Electrically driven Bose-Einstein condensation of magnons in antiferromagnets

Abstract

We explore routes to realize electrically driven Bose-Einstein condensation of magnons in insulating antiferromagnets. Even in insulating antiferromagnets, the localized spins can strongly couple to itinerant spins in adjacent metals via spin-transfer torque and spin pumping. We describe the formation of steady-state magnon condensates controlled by a spin accumulation polarized along the staggered field in an adjacent normal metal. Two types of magnons, which carry opposite magnetic moments, exist in antiferromagnets. Consequently, and in contrast to ferromagnets, Bose-Einstein condensation can occur for either sign of the spin accumulation. This condensation may occur even at room temperature when the interaction with the normal metal is fast compared to the relaxation processes within the antiferromagnet. In antiferromagnets, the operating frequencies of the condensate are orders of magnitude higher than in ferromagnets.

Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons

“…As detailed in the supplemental material [59](see, also, references [61][62][63][64][65][66] therein), the interaction Hamiltonian [Eq. (3)] couples the NM electrons with the A and B sublattices of the AFMI: In order to obtain an effective interacting theory for electrons in NM, we integrate out the magnons, using a canonical transformation [60].…”

“…From the interaction Hamiltonian we obtain, for coupling to sublattice A and B respectively [20,61],…”

Spin transport in thick insulating antiferromagnetic films

“…In addition, it was shown that thermal magnon transport takes place at zero spin bias when the sublattice symmetry is broken at the interfaces, e.g., induced by interfacial magnetically uncompensated AF order [20]. Complementarily, coherent spin transport induced by spin accumulation has been earlier considered and predicted to result in spin superfluidity [21,22] or Bose-Einstein condensates of magnons [23]. Recently, it has been shown via non-local spin transport measurements that magnons remarkably propagate at long distances in insulating AFs; α-Fe 2 O 3 [24], Cr 2 O 3 [25] and MnPS 3 [26].…”

Superconductivity at metal-antiferromagnetic insulator interfaces

“…We disregard terms of second order in the magnon operators from H Int . Then, the total Hamiltonian H = H L AFI + H R AFI + H NM + H Int is given by [5]…”

“…Even so, AFIs have received less attention than ferromagnetic insulators (FIs) in spintronics. A standard model for the interfacial tie is an exchange coupling between the itinerant electrons and the localized spins [4][5][6]. In this formalism, the electrons experience a staggered field and scatter through two different scattering channels: a regular channel and an Umklapp channel [4,5].…”