9 research outputs found
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
Fermionic random transverse-field Ising spin chain
The interplay of spin and charge fluctuations in the random transverse-field
Ising spin chain on the fermionic space is investigated. The finite chemical
potential, which controls the charge fluctuations, leads to the appearance of
the quantum critical region in the phase diagram where the magnetic
correlations are quenched by nonmagnetic sites. Regions of nonmonotonous
temperature dependence of spin-spin correlation length appear at nonzero .
The results on the one-fermion density of states of the model are discussed.Comment: 10 pages, 2 figures included, citation correcte
conInvestigation of Sr2RuO4-Pt tacts in an applied magnetic field
We investigated the spin-triplet superconductor Sr 2 RuO 4 by means of conductance measurements of normal conductor/ superconductor point contacts. We present results that show a linear dependence of the excess current as a function of temperature and applied magnetic fields over a wide range of the phase diagram. Applying a magnetic field larger than the upper critical field B c2 suppresses completely the features related to superconductivity and a conductance minimum at V = 0 occurs which becomes more pronounced with increasing field and persists even above T c up to several K. \ua9 2003 Elsevier B.V. All rights reserved
conInvestigation of Sr2RuO4-Pt tacts in an applied magnetic field
We investigated the spin-triplet superconductor Sr 2 RuO 4 by means of conductance measurements of normal conductor/ superconductor point contacts. We present results that show a linear dependence of the excess current as a function of temperature and applied magnetic fields over a wide range of the phase diagram. Applying a magnetic field larger than the upper critical field B c2 suppresses completely the features related to superconductivity and a conductance minimum at V = 0 occurs which becomes more pronounced with increasing field and persists even above T c up to several K. \ua9 2003 Elsevier B.V. All rights reserved
Physikalisch-technische Eigenschaften oxidischer Supraleiter und ihre potentiellen Anwendungen in der Mikroelektronik Schlussbericht
With 121 refs., 6 tabs., 85 figs.SIGLEAvailable from TIB Hannover: F93B455+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman