What constitutes a nanoswitch? A Perspective

Progress in the last two decades has effectively integrated spintronics and nanomagnetics into a single field, creating a new class of spin-based devices that are now being used both to Read (R) information from magnets and to Write (W) information onto magnets. Many other new phenomena are being investigated for nano-electronic memory as described in Part II of this book. It seems natural to ask whether these advances in memory devices could also translate into a new class of logic devices. What makes logic devices different from memory is the need for one device to drive another and this calls for gain, directionality and input-output isolation as exemplified by the transistor. With this in mind we will try to present our perspective on how W and R devices in general, spintronic or otherwise, could be integrated into transistor-like switches that can be interconnected to build complex circuits without external amplifiers or clocks. We will argue that the most common switch used to implement digital logic based on complementary metal oxide semiconductor (CMOS) transistors can be viewed as an integrated W-R unit having an input-output asymmetry that give it gain and directionality. Such a viewpoint is not intended to provide any insight into the operation of CMOS switches, but rather as an aid to understanding how W and R units based on spins and magnets can be combined to build transistor-like switches. Next we will discuss the standard W and R units used for magnetic memory devices and present one way to integrate them into a single unit with the input electrically isolated from the output. But we argue that this integrated W-R unit would not provide the key property of gain. We will then show that the recently discovered giant spin Hall effect could be used to construct a W-R unit with gain and suggest other possibilities for spin switches with gain.Comment: 27 pages. To appear in Emerging Nanoelectronic Devices, Editors: An Chen, James Hutchby, Victor Zhirnov and George Bourianoff, John Wiley & Sons (to be published

Quantum Chaos with a Bose-einstein Condensate

The purpose of this research was to experimentally study a quantum delta-kicked accelerator utilizing a Bose Einstein condensate (BEC) of Rb87 atoms. An all optical method was chosen to create a BEC. Generalization of the quantum theory of the quantum accelerator modes to include the higher order QAM's observed in cold atomic systems was also among the topics studied in this research. The underlying pseudoclassical phase space structure of the quantum delta-kicked accelerator was experimentally explored. This was achieved by exposing a Bose-Einstein condensate to a spatially corrugated potential created by pulses of an off-resonant standing light wave. For the first time quantum accelerator modes were realized in such a system. By utilizing the narrow momentum distribution of the condensate the discrete momentum state structure of a quantum accelerator mode was observed. These experiments allowed us to directly measure the size of the structures in the phase space of the delta-kicked accelerator. We also found that the phase space structures in the pseudoclassical model are given by the interference of the different momentum diffraction orders of the matter wave from standing light waves. This discovery allowed us to generalize the quantum theory of accelerator modes to explain higher order accelerator modes observed in cold atomic systems.Department of Physic

All Spin Logic device with inbuilt Non-Reciprocity

The need for low power alternatives to digital electronic circuits has led to increasing interest in logic devices where information is stored in nanomagnets. This includes both nanomagnetic logic (NML) where information is communicated through magnetic fields of nanomagnets and all-spin logic (ASL) where information is communicated through spin currents. A key feature needed for logic implementation is non-reciprocity, whereby the output is switched according to the input but not the other way around, thus providing directed information transfer. The objective of this paper is to draw attention to possible ASL-based schemes that utilize the physics of spin-torque to build in non-reciprocity similar to transistors that could allow logic implementation without the need for special clocking schemes. We use an experimentally benchmarked coupled spin-transport/ magnetization-dynamics model to show that a suitably engineered single ASL unit indeed switches in a non-reciprocal manner. We then present heuristic arguments explaining the origin of this directed information transfer. Finally we present simulations showing that individual ASL devices with inbuilt directionality can be cascaded to construct circuits.Comment: 7 pages, 8 figures, To appear in IEEE Trans. Mag

Photoassociation spectroscopy of a Spin-1 Bose-Einstein condensate

We report on the high resolution photoassociation spectroscopy of a $^{87}$Rb spin-1 Bose-Einstein condensate to the $1_\mathrm{g} (P_{3/2}) v = 152$ excited molecular states. We demonstrate the use of spin dependent photoassociation to experimentally identify the molecular states and their corresponding initial scattering channel. These identifications are in excellent agreement with the eigenvalues of a hyperfine-rotational Hamiltonian. Using the observed spectra we estimate the change in scattering length and identify photoassociation laser light frequency ranges that maximize the change in the spin-dependent mean-field interaction energy.Comment: 5 pages, 4 figure