Tuning the ground state of strongly interacting low-dimensional electron systems by pressure: the cuprate spin ladder compounds

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Within this project the charge dynamics of the spin ladder and spin chain system M14Cu24O41 with M=La,Y,Sr or Ca will be studied as a function of temperature and external pressure by reflectivity measurements over a broad frequency range, from the far-infrared up to the ultraviolet. The studied materials will include the compounds Sr14-xCaxCu24O41, which become superconducting under high pressure for high Ca contents. Specific questions, which will be addressed, are the distribution of holes among the ladder and chain subsystems as a function of Ca content x, temperature and pressure, the importance of electron-phonon coupling and the dimensionality of the system. For the underdoped materials La3Sr3Ca8Cu24O41 and Y3Sr11Cu24O41 we will explore the stability of the charge-density-wave state (insulating hole Wigner crystal state) regarding the application of pressure for the first time.