TY  - THES
AU  - Kuespert, Julia
TI  - Competing States in the Unconventional Superconductor La<sub>2−x</sub>Sr<sub>x</sub>CuO<sub>4</sub>
PB  - University of Zurich
VL  - Dissertation
M1  - PUBDB-2025-05522
SP  - 127
PY  - 2024
N1  - Dissertation, University of Zurich, 2024
AB  - In strongly correlated systems, phases and states are often highly intertwined. New insights can be gained by influencing the interplay of the phenomena, for example, by temperature, magnetic field, or strain. Benefiting from all three tuning knobs, we contributed to the research on the intriguing phase diagram of (La-based) cuprates. The experiments were mostly carried out at x-ray diffraction and angle-resolved photoemission endstations of state-of-the-art synchrotrons. The first pair of interacting states examined was the superconducting gap and the pseudogap. In a high-resolution angle-resolved photoemission spectroscopy study, we extract the evolution of the antinodal gap as a function of temperature. The gap increases below the pseudogap onset. From the linear decrease with temperature below the superconducting transition at we deduce, that the two orders are competing. Lowering the temperature, integrated spectral weight reduces in the pseudogap state, but starts to regain already before the onset of superconductivity. Thus, superconductivity and the pseudogap interact with a third energy scale, possibly linked to charge order. Charge order upon application of compressive pressure in LaSrCuO (LSCO) was investigated by diffraction for the greater part of the here presented work. Stripe order in LSCO manifests in the and planes, where are the Miller indices. If pressure is applied along the Cu-O direction, stripe order peaks enhance by a factor of two in the direction perpendicular to the strain. They are suppressed to the background in the direction along the strain. Uniaxial pressure along the Cu-O direction lifts the domain degeneracy of both spin and charge order domains. This on one hand determines the fundamental symmetry of charge and spin order to be uniaxial stripes instead of a checkerboard structure. On the other hand, it confirms that the two orders in LSCO are strongly intertwined. By comparing experimentally measured and simulated diffraction patterns, we showed, that the space group of LSCO in the charge ordered state is not orthorhombic as the average crystal structure, but monoclinic. In another hard x-ray diffraction study, we applied pressure along the -axis of LSCO . Within the superconducting phase, the charge order amplitude raises with strain, while it is not affected in the normal state. Adding a magnetic field along the -axis to the system, we initially, without pressure, reproduce the well-known augmentation of charge order below as superconductivity is weakened. Charge order in LSCO with strain along the -axis and fields up to 10,T is still boosted within the superconducting phase. However, the increase is lower than if there was solely the magnetic field. The magnetic field does not have an effect in the normal state. Our observations point towards uniaxial -axis strain in LSCO coupling directly to the competing interaction of superconductivity and charge order.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.5167/UZH-267112
UR  - https://bib-pubdb1.desy.de/record/642367
ER  -