Decay of persistent precessing domains in3He-Bat very low temperatures

Abstract

The B phase of superfluid 3 He can support regions of extremely long-lived coherent spin precession at ultralow temperatures, known as persistent precessing domains (PPD). The domains have been described in terms of a Bose-Einstein condensate of magnons and in terms of Q balls in field theory. The domains form in a magnetic field minimum along the vertical axis of a cylindrical cell. When far from the ends of the cell, the PPD lifetime grows exponentially on decreasing temperature. When the PPD is close to the horizontal end wall of the cell, an extra surface dissipation mechanism dominates at low temperatures. We present measurements of the PPD generated at various locations in the cell over a broad range of temperatures below 0.3 T C . We compare the measured properties with theoretical expectations for spin-wave modes. We present model calculations of different dissipation mechanisms and we compare these to the measured lifetimes.

Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural Traps in Superfluid 3He-B

“…As the density of the normal component rapidly decreases with decreasing temperature, the lifetime of the condensates increases and can exceed half an hour in the case when the con-densate is well isolated from the walls [14]. Eventually, the lifetime is limited by an approximately temperature-independent relaxation process [13] which has not been identified before this work.…”

“…At temperatures where the trapped magnon condensates are observed, Leggett-Takagi relaxation becomes negligible and spin diffusion was identified as the main mechanism responsible for the temperature dependence of the relaxation of such condensates [13]. As the density of the normal component rapidly decreases with decreasing temperature, the lifetime of the condensates increases and can exceed half an hour in the case when the con-densate is well isolated from the walls [14].…”

Microkelvin Thermometry with Bose–Einstein Condensates of Magnons and Applications to Studies of the AB Interface in Superfluid $$^3$$ 3 He

“…(4). The situation is significantly simplified in the axially symmetric harmonic trap [17], where the Eq. (4) becomes…”

“…The decay rate of this signal measures the loss of magnons from the trap. In a trap which is well isolated from the sample walls two loss mechanisms have been identified: spin diffusion through the normal component [17,19] and radiation damping owing to the interaction with the pick-up circuit [19].…”

Quasiclassical Theory of Spin Dynamics in Superfluid $$^3$$ 3 He: Kinetic Equations in the Bulk and Spin Response of Surface Majorana States

“…Recently, the technique based on the relaxation of a magnon condensate has been developed [33,34,35,36,37,38]. In principle, it can be used for the identification of surface Andreev-Majorana states although this approach has several difficulties discussed below.…”