442 research outputs found
Topology, geometry and quantum interference in condensed matter physics
The methods of quantum field theory are widely used in condensed matter
physics. In particular, the concept of an effective action was proven useful
when studying low temperature and long distance behavior of condensed matter
systems. Often the degrees of freedom which appear due to spontaneous symmetry
breaking or an emergent gauge symmetry, have non-trivial topology. In those
cases, the terms in the effective action describing low energy degrees of
freedom can be metric independent (topological). We consider a few examples of
topological terms of different types and discuss some of their consequences. We
will also discuss the origin of these terms and calculate effective actions for
several fermionic models. In this approach, topological terms appear as phases
of fermionic determinants and represent quantum anomalies of fermionic models.
In addition to the wide use of topological terms in high energy physics, they
appeared to be useful in studies of charge and spin density waves, Quantum Hall
Effect, spin chains, frustrated magnets, topological insulators and
superconductors, and some models of high-temperature superconductivity.Comment: lecture notes, 44 page
Current driven magnetization dynamics in ferromagnetic nanowires with Dzyaloshinskii-Moriya interaction
We study current induced magnetization dynamics in a long thin ferromagnetic
wire with Dzyaloshinskii-Moriya interaction (DMI). We find a spiral domain wall
configuration of the magnetization and obtain an analytical expression for the
width of the domain wall as a function of the interaction strengths. Our
findings show that above a certain value of DMI a domain wall configuration
cannot exist in the wire. Below this value we determine the domain wall
dynamics for small currents, and calculate the drift velocity of the domain
wall along the wire. We show that the DMI suppresses the minimum value of
current required to move the domain wall. Depending on its sign, the DMI
increases or decreases the domain wall drift velocity.Comment: 4 pages, 2 figure
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