1,139 research outputs found
Atomic Diffusion in the Surface State of Mott Insulator NiS2
We present resistivity measurements of Mott insulator NiS2 single crystals
after heat treatment. We find a strong increase of the low temperature
resistivity that relaxes back towards the pristine behaviour over several days
with a time constant of 45 h at room temperature. The low temperature
resistivity has previously been shown to be dominated by surface conduction (T.
Thio and J. Bennett, PRB 50 10574 1994). Consequently, the changes induced by
heat treatment are attributed to changes to surface states. Our results suggest
the creation of vacancies in the surface that re refilled from the bulk via
atomic diffusion. We estimate a diffusion constant of
m/s at room temperature. We identify sulphur vacancies as the most likely
to form via oxidisation of sulphur forming volatile SO2 during heat treatment.
Our results point towards these sulphur vacancies to be the source of surface
state localisation in NiS2.Comment: 6 pages, 6 figures. Journal of Magnetism and Magnetic Materials
(2015
Quantum criticality in Yb(Rh0.97Co0.03)2Si2 probed by low-temperature resistivity
Quantum criticality in Yb(Rh0.97Co0.03)2Si2 is investigated by means of
resistivity and magnetoresistance. The partial substitution of Co leads to a
stabilization of the magnetism as expected according to the application of
chemical pressure for Yb systems. However, the signature of the Kondo-breakdown
remains at the same position in the temperature-magnetic field phase diagram
compared to stoichiometric YbRh2Si2. As a consequence, the Kondo-breakdown is
situated within the antiferromagnetic phase. These results fit well within the
global phase diagram under chemical pressure [1].Comment: 4 pages, 4 figures, submitted to ICM/SCES200
Break up of heavy fermions at an antiferromagnetic instability
We present results of high-resolution, low-temperature measurements of the
Hall coefficient, thermopower, and specific heat on stoichiometric YbRh2Si2.
They support earlier conclusions of an electronic (Kondo-breakdown) quantum
critical point concurring with a field induced antiferromagnetic one. We also
discuss the detachment of the two instabilities under chemical pressure. Volume
compression/expansion (via substituting Rh by Co/Ir) results in a
stabilization/weakening of magnetic order. Moderate Ir substitution leads to a
non-Fermi-liquid phase, in which the magnetic moments are neither ordered nor
screened by the Kondo effect. The so-derived zero-temperature global phase
diagram promises future studies to explore the nature of the Kondo breakdown
quantum critical point without any interfering magnetism.Comment: minor changes, accepted for publication in JPS
Anisotropic Zeeman Splitting in YbNi4P2
The electronic structure of heavy-fermion materials is highly renormalised at
low temperatures with localised moments contributing to the electronic
excitation spectrum via the Kondo effect. Thus, heavy-fermion materials are
very susceptible to Lifshitz transitions due to the small effective Fermi
energy arising on parts of the renormalised Fermi surface. Here, we study
Lifshitz transitions that have been discovered in YbNi4P2 in high magnetic
fields. We measure the angular dependence of the critical fields necessary to
induce a number of Lifshitz transitions and find it to follow a simple
Zeeman-shift model with anisotropic g-factor. This highlights the coherent
nature of the heavy quasiparticles forming a renormalised Fermi surface. We
extract information on the orientation of the Fermi surface parts giving rise
to the Lifshitz transitions and we determine the anisotropy of the effective
g-factor to be in good agreement with the crystal field
scheme of YbNi4P2.Comment: 10 pages, 5 figures, prepared for resubmission to SciPos
Incoherent multi-gap optical solitons in nonlinear photonic lattices
We demonstrate numerically that partially incoherent light can be trapped in
the spectral band gaps of a photonic lattice, creating partially incoherent
multi-component spatial optical solitons in a self-defocusing nonlinear
periodic medium. We find numerically such incoherent multi-gap optical solitons
and discuss how to generate them in experiment by interfering incoherent light
beams at the input of a nonlinear periodic medium.Comment: 9 pages, 5 figure
Hall effect in heavy-fermion metals
The heavy fermion systems present a unique platform in which strong
electronic correlations give rise to a host of novel, and often competing,
electronic and magnetic ground states. Amongst a number of potential
experimental tools at our disposal, measurements of the Hall effect have
emerged as a particularly important one in discerning the nature and evolution
of the Fermi surfaces of these enigmatic metals. In this article, we present a
comprehensive review of Hall effect measurements in the heavy-fermion
materials, and examine the success it has had in contributing to our current
understanding of strongly correlated matter. Particular emphasis is placed on
its utility in the investigation of quantum critical phenomena which are
thought to drive many of the exotic electronic ground states in these systems.
This is achieved by the description of measurements of the Hall effect across
the putative zero-temperature instability in the archetypal heavy-fermion metal
YbRhSi. Using the CeIn (with Co, Ir) family of systems as
a paradigm, the influence of (antiferro-)magnetic fluctuations on the Hall
effect is also illustrated. This is compared to prior Hall effect measurements
in the cuprates and other strongly correlated systems to emphasize on the
generality of the unusual magnetotransport in materials with non-Fermi liquid
behavior.Comment: manuscript accepted in Adv. Phy
El carnaval rural en el río Magdalena
El carnaval, tradición de origen occidental que evoca antiguos ritos de propiciación a dioses griegos y romanos anteriores al cristianismo, llegó al nuevo mundo con los europeos. Su asentamiento, su significado social y simbólico y las transformaciones que ha experimentado en las diversas comunidades rurales y urbanas de América Latina se han convertido en temas de estudios sociopolíticos, antropológicos y estéticos
Electrical resistivity ofYb(Rh1-xCox)2Si2 single crystals at low temperatures
We report low-temperature measurements of the electrical resistivity of
Yb(Rh1-xCox)2Si2 single crystals with 0 <= x <= 0.12. The isoelectronic
substitution of Co on the Rh site leads to a decrease of the unit cell volume
which stabilizes the antiferromagnetism. Consequently, the antiferromagnetic
transition temperature increases upon Co substitution. For x = 0.07 Co content
a subsequent low-temperature transition is observed in agreement with
susceptibility measurements and results on YbRh2Si2 under hydrostatic pressure.
Above the Neel transition the resistivity follows a non-Fermi liquid behavior
similar to that of YbRh2Si2.Comment: 4 pages, submitted to SCES0
Lifshitz transitions and quasiparticle de-renormalization in YbRhSi
We study the effect of magnetic fields up to 15 T on the heavy fermion state
of YbRhSi via Hall effect and magnetoresistance measurements down to 50
mK. Our data show anomalies at three different characteristic fields. We
compare our data to renormalized band structure calculations through which we
identify Lifshitz transitions associated with the heavy fermion bands. The Hall
measurements indicate that the de-renormalization of the quasiparticles, {\it
i.e} the destruction of the local Kondo singlets, occurs smoothly while the
Lifshitz transitions occur within rather confined regions of the magnetic
field.Comment: 7 pages, 5 figure
Comment on "Zeeman-Driven Lifshitz Transition: A Model for the Experimentally Observed Fermi-Surface Reconstruction in YbRh2Si2"
In Phys. Rev. Lett. 106, 137002 (2011), A. Hackl and M. Vojta have proposed
to explain the quantum critical behavior of YbRh2Si2 in terms of a
Zeeman-induced Lifshitz transition of an electronic band whose width is about 6
orders of magnitude smaller than that of conventional metals. Here, we note
that the ultra-narrowness of the proposed band, as well as the proposed
scenario per se, lead to properties which are qualitatively inconsistent with
the salient features observed in YbRh2Si2 near its quantum critical point.Comment: 3 page
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