arXiv subjects

Nadya Mason

Publications and source records attributed to Nadya Mason.

43 records · Page 3Linked to original sources

arXiv2010

Magnetoresistance in Single Layer Graphene: Weak Localization and Universal Conductance Fluctuation Studies

We report measurements of magnetoresistance in single-layer graphene as a function of gate voltage (carrier density) at 250 mK. By examining signatures of weak localization (WL) and universal conductance fluctuations (UCF), we find a consistent picture of phase coherence loss due to electron-electron interactions. The gate-dependence of the elastic scattering terms suggests that the effect of trigonal warping, i.e., the non-linearity of the dispersion curves, may be strong at high carrier densities, while intra-valley scattering may dominate close to the Dirac point. In addition, a decrease in UCF amplitude with decreasing carrier density can be explained by a corresponding loss of phase coherence.

cond-mat.mtrl-sci↗

arXiv2010

Non-equilibrium Tunneling Spectroscopy in Carbon Nanotubes

We report measurements of the non-equilibrium electron energy distribution in carbon nanotubes. Using tunneling spectroscopy via a superconducting probe, we study the shape of the local electron distribution functions, and hence energy relaxation rates, in nanotubes that have bias voltages applied between their ends. At low temperatures, electrons interact weakly in nanotubes of a few microns channel length, independent of end-to-end conductance values. Surprisingly, the energy relaxation rate can increase substantially when the temperature is raised to only 1.5 K.

cond-mat.mes-hall↗

arXiv2010

Probing the mechanical properties of graphene using a corrugated elastic substrate

The exceptional mechanical properties of graphene have made it attractive for nano-mechanical devices and functional composite materials. Two key aspects of graphene's mechanical behavior are its elastic and adhesive properties. These are generally determined in separate experiments, and it is moreover typically difficult to extract parameters for adhesion. In addition, the mechanical interplay between graphene and other elastic materials has not been well studied. Here, we demonstrate a technique for studying both the elastic and adhesive properties of few-layer graphene (FLG) by placing it on deformable, micro-corrugated substrates. By measuring deformations of the composite graphene-substrate structures, and developing a related linear elasticity theory, we are able to extract information about graphene's bending rigidity, adhesion, critical stress for interlayer sliding, and sample-dependent tension. The results are relevant to graphene-based mechanical and electronic devices, and to the use of graphene in composite, flexible, and strain-engineered materials.

cond-mat.mes-hall↗

arXiv2009

Superconducting Tunneling Spectroscopy of a Carbon Nanotube Quantum Dot

We report results on superconducting tunneling spectroscopy of a carbon nanotube quantum dot. Using a three-probe technique that includes a superconducting tunnel probe, we map out changes in conductance due to band structure, excited states, and end-to-end bias. The superconducting probe allows us to observe enhanced spectroscopic features, such as robust signals of both elastic and inelastic co-tunneling. We also see evidence of inelastic scattering processes inside the quantum dot.

cond-mat.str-el↗

arXiv2001

Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment

We present results on disordered amorphous films which are expected to undergo a field-tuned Superconductor-Insulator Transition.The addition of a parallel ground plane in proximity to the film changes the character of the transition.Although the screening effects expected from "dirty-boson" theories are not evident,there is evidence that the ground plane couples a certain type of dissipation into the system,causing a dissipation-induced phase transition.The dissipation due to the phase transition couples similarly into quantum phase transition systems such as superconductor-insulator transitions and Josephson junction arrays.

cond-mat.supr-con↗

arXiv2000

Effects of dissipation on quantum phase transitions

We discuss the effect of dissipation on quantum phase transitions. In particular we concentrate on the Superconductor to Insulator and Quantum-Hall to Insulator transitions. By invoking a phenomenological parameter $α$ to describe the coupling of the system to a continuum of degrees of freedom representing the dissipative bath, we obtain new phase diagrams for the quantum Hall and superconductor-insulator problems. Our main result is that, in two-dimensions, the metallic phases observed in finite magnetic fields (possibly also strictly zero field) are adiabatically deformable from one to the other. This is plausible, as there is no broken symmetry which differentiates them.

cond-mat.mes-hall↗

arXiv2000

True Superconductivity in a 2D "Superconducting-Insulating" System

We present results on disordered amorphous films which are expected to undergo a field-tuned Superconductor-Insulator Transition. Based on low-field data and I-V characteristics, we find evidence of a low temperature Metal-to-Superconductor transition. This transition is characterized by hysteretic magnetoresistance and discontinuities in the I-V curves. The metallic phase just above the transition is different from the "Fermi Metal" before superconductivity sets in.

cond-mat.supr-con↗