Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X25: Magnon BEC and Spin SuperfluidityInvited
|
Hide Abstracts |
Sponsoring Units: GMAG DCMP Chair: Wei Han, Peking Univ Room: LACC 403B |
Friday, March 9, 2018 8:00AM - 8:36AM |
X25.00001: Observation of room-temperature magnon supercurrents Invited Speaker: Burkard Hillebrands Finding new ways for fast and efficient processing and transfer of data is one the most challenging tasks nowadays. Elementary spin excitations - magnons (spin wave quanta) - open up a very promising direction. Magnons are bosons, and thus they are able to form spontaneously a spatially extended, coherent ground state, a Bose-Einstein condensate (BEC). The BEC can be conveniently created in a single-crystal film of yttrium iron garnet even at room temperature using parametric pumping. An extraordinary challenge is the use of this macroscopic quantum state for information transfer and processing. Recently we have succeeded to create a magnon supercurrent in such a macroscopic quantum state by introducing a spatial phase gradient to the wave function created by local heating. The temporal evolution of the magnon BEC and the supercurrent was studied by means of time- and wavevector-resolved Brillouin light scattering spectroscopy. We have found that local heating in the focal point of a probing laser beam leads to a decay of the BEC, which is a fingerprint of the outflow of condensed magnons driven by a thermally induced phase gradient. I will demonstrate non-local probing of the magnon supercurrent, which provides direct evidence of the condensate propagation. By utilizing a separate pulsed blue laser for heating purpose, we are able to control the phase gradient, while a low-power green laser is used for local probing of the condensate area. The supercurrent pulse is detected on an undisturbed background of the slowly decaying magnon BEC. The occurrence of the supercurrent directly confirms the phase coherency of the magnon condensate and opens door to studies in the general field of magnonic macroscopic quantum transport phenomena at room temperature as a novel approach in the field of information processing. |
Friday, March 9, 2018 8:36AM - 9:12AM |
X25.00002: Spin superfluidity: superfluid 3He, solids, spinor BEC Invited Speaker: Edouard Sonin Spin superfluidity has already been discussed from 70s of the last century. The interest to this phenomenon was revived after emergence of spintronics. Manifestation of spin superfluidity is a metastable spin supercurrent proportional to the gradient of the phase (spin rotation angle in a plane) and is not accompanied by dissipation, in contrast to a dissipative spin diffusion current proportional to the gradient of spin density. The supercurrent state is a helical spin structure, but in contrast to equilibrium helical structures is metastable. An elementary process of relaxation of the supercurrent is phase slip. In this process, a vortex with 2π phase variation around it crosses streamlines of the supercurrent decreasing the total phase variation across streamlines by 2π. Phase slips are suppressed by energetic barriers for vortex creation, which disappear when phase gradients reach critical values determined by the criterion similar to the famous Landau criterion for mass (charge) superfluidity. |
Friday, March 9, 2018 9:12AM - 9:48AM |
X25.00003: Spin superconductor and electric dipole superconductor Invited Speaker: Xincheng Xie We propose the concept of the spin superconductor (SSC), a counterpart to the charge superconductor. We carry out theoretical study to show the existence of a spin superconductor in a ferromagnetic graphene, in which the spin-polarized electron-hole excitons play the roles of the `Cooper' pairs. We present a BCS-type theory and the Laudau-Ginzburg theory for the SSC. With the "London-type equations" of the super-spin-current density, we show the existence of an electric "Meissner effect" against a spatial varying electric field. We further study a SSC/normal conductor/SSC junction and predict a spin-current Josephson effect. Recent experimental results showing spin superconductor in canted antiferromagnetic Cr2O3 via nonlocal spin transport will be reported. |
Friday, March 9, 2018 9:48AM - 10:24AM |
X25.00004: Magnon condensation and hydrodynamics Invited Speaker: Yaroslav Tserkovnyak Thermoelectric means to induce and control magnon condensation in magnetic insulators is garnering much attention in the field of spin caloritronics. A complimentary thrust in spintronics concerns two-fluid spin hydrodynamics, either as a result of this nonequilibrium condensation or as innately pertaining to the spin-superfluid properties of a magnetic material. I will review recent developments, with a focus on the experimental signatures of the underlying interplay between the coherent and incoherent degrees of freedom. The relevant materials of interest will progress from ferromagnets to antiferromagnets to disordered spin systems. |
(Author Not Attending)
|
X25.00005: Spin Superfluidity in Uniaxial and Biaxial Antiferromagnetic Insulators Invited Speaker: Arne Brataas Antiferromagnets may exhibit spin superfluidity since there is no long-range dipole interaction. We seek to establish that this phenomenon occurs in typical insulators. We investigate non-local spin transport in two scenarios, a uniaxial antiferromagnet and a planar antiferromagnetic insulator with a weak easy-axis anisotropy. In these systems, the anisotropy hinders spin superfluidity by creating a substantial threshold that the current must overcome. Nevertheless, we show that applying a magnetic field removes this obstacle near the spin-flop transition of the antiferromagnet. Importantly, the spin superfluidity can then persist across many micrometers, even in dirty samples. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700