Magnetotransport of dirty-limit van Hove singularity quasiparticles

Tuning of electronic density-of-states singularities is a common route to unconventional metal physics. Conceptually, van Hove singularities are realized only in clean two-dimensional systems. Little attention has therefore been given to the disordered (dirty) limit. Here, we provide a magnetotransport study of the dirty metamagnetic system calcium-doped strontium ruthenate. Fermi liquid properties persist across the metamagnetic transition, but with an unusually strong variation of the Kadowaki-Woods ratio. This is revealed by a strong decoupling of inelastic electron scattering and electronic mass inferred from density-of-state probes. We discuss this Fermi liquid behavior in terms of a magnetic field tunable van Hove singularity in the presence of disorder. More generally, we show how dimensionality and disorder control the fate of transport properties across metamagnetic transitions.

Interface and surface stabilization of the polarization in ferroelectric thin films

Ferroelectric perovskites present a switchable spontaneous polarization and are promising energy-efficient device components for digital information storage. Full control of the ferroelectric polarization in ultrathin films of ferroelectric perovskites needs to be achieved in order to apply this class of materials in modern devices. However, ferroelectricity itself is not well understood in this nanoscale form, where interface and surface effects become particularly relevant and where loss of net polarization is often observed. In this work, we show that the precise control of the structure of the top surface and bottom interface of the thin film is crucial toward this aim. We explore the properties of thin films of the prototypical ferroelectric lead titanate (PbTiO3) on a metallic strontium ruthenate (SrRuO3) buffer using a combination of computational (density functional theory) and experimental (optical second harmonic generation) methods. We find that the polarization direction and strength are influenced by chemical and electronic processes occurring at the epitaxial interface and at the surface. The polarization is particularly sensitive to adsorbates and to surface and interface defects. These results point to the possibility of controlling the polarization direction and magnitude by engineering specific interface and surface chemistries.

Analysis of Metal-Insulator Crossover in Strained SrRuO3 Thin Films by X-ray Photoelectron Spectroscopy

The electronic properties of strontium ruthenate SrRuO3 perovskite oxide thin films are modified by epitaxial strain, as determined by growing on different substrates by pulsed laser deposition. Temperature dependence of the transport properties indicates that tensile strain deformation of the SrRuO3 unit cell reduces the metallicity of the material as well as its metal-insulator-transition (MIT) temperature. On the contrary, the shrinkage of the Ru–O–Ru buckling angle due to compressive strain is counterweighted by the increased overlap of the conduction Ru-4d orbitals with the O-2p ones due to the smaller interatomic distances resulting into an increased MIT temperature, i.e., a more conducting material. In particular, in the more metallic samples, the core level X-ray photoemission spectroscopy lineshapes show the occurrence of an extra-peak at the lower binding energies of the main Ru-3d peak that is attributed to screening, as observed in volume sensitive photoemission of the unstrained material.

Диэлектрические параметры упруго напряженных, гетероэпитаксиальных пленок SrTiO-=SUB=-3-=/SUB=-

Three-layer epitaxial SrRuO_3/SrTiO_3/SrRuO_3 heterostructures with the 900-nm-thick intermediate layer of strontium titanate have been grown on single-crystal (001)La_0.29Sr_0.71Al_0.65Ta_0.35O_3 substrates by the laser evaporation method. Plane-parallel film capacitors have been formed on the basis of the grown heterostructures using photolithography and ion etching. Temperature dependences of the dissipation factor have been measured for these capacitors at different bias voltages applied to strontium ruthenate electrodes. Temperature dependences of the permittivity of the intermediate SrTiO_3 layer in the formed capacitor structures are visualized with compensation of the internal electric field and without it. The reasons for the sharp increase in the dielectric loss in the formed film capacitors at temperatures below 50 K are analyzed.

Реакция диэлектрических параметров пленок (110)SrTiO-=SUB=-3-=/SUB=- на формирование в их объеме сегнетоэлектрических доменов

Three-layer SrRuO_3/SrTiO_3/SrRuO_3 heterostructures were grown by laser evaporation on (110)LaAlO_3 substrates. Photolithography and ion etching are used to form plane-parallel film capacitors, in which a layer of strontium titanate is placed between two film electrodes of strontium ruthenate. Data on the structure and orientation of the intermediate SrTiO_3 layer in the grown heterostructures were obtained. The variation of the dielectric constant and dielectric loss of the SrTiO_3 intermediate layer upon varying the temperature and intensity of an external electric field was studied.

Electronic and magnetic properties of strontium ruthenate thin films

SrRuO3 is an itinerant ferromagnet with a Curie temperature of ~160K. There has been a sharp increase in scientific interest towards this material and its intriguing features, such as its magnetic anisotropy, and anomalous transport properties which are incompatible with Drude model. In this study, several thin films of strontium ruthenate were grown and characterised in quality and quantity, employing techniques such as X-ray diffraction and atomic force microscopy. The results are presented and described as crystallographic and topographic findings; finally, based on the findings, adjustments and further study are proposed.