26 research outputs found
Superconducting and Magnetic Properties of Nb/Pd_1-xFe_x/Nb Triple Layers
The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers
with constant Nb layer thickness d_Nb=200 A and different interlayer
thicknesses are investigated. The thickness dependence of the magnetization and
of the superconducting transition temperature shows that for small iron
concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state
for very thin films whereas ferromagnetic order is established for x>=0.13. The
parallel critical field B_c2II(T) exhibits a crossover from two-dimensional
(2D) behavior where the Nb films are coupled across the interlayer, towards a
2D behavior of coupled Nb films with increasing d_PdFe or x. This 2D-2D
crossover allows a determination of the penetration depth xi_F of Cooper pairs
into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic
interlayer xi_ is found to be independent of x.Comment: 9 pages, 8 figure
Anomalous Hall effect in the noncollinear antiferromagnet Mn5Si3
Metallic antiferromagnets with noncollinear orientation of magnetic moments
provide a playground for investigating spin-dependent transport properties by
analysis of the anomalous Hall effect. The intermetallic compound Mn5Si3 is an
intinerant antiferromagnet with collinear and noncollinear magnetic structures
due to Mn atoms on two inequivalent lattice sites. Here, magnetotransport
measurements on polycrystalline thin films and a single crystal are reported.
In all samples, an additional contribution to the anomalous Hall effect
attributed to the noncollinear arrangment of magnetic moments is observed.
Furthermore, an additional magnetic phase between the noncollinear and
collinear regimes above a metamagnetic transition is resolved in the single
crystal by the anomalous Hall effect.Comment: 7 pages, 4 figure
Conductance oscillations in mesoscopic rings: microscopic versus macroscopic picture
The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the
presence of a magnetic field can be modulated by application of a DC-bias
current I_DC. We address the question of how a variation of I_DC and hence of
the microscopic phases of the electronic wave functions results in the
macroscopic phase of the conductance oscillations. Whereas the first one can be
varied continuously the latter has to be quantized for a ring in two-wire
configuration by virtue of the Onsager symmetry relations. We observe a
correlation between a phase flip by +/- pi and the amplitude of the
oscillations.Comment: 4 pages, 4 figure
Time-resolved collapse and revival of the Kondo state near a quantum phase transition
One of the most successful paradigms of many-body physics is the concept of
quasiparticles: excitations in strongly interacting matter behaving like weakly
interacting particles in free space. Quasiparticles in metals are very robust
objects. Yet, when a system's ground state undergoes a qualitative change at a
quantum critical point (QCP), the quasiparticles may disintegrate and give way
to an exotic quantum-fluid state of matter. The nature of this breakdown is
intensely debated, because the emergent quantum fluid dominates the material
properties up to high temperature and might even be related to the occurence of
superconductivity in some compounds. Here we trace the dynamics of
heavy-fermion quasiparticles in CeCuAu and monitor their
evolution towards the QCP in time-resolved experiments, supported by many-body
calculations. A terahertz pulse disrupts the many-body heavy-fermion state.
Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion
state recovers, with a coherence time 100 times longer than typically
associated with correlated metals. The quasiparticle weight collapses towards
the QCP, yet its formation temperature remains constant -- phenomena believed
to be mutually exclusive. Coexistence in the same experiment calls for
revisions in our view on quantum criticality.Comment: Published version, including data on CeCu6, CeCu5.9Au0.1, and
CeCu5Au1 and extended Supplementary Information. 7 pages, 4 figures,
Supplementary Information: 5 pages, 3 figure
Tricritical behaviour of Ising spin glasses with charge fluctuations
We show that tricritical points displaying unusal behaviour exist in phase
diagrams of fermionic Ising spin glasses as the chemical potential or the
filling assumes characteristic values. Exact results for infinite range
interaction and a one loop renormalization group analysis of thermal
tricritical fluctuations for finite range models are presented. Surprising
similarities with zero temperature transitions and a new tricritical
point of metallic quantum spin glasses are derived.Comment: 4 pages, 1 Postscript figure, minor change