Archive for the ‘2019’ Category

Posted by Kenneth Burch On September - 5 - 2019 Comments Off on Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor

Combining topology and superconductivity providesa powerful tool for investigating fundamental physics as well as aroute to fault-tolerant quantum computing. There is mountingevidence that the Fe-based superconductor FeTe0.55Se0.45 (FTS)may also be topologically nontrivial. Should the superconductingorder be s±, then FTS could be a higher order topologicalsuperconductor with helical hinge zero modes (HHZMs). To testthe presence of these modes, we have fabricated normal-metal/superconductor junctions on different surfaces via 2D atomic crystalheterostructures. As expected, junctions in contact with the hingereveal a sharp zero bias anomaly that is absent when tunnelingpurely into the c-axis. Additionally, the shape and suppression withtemperature are consistent with highly coherent modes  [ Read More ]

Posted by Kenneth Burch On April - 22 - 2019 Comments Off on Coulomb blockade in an atomically thin quantum dot

Gate-tunable quantum-mechanical tunneling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot. Depending on the tunnel-coupling strength, this capability facilitates single spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir. Van der Waals (vdW) heterostructures, in which a wide range of unique atomic  [ Read More ]

Posted by Kenneth Burch On March - 14 - 2019 Comments Off on Colossal Bulk Photovoltaic Effect in a Type-I Weyl Semimetal

Broadband, efficient and fast conversion of light to electricity is crucial for sensing and clean energy. The bulk photovoltaic effect (BPVE) is a second-order nonlinear optical effect that intrinsically converts light into electrical current. Here, we demonstrate a large mid-infrared BPVE in microscopic devices of the Weyl semimetal TaAs. This discovery results from combining recent developments in Weyl semimetals, focused-ion beam fabrication and theoretical works suggesting a connection between BPVE and topology. We also present a detailed symmetry analysis that allows us to separate the shift current response from photothermal effects. The magnitude and wavelength range of the assigned shift  [ Read More ]