Insulating Ferromagnetic Substrate for Topological Insulators

A ferromagnetic insulating substrate for the epitaxial growth of topological insulators Cr2Ge2Te6 is proposed as an insulating ferromagnetic substrate for the growth of tetradymite-type topological insulators, based on a refined characterization ...

Pic_CGS_2013

Ferromagnetism and infrared electrodynamics of Ga1-xMnxAs

We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga1-xMnxAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature TC with respect to the IR ...

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Hybrid High-Temperature-Superconductor–Semiconductor Tunnel Diode

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 ...

prxSCSC

Welcome to Burch Group at the University of Toronto
We investigate the optical properties of various materials to reveal the physics governing their properties.
The group also pursues research into novel optical devices.

Pic_CGS_2013

A ferromagnetic insulating substrate for the epitaxial growth of topological insulators Cr2Ge2Te6 is proposed as an insulating ferromagnetic substrate for the growth of tetradymite-type topological insulators, based on a refined characterization of its transport, magnetic, optical, and calculated electronic properties. It is found to be a soft ferromagnet with no visible magnetic domains over relatively large length scales and to be highly insulating with an indirect band gap and low carrier concentration. Further we present the fabrication of Bi2Te3-Cr2Ge2Te6 heterostructure samples by chemical vapor deposition and show that crystals of the two phases are oriented such that the hexagonal Te planes  [ Read More ]

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We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga1-xMnxAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature TC with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find nonmonotonic behavior of trends in TC with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found  [ Read More ]

Tian_APL_STO_Cover_2013

Epitaxial buffer layers enable the many functionalities found in perovskites to be integrated with silicon. However, epitaxial growth of SrTiO3 on silicon is tricky and has so far only been achieved by molecular beam epitaxy. Nonetheless, previous investigations of these films were limited by the amorphous layer occurring at the interface. Through a combination of improved interface quality and an improved model, we report the optical properties of SrTiO3 films on Si(100) investigated by spectroscopic ellipsometry. We find that the data are best described by a model with two different SrTiO3 layers, potentially resulting from variations in the oxygen content.  [ Read More ]

prxSCSC

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) 

Bi2212_Structure

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 ]