59 research outputs found
Low temperature magnetic structure of CeRhIn by neutron diffraction on absorption-optimized samples
Two aspects of the ambient pressure magnetic structure of heavy fermion
material CeRhIn have remained under some debate since its discovery:
whether the structure is indeed an incommensurate helix or a spin density wave,
and what is the precise magnitude of the ordered magnetic moment. By using a
single crystal sample optimized for hot neutrons to minimize neutron absorption
by Rh and In, here we report an ordered moment of . In
addition, by using spherical neutron polarimetry measurements on a similar
single crystal sample, we have confirmed the helical nature of the magnetic
structure, and identified a single chiral domain
Band-dependent normal-state coherence in SrRuO: Evidence from Nernst effect and thermopower measurements
We present the first measurement on Nernst effect in the normal state of
odd-parity, spin-triplet superconductor SrRuO. Below 100 K, the
Nernst signal was found to be negative, large, and, as a function of magnetic
field, nonlinear. Its magnitude increases with the decreasing temperature until
reaching a maximum around 20 - 25 K, below which it starts to
decrease linearly as a function of temperature. The large value of the Nernst
signal appears to be related to the multiband nature of the normal state and
the nonlinearity to band-dependent magnetic fluctuation in SrRuO.
We argue that the sharp decrease in Nernst signal below is due to the
suppression of quasiparticle scattering and the emergence of band-dependent
coherence in the normal state. The observation of a sharp kink in the
temperature dependent thermopower around and a sharp drop of Hall angle
at low temperatures provide additional support to this picture.Comment: 4 pages, 4 figures; added figures, revised content; accepted by PR
Tunable Emergent Heterostructures in a Prototypical Correlated Metal
At the interface between two distinct materials desirable properties, such as
superconductivity, can be greatly enhanced, or entirely new functionalities may
emerge. Similar to in artificially engineered heterostructures, clean
functional interfaces alternatively exist in electronically textured bulk
materials. Electronic textures emerge spontaneously due to competing
atomic-scale interactions, the control of which, would enable a top-down
approach for designing tunable intrinsic heterostructures. This is particularly
attractive for correlated electron materials, where spontaneous
heterostructures strongly affect the interplay between charge and spin degrees
of freedom. Here we report high-resolution neutron spectroscopy on the
prototypical strongly-correlated metal CeRhIn5, revealing competition between
magnetic frustration and easy-axis anisotropy -- a well-established mechanism
for generating spontaneous superstructures. Because the observed easy-axis
anisotropy is field-induced and anomalously large, it can be controlled
efficiently with small magnetic fields. The resulting field-controlled magnetic
superstructure is closely tied to the formation of superconducting and
electronic nematic textures in CeRhIn5, suggesting that in-situ tunable
heterostructures can be realized in correlated electron materials
A microscopic Kondo lattice model for the heavy fermion antiferromagnet CeIn
Electrons at the border of localization generate exotic states of matter
across all classes of strongly correlated electron materials and many other
quantum materials with emergent functionality. Heavy electron metals are a
model example, in which magnetic interactions arise from the opposing limits of
localized and itinerant electrons. This remarkable duality is intimately
related to the emergence of a plethora of novel quantum matter states such as
unconventional superconductivity, electronic-nematic states, hidden order and
most recently topological states of matter such as topological Kondo insulators
and Kondo semimetals and putative chiral superconductors. The outstanding
challenge is that the archetypal Kondo lattice model that captures the
underlying electronic dichotomy is notoriously difficult to solve for real
materials. Here we show, using the prototypical strongly-correlated
antiferromagnet CeIn, that a multi-orbital periodic Anderson model embedded
with input from ab initio bandstructure calculations can be reduced to a simple
Kondo-Heisenberg model, which captures the magnetic interactions
quantitatively. We validate this tractable Hamiltonian via high-resolution
neutron spectroscopy that reproduces accurately the magnetic soft modes in
CeIn, which are believed to mediate unconventional superconductivity. Our
study paves the way for a quantitative understanding of metallic quantum states
such as unconventional superconductivity
A microscopic Kondo lattice model for the heavy fermion antiferromagnet CeIn
Electrons at the border of localization generate exotic states of matter across all classes of strongly correlated electron materials and many other quantum materials with emergent functionality. Heavy electron metals are a model example, in which magnetic interactions arise from the opposing limits of localized and itinerant electrons. This remarkable duality is intimately related to the emergence of a plethora of novel quantum matter states such as unconventional superconductivity, electronic-nematic states, hidden order and most recently topological states of matter such as topological Kondo insulators and Kondo semimetals and putative chiral superconductors. The outstanding challenge is that the archetypal Kondo lattice model that captures the underlying electronic dichotomy is notoriously difficult to solve for real materials. Here we show, using the prototypical strongly-correlated antiferromagnet CeIn, that a multi-orbital periodic Anderson model embedded with input from ab initio bandstructure calculations can be reduced to a simple Kondo-Heisenberg model, which captures the magnetic interactions quantitatively. We validate this tractable Hamiltonian via high-resolution neutron spectroscopy that reproduces accurately the magnetic soft modes in CeIn, which are believed to mediate unconventional superconductivity. Our study paves the way for a quantitative understanding of metallic quantum states such as unconventional superconductivity
Does Presentation Format Influence Visual Size Discrimination in Tufted Capuchin Monkeys (Sapajus spp.)?
Most experimental paradigms to study visual cognition in humans and non-human species are based on discrimination tasks involving the choice between two or more visual stimuli. To this end, different types of stimuli and procedures for stimuli presentation are used, which highlights the necessity to compare data obtained with different methods. The present study assessed whether, and to what extent, capuchin monkeys\u27 ability to solve a size discrimination problem is influenced by the type of procedure used to present the problem. Capuchins\u27 ability to generalise knowledge across different tasks was also evaluated. We trained eight adult tufted capuchin monkeys to select the larger of two stimuli of the same shape and different sizes by using pairs of food items (Experiment 1), computer images (Experiment 1) and objects (Experiment 2). Our results indicated that monkeys achieved the learning criterion faster with food stimuli compared to both images and objects. They also required consistently fewer trials with objects than with images. Moreover, female capuchins had higher levels of acquisition accuracy with food stimuli than with images. Finally, capuchins did not immediately transfer the solution of the problem acquired in one task condition to the other conditions. Overall, these findings suggest that - even in relatively simple visual discrimination problems where a single perceptual dimension (i.e., size) has to be judged - learning speed strongly depends on the mode of presentation
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