We report the demonstration of hybrid high-Tc-superconductor–semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices are fabricated by our newly developed mechanical-bonding technique, resulting in high-Tc-superconductor–semiconductor tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi2Sr2CaCu2O8+δ combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity, similarly to spectra obtained in scanning-tunneling microscopy, and is in good agreement with theoretical predictions for a d-wave-superconductor–normal-material junction. Additional junctions are demonstrated using Bi2Sr2CaCu2O8+δ combined with graphite or Bi2Te3. Our results pave the way for new methods in unconventional superconductivity studies, novel materials, and quantum technology applications. PHYSICAL REVIEW X 2, 041019 (2012) 

Structural study of Bi2Sr2CaCu2O8+δ exfoliated nanocrystals We demonstrate that structural and spectroscopic information can be obtained on exfoliated nanocrystals as thin as 6nm. This can be achieved by using a combination of micro X-ray fluorescence (lXRF), micro X-ray absorption near-edge spectroscopy (lXANES), and X-ray microdiffraction (lXRD) techniques. Highly focused, tunable X-ray beams available at synchrotron sources enable one to use these non-invasive characterization tools to study exfoliated samples on a variety of substrates. As an example, we focused on exfoliated nanocrystals of the high temperature superconductor Bi2Sr2CaCu2O8þd. lXRF is used to locate the sample of desired thickness; lXANES and lXRD  [ Read More ]

Our team has developed a simple new technique using Scotch poster tape that has enabled us to induce high-temperature superconductivity in a semiconductor for the first time. Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive Majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi2Se3 and Bi2Te3 via proximity to Bi2Sr2CaCu2O8+δ, to access higher temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique that we developed, enabling the fabrication of high-quality junctions between materials,  [ Read More ]

In bismuth ferrite (BiFeO3), antiferromagnetic and ferroelectric order coexist at room temperature, making it of particular interest for studying magnetoelectric coupling. The mutual control of magnetic and electric properties is very useful for a wide variety of applications. This has led to an enormous amount of research into the properties of BiFeO3. Nonetheless, one of the most fundamental aspects of this material, namely the symmetries of the lattice vibrations, remains controversial.We present a comprehensive Raman study of BiFeO3 single crystals with the approach of monitoring the Raman spectra while rotating the polarization direction of the excitation laser. Our method results  [ Read More ]