Periodic Reporting for period 4 - MARS (Electronic Order, Magnetism, and Unconventional Superconductivity probed in Real-Space)
Período documentado: 2020-03-01 hasta 2020-08-31
For this purpose, a unique milli-Kelvin scanning tunnelling microscope (STM) is being built, which will make possible to access the ground states of all these systems, and to achieve maximum resolution in energy and real-space. This new instrument aims at studying the most important classes of unconventional superconductors, viz. cuprate, iron-arsenide, and heavy-fermion superconductors.
Further experimental and theoretical work within this project aims to better rationalize the physics of unconventional superconductors and correlated phases. For example, we address nematicity in iron-based superconductors as well as strongly underdoped correlated phases close to the Mott transition, including the mechanism of the doping-induced insulator-metals transition. Thus we hope contributed to the still sought-after complete rationalization of this physics which indeed is the crucial milestone required to eventually achieve superconductivity at technologically better exploitable temperatures. This, eventually, can be expected to open up new technologies ranging from energy saving to quantum computing.
In addition to this constructive work, numerous experimental studies mainly using scanning tunneling spectroscopy but als transport experiments have been performed on several types of unconventional superconductors and closely related correlated electron systems. Here we highlight two fields which are not only representative for our research, but also bear the capability to generate further novel experimental approaches to the quantum phases that eventually constitute unconventional superconductivity: One example concerns the nematicity of iron-based superconductors. Here we have scrutinized ways to reveal nematic fluctuations, e.g. by analyzing the long-wavelength Friedel-oscillations in a particularly clean materials (LiFeAs) or by studying the nematic susceptibility by elastotransport. Another concerns the discovery of spectroscopic signatures of the internal degrees of freedom of the spin-polaron, i.e. a confined charged particle in an antiferromagnetic background by performing low-temperature scanning tunneling spectroscopy on the spin-orbit coupling induced antiferromagnetic Mott insulator Sr2IrO4. These and other results are constantly being disseminated through scientific journals, talks, and poster presentation at conferences.
In addition, we have obtained new insights into the physics of iron based superconductors. In particular, our work on the iron-pnictides revealed a very unconventional change of the superconducting state in LiFeAs. This finding underpins the special role of this material among the iron pnictides. Furthermore, the observed signature of the electron-boson interaction in the quasiparticle interference constitutes a new general approach towards exploring the electron-boson interaction in complex materials. We expect that its application to unconventional superconductors will promote the rationalization of the physics of such systems.
Furthermore, the first-time detection of the ladder spectrum of the spin polaron in an antiferromagnetic Mott insulator and the revelation of a percolative nature of the insulator-metal transition in Sr2IrO4 represents a milestone in understanding the nature of correlated electrons, in particular the motion of charges in an antiferromagnetic background.