511 research outputs found
Skill-Related Uncertainty and Expected Value in 5-to 7-Year-Olds
Studies using an Information Integration approach have shown that children from four years have a good intuitive understanding of probability and expected value. Experience of skill-related uncertainty may provide one naturalistic opportunity to develop this intuitive understanding. To test the viability of this view, 16 5- and 16 7-year-olds played a marble rolling game in which size of the target and distance from it varied factorially. Task difficulty judgements (prior to practical experience with the game) reflected both objective task structure and subsequent performance for both age groups. Children then judged how happy they would be playing games of variable difficulty for different prizes. These judgements had the multiplicative structure predicted by the normative expected value model, again for both age groups. Thus children can use task difficulties as estimates of personal success probability in skill-related tasks. Our findings therefore extend previous work on early probability understanding from games of chance to games of skill
An STM perspective on hexaborides: Surface states of the Kondo insulator SmB
Compounds within the hexaboride class of materials exhibit a wide variety of
interesting physical phenomena, including polaron formation and quadrupolar
order. In particular, SmB has recently drawn attention as it is considered
a prototypical topological Kondo insulator. Evidence in favor of this concept,
however, has proven experimentally difficult and controversial, partly because
of the required temperatures and energy resolution. Here, a powerful tool is
Scanning Tunneling Microscopy (STM) with its unique ability to give local,
microscopic information that directly relates to the one-particle Green's
function. Yet, STM on hexaborides is met with its own set of challenges. This
article attempts to review the progress in STM investigations on hexaborides,
with emphasis on SmB and its intriguing properties.Comment: unrevised version, published version is open acces
Re-entrant magnetic field induced charge and spin gaps in the coupled dual-chain quasi-one dimensional organic conductor Perylene[Pt(mnt)]
An inductive method is used to follow the magnetic field-dependent
susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP)
ordered state behavior in the dual chain organic conductor
Perylene[Pt(mnt)]. In addition to the coexisting SP-CDW state phase
below 8 K and 20 T, the measurements show that a second spin-gapped phase
appears above 20 T that coincides with a field-induced insulating phase. The
results support a strong coupling of the CDW and SP order parameters even in
high magnetic fields, and provide new insight into the nature of the magnetic
susceptibility of dual-chain spin and charge systems.Comment: 6 pages, 6 figure
Analytical results for the Coqblin-Schrieffer model with generalized magnetic fields
Using the approach alternative to the traditional Thermodynamic Bethe Ansatz,
we derive analytical expressions for the free energy of Coqblin-Schrieffer
model with arbitrary magnetic and crystal fields. In Appendix we discuss two
concrete examples including the field generated crossover from the SU(4) to the
SU(2) symmetry in the SU(4)-symmetric model.Comment: 5 page
From Jeff=1/2 insulator to p-wave superconductor in single-crystal Sr2Ir1-xRuxO4 (0 < x< 1)
Sr2IrO4 is a magnetic insulator assisted by strong spin-orbit coupling (SOC)
whereas the Sr2RuO4 is a p-wave superconductor. The contrasting ground states
have been shown to result from the critical role of the strong SOC in the
iridate. Our investigation of structural, transport, and magnetic properties
reveals that substituting 4d Ru4+ (4d4) ions for 5d Ir4+(5d5) ions in Sr2IrO4
directly adds holes to the t2g bands, reduces the SOC and thus rebalances the
competing energies in single-crystal Sr2Ir1-xRuxO4. A profound effect of Ru
doping driving a rich phase diagram is a structural phase transition from a
distorted I41/acd to a more ideal I4/mmm tetragonal structure near x=0.50 that
accompanies a phase transition from an antiferromagnetic-insulating state to a
paramagnetic-metal state. We also make a comparison drawn with Rh doped
Sr2IrO4, highlighting important similarities and differences.Comment: 18 pages,7 figure
Magneto-electric effect in NdCrTiO5
We have measured the dielectric constant and the pyroelectric current of
orthorhombic (space group ) NdCrTiO polycrystalline samples. The
dielectric constant and the pyroelectric current show features associated with
ferroelectric transitions at the antiferromagnetic transition temperature
( = 21 K). The effect of magnetic fields is to enhance the
features almost linearly up to the maximum measured field (7 T) with a
spontaneous polarization value of C/m. Two possible
scenarios, the linear magnetoelectric effect and multiferroicity
(antiferromagnetism + ferroelectricity), are discussed as possible explanations
for the observations.Comment: 7 pages, 6 figure
Zero-temperature Phase Diagram For Strongly-Correlated Nanochains
Recently there has been a resurgence of intense experimental and theoretical
interest on the Kondo physics of nanoscopic and mesoscopic systems due to the
possibility of making experiments in extremely small samples. We have carried
out exact diagonalization calculations to study the effect of the energy
spacing of the conduction band on the ground-state properties of a
dense Anderson model nanochain. The calculations reveal for the first time that
the energy spacing tunes the interplay between the Kondo and RKKY interactions,
giving rise to a zero-temperature versus hybridization phase diagram
with regions of prevailing Kondo or RKKY correlations, separated by a {\it free
spins} regime. This interplay may be relevant to experimental realizations of
small rings or quantum dots with tunable magnetic properties.Comment: 8 pages, 3 figures. J. Appl. Phys. (in press
Debye relaxation in high magnetic fields
Dielectric relaxation is universal in characterizing polar liquids and
solids, insulators, and semiconductors, and the theoretical models are well
developed. However, in high magnetic fields, previously unknown aspects of
dielectric relaxation can be revealed and exploited. Here, we report low
temperature dielectric relaxation measurements in lightly doped silicon in high
dc magnetic fields B both parallel and perpendicular to the applied ac electric
field E. For B//E, we observe a temperature and magnetic field dependent
dielectric dispersion e(w)characteristic of conventional Debye relaxation where
the free carrier concentration is dependent on thermal dopant ionization,
magnetic freeze-out, and/or magnetic localization effects. However, for BperpE,
anomalous dispersion emerges in e(w) with increasing magnetic field. It is
shown that the Debye formalism can be simply extended by adding the Lorentz
force to describe the general response of a dielectric in crossed magnetic and
electric fields. Moreover, we predict and observe a new transverse dielectric
response EH perp B perp E not previously described in magneto-dielectric
measurements. The new formalism allows the determination of the mobility and
the ability to discriminate between magnetic localization/freeze out and
Lorentz force effects in the magneto-dielectric response.Comment: 19 pages, 6 figure
Non-Fermi-liquid behavior in nearly ferromagnetic metallic SrIrO3 single crystals
We report transport and thermodynamic properties of single-crystal SrIrO3 as
a function of temperature T and applied magnetic field H. We find that SrIrO3
is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized
by the following properties: (1) small ordered moment but no evidence for
long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility
that diverges as T or T1/2 at low temperatures, depending on the applied field;
(3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied
fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence
of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based
on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound
that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0
and H = 0.23 T)
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