10 research outputs found
Current-induced cooling phenomenon in a two-dimensional electron gas under a magnetic field
We investigate the spatial distribution of temperature induced by a dc
current in a two-dimensional electron gas (2DEG) subjected to a perpendicular
magnetic field. We numerically calculate the distributions of the electrostatic
potential phi and the temperature T in a 2DEG enclosed in a square area
surrounded by insulated-adiabatic (top and bottom) and isopotential-isothermal
(left and right) boundaries (with phi_{left} < phi_{right} and T_{left}
=T_{right}), using a pair of nonlinear Poisson equations (for phi and T) that
fully take into account thermoelectric and thermomagnetic phenomena, including
the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. We find that, in the
vicinity of the left-bottom corner, the temperature becomes lower than the
fixed boundary temperature, contrary to the naive expectation that the
temperature is raised by the prevalent Joule heating effect. The cooling is
attributed to the Ettingshausen effect at the bottom adiabatic boundary, which
pumps up the heat away from the bottom boundary. In order to keep the adiabatic
condition, downward temperature gradient, hence the cooled area, is developed
near the boundary, with the resulting thermal diffusion compensating the upward
heat current due to the Ettingshausen effect.Comment: 25 pages, 7 figure
Evidence of Novel Quasiparticles in a Strongly Interacting Two-Dimensional Electron System: Giant Thermopower and Metallic Behaviour
We report thermopower () and electrical resistivity ()
measurements in low-density (10 m), mesoscopic two-dimensional
electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin
temperatures. We observe at temperatures 0.7 K a linearly growing
as a function of temperature indicating metal-like behaviour. Interestingly
this metallicity is not Drude-like, showing several unusual characteristics: i)
the magnitude of exceeds the Mott prediction valid for non-interacting
metallic 2DESs at similar carrier densities by over two orders of magnitude;
and ii) in this regime is two orders of magnitude greater than
the quantum of resistance and shows very little temperature-dependence.
We provide evidence suggesting that these observations arise due to the
formation of novel quasiparticles in the 2DES that are not electron-like.
Finally, and show an intriguing decoupling in their
density-dependence, the latter showing striking oscillations and even sign
changes that are completely absent in the resistivity.Comment: QFS2012 Conference proceedings, Journal of Low Temperature Physics,
accepted (figure and discussion added upon referee suggestions