2,144 research outputs found
Quantum oscillations in a topological insulator Bi_{1-x}Sb_{x}
We have studied transport and magnetic properties of Bi_{1-x}Sb_x, which is
believed to be a topological insulator - a new state of matter where an
insulating bulk supports an intrinsically metallic surface. In nominally
insulating Bi_{0.91}Sb_{0.09} crystals, we observed strong quantum oscillations
of the magnetization and the resistivity originating from a Fermi surface which
has a clear two-dimensional character. In addition, a three-dimensional Fermi
surface is found to coexist, which is possibly due to an unusual coupling of
the bulk to the surface. This finding demonstrates that quantum oscillations
can be a powerful tool to directly probe the novel electronic states in
topological insulators.Comment: 4 pages, 4 figure
Oscillatory angular dependence of the magnetoresistance in a topological insulator Bi_{1-x}Sb_{x}
The angular-dependent magnetoresistance and the Shubnikov-de Haas
oscillations are studied in a topological insulator Bi_{0.91}Sb_{0.09}, where
the two-dimensional (2D) surface states coexist with a three-dimensional (3D)
bulk Fermi surface (FS). Two distinct types of oscillatory phenomena are
discovered in the angular-dependence: The one observed at lower fields is shown
to originate from the surface state, which resides on the (2\bar{1}\bar{1})
plane, giving a new way to distinguish the 2D surface state from the 3D FS. The
other one, which becomes prominent at higher fields, probably comes from the
(111) plane and is obviously of unknown origin, pointing to new physics in
transport properties of topological insulators.Comment: 4 pages, 5 figures, revised version with improved data and analysi
Cardinal interpolation and spline fucntions V. The B-splines for cardinal Hermite interpolation
AbstractIn the third paper of this series on cardinal spline interpolation [4] Lipow and Schoenberg study the problem of Hermite interpolation S(v) = Yv, S′(v) = Yv′,…,S(r−1)(v) = Yv(r−1) for allv. The B-splines are there conspicuous by their absence, although they were found very useful for the case γ = 1 of ordinary (or Lagrange) interpolation (see [5–10]). The purpose of the present paper is to investigate the B-splines for the case of Hermite interpolation (γ > 1). In this sense the present paper is a supplement to [4] and is based on its results. This is done in Part I. Part II is devoted to the special case when we want to solve the problem S(v) = Yv, S′(v) = Yv′ for all v by quintic spline functions of the class C‴(– ∞, ∞). This is the simplest nontrivial example for the general theory. In Part II we derive an explicit solution for the problem (1), where v = 0, 1,…, n
Residual influence of macronutrient enrichment on the aquatic food web of an Okefenokee Swamp abandoned bird rookery
We present evidence for residual nutrient enrichment of diverse components of a blackwater marsh, by a biotic component of the ecosystem itself. Thousands of nesting white ibis (Eudocimus albus) that foraged over a 20-km radius fertilized a rookery with guano within Okefenokee Swamp. Georgia. USA. One to two yr after the birds abandoned it. this marsh showed continued enrichment effects. Elevated available phosphorus in sediments, as measured by equilibrium phosphate concentration, contributed to enhanced biomass of phytoplankton in the overlying water column. Planktivorous fish were greater in biomass than at reference sites. Experimental phosphorus and nitrogen fertilization of enclosures at a reference site (at levels representing residual enrichment after birds had left) caused zooplankton biomass to increase significantly. These results demonstrate that this blackwater ecosystem was macronutrient limited, and manifested residual enrichment effects of wading birds on sediments, and a positive effect of sediments on phytoplankton. Results also suggest further indirect positive effects of birds on higher trophic levels (zooplankton and fish), via macronutrient transfers
Jensen-Shannon divergence as a measure of distinguishability between mixed quantum states
We discuss an alternative to relative entropy as a measure of distance
between mixed quantum states. The proposed quantity is an extension to the
realm of quantum theory of the Jensen-Shannon divergence (JSD) between
probability distributions. The JSD has several interesting properties. It
arises in information theory and, unlike the Kullback-Leibler divergence, it is
symmetric, always well defined and bounded. We show that the quantum JSD (QJSD)
shares with the relative entropy most of the physically relevant properties, in
particular those required for a "good" quantum distinguishability measure. We
relate it to other known quantum distances and we suggest possible applications
in the field of the quantum information theory.Comment: 14 pages, corrected equation 1
Magnetic quantum oscillations in nanowires
Analytical expressions for the magnetization and the longitudinal
conductivity of nanowires are derived in a magnetic field, B. We show that the
interplay between size and magnetic field energy-level quantizations manifests
itself through novel magnetic quantum oscillations in metallic nanowires. There
are three characteristic frequencies of de Haas-van Alphen (dHvA) and
Shubnikov-de Haas (SdH) oscillations, F=F_0,F_1, and F_2 in contrast with a
single frequency F'_0 in simple bulk metals. The amplitude of oscillations is
strongly enhanced in some "magic" magnetic fields. The wire cross-section S can
be measured along with the Fermi surface cross-section, S_F
Combination quantum oscillations in canonical single-band Fermi liquids
Chemical potential oscillations mix individual-band frequencies of the de
Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) magneto-oscillations in
canonical low-dimensional multi-band Fermi liquids. We predict a similar mixing
in canonical single-band Fermi liquids, which Fermi-surfaces have two or more
extremal cross-sections. Combination harmonics are analysed using a single-band
almost two-dimensional energy spectrum. We outline some experimental conditions
allowing for resolution of combination harmonics
Wootters' distance revisited: a new distinguishability criterium
The notion of distinguishability between quantum states has shown to be
fundamental in the frame of quantum information theory. In this paper we
present a new distinguishability criterium by using a information theoretic
quantity: the Jensen-Shannon divergence (JSD). This quantity has several
interesting properties, both from a conceptual and a formal point of view.
Previous to define this distinguishability criterium, we review some of the
most frequently used distances defined over quantum mechanics' Hilbert space.
In this point our main claim is that the JSD can be taken as a unifying
distance between quantum states.Comment: 15 pages, 3 figures, changed content, added reference for last
sectio
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