Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session E3: Condensed Matter II |
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Chair: Neil Harrison, Los Alamos National Laboratory Room: Macey Center Auditorium |
Friday, October 26, 2012 4:30PM - 5:06PM |
E3.00001: The Planar Nernst Effect and the Search for Thermal Spin Currents in Ferromagnetic Metals Invited Speaker: Barry Zink One possible model for future nanoelectronic circuits that will be faster and more efficient is based on the spin, rather than only the charge of electrons. An essential ingredient for this future is a reliable source of a pure spin current, a transfer of angular momentum without flow of charge. Over the past few years some groups have reported that such a spin current can be generated simply by applying a thermal gradient to a ferromagnetic material. This effect, called the spin Seebeck effect (SSE), has generated tremendous interest in the interaction of heat, charge and spin in ferromagnetic systems. In this talk we will present our own recent measurements of thermoelectric and thermomagnetic effects in thin film metallic ferromagnets. These are enabled by a micromachined thermal isolation platform that removes potentially confounding effects introduced in such measurements by the presence of a highly thermally conductive bulk substrate. One of the main results is the observation of a transverse thermopower, called the planar Nernst effect (PNE), that is caused by spin-dependent scattering. This PNE should therefore be present in any attempted measurement of the SSE in a metal system where spin-dependent scattering of electrons occurs. Furthermore our ``zero substrate" experiment shows no signal with the symmetry of the SSE, suggesting the presence of the substrate is required to cause such a signal. Further experiments are required to determine if a pure spin current is actually involved in the generation of the signal associated with the SSE in metal films. [Preview Abstract] |
Friday, October 26, 2012 5:06PM - 5:18PM |
E3.00002: Role of Nuclear Quadrupole Coupling on Decoherence and Relaxation of Central Spins in Quantum Dots Nikolai Sinitsyn, Yan Li, Scott Crooker, Avadh Saxena, Darryl Smith Strain-induced gradients of local electric fields in semiconductor quantum dots can couple to the quadrupole moments of nuclear spins. We develop a theory describing the influence of this quadrupolar coupling on the spin correlators of electron and hole ``central'' spins localized in such dots. We show that when the QC strength is comparable to or larger than the hyperfine coupling strength between nuclei and the central spin, the relaxation rate of the central spin is strongly enhanced and can be exponential. We demonstrate a good agreement with our recent experiments on spin noise measurements in hole-doped (In,Ga)As self-assembled quantum dots. [Preview Abstract] |
Friday, October 26, 2012 5:18PM - 5:30PM |
E3.00003: Characterizing InGaAs quantum dot chains Tyler Park, John Colton, Jeff Farrer, Ken Clark, David Meyer, Scott Thalman, Haeyeon Yang We are studying epitaxially grown quantum dot chains by photoluminescence spectroscopy and transmission electron microscopy. Quantum dots and dot chains have potential use in optoelectronics and quantum computing. By studying these quantum dot samples by optical methods, we are able to determine the quality and geometry of the grown samples. Our photoluminescence study has shown peaks corresponding to structure in the sample. Our study using optical and analytical transmission electron microscopy methods is on going, but current results show that composition and structure is what is expected. [Preview Abstract] |
Friday, October 26, 2012 5:30PM - 5:42PM |
E3.00004: The Effect of Correlated Energetic Disorder on Charge Transport in Organic Semiconductors Jonathan Allen, Sebastian R\"oding, Charles Cherqui, David Dunlap In their 1995 paper describing a Monte Carlo simulation for dissociation of an electron-hole pair in the presence of Gaussian energetic disorder, Albrect and B\"{a}ssler reported a surprising result. They found that increasing the width $\sigma$ of the energetic disorder increases the quantum yield $\Phi$. They attributed this behavior to the tendency for energy fluctuations to compete against the Coulombic pair attraction, driving the electron-hole pair apart at short distances where, without disorder, recombination would be almost certain. We have expanded upon this notion, and introduced spatial correlation into the energetic disorder. By correlating the energetic disorder, we have demonstrated even larger quantum yields in simulation, attributable to the tendency of correlation to drive the charges further apart spatially than merely random disorder. Our results generally support the findings of Greenham et al. in that a larger correlation radius gives a larger quantum yield. In addition to larger quantum yield, we believe that correlated disorder could be used to create pathways for charge transport within a material, allowing the charge carrier behavior to be tuned. [Preview Abstract] |
Friday, October 26, 2012 5:42PM - 5:54PM |
E3.00005: Magnetic properties of 3d-metal Prussian Blue Analogs Manjita Shrestha, Sourav Adak, Heinz Nakotte, Luke L. Daemen, Monika Hartl, Vivien Zapf Prussian Blue Analogs consists of MC$_{6}$ and AN$_{6}$ octahedra connected by cyanide ligands (M, A$=$ metals). They typically crystallize in cubic structures. We have studied temperature and field dependence of the magnetization and the susceptibility of 3d-metal Prussian Blue Analogs, namely the hexacyanocobaltates, -ferrates and -chromates. All compounds exhibit modified Curie --Weiss behavior in the paramagnetic region. The observed effective moments of those compounds were compared with the ones of the respective free-ion values. Furthermore, we find evidence that a few of the compounds exhibit a transition to long-range magnetic order at low temperatures. [Preview Abstract] |
Friday, October 26, 2012 5:54PM - 6:06PM |
E3.00006: Designing a study of the Spin Seebeck Effect Grant Riley, Jason Liu, Gerri Roberts, Kristen Buchanan The Spin Seebeck Effect (SSE) refers to the recently discovered generation of a spin voltage as a result of an applied temperature gradient. The SSE has been observed in ferromagnetic (FM) metals, semiconductors, and insulators. This area of research has attracted much interest because it may provide a means to make use of waste heat from electronic devices. While several theories have been presented, there are still open questions regarding the physical mechanism of this effect. Recent experimental evidence suggests that magnons and phonons play a role in thermal spin physics; however, the experiments done to date are performed primarily through detection of a voltage via the Inverse Spin Hall Effect that is due to the steady-state accumulation of a spin distribution across the FM material and consequently provide only indirect information on the magnons. Here we will discuss an experimental setup that we have designed to explore the role of magnons in the SSE using Brillouin light scattering. [Preview Abstract] |
Friday, October 26, 2012 6:06PM - 6:18PM |
E3.00007: Direct observation of microwave-driven nonlinear three magnon splitting and confluence processes in yttrium iron garnet films by time-resolved Brillouin light scattering Jason Liu, Grant Riley, C\'esar Ord\'o\~nez-Romero, Boris Kalinikos, Kristen Buchanan Low-loss yttrium iron garnet (YIG) films provide a model system for the study of nonlinear spin wave processes. One such process is known as parametric pumping. This involves the conversion of spin waves or magnons at the pumping frequency $f_{p}$ into two magnons, both with frequencies of $f_{p}$/2, through a process known as three magnon splitting. The three magnon splitting and confluence processes, that is the subsequent recombination of the parametrically pumped magnons, were observed recently in YIG films using Brillouin light scattering (BLS) in both the magnetostatic surface wave (MSW) and the backward volume wave (MSBVW) configurations. These experiments were done, however, using continuous wave microwave excitations and no time-resolved information was obtained. In this work we explore the time-evolution of the splitting and confluence processes in the MSBVW configuration using time resolved BLS. Pulsed microwave excitations from a microstrip transducer were used to excite propagating spin waves in a long and narrow YIG film stip. Examination of the arrival times of the scattered photons shows that there are subsequent time delays between the $f_{p}$ and $f_{p}$/2 signals, and between the $f_{p}$/2 and $f_{c}$ signals. [Preview Abstract] |
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