APS March Meeting Videos

In an electronic system with two closely spaced but isolated conductors, current that is sourced in one conductor can induce a current or voltage in the second conductor. This phenomenon, known as “Coulomb drag”, represents a powerful approach to probe Coulomb interactions and electron correlations. Here we examine Coulomb drag in a pair of nanowires created with conductive-AFM lithography at the LaAlO3/SrTiO3 interface. Coulomb drag measurements are performed by sourcing current in one wire and measuring the induced voltage or current in the other wire. Experimental features depend strongly on magnetic field. At low magnetic fields, the wires can be superconducting, leading to large drag resistance when the wire is driven past the critical current. At high magnetic field, distinct oscillations are observed that are associated with the electron subband structure in the wires. 

Nano-engineered graphene devices can exhibit novel and useful electronic and optical properties, many of which depend critically on controlling the chemical potential relative to the charge-neutrality point. Complex-oxide heterostructures enable reconfigurable control of conductive nanostructures, making them an interesting platform for controlling the electronic properties of graphene at nanoscale dimensions. Here we report the fabrication of graphene/LaAlO3/SrTiO3 heterostructures with nanoscale programmable control of the charge-neutrality point. Magnetotransport measurements of superlattice structures show characteristic interference features that can be associated with the electronically patterned interface. We discuss possible new directions based on this highly versatile hybrid platform.

Graphene is a promising tunable plasmonic material in the terahertz regime. Plasmons can be induced in graphene by femtosecond laser excitation, and their resonance frequency can be gate-tuned over a broad terahertz range. Another 2D electron system, the complex-oxide heterostructure LaAlO3/SrTiO3, has been shown to exhibit great promise for control and detection of broadband THz emission at extreme nanoscale dimensions. Recently, we have successfully integrated these two platforms: we have created graphene/LaAlO3/SrTiO3 structures with high mobility in the graphene channel and oxide nanostructures directly underneath the graphene layer. Here we describe new experiments that probe graphene plasmonic behavior using this nanoscale THz spectrometer using ultrafast optical techniques. This unprecedented control of THz radiation at 10 nm length scales creates a pathway toward hybrid THz functionality in graphene/LaAlO3/SrTiO3 heterostructures.

  Clean one-dimensional electron transport has been observed in very few material systems. The development of exceptionally clean electron waveguides formed at the interface between complex oxides LaAlO$_3$ and SrTiO$_3$ enables low-dimensional transport to be explored with newfound flexibility. This material system not only supports ballistic one-dimensional transport, but possesses a rich phase diagram and strong attractive electron-electron interactions which are not present in other solid-state systems. Here we report an unusual phenomenon in which quantized conductance increases by steps that themselves increase sequentially in multiples of e2/h. The overall conductance exhibits a Pascal-like sequence: 1, 3, 6, 10 … e2/h, which we ascribe to ballistic transport of 1, 2, 3, 4 ... “bunches” of electrons. We will discuss how subband degeneracies can occur in non-interacting models that have carefully tuned parameters. Strong attractive interactions are required, however, for these subbands to “lock” together. This Pascal liquid phase provides a striking example of the consequences of strong attractive interactions in low-dimensional environments.

Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides (TMDC) have attracted intense research interest in the past decade. Their unique electronic and optical properties offer the promise of novel optoelectronic applications in the terahertz regime. Recently, generation and detection of broadband terahertz (~10 THz bandwidth) emission from 10-nm-scale LaAlO3/SrTiO3 nanostructures created by conductive atomic force microscope (c-AFM) lithography has been demonstrated. This unprecedented control of THz emission at 10 nm length scales creates a pathway toward hybrid THz functionality in 2D-material/LaAlO3/SrTiO3 heterostructures. Here we report initial efforts in THz spectroscopy of 2D nanoscale materials with resolution comparable to the dimensions of the nanowire (10 nm). Systems under investigation include graphene, single-layer molybdenum disulfide (MoS2), and tungsten diselenide (WSe2) nanoflakes.

Interfacial ferromagnetism in LaAlO3/SrTiO3 (LAO/STO) heterostructures has been probed by a variety of techniques. Recently, magnetic force microscopy (MFM) was used to image ferromagnetic domains that are electrically tunable at room temperature when the samples were grown in certain conditions. Optical techniques provide powerful tools for probing magnetic phenomena, and recently magnetic circular dichroism has been observed in reduced bulk STO crystals. Here we describe a scanning magneto-optical Kerr imaging system that could achieve sub-micrometer precision and 10−4 rad/√ Hz sensitivity with a 150 fs pulsed-laser centered at 425 nm. Such capability would make pump and probe measurement on the gate-tunable LAO/STO ferromagnetism and ultrafast imaging of domain dynamics possible.

We investigate the interaction between high-temperature superconductor Bi2Sr2CaCu2O8+δ (BSCCO) flakes deposited on the oxide heterostructure LaAlO3/SrTiO3 (LAO/STO). Conductive-atomic force microscope (c-AFM) lithography will be used to create nanowires at the LAO/STO interface that couple to the BSCCO. Through coupling of these materials, we will be able to study phenomena such as the proximity effect and coulomb drag.