67 research outputs found
Scanning tunneling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets
The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability
Naturfagslæreres vidensgrundlag
I artiklen præsenteres en model for naturfagslærernes vidensgrundlag. Modellen er udviklet med udgangspunkt i litteratur om PCK (Pedagogical Content Knowledge) samtidig med at den er søgt tilpasset danske forhold. Modellen tager udgangspunkt i at naturfagslærernes vidensgrundlag baserer sig på fire vidensdomæner, nemlig Almendidaktisk viden, Faglig viden, PCK og Kontekstviden, og at der i undervisningen foregår et samspil mellem disse. Artiklen giver et overblik over de elementer der indgår i naturfagslærernes vidensgrundlag og diskuterer forholdet mellem dette og lærerkompetence. Den etablerede model vil kunne anvendes i forbindelse med design og analyse af læreruddannelser og til at følge hvorledes kravene til lærernes viden forskyder sig, fx i forbindelse med uddannelsesreformer
Andreev Bound States at the Interface of Antiferromagnets and d-wave Superconductors
We set up a simple transfer matrix formalism to study the existence of bound
states at interfaces and in junctions between antiferromagnets and d-wave
superconductors. The well-studied zero energy mode at the {110} interface
between an insulator and a d-wave superconductor is spin split when the
insulator is an antiferromagnet. This has as a consequence that any competing
interface induced superconducting order parameter that breaks the time reversal
symmetry needs to exceed a critical value before a charge current is induced
along the interface.Comment: 4 pages, 3 figure
Kondo-enhanced Andreev tunneling in InAs nanowire quantum dots
We report measurements of the nonlinear conductance of InAs nanowire quantum
dots coupled to superconducting leads. We observe a clear alternation between
odd and even occupation of the dot, with sub-gap-peaks at
markedly stronger(weaker) than the quasiparticle tunneling peaks at
for odd(even) occupation. We attribute the enhanced
-peak to an interplay between Kondo-correlations and Andreev tunneling
in dots with an odd number of spins, and substantiate this interpretation by a
poor man's scaling analysis
Two nonmagnetic impurities in the DSC and DDW state of the cuprate superconductors as a probe for the pseudogap
The quantum interference between two nonmagnetic impurities is studied
numerically in both the d-wave superconducting (DSC) and the d-density wave
(DDW) state. In all calculations we include the tunnelling through excited
states from the CuO planes to the BiO layer probed by the STM tip. Compared
to the single impurity case, a systematic study of the modulations in the
two-impurity local density of states can distinguish between the DSC or DDW
states. This is important if the origin of the pseudogap phase is caused by
preformed pairs or DDW order. Furthermore, in the DSC state the study of the
LDOS around two nonmagnetic impurities provide further tests for the potential
scattering model versus more strongly correlated models.Comment: 6 pages, 6 figure
Checkerboard local density of states in striped domains pinned by vortices
Within a Green's function formalism we calculate the electronic structure
around static extended magnetic and non-magnetic perturbations in a d-wave
superconductor. In partucular, we discuss recent elastic neutron scattering and
scanning tunneling experiments on High-T_c cuprates exposed to an applied
magnetic field. A physical picture consisting of antiferromagnetic vortex cores
operating as pinning centers for surrounding stripes is qualitatively
consistent with the neutron data provided the stripes have the usual antiphase
modulation. The low energy electronic structure in such a region reveals a
checkerboard interference pattern consistent with recent scanning tunneling
experiments.Comment: 5 pages, 4 figure
SO(5) theory of insulating vortex cores in high- materials
We study the fermionic states of the antiferromagnetically ordered vortex
cores predicted to exist in the superconducting phase of the newly proposed
SO(5) model of strongly correlated electrons. Our model calculation gives a
natural explanation of the recent STM measurements on BSCCO, which in
surprising contrast to YBCO revealed completely insulating vortex cores.Comment: 4 pages, 1 figur
Quantum interference between multiple impurities in anisotropic superconductors
We study the quantum interference between impurities in d-wave
superconductors within a potential scattering formalism that easily applies to
multiple impurities. The evolution of the low-energy local density of states
for both magnetic and nonmagnetic short-ranged scatterers are studied as a
function of the spatial configuration of the impurities. Further we discuss the
influence of subdominant bulk superconducting order parameters on the
interference pattern from multiple impurities.Comment: 4 pages, 6 figure
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