7,809 research outputs found
A mechanism for unipolar resistance switching in oxide non-volatile memory devices
Building on a recently introduced model for non-volatile resistive switching,
we propose a mechanism for unipolar resistance switching in
metal-insulator-metal sandwich structures. The commutation from the high to low
resistance state and back can be achieved with successive voltage sweeps of the
same polarity. Electronic correlation effects at the metal-insulator interface
are found to play a key role to produce a resistive commutation effect in
qualitative agreement with recent experimental reports on binary transition
metal oxide based sandwich structures.Comment: 4 pages, 2 figure
Critical Current of the Spin-Triplet Superconducting Phase in SrRuO
There have been two different proposals for the spin-triplet order parameter
of the superconducting phase in SrRuO; an -wave order parameter and
the multigap model where some of the bands have the line node. In an effort to
propose an experiment that can distinguish two cases, we study the behavior of
the supercurrent and compute the critical current for these order parameters
when the sample is a thin film with the thickness where is
the coherence length. It is found that the supercurrent behaves very
differently in two models. This will serve as a sharp test for the
identification of the correct order parameter.Comment: 4 pages, 1 figur
Preservice teachers’ pictorial strategies for a multistep multiplicative fraction problem
Previous research has documented that preservice teachers (PSTs) struggle with under- standing fraction concepts and operations, and misconceptions often stem from their understanding of the referent whole. This study expands research on PSTs’ understanding of wholes by investigating pictorial strategies that 85 PSTs constructed for a multistep fraction task in a multiplicative context. The results show that many PSTs were able to construct valid pictorial strategies, and the strategies were widely diverse with respect to how they made sense of an unknown referent whole of a fraction in multiple steps, how they represented the wholes in their drawings, in which order they did multiple steps, and which type of model they used (area or set). Based on their wide range of pictorial strategies, we discuss potential benefits of PSTs’ construction of their own representations for a word problem in developing problem solving skills
Molecular transistor coupled to phonons and Luttinger-liquid leads
We study the effects of electron-phonon interactions on the transport
properties of a molecular quantum dot coupled to two Luttinger-liquid leads. In
particular, we investigate the effects on the steady state current and DC noise
characteristics. We consider both equilibrated and unequilibrated on-dot
phonons. The density matrix formalism is applied in the high temperature
approximation and the resulting semi-classical rate equation is numerically
solved for various strengths of electron-electron interactions in the leads and
electron-phonon coupling. The current and the noise are in general smeared out
and suppressed due to intralead electron interaction. On the other hand, the
Fano factor, which measures the noise normalized by the current, is more
enhanced as the intralead interaction becomes stronger. As the electron-phonon
coupling becomes greater than order one, the Fano factor exhibits
super-Poissonian behaviour.Comment: 11 pages, 11 figure
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Unconventional charge order in a co-doped high-Tc superconductor
Charge-stripe order has recently been established as an important aspect of cuprate high-Tc
superconductors. However, owing to the complex interplay between competing phases and
the influence of disorder, it is unclear how it emerges from the parent high-temperature state.
Here we report on the discovery of an unconventional ordered phase between charge-stripe
order and (pseudogapped) metal in the cuprate La1.8xEu0.2SrxCuO4. We use three
complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and
specific heat—to demonstrate that the order appears through a sharp phase transition and
exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is
a state, which preserves translational symmetry: a charge nematic. We thus resolve the
process of charge-stripe development in cuprates, show that this nematic phase is distinct
from high-temperature pseudogap and establish a link with other strongly correlated
electronic materials with prominent nematic order
|V_ub| and |V_cb|, Charm Counting and Lifetime Differences in Inclusive Bottom Hadron Decays
Inclusive bottom hadron decays are analyzed based on the heavy quark
effective field theory (HQEFT). Special attentions in this paper are paid to
the b\to u transitions and nonspectator effects. As a consequence, the CKM
quark mixing matrix elements |V_ub| and |V_cb| are reliably extracted from the
inclusive semileptonic decays B\to X_u e \nu and B\to X_c e \nu. Various
observables, such as the semileptonic branch ratio B_SL, the lifetime
differences among B^-, B^0, B_s and \Lambda_b hadrons, the charm counting n_c,
are predicted and found to be consistent with the present experimental data.Comment: 20 pages, Revtex, 4 figures and 2 table
Uncovering the Hidden Order in URu2Si2 by Impurity Doping
We report the use of impurities to probe the hidden order parameter of the
strongly correlated metal URu_2Si_2 below the transition temperature T_0 ~ 17.5
K. The nature of this order parameter has eluded researchers for more than two
decades, but is accompanied by the development of a partial gap in the single
particle density of states that can be detected through measurements of the
electronic specific heat and nuclear spin-lattice relaxation rate. We find that
impurities in the hidden order phase give rise to local patches of
antiferromagnetism. An analysis of the coupling between the antiferromagnetism
and the hidden order reveals that the former is not a competing order parameter
but rather a parasitic effect of the latter.Comment: 4 pages, 4 figure
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