We study the ternary clathrate Pr3Pd20Si6 in specific heat and AC-susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic (AFM) and antiferroquadrupolar (AFQ) ordering on two sublattices of inequivalent Pr sites
. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the AFM ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. Pr3Pd20Si6 is therefore one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.
The electronic states in a corner-overgrown bent GaAs/AlGaAs quantum well heterostructure are studied with numerical Hartree simulations. Transmission electron microscope pictures of the junction justify the sharp-corner assumption. In a tilted magne
tic field both facets of the bent quantum well are brought to a quantum Hall (QH) state, and the corner hosts an unconventional hybrid system of two coupled counter-propagating quantum Hall edges and an additional one-dimensional accumulation wire. A subsystems model is introduced, whereby the total hybrid dispersion and wavefunctions are explained in terms of the constituent QH edge- and accumulation wire-subsystem dispersions and wavefunctions. At low magnetic fields, orthonormal basis wavefunctions of the hybrid system can be accurately estimated by projecting out the lowest bound state of the accumulation wire from the edge state wavefunctions. At high magnetic fields, the coupling between the three subsystems increases as a function of the applied magnetic field, in contrast to coplanar barrier-junctions of QH systems, leading to large anticrossing gaps between the subsystem dispersions. These results are discussed in terms of previously reported experimental data on bent quantum Hall systems.
Transport studies of a bent quantum Hall junction at integer filling factors show strongly insulating states at higher fields. In this paper we analyze the strongly insulating behavior as a function of temperature T and dc bias V, in order to classif
y the localization mechanisms responsible for the insulating state. The temperature dependence suggests a crossover from activated nearest-neighbor hopping at higher T to variable-range hopping conduction at lower T. The base temperature electric field dependence is consistent with 1D variable-range hopping conduction. We observe almost identical behavior at filling factors 1 and 2, and discuss how the bent quantum Hall junction conductance appears to be independent of the bulk spin state. Various models of 1D variable-range hopping which either include or ignore interactions are compared, all of which are consistent with the basic model of disorder coupled counter-propagating quantum Hall edges.
