fRG treatment of the 0.7 analog in quantum point contacts*

We use a recently developed fRG method (extended coupled-ladder
approximation) to study the so-called 0.7-analog in quantum point
contacts that is experimentally observed (PhysRevLett.91.136404) to
arise at the crossing of the 1st and 2nd subband at sufficiently high
magnetic fields. We demonstrate that we can reproduce the measured
magnetic field dependence of the differential conductance at the
0.7-analog, using a QPC model with two bands and short-ranged
interactions. In particular, we reproduce the fact that the magnetic
field dependence is qualitatively different, depending on whether the
analog is approached from higher or lower magnetic fields.
We argue that the 0.7-analog physics can be explained in a similar
manner as the 0.7-anomaly, evoking a smeared van Hove singularity in the
local density of states (nature12421). However, the screening effects of
the electrons in the lowest subband are of critical importance. We
demonstrate that this screening causes the above-mentioned asymmetry in
the magnetic field dependence of the conductance and study its
dependence on the ratio of intra- to interband interaction strength.