Tunneling spectroscopy of the two-dimensional electron gas
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2005
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| Online Access: | http://hdl.handle.net/1721.1/9387 |
| _version_ | 1811092546389016576 |
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| author | Chan, Ho Bun, 1969- |
| author2 | Raymond C. Ashoori. |
| author_facet | Raymond C. Ashoori. Chan, Ho Bun, 1969- |
| author_sort | Chan, Ho Bun, 1969- |
| collection | MIT |
| description | Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999. |
| first_indexed | 2024-09-23T15:19:55Z |
| format | Thesis |
| id | mit-1721.1/9387 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T15:19:55Z |
| publishDate | 2005 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/93872019-04-12T17:23:41Z Tunneling spectroscopy of the two-dimensional electron gas Chan, Ho Bun, 1969- Raymond C. Ashoori. Massachusetts Institute of Technology. Dept. of Physics. Massachusetts Institute of Technology. Dept. of Physics. Physics. Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999. Includes bibliographical references (p. 155-161). We measure the single particle density of states (DOS) of a two-dimensional electron system (2DES) in a GaAs/AlGaAs heterostructure. Using a technique that we call "Time Domain Capacitance Spectroscopy" (TDCS), we measure the complete current-voltage characteristics for tunneling into the 2DES without making ohmic contacts to it. TDCS detects the tunneling current in regimes difficult to access by conventional methods, such as when the in-plane conductance is low. For the first time we detect the contributions of localized states to the tunneling current. The DOS of an interacting 2DES in the diffusive limit displays logarithmic energy dependence near the Fermi level. Using TDCS, we measure the voltage dependence of the tunneling conductance of a semiconductor 2DES and observe the logarithmic Coulomb anomaly for the first time in 2D systems other than thin metal films. As we increase the density, this suppression in tunneling conductance narrows and recedes. Nevertheless suppression reappears when we apply a magnetic field perpendicular to the 2D plane. We find that the tunneling conductance depends linearly on voltage near zero bias for all magnetic field strengths and electron densities. Moreover, the slopes of this linear gap are strongly field dependent. The data are suggestive of a new model of the tunneling gap in the presence of disorder and screening. We also use TDCS to study the interactions among electronic spins. By applying excitations less than kT, we observe that equilibrium tunneling into spin-polarized quantum Hall states (v=l, 3, 1/3) occurs at two distinct tunneling rates for samples of very high mobility. Some electrons tunnel into the 2DES at a fast rate while the rest tunnel at a rate up to 2 orders of magnitude slower. Such novel double-rate tunneling is not observed at even-integer filling fractions where the 2DES is not spin-polarized. The dependence of the two rates on magnetic field, temperature and tunnel barrier thickness suggests that slow in-plane spin relaxation, possibly related to formation of Skyrmions, leads to a bottleneck for tunneling of electrons. by Ho Bun Chan. Ph.D. 2005-08-22T20:47:25Z 2005-08-22T20:47:25Z 1999 1999 Thesis http://hdl.handle.net/1721.1/9387 44968282 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 161 p. 11778589 bytes 11778346 bytes application/pdf application/pdf application/pdf Massachusetts Institute of Technology |
| spellingShingle | Physics. Chan, Ho Bun, 1969- Tunneling spectroscopy of the two-dimensional electron gas |
| title | Tunneling spectroscopy of the two-dimensional electron gas |
| title_full | Tunneling spectroscopy of the two-dimensional electron gas |
| title_fullStr | Tunneling spectroscopy of the two-dimensional electron gas |
| title_full_unstemmed | Tunneling spectroscopy of the two-dimensional electron gas |
| title_short | Tunneling spectroscopy of the two-dimensional electron gas |
| title_sort | tunneling spectroscopy of the two dimensional electron gas |
| topic | Physics. |
| url | http://hdl.handle.net/1721.1/9387 |
| work_keys_str_mv | AT chanhobun1969 tunnelingspectroscopyofthetwodimensionalelectrongas |