262 research outputs found
Luttinger theorem for the strongly correlated Fermi liquid of composite fermions
While an ordinary Fermi sea is perturbatively robust to interactions, the
paradigmatic composite-fermion (CF) Fermi sea arises as a non-perturbative
consequence of emergent gauge fields in a system where there was no Fermi sea
to begin with. A mean-field picture suggests two Fermi seas, of composite
fermions made from electrons or holes in the lowest Landau level, which occupy
different areas away from half filling and thus appear to represent distinct
states. We show that in the microscopic theory of composite fermions, which
satisfies particle-hole symmetry in the lowest Landau level to an excellent
degree, the Fermi wave vectors at filling factors and are the
same, and are generally consistent with the experimental findings of Kamburov
{\em et al.} [Phys. Rev. Lett. {\bf 113}, 196801 (2014)]. Our calculations
suggest that the area of the CF Fermi sea may slightly violate the Luttinger
area rule.Comment: 21 pages, 17 figures including supplemental material, published
versio
Current-induced gap opening in interacting topological insulator surfaces
Two-dimensional topological insulators (TIs) host gapless helical edge states
that are predicted to support a quantized two-terminal conductance.
Quantization is protected by time-reversal symmetry, which forbids elastic
backscattering. Paradoxically, the current-carrying state itself breaks the
time-reversal symmetry that protects it. Here we show that the combination of
electron-electron interactions and momentum-dependent spin polarization in
helical edge states gives rise to feedback through which an applied current
opens a gap in the edge state dispersion, thereby breaking the protection
against elastic backscattering. Current-induced gap opening is manifested via a
nonlinear contribution to the system's characteristic, which persists
down to zero temperature. We discuss prospects for realizations in recently
discovered large bulk band gap TIs, and an analogous current-induced gap
opening mechanism for the surface states of three-dimensional TIs.Comment: 6 pages, 2 figures, published versio
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