%0 Journal Article
%A Placke, B.
%A Bosco, S.
%A DiVincenzo, David
%T A model study of present-day Hall-effect circulators
%J EPJ Quantum Technology
%V 4
%N 1
%@ 2196-0763
%C Berlin
%I Springer Open
%M FZJ-2018-01063
%P 5
%D 2017
%X Stimulated by the recent implementation of a three-port Hall-effect microwave circulator of Mahoney et al. (MEA), we present model studies of the performance of this device. Our calculations are based on the capacitive-coupling model of Viola and DiVincenzo (VD). Based on conductance data from a typical Hall-bar device obtained from a two-dimensional electron gas (2DEG) in a magnetic field, we numerically solve the coupled field-circuit equations to calculate the expected performance of the circulator, as determined by the $S$ parameters of the device when coupled to 50$\Omega$ ports, as a function of frequency and magnetic field. Above magnetic fields of 1.5T, for which a typical 2DEG enters the quantum Hall regime (corresponding to a Landau-level filling fraction $\nu$ of 20), the Hall angle $\theta_H=\tan^{-1}\sigma_{xy}/\sigma_{xx}$ always remains close to $90^\circ$, and the $S$ parameters are close to the analytic predictions of VD for $\theta_H=\pi/2$. As anticipated by VD, MEA find the device to have rather high (k$\Omega$) impedance, and thus to be extremely mismatched to $50\Omega$, requiring the use of impedance matching. We incorporate the lumped matching circuits of MEA in our modeling and confirm that they can produce excellent circulation, although confined to a very small bandwidth. We predict that this bandwidth is significantly improved by working at lower magnetic field when the Landau index is high, e.g. $\nu=20$, and the impedance mismatch is correspondingly less extreme. Our modeling also confirms the observation of MEA that parasitic port-to-port capacitance can produce very interesting countercirculation effects.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000407196900001
%R 10.1140/epjqt/s40507-017-0057-9
%U https://juser.fz-juelich.de/record/842890