SSO Seminar
Wednesday, February 26, 2014 - 16:00 to 17:00
Weniger 304
Event Speaker: 
Tal Sharf, Lee Aspitarte, Daniel Gruss
Local Contact: 
Guenter Schneider

Tal Sharf et al
Abstract: T37.00002 : Elemental charge sensitivity of liquid-gated carbon nanotube transistors

Electron transport in carbon nanotubes (CNTs) is extremely sensitive to electrostatic~perturbations, suggesting that CNT field-effect transistors (FETs) are promising candidates for~low-power digital switches and high-performance sensors. In this work,~we show that the perturbation caused by a single elemental charge~strongly affects the room temperature conductance of a CNT FET. We make~use of naturally occurring activated charge traps in SiO2 to observe~random telegraph signals which reach 20{\%} of the baseline signal. Our~measurements are made in a liquid-gated environment where these~telegraph signals are persistent over long time scales and tunable by~gate-voltage. Gate-voltage dependence is compared to non-equilibrium~Greens function calculations. We verify the theoretically predicted~relationship between signal magnitude and gate voltage, and show that~this relationship differs dramatically from predictions based simply on~transconductance. Our measurements confirm the exciting possibility of~detecting elemental charges at room temperature, and verify a~theoretical framework for predicting conductance changes due to motion~of an elemental charge near a CNT FET.
Lee Aspitarte et al
Abstract: T37.00005 : Photothermoelectric Effect in Suspended Semiconducting Carbon Nanotubes

We have performed scanning photocurrent microscopy measurements of field-effect transistors (FETs) made from individual suspended carbon nanotubes (CNTs).Photocurrent generation in individual carbon nanotube based devices has been previously attributed the photovoltaic effect, in contrast to graphene based devices which are dominated by the photothermoelectric effect. In this work, we present the first measurements of strong photothermoelectric currents in individual suspended carbon nanotube field-effect transistors. In certain electrostatic doping regimes light induced temperature gradients lead to significant thermoelectric currents which oppose and overwhelm the photovoltaic contribution. Our measurements give new insight into the tunable and spatially inhomogeneous Seebeck coefficient of electrostatically-gated CNTs and demonstrate a new mechanism for optimizing CNT-based photodetectors and energy harvesting devices.
Daniel Gruss et al
Abstract: Y35.00010 : Characterizing a conducting-to-nonconducting transition in an inhomogeneous Hubbard model out of equilibrium via tDMRG simulations

The study of time-dependent, many-body transport phenomena is increasingly within reach of ultra-cold atom experiments. These systems not only allow experimental emulation of solid state systems, but allow us to probe the dynamics of transport at a previously unreachable level of detail. We will discuss computational results for the dynamics of fermionic transport in optical lattices that emulate an inhomogeneous Hubbard model. We demonstrate that this system displays a many-body, nonequilibrium conducting to nonconducting transition that depends on the interaction strength and filling.\footnote{New J. Phys. 15 063026} We characterize the transition by deconstructing the dynamical behavior of the fermionic density. We will also discuss these results in the context of present-day cold atom experiments.