Current research

In Laroche Lab, we specialize in designing and fabricating nano-structures to study the fascinating effects that arise when different materials and/or devices are interacting at the nanoscale.  Utilizing state-of-the-art material systems with low disorder such as GaAs/AlGaAs heterostructures, InAs nanowires with an aluminium epilayer and InSb nanowires, we engineer coupled systems where novel phenomena occur, and attempt to harness their properties for future nano-electronics and quantum computing applications.  The devices under study are characterized through electrical transport in a dilution refrigerator at ultra-low temperatures, in the range of a few tens of milikelvin, and in the presence of a magnetic field.

Coulomb drag between coupled 1D systems

Despite their conceptual simplicity, one-dimensional systems remain a challenge to understand owing to the enhanced correlations and interactions that occur due to their restricted phase-space.  As such, the simple Fermi-liquid model describing the physics of solid-state electrons in 2D and 3D no longer holds in 1D, where electronic transport is instead described by the Luttinger-liquid model which accounts for these enhanced interactions.  Experimentally studying the intrinsic properties of 1D systems is also a challenging task.  Standard measurements generally probe processes occurring in the high dimensional system leads, thereby providing no information about the nature of electron-electron interactions inside the 1D system itself.  In contrast, experiments in coupled 1D systems, such as Coulomb drag, effectively probe electron-electron interactions.  By using dual side processing on GaAs/AlGaAs bilayer systems, two independently contacted quantum wires can be fabricated such that they are less than 15 nm apart.

We will use this platform, to perform Coulomb drag measurements, where a current in a quantum wire induces a voltage drop in the adjacent wire solely through Coulomb interactions.  By measuring the dependence of the drag signal as a function of temperature, 1D density, magnetic field, geometry and material parameters, we will extract crucial information about the nature of Luttinger-liquids and about the strength of electron-electron interactions in a 1D systems.

 

Relevant publications :

1D-1D Coulomb Drag Signature of a Luttinger Liquid.  D. Laroche, G. Gervais, M. P. Lilly and J. L. Reno, Science, 343, 631 (2014).
Positive and Negative Coulomb Drag in Vertically Integrated One-Dimensional Quantum Wires.  D. Laroche, G. Gervais, M. P. Lilly and J. L. Reno, Nature Nanotechnolgy, 6, 793 (2011).

Majorana zero modes in hybrid superconductor-semiconductor devices

Topological quantum computations offer a promising approach to fault-tolerant quantum computing by encoding and manipulating the quantum information non-locally in a non-Abelian degenerate ground state that is intrinsically immune against disorder.  Majorana-Zero-Modes (MZMs) in nanowires with induced superconductivity and strong spin-orbit coupling under a magnetic field are arguably the front-runner in establishing topological quantum bits, with numerous signatures of MZMs having been experimentally observed.  In Laroche lab, we will use novel techniques to further measure the properties of these promising systems.

In addition, we will work towards developing a novel platform for the observation of MZMs, or their fractional counter-part the parafermions, in the absence of an applied magnetic field.  The material of choice for this platform is hybrid superconductor-semiconductor nanowire pairs coupled to a common superconductor.  By designing nanowire networks with sufficiently large electron-electron interactions, induced proximity can arise through crossed-Andreev reflections, which will naturally give rise to MZMs or parafermions, even without an applied magnetic field.

           Crossed-Andreev reflections

Relevant publications :

Observation of the 4π-periodic Josephson effect in InAs nanowires.  D. Laroche, D. Bouman, D. J. van Woerkom, A. Proutski, C. Murthy, D. I. Pikulin, C. Nayak, R. J. J. van Gulik, J.
Nygård, P. Krogstrup, L. P. Kouwenhoven, A. Geresdi. Nature Communications 10, 245 (2019).

Exotic phenomena in coupled Ge/SiGe bilayers

Ge/SiGe heterostructures have been showing great promises in the recent year.  Their nearly defect free growth, significant spin-orbit interaction and the possibility to induce superconductivity make these structures a promising platform both for fundamental research and quantum computing applications.  Utilizing the expertise developed in GaAs/AlGaAs bilayer systems, we will engineer devices where the density and the electronic confinement of Ge/SiGe bilayers can be controlled simultaneously from both side.  This will open up exciting research opportunities in the field of vertically coupled wires and bilayer exciton condensation.

Example of a Si/SiGe bilayer

       

Relevant publications :

Magneto-transport of an electron bilayer system in an undoped Si/SiGe double-quantum-well heterostructure. D. Laroche, S.-H. Huang, E. Nielsen, C. W. Liu, J.-Y. Li and T. M. Lu, Applied Physics Letters, 106, 143503 (2015).