20,563 research outputs found
Polar codes and polar lattices for the Heegard-Berger problem
Explicit coding schemes are proposed to achieve the rate-distortion function of the Heegard-Berger problem using polar codes. Specifically, a nested polar code construction is employed to achieve the rate-distortion function for doublysymmetric binary sources when the side information may be absent. The nested structure contains two optimal polar codes for lossy source coding and channel coding, respectively. Moreover, a similar nested polar lattice construction is employed when the source and the side information are jointly Gaussian. The proposed polar lattice is constructed by nesting a quantization polar lattice and a capacity-achieving polar lattice for the additive white Gaussian noise channel
Effect of Ga doping on charge transport mechanism of La0.85Zr0.15Mn1−xGaxO3
[[abstract]]Structural properties, temperature-dependent resistivity ρ(T) and thermoelectric power S(T) of La0.85Zr0.15Mn1−xGaxO3 (LZMGO) manganites with 0.0 ≤ x ≤ 0.06 have been extensively investigated. It is found that the Mn–O–Mn bond angle decreases and the Mn–O bond length increases with increasing Ga content, indicative of a significant distortion of MnO6 octahedra in LZMGO. The local lattice distortion and suppression of double exchange ferromagnetism induced by the Ga doping shift both Curie temperature (TC) and metal-insulator transition temperature (TMI) toward lower temperatures. Followed by the metal-insulator transition, ρ(T) exhibits an insulatinglike behavior accompanied by a relatively small value of S(T) below T∗ at low temperatures. An anomalous peak observed in S(T) is attributed to an enhancement of electron-magnon interaction caused by the Ga doping and a decrease in magnetic entropy near TMI. Three different charge transport mechanisms were identified in three temperature regions based on detailed analyses of ρ(T) and S(T) data. The small-polaron hopping mechanism governs the charge transport in the high-temperature paramagnetic region (T>TMI). The polaron binding energy determined from the ρ(T) and S(T) data increases with increasing Ga content, suggesting that polaron in La0.85Zr0.15MnO3 has a magnetic nature. In addition, the electron-magnon scattering dominates the charge transport in the intermediate-temperature metallic region (T∗<T<TMI), whereas the transport behavior in the low-temperature insulating region (T<T∗) can be described by the three-dimensional variable-range-hopping model.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙
Effect of Cr deficiency on physical properties of triangular-lattice antiferromagnets CuCr1−xO2 (0 ≦ x ≦ 0.10)
[[abstract]]Structural, transport, and magnetoelectric (ME) properties of delafossite oxides CuCr1-xO2 with 0 <= x <= 0.10 were extensively investigated. The Rietveld refinement shows that the Cu-O bond length decreases with increasing Cr deficiency, indicative of the presence of a mixed valence state of Cu+/Cu2+ and an enhancement of the hybridization between Cu 3d and O 2p orbitals. As a result, it leads to a decrease of room-temperature resistivity by two orders of magnitude. The deduced effective moment for the Cr-deficient samples is larger than the one only taking into account the contribution from Cr3+ with S = 3/2. This demonstrates that Cu2+ is present in the Cr-deficient samples, giving rise to excess holes at the Cu site. Below TN(Cr) ∼ 24 K, the magnetocapacitance [[variant_greek_epsilon](H)-[variant_greek_epsilon](0)]/[variant_greek_epsilon](0) exhibits a distinct field dependence and deviates from the square of magnetization M2. These findings suggest that the ME coupling in CuCr1-xO2 with higher x is modulated by an increase of the spin fluctuations in the CrO2 triangular lattice through the interplay between charge and spin degrees of freedom.[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子
Relative Entropy and Holography
Relative entropy between two states in the same Hilbert space is a
fundamental statistical measure of the distance between these states. Relative
entropy is always positive and increasing with the system size. Interestingly,
for two states which are infinitesimally different to each other, vanishing of
relative entropy gives a powerful equation for the first
order variation of the entanglement entropy and the expectation
value of the \modu Hamiltonian . We evaluate relative entropy between
the vacuum and other states for spherical regions in the AdS/CFT framework. We
check that the relevant equations and inequalities hold for a large class of
states, giving a strong support to the holographic entropy formula. We
elaborate on potential uses of the equation for vacuum
state tomography and obtain modified versions of the Bekenstein bound.Comment: 75 pages, 3 figures, added reference
Experimental Evidence for Intra- and Inter-Unit-Cell Josephson Junctions in a YBaqCu307 —$ Single Crystal
[[abstract]]Modulation of the dynamic resistance versus the magnetic field of YBa2Cu3O7-δ single crystal shows two groups of peak structures with nearly uniform magnetic field spacings. The spacings suggest two kinds of Josephson junctions: one formed by the CuO2-Y-CuO2 atomic planes within each unit cell and the other formed by the CuO2 bilayers between different unit cells. The intra-unit-cell junctions appear first as the temperature is lowered from Tc. The existence of CuO2-Y-CuO2 Josephson junctions implies two-dimensional superconductivity in the CuO2 atomic planes.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子
Correlation between A-site randomness and magnetic phase transition in half-doped manganite Pr0.5Ba0.5MnO3
[[abstract]]The interplay between A-site randomness and magnetic phase transition in half-doped manganite Pr0.5Ba0.5MnO3 (PBMO) was extensively investigated. The H/M versus M2 isotherms show that the A-site ordered PBMO undergoes a second-order magnetic phase transition from paramagnetism to ferromagnetism, whereas the A-site disordered PBMO exhibits a fluctuation-driven first-order transition arising from a competing order phase possibly existing in the paramagnetic state. A step-like transition in magnetization and resistivity with a sharp width of ΔH/H ~ 10−3 was only observed in the A-site partially ordered PBMO at 2 K, indicating that the metamagnetic transition is associated with a competition between randomly distributed short-range ferromagnetic and antiferromagnetic phases. These findings provide evidence that the A-site randomness not only suppresses A-type antiferromagnetism also moderately weakens long-range ferromagnetism in the A-site ordered PBMO.[[incitationindex]]SCI[[booktype]]電子
Fate of the Peak Effect in a Type-II Superconductor: Multicriticality in the Bragg-Glass Transition
We have used small-angle-neutron-scattering (SANS) and ac magnetic
susceptibility to investigate the global magnetic field H vs temperature T
phase diagram of a single crystal Nb in which a first-order transition of
Bragg-glass melting (disordering), a peak effect, and surface superconductivity
are all observable. It was found that the disappearance of the peak effect is
directly related to a multicritical behavior in the Bragg-glass transition.
Four characteristic phase boundary lines have been identified on the H-T plane:
a first-order line at high fields, a mean-field-like continuous transition line
at low fields, and two continuous transition line associated with the onset of
surface and bulk superconductivity. All four lines are found to meet at a
multicritical point.Comment: 4 figure
Anomalous physical properties of underdoped weak-ferromagnetic superconductor RuSrEuCuO
Similar to the optimal-doped, weak-ferromagnetic (WFM induced by canted
antiferromagnetism, T = 131 K) and superconducting (T = 56 K)
RuSrGdCuO, the underdoped RuSrEuCuO
(T = 133 K, T = 36 K) also exhibited a spontaneous vortex state
(SVS) between 16 K and 36 K. The low field (20 G) superconducting
hysteresis loop indicates a weak and narrow Meissner state region of average
lower critical field B(T) = B(0)[1 -
(T/T)], with B(0) = 7 G and T = 16 K. The
vortex melting transition (T = 21 K) below T obtained from
the broad resistivity drop and the onset of diamagnetic signal indicates a
vortex liquid region due to the coexistence and interplay between
superconductivity and WFM order. No visible jump in specific heat was observed
near T for Eu- and Gd-compound. This is not surprising, since the
electronic specific heat is easily overshadowed by the large phonon and
weak-ferromagnetic contributions. Furthermore, a broad resistivity transition
due to low vortex melting temperature would also lead to a correspondingly
reduced height of any specific heat jump. Finally, with the baseline from the
nonmagnetic Eu-compound, specific heat data analysis confirms the magnetic
entropy associated with antiferromagnetic ordering of Gd (J = S = 7/2)
at 2.5 K to be close to ln8 as expected.Comment: 7 figure
Striped Magnetic Ground State of the Kagome Lattice in Fe4Si2Sn7O16
We have experimentally identified a new magnetic ground state for the kagome
lattice, in the perfectly hexagonal Fe2+ (3d6, S = 2) compound Fe4Si2Sn7O16.
Representational symmetry analysis of neutron diffraction data shows that below
T_N = 3.5 K, the spins on 2/3 of the magnetic ions order into canted
antiferromagnetic chains, separated by the remaining 1/3 which are
geometrically frustrated and show no long-range order down to at least T = 0.1
K. Moessbauer spectroscopy confirms that there is no static order on the latter
1/3 of the magnetic ions - i.e., they are in a liquid-like rather than a frozen
state - down to at least 1.65 K. A heavily Mn-doped sample
Fe1.45Mn2.55Si2Sn7O16 has the same magnetic structure. Although the propagation
vector q = (0, 1/2 , 1/2 ) breaks hexagonal symmetry, we see no evidence for
magnetostriction in the form of a lattice distortion within the resolution of
our data. We discuss the relationship to partially frustrated magnetic order on
the pyrochlore lattice of Gd2Ti2O7, and to theoretical models that predict
symmetry breaking ground states for perfect kagome lattices.Comment: 5 pages, 5 figure
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