Quantum matter in high magnetic fields

Abstract:

Magnetoresistance is observed in non-ferromagnetic oxides containing FeIV which have magnetic behaviour characteristic of small magnetic clusters.

Abstract:

Experiments on three double-layer (n=2) Ruddlesden-Popper (RP) systems are reported. Doping Sr1.8La1.2Mn2O7 (Tc = 126 K) with Nd to form Sr1.8La1.2- xNdxMn2O7 leads to a reduction in Curie temperature for low doping levels (x = 0.2), and to behavior reminiscent of Sr1.8Nd1.2Mn2O7 for x≥0.7. This suggests that it may be possible to control the temperature of maximum magnetoresistance chemically in these phases. The application of pressure (0

2NdMn2O7 to resemble those of Sr 1.9Nd1.1Mn2O7. The changes can be explained by considering the relative strength of ferromagnetic and antiferromagnetic interactions within the material. Finally, the need for careful phase analysis of n = 2 RP materials is demonstrated by the misleading magnetization data recorded for a sample of Sr1.8Sm 1.2Mn2O7 containing ∼2.8% of an n = ∞ perovskite phase. © 1998 American Institute of Physics.

Abstract:

We investigate the high-pressure phase of the iron-based superconductor FeSe0.89S0.11 using transport and tunnel diode oscillator studies using diamond anvil cells. We construct detailed pressuretemperature phase diagrams that indicate that the superconducting critical temperature is strongly enhanced by more than a factor of four towards 40K above 4GPa. The resistivity data reveal signatures of a fan-like structure of non-Fermi liquid behaviour which could indicate the existence of a putative quantum critical point buried underneath the superconducting dome around 4.3GPa. With further increasing the pressure, the zero-field electrical resistivity develops a non-metallic temperature dependence and the superconducting transition broadens significantly. Eventually, the system fails to reach a fully zero-resistance state, and the finite resistance at low temperatures becomes strongly current-dependent. Our results suggest that the high-pressure, high-Tc phase of iron chalcogenides is very fragile and sensitive to uniaxial effects of the pressure medium, cell design and sample thickness. These high-pressure region could be understood assuming a real-space phase separation caused by nearly concomitant electronic and structural instabilities.