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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Spin dependent transport in semiconductor and semimetal materials

Lee, Kiyoung January 2012 (has links)
No description available.
22

STRUCTURE AND MAGNETISM OF Mn-DOPED Si THIN FILMS GROWN BY MOLECULAR BEAM EPITAXY

Kahwaji, Samer 17 April 2013 (has links)
The structure and magnetism of ultrathin Mn layers grown by molecular beam epitaxy (MBE) on Si(001) are investigated. X-ray absorption fine structure (XAFS) shows that a metastable MnSi phase with a B2-like (CsCl) crystal structure forms and superconducting quantum interference device (SQUID) magnetometry measurements reveal that the B2 structure is ferromagnetic with a Mn moment of 0.33 µB and a Curie temperature TC > 400 K. A change in the Si capping layer growth temperature, TSi, produces a MnSi phase with a B20-like structure, which exhibits a small moment and a TC below 20 K. Surfactant mediated growth of Mn ?-doped Si films and co-deposited Si1-xMnx alloys shows that a Pb surfactant strongly alters the structure and magnetism of these systems. For the ?-doped films, analysis of the crystal structure and magnetic properties over a range of growth parameters identified three distinct Mn-Si phases. With Pb, a sample with a coverage ?Mn = 0.26 monolayer and TSi = 200 ºC develops a ferromagnetic phase with a Mn moment of 1.56 µB and a TC > 400 K, whereas TC drops to zero for a sample grown without Pb. For TSi > 200 ºC, nano-disks with MnSi-B20 type structure form with a TC ? 170 K. A possible correlation exists between the remanent moment and the fraction of Mn occupying Si substitutional sites, which suggests that a dilute Si1-xMnx may be forming in the matrix. Density functional theory (DFT) shows that Pb lowers the formation energy of Si vacancies by 0.92 eV, which enhances the substitutional incorporation of Mn. In the absence of Pb, the co-deposited Si1-xMnx films undergo a 2D spinodal decomposition and form nanocolumns. The nanocolumns are amorphous and paramagnetic. In contrast, in the samples grown with Pb, MnSi1.7 nanorods form in the plane of the films and exhibit two ferromagnetic transitions at TC1 ? 40 K and TC2 > 400 K when x = 0.5%. While TC1 is consistent with TC of bulk MnSi1.7 crystals, TC2 is believed to originate from Mn diluted in the Si matrix.
23

Nanoscale quantum transport for quantum information processing

Qassemi Maloomeh, Farzad January 2012 (has links)
In this thesis, I study quantum transport of electron (e.g., current and noise) in quantum dots exploring microscopic processes responsible for spin-relaxation in double quantum dots in Pauli spin blockade regime. This is a regime where current is blocked due to the spin configuration of electrons in the dot. The Pauli spin blockade provides a means for preparation, manipulation and readout in spin qubits. Hence, understanding the underlying mechanism which lifts this blockade is extremely important. First, I have developed a theory of spin-flip cotunneling (higher order tunneling) processes in double quantum dots in the Pauli spin blockade regime. Utilizing this theory, I have calculated the full analytical dependence of the stationary current on applied magnetic fields, gate voltages, and an inter-dot tunnel coupling in Pauli spin blockade. This work is important for understanding the nature of leakage, especially in systems where other spin-flip mechanisms (due, e.g., hyperfine coupling to nuclear spins or spin-orbit coupling) are weak, including silicon and carbon nanotube or graphene quantum dots. This theory explains recent experiments on carbon nanotubes and silicon double quantum dot. In addition, I propose a new scheme based on the current noise to probe spin relaxation mechanisms in double quantum dot in the Pauli spin blockade regime, where spin-selection rule applies. As a result, I provide a simple closed-form expression which can be used to fit experimental data to extract multiple spin-relaxation rates, even at very low energy splitting. This method allows for the characterization of different aspects of decay process in these systems.
24

Nanoscale quantum transport for quantum information processing

Qassemi Maloomeh, Farzad January 2012 (has links)
In this thesis, I study quantum transport of electron (e.g., current and noise) in quantum dots exploring microscopic processes responsible for spin-relaxation in double quantum dots in Pauli spin blockade regime. This is a regime where current is blocked due to the spin configuration of electrons in the dot. The Pauli spin blockade provides a means for preparation, manipulation and readout in spin qubits. Hence, understanding the underlying mechanism which lifts this blockade is extremely important. First, I have developed a theory of spin-flip cotunneling (higher order tunneling) processes in double quantum dots in the Pauli spin blockade regime. Utilizing this theory, I have calculated the full analytical dependence of the stationary current on applied magnetic fields, gate voltages, and an inter-dot tunnel coupling in Pauli spin blockade. This work is important for understanding the nature of leakage, especially in systems where other spin-flip mechanisms (due, e.g., hyperfine coupling to nuclear spins or spin-orbit coupling) are weak, including silicon and carbon nanotube or graphene quantum dots. This theory explains recent experiments on carbon nanotubes and silicon double quantum dot. In addition, I propose a new scheme based on the current noise to probe spin relaxation mechanisms in double quantum dot in the Pauli spin blockade regime, where spin-selection rule applies. As a result, I provide a simple closed-form expression which can be used to fit experimental data to extract multiple spin-relaxation rates, even at very low energy splitting. This method allows for the characterization of different aspects of decay process in these systems.
25

Optically-injected spin current and its scattering effect in semiconductor quantum wells

Hu, Kaige. January 2007 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.
26

Spin transport studies in nanoscale spin valves and magnetic tunnel junctions

Patibandla, Sridhar. January 1900 (has links)
Thesis (Ph.D.)--Virginia Commonwealth University, 2008. / Prepared for: Dept. of Electrical Engineering. Title from thesis description page. Includes bibliographical references.
27

Effects of spin current in ferromagnets

He, Jiexuan, January 2008 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 4, 2009) Vita. Includes bibliographical references.
28

Electron and hole spins in quantum dots

Pingenot, Joseph Albert Ferguson. Flatté, Michael E. January 2009 (has links)
Thesis (Ph.D.)--University of Iowa, 2009. / Thesis supervisor: Michael E. Flatté. Includes bibliographical references (leaves 234-242).
29

Electrical current converted from optically excited spin current /

Hau, Wing Yu. January 2008 (has links)
Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references. Also available in electronic version.
30

Spin-polarized transport across EuS/III-V semiconductor heterostructure interfaces

Trbovic, Jelena. Von Molnar, S. January 2006 (has links)
Thesis (Ph. D.)--Florida State University, 2006. / Advisor: Stephan von Molnar, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed June 9, 2006). Document formatted into pages; contains xiv, 93 pages. Includes bibliographical references.

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