) development board using hardware description language (VHDL). To this purpose, Intel’s systems integration tool Platform designer is used to convert the implementation to an IP core. The implemented FIR and IIR filters include different filter types such as lowpass, highpass, bandpass and bandstop. All the filters have a pipeline architecture as well as adjustable parameters such as filter order, frequency specifications and resolution. The coefficients of the filters are calculated according to the user's specifications. The calculated coefficients are verified using simulation. Furthermore the IP has been validated on hardware by the FPGA board MAX DE-10 lite. The IP is also analyzed regarding timing and power consumtion with good results. FIR filters of different types have been implemented and tested up to 501 taps with a coefficient width of 24 bits, which covered just below 50% of the available logic gates on the MAX 10-DE lite board with 50000 gates in total. The FIR filters have an option to be used with a Kaiser window with a maximum tap level of 51. Different IIR filters have also been implemented and tested on the hardware. However, the results have shown that the IIR filters do not perform so well, especially those of order higher than 6. One of the main reasons for this is the overflow caused by instability of the IIR.

Antiferromagnetic and superconducting proximity effects in YBa2Cu3O7-delta/PrBa2Cu3O7-delta superlattices

We investigate the interplay between the antiferromagnetic and superconducting order parameters in YBCO/PBCO superlattices by inelastic light scattering. The ratio of superconducting to antiferromagnetic order is varied through different modulations 4/6, 4/9 and 4/12 of (Y/P)BCO layers. This allows us to identify the proximity effect of the superconducting order parameter into the antiferromagnetic barrier as signified, e.g., by the sharpening of the two-magnon excitation. This proximity effect as well as gap feature and phonon anomalies reveals the delicate interplay between superconducting and antiferromagnetic order parameters

Antiferromagnetic and superconducting proximity effects in YBa2Cu3O7-delta/PrBa2Cu3O7-delta superlattices

We investigate the interplay between the antiferromagnetic and superconducting order parameters in YBCO/PBCO superlattices by inelastic light scattering. The ratio of superconducting to antiferromagnetic order is varied through different modulations 4/6, 4/9 and 4/12 of (Y/P)BCO layers. This allows us to identify the proximity effect of the superconducting order parameter into the antiferromagnetic barrier as signified, e.g., by the sharpening of the two-magnon excitation. This proximity effect as well as gap feature and phonon anomalies reveals the delicate interplay between superconducting and antiferromagnetic order parameters