19 research outputs found
- transitions in a Josephson junction of irradiated Weyl semimetal
We propose a setup for the experimental realization of unexpected and
anisotropic - transitions of the Josephson current, in a junction whose
link is made of irradiated Weyl semi-metal (WSM), due to the presence of chiral
nodes. We show using a Green's function technique that the Josephson current
through a time-reversal symmetric WSM has anisotropic periodic oscillations as
a function of , where is the (relevant) separation of the chiral
nodes and is the length of the sample. This is unexpected, for
time-reversal symmetric systems, although it has been shown earlier for
time-reversal symmetry breaking WSMs. We then show that the effective value of
can be tuned with precision by irradiating the sample with photons
resulting in - transitions of the critical current. Finally, we discuss
the robustness of our setup
Spin Mode-Switching at the Edge of a Quantum Hall System
Quantum Hall states can be characterized by their chiral edge modes. Upon
softening the edge potential, the edge has long been known to undergo
spontaneous reconstruction driven by charging effects. In this paper we
demonstrate a qualitatively distinct phenomenon driven by exchange effects, in
which the ordering of the edge modes at switches abruptly as the edge
potential is made softer, while the ordering in the bulk remains intact. We
demonstrate that this phenomenon is robust, and has many verifiable
experimental signatures in transport.Comment: 5 pages + supplemental materia
Chiral nodes and oscillations in the Josephson current in Weyl semimetals
The separation of the Weyl nodes in a broken time-reversal symmetric Weyl
semimetal leads to helical quasi-particle excitations at the Weyl nodes, which,
when coupled with overall spin conservation allows only inter-nodal transport
at the junction of the Weyl semimetal with a superconductor. This leads to an
unusual periodic oscillation in the Josephson current as a function of ,
where is the length of the Weyl semimetal and is the inter-nodal
distance. This oscillation is robust and should be experimentally measurable,
providing a direct path to confirming the existence of chiral nodes in the Weyl
semimetal.Comment: 4+1 Pages + Appendix, V2: Accepted version to be published on Phys.
Rev. B (Rapid Comm
Transport and STM studies of hyperbolic surface states of topological insulators
Motivated by the transmission of topological surface states through atomic
scale steps, we study the transport of gapless Dirac fermions on hyperbolic
surfaces. We confirm that, independent of the curvature of the hyperbolae and
the sharpness of the corners, no backward scattering takes place and
transmission of the topological surface states is completely independent of the
geometrical shape (within the hyperbolic model) of the surface. The density of
states of the electrons, however, shows a dip at concave step edges which can
be measured by an STM tip. We also show that the tunneling conductance measured
by a polarized scanning tunneling probe exhibits an unconventional dependence
on the polar and azimuthal angles of the magnetization of the tip as a function
of the curvature of the surface and the sharpness of the edge.Comment: 7 pages, 7 figure
Boost driven transition in the superconductivity proximitized edge of a quantum spin Hall insulator
We investigate the effects of introducing a boost (a Zeeman field parallel to
the spin quantization axis) at the proximitized helical edge of a
two-dimensional (2D) quantum spin Hall insulator. Our self-consistent analysis
finds that a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting phase may
emerge at the edge when the boost is larger than a critical value tied to the
induced pairing gap. A non-trivial consequence of retaining the 2D bulk in the
model is that this boundary FFLO state supports a finite magnetization as well
as finite current (flowing along the edge). This has implications for a proper
treatment of the ultra-violet cutoff in analyses employing the effective
one-dimensional (1D) helical edge model. Our results may be contrasted with
previous studies of such 1D models, which found that the FFLO phase either does
not appear for any value of the boost (in non-self-consistent calculations), or
that it self-consistently appears even for infinitesimal boost, but carries no
current and magnetization.Comment: 6 pages, 5 figure
Symmetry and correlation effects on band structure explain the anomalous transport properties of (111) LaAlO/SrTiO
The interface between the two insulating oxides SrTiO and LaAlO gives
rise to a two-dimensional electron system with intriguing transport phenomena,
including superconductivity, which are controllable by a gate. Previous
measurements on the (001) interface have shown that the superconducting
critical temperature, the Hall density, and the frequency of quantum
oscillations, vary nonmonotonically and in a correlated fashion with the gate
voltage. In this paper we experimentally demonstrate that the (111) interface
features a qualitatively distinct behavior, in which the frequency of
Shubnikov-de Haas oscillations changes monotonically, while the variation of
other properties is nonmonotonic albeit uncorrelated. We develop a theoretical
model, incorporating the different symmetries of these interfaces as well as
electronic-correlation-induced band competition. We show that the latter
dominates at (001), leading to similar nonmonotonicity in all observables,
while the former is more important at (111), giving rise to highly curved Fermi
contours, and accounting for all its anomalous transport measurements.Comment: 6+7 pages, 4+6 figures, Published Versio
A complete 3D numerical study of the effects of pseudoscalar-photon mixing on quasar polarizations
We present the results of three-dimensional simulations of quasar
polarizations in the presence of pseudoscalar-photon mixing in the
intergalactic medium. The intergalactic magnetic field is assumed to be
uncorrelated in wave vector space but correlated in real space. Such a field
may be obtained if its origin is primordial. Furthermore we assume that the
quasars, located at cosmological distances, have negligible initial
polarization. In the presence of pseudoscalar-photon mixing we show, through a
direct comparison with observations, that this may explain the observed large
scale alignments in quasar polarizations within the framework of big bang
cosmology. We find that the simulation results give a reasonably good fit to
the observed data.Comment: 15 pages, 8 figures, significant changes, to appear in EPJ