Giant magnetic suppression of tunneling out of a 2D electron system

Abstract

We have measured tunneling rates out of an electron layer trapped at a liquid-helium-vacuum interface in the presence of a magnetic field. When the field is transverse to the escape direction we find a striking suppression of the tunneling rates: a field of 3000 G at 40 mK reduces the tunneling current by four orders of magnitude. As the temperature increases the magnetic suppression of tunneling diminishes until it disappears completely above 250 mK. By contrast parallel fields have no effect on the tunneling rates.PACS numbers: 73.40.Gk, 73.20.Dx The transport of electrons through potential barriers in the presence of a magnetic field is a powerful tool for understanding the physics of tunneling in the presence of correlations and in various applications such as the design and control of tunneling devices [1][2][3][4][5]. Experiments on magnetotunneling (MT) have thus far focused on semiconductor heterostructures [1,5] where the magnetic field has only a slight effect on the tunneling rates. The relative importance of the magnetic field may be estimated by comparing the time to complete a cyclotron precession, ~ o^T 1 , to a characteristic time scale of tunneling which is usually taken as [6] T ~ f** dz/sj2 [U(z) -E]/m. Here cv c = eB/m*c is the cyclotron frequency, ra, e, and E are the electronic mass, charge, and total energy, U(z) is its potential energy, B is the magnetic field amplitude, and 21,22 are the turning points of the potential.In this Letter we report on measurements of MT for surface state electrons trapped at a liquid-heliumvacuum interface. In this system the barrier size and the electron densities are readily tuned in situ over a wide range of parameters that are not accessible in heterostructures [7][8][9]. The barriers can be made very wide and shallow so that r ~ 20 psec is two orders of magnitude larger than in heterostructures and the strong magnetic field limit (00 C T > 1) is reached for fields as low as 2500 G. For these barriers we observe a strong suppression of the tunneling rates in the presence of a transverse magnetic field B t (transverse to the direction of tunneling and parallel to the electron layer). As illustrated in Figs. 1-3 the tunneling currents depend exponentially on B*l and exhibit an unexpected temperature and density dependence.Our experimental setup consists of a cylindrical cell of height 2.5=b0.05 mm that is half filled with liquid helium supporting the electron disk. The electrons are prevented from escaping to the sides with a negatively biased guard ring of diameter 18±0.05 mm. A voltage V t applied between the top plate of the cell and the grounded bottom plate creates an external field with which the electrons can be pressed toward or extracted from the surface. The cell is positioned at the center of a double split superconducting magnet that can provide up to 0.5 T of either transverse and/or parallel field. The electron density is determined from the plasmon spectrum of the electron disk which is measured with an rf spectrometer. From the known 2D ...

Enhancement of Tunneling from a Correlated 2D Electron System by a Many-Electron Mössbauer-Type Recoil in a Magnetic Field

“…We discuss tunneling from 2DES on helium and in single quantum well heterostructures. The results explain and give a no parameter fit to the experimental data [5], see Fig. 1.…”

“…They show up dramatically in various unusual transport properties. One of the most broadly used techniques for investigating many-electron effects is tunneling [3], a recent example being the observation [4] of the giant increase of interlayer tunneling in doublelayer heterostructures, apparently related to the onset of interlayer correlations.For electrons on helium, an exponentially strong deviation from the single-electron rate of tunneling transverse to a magnetic field has been known experimentally since 1993 [5], but remained unexplained. Such a field couples the tunneling motion away from the 2DES to the in-plane degrees of freedom.…”

“…For electrons on helium, an exponentially strong deviation from the single-electron rate of tunneling transverse to a magnetic field has been known experimentally since 1993 [5], but remained unexplained. Such a field couples the tunneling motion away from the 2DES to the in-plane degrees of freedom.…”

Tunneling decay in a magnetic field

“…This system was experimentally investigated in Ref. 10 , and showed an unexpected dependence of the tunneling rate on B and electron density that we recently addressed 11,23 .…”

“…This change, in turn, strongly depends on properties of the system, as in the well-known effect of giant hopping magnetoresistance in solids 1 . Therefore tunneling in a magnetic field has been broadly used as a sensitive and revealing probe of electron systems in solids, including quantum Hall systems 2-5 , two-layer heterostructures away from the quantum Hall region [6][7][8][9] , and correlated electron layers on the surface of liquid helium 10,11 . Correlated two-dimensional (2D) electron systems are currently attracting much interest 12 .…”