2 research outputs found
Evidence for massive bulk Dirac Fermions in PbSnSe from Nernst and thermopower experiments
The lead chalcogenides (Pb,Sn)Te and (Pb,Sn)Se are the first examples of
topological crystalline insulators (TCI) predicted \cite{Fu,Hsieh} (and
confirmed \cite{Hasan,Story,Takahashi}) to display topological surface Dirac
states (SDS) that are protected by mirror symmetry. A starting premise
\cite{Hsieh} is that the SDS arise from bulk states describable as massive
Dirac states \cite{Wallis,Svane}, but this assumption is untested. Here we show
that the thermoelectric response of the bulk states display features specific
to the Dirac spectrum. We show that, in the quantum limit, the lowest Landau
Level (LL) is singly spin-degenerate, whereas higher levels are doubly
degenerate. The abrupt change in spin degeneracy leads to a large step-decrease
in the thermopower . In the lowest LL, displays a striking
linear increase vs. magnetic field. In addition, the Nernst signal undergoes an
anomalous sign change when the bulk gap inverts at 180 K.Comment: 16 pages, 8 figure
Effect of strain on stripe phases in the Quantum Hall regime
Spontaneous breaking of rotational symmetry and preferential orientation of
stripe phases in the quantum Hall regime has attracted considerable
experimental and theoretical effort over the last decade. We demonstrate
experimentally and theoretically that the direction of high and low resistance
of the two-dimensional (2D) hole gas in the quantum Hall regime can be
controlled by an external strain. Depending on the sign of the in-plane shear
strain, the Hartree-Fock energy of holes or electrons is minimized when the
charge density wave (CDW) is oriented along [110] or [1-10] directions. We
suggest that shear strains due to internal electric fields in the growth
direction are responsible for the observed orientation of CDW in pristine
electron and hole samples.Comment: 10 pages, 3 figure