News


Room-temperature quantum transport signatures in graphene/LaAlO3/SrTiO3 heterostructures

  • By Workstudy
  • 9 February 2016

The pseudospin quantum degree of freedom is one of the most remarkable properties of graphene that distinguishes it from ordinary two-dimensional metals and semiconductors. Pseudospin quantum interference leads to weak antilocalization (WAL) and is influenced strongly by point defects and thermal perturbations that break chirality and destroy phase coherence.


Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation

  • By Workstudy
  • 11 January 2016

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation. Nominally conductive interfaces are rendered insulating by solvent immersion, which deprotonates the hydroxylated LAO surface; interface conductivity is restored by exposure to light, which induces reprotonation via photocatalytic oxidation of adsorbed water. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures and X-ray photoelectron spectroscopy. This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry.


Photoconductive response of a single Au nanorod coupled to LaAlO3/SrTiO3 nanowires

  • By Workstudy
  • 29 May 2015

Terahertz (THz) spectroscopy is an important tool that provides resonant access to free carrier motion, molecular rotation, lattice vibrations, excitonic, spin, and other degrees of freedom. Current methods using THz radiation suffer from limits due to diffraction or low-sensitivity, preventing application at the scale of single nanoscale objects.


Electron pairing without superconductivity

  • By Workstudy
  • 29 May 2015

Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors—two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances—paired electron states—that bifurcate above a critical pairing field Bp of about 1–4 tesla, an order of magnitude larger than the superconducting critical magnetic field. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. 


Electric field effects in graphene/LaAlO3/SrTiO3 heterostructures and nanostructures

  • By Workstudy
  • 20 March 2015

We report the development and characterization of graphene/LaAlO3/SrTiO3 heterostructures. Complex-oxide heterostructures are created by pulsed laser deposition and are integrated with graphene using both mechanical exfoliation and transfer from chemical-vapor deposition on ultraflat copper substrates.

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