Magnetic Excitations in Magnetically Ordered Superfluids

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This project supports the study of a new kind of "superfluid" (a spinor Bose-Einstein condensate) which not only flows without resistance (one of the characteristics of superfluids) but also presents magnetic order (like a bar magnet). This superfluid is made up of an atomic gas that is cooled to extremely low temperatures and confined by a so-called "optical tweezer trap" (created by laser light) within a vacuum chamber. The researchers supported by this project will examine the magnetic characteristics of this gaseous material, and also clarify ways in which the magnetism and superfluidity of this material influence one another. The broader goal of this work is to help understand materials better, in particular those materials where the theory of quantum mechanics plays a dominant role (such materials can be expected to be increasingly put to use, particularly when they involve short length scales such as in the microelectronics industry). Toward this goal, the magnetic superfluid studied here is a useful test subject, one for which all of the basic physics underlying the material properties is believed to be known, and to which one can apply very precise and sensitive measurement techniques. The project will take place at a public University, and will support the training of graduate students in that setting. The project is focused on three specific aims. The first is to characterize magnons in magnetically ordered superfluids. These magnons are the elementary magnetic excitations of these materials. A variety of approaches, many based on directly imaging the propagation of magnon waves, will be used to measure the magnon energy, damping, magnetic moment, and nonlinearities, and also to clarify the role of long-range magnetic dipole interactions. The second aim of this project is to study the condensation of magnons within ferromagnetic superfluids, related to the phenomenon of magnon condensation in solid-state magnetic materials. The third aim is to study the influence of spatially varying magnetization (spin textures) on mass currents and spin currents. This work will study differences between the study of scalar superfluids and magnetically ordered superfluids, with the goal of identifying the basic processes in the hydrodynamics of spinor Bose-Einstein condensates (something one might call "superfluid magnetohydrodynamics").