4,154 research outputs found
Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor
The precessing magnetization of a magnetic islands coupled to a quantum spin
Hall edge pumps charge along the edge. Conversely, a bias voltage applied to
the edge makes the magnetization precess. We point out that this device
realizes an adiabatic quantum motor and discuss the efficiency of its operation
based on a scattering matrix approach akin to Landauer-B"uttiker theory.
Scattering theory provides a microscopic derivation of the
Landau-Lifshitz-Gilbert equation for the magnetization dynamics of the device,
including spin-transfer torque, Gilbert damping, and Langevin torque. We find
that the device can be viewed as a Thouless motor, attaining unit efficiency
when the chemical potential of the edge states falls into the
magnetization-induced gap. For more general parameters, we characterize the
device by means of a figure of merit analogous to the ZT value in
thermoelectrics.Comment: 9 pages, 2 figures. Contribution to a special issue in Physica E on
"Frontiers in quantum electronic transport" - in memory of Markus B"uttike
Building fracton phases by Majorana manipulation
Fracton topological phases host fractionalized topological quasiparticles with restricted mobility, with promising applications to fault-tolerant quantum computation. While a variety of exactly solvable fracton models have been proposed, there is a need for platforms to realize them experimentally. We show that a rich set of fracton phases emerges in interacting Majorana band models whose building blocks are within experimental reach. Specifically, our Majorana constructions overcome a principal obstacle, namely, the implementation of the complicated spin cluster interactions underlying fracton stabilizer codes. The basic building blocks of the proposed constructions include Coulomb blockaded Majorana islands and weak interisland Majorana hybridizations. This setting produces a wide variety of fracton states and promises numerous opportunities for probing and controlling fracton phases experimentally. Our approach also reveals the relation between fracton phases and Majorana fermion codes and further generates a hierarchy of fracton spin liquids
Elastic theory of quantum Hall smectics: effects of disorder
We study the effect of disorder on quantum Hall smectics within the framework
of an elastic theory. Based on a renormalization group calculation, we derive
detailed results for the degrees of translational and orientational order of
the stripe pattern at zero temperature and carefully map out the disorder and
length-scale regimes in which the system effectively exhibits smectic, nematic,
or isotropic behavior. We show that disorder always leads to a finite density
of free dislocations and estimate the scale on which they begin to appear.Comment: 4 pages latex with 1 EPS figur
Quasilinear spin voltage profiles in spin thermoelectrics
Recent experiments show that spin thermoelectrics is a promising approach to
generate spin voltages. While spin chemical potentials are often limited to a
surface layer of the order of the spin diffusion length, we show that
thermoelectrically induced spin chemical potentials can extend much further in
itinerant ferromagnets with paramagnetic impurities. In some cases,
conservation laws, e.g., for a combination of spin and heat currents, give rise
to a linear spin voltage profile. More generally, we find quasilinear profiles
involving a spin thermoelectric length scale which far exceeds the spin
diffusion length.Comment: 4+ page
- …