Electronic energy band structure of solids Quarterly status report, 16 Mar. - 15 Jun. 1967

Piezoresistance and piezo-Hall effect in semiconducting strontium titanium oxid

Testing Lorentz invariance by use of vacuum and matter filled cavity resonators

We consider tests of Lorentz invariance for the photon and fermion sector that use vacuum and matter-filled cavities. Assumptions on the wave-function of the electrons in crystals are eliminated from the underlying theory and accurate sensitivity coefficients (including some exceptionally large ones) are calculated for various materials. We derive the Lorentz-violating shift in the index of refraction n, which leads to additional sensitivity for matter-filled cavities ; and to birefringence in initially isotropic media. Using published experimental data, we obtain improved bounds on Lorentz violation for photons and electrons at levels of 10^-15 and below. We discuss implications for future experiments and propose a new Michelson-Morley type experiment based on birefringence in matter.Comment: 15 pages, 8 table

Enhanced effective mass in doped SrTiO3 and related perovskites

The effective mass is one of the main factors determining the Seebeck coefficient and electronic conductivity. Nb-doping increases the effective mass because of two reasons, lattice constants increase and electronic effects. In this ab-initio study the effective mass is estimated from the curvature of electronic bands and it could be clarified that the deformation of SrTiO3 crystals has a significant influence on bandgap and effective DOS and band mass, which are both in excellent agreement to experimental data. However, the electronic effect due to the e2g- band flattening near the Gamma-point due to Nb-doping up to 0.2 at% is the main factor for the increase of effective mass. Doping of La shows a linear decrease of the effective mass; this is explained by the different surrounding of A- and B-site. Substitution of other elements like Ba on the A-site and V on the B-site in SrTiO3 were also found to increase the effective mass.Comment: 10 pages, 11 figures, 3 table

Ideal Bose gas in fractal dimensions and superfluid 4^4He in porous media

Physical properties of ideal Bose gas with the fractal dimensionality between D=2 and D=3 are theoretically investigated. Calculation shows that the characteristic features of the specific heat and the superfluid density of ideal Bose gas in fractal dimensions are strikingly similar to those of superfluid Helium-4 in porous media. This result indicates that the geometrical factor is dominant over mutual interactions in determining physical properties of Helium-4 in porous media.Comment: 13 pages, 6 figure

Field-induced water electrolysis switches an oxide semiconductor from an insulator to a metal

Here we demonstrate that water-infiltrated nanoporous glass electrically switches an oxide semiconductor from an insulator to metal. We fabricated the field effect transistor structure on an oxide semiconductor, SrTiO3, using 100%-water-infiltrated nanoporous glass - amorphous 12CaO*7Al2O3 - as the gate insulator. For positive gate voltage, electron accumulation, water electrolysis and electrochemical reduction occur successively on the SrTiO3 surface at room temperature, leading to the formation of a thin (~3 nm) metal layer with an extremely high electron concentration of 10^15-10^16 cm^-2, which exhibits exotic thermoelectric behaviour.Comment: 21 pages, 12 figure

Clinical and genetic aspects of bicuspid aortic valve:a proposed model for family screening based on a review of literature

Bicuspid aortic valve (BAV) is the most common congenital cardiac defect causing serious morbidity including valvular dysfunction and thoracic aortic aneurysms (TAA) in around 30% of BAV patients. Cardiological screening of first-degree relatives is advised in recent guidelines given the observed familial clustering of BAV. However, guidelines regarding screening of family members and DNA testing are not unequivocal. The aim of this review is to provide an overview of the literature on echocardiographic screening in first-degree relatives of BAV patients and to propose a model for family screening. In addition, we provide a flowchart for DNA testing. We performed a PubMed search and included studies providing data on echocardiographic screening in asymptomatic relatives of BAV patients. Nine studies were included. In 5.8-47.4% of the families BAV was shown to be familial. Of the screened first-degree relatives 1.8-11% was found to be affected with BAV. Results regarding a potential risk of TAA in first-degree relatives with a tricuspid aortic valve (TAV) were conflicting. The reported familial clustering of BAV underlines the importance of cardiological screening in relatives. After reviewing the available family history, patient characteristics and the results of cardiological screening in relatives, follow-up in relatives with a TAV and/or DNA testing may be advised in a subset of families. In this study we propose a model for the clinical and genetic work-up in BAV families, based on the most extensive literature review on family screening performed until now

Photogenerated Carriers in SrTiO3 Probed by Mid-Infrared Absorption

Infrared absorption spectra of SrTiO$_3$ have been measured under above-band-gap photoexcitations to study the properties of photogenerated carriers, which should play important roles in previously reported photoinduced phenomena in SrTiO$_3$. A broad absorption band appears over the entire mid-infrared region under photoexcitation. Detailed energy, temperature, and excitation power dependences of the photoinduced absorption are reported. This photo-induced absorption is attributed to the intragap excitations of the photogenerated carriers. The data show the existence of a high density of in-gap states for the photocarriers, which extends over a wide energy range starting from the conduction and valence band edges.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp

Tuning of metal-insulator transition of two-dimensional electrons at parylene/SrTiO3_3 interface by electric field

Electrostatic carrier doping using a field-effect-transistor structure is an intriguing approach to explore electronic phases by critical control of carrier concentration. We demonstrate the reversible control of the insulator-metal transition (IMT) in a two dimensional (2D) electron gas at the interface of insulating SrTiO$_3$ single crystals. Superconductivity was observed in a limited number of devices doped far beyond the IMT, which may imply the presence of 2D metal-superconductor transition. This realization of a two-dimensional metallic state on the most widely-used perovskite oxide is the best manifestation of the potential of oxide electronics