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The three central phenomena of cuprate (copper oxide) superconductors are linked by a common doping level p*—at which the enigmatic pseudogap phase ends and the resistivity exhibits an anomalous linear dependence on temperature, and around which the superconducting phase forms a dome-shaped area in the phase diagram1. However, the fundamental nature of p* remains unclear, in particular regarding whether it marks a true quantum phase transition. Here we measure the specific heat C of the cuprates Eu-LSCO and Nd-LSCO at low temperature in magnetic fields large enough to suppress superconductivity, over a wide doping range2 that includes p*. As a function of doping, we find that Cel/T is strongly peaked at p* (where Cel is the electronic contribution to C) and exhibits a log(1/T) dependence as temperature T tends to zero. These are the classic thermodynamic signatures of a quantum critical point3-5, as observed in heavy-fermion6 and iron-based7 superconductors at the point where their antiferromagnetic phase comes to an end. We conclude that the pseudogap phase of cuprates ends at a quantum critical point, the associated fluctuations of which are probably involved in d-wave pairing and the anomalous scattering of charge carriers. Measurements of the specific heat of two cuprate materials at low temperature in magnetic fields large enough to suppress superconductivity and over a wide doping range reveal that the pseudogap phase of cuprates ends at a quantum critical point. [ABSTRACT FROM AUTHOR]

The discovery of the spin-ice phase in Dy2Ti2O7 numbers among the most significant findings in magnetic materials in over a decade. Spin ice has since been associated with the manifestation of magnetic monopoles and may even inform our understanding of emergent quantum electrodynamics. The spin-ice model is based on an elegant analogy to Pauling's model of geometrical frustration in water ice, and predicts the same residual entropy, as confirmed by numerous measurements. Here we present results for the specific heat of Dy2Ti2O7, demonstrating why previous measurements were unable to correctly capture its low-temperature behaviour. By carefully tracking the flow of heat into and out of the material, we observe a non-vanishing specific heat that has not previously been detected. This behaviour is confirmed in two samples of Dy2Ti2O7, in which cooling below 0.6 K reveals a deviation from Pauling's residual entropy, calling into question the true magnetic ground state of spin ice. [ABSTRACT FROM AUTHOR]

Results of systematic high-frequency electron spin resonance (ESR) studies of BaCrO, a weakly coupled $S=\frac{1}{2}$ dimer system, in magnetic fields up to 25 T are reported. Two pairs of ESR gapped modes corresponding to transitions from a spin-singlet ground state to the first excited triplet states with gaps, Δ=563 GHz and Δ=399 GHz, are revealed below H=12.5 T. The detection of the ground-state excitations by means of ESR clearly indicates the presence of a non-secular term allowing these transitions. A complex structure of the microwave absorption spectrum in magnetic fields above H is observed, those peculiarities are discussed. [ABSTRACT FROM AUTHOR]

Electrical resistance is a crucial and well-understood property of systems ranging from computer microchips to nerve impulse propagation in the human body. Here we study the motion of magnetic charges in spin ice and find that extra spins inserted in Dy2Ti2O7 trap magnetic monopole excitations and provide the first example of how defects in a spin-ice material obstruct the flow of monopoles-a magnetic version of residual resistance. We measure the time-dependent magnetic relaxation in Dy2Ti2O7 and show that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we show that surface effects and a very low level of stuffed spins (0.30%)-magnetic Dy ions substituted for non-magnetic Ti ions-cause these signatures in the relaxation. In addition, we find evidence that the rapidly diverging experimental timescale is due to a temperature-dependent attempt rate proportional to the monopole density. [ABSTRACT FROM AUTHOR]

An aluminum tungstate-scandium tungstate solid solution was successfully grown in a single crystal form by modified Czochralski (CZ) method. The crystal grown was transparent and a satisfactory quality was examined by a polarizing microscope measurement. The Al3+ ion conductivity was considerably improved by forming the solid solution and these by expanding the crystal lattice size. The lattice expansion contributes greatly to enhancing the Al3+ ion conducting behavior especially along c-axis among the three axes in the orthorhombic symmetry. By comparing the ion conducting characteristics between each axis of the single crystal and the polycrystal, the enhancement of the Al3+ ion conductivity is ascribed to the cooperative effects of both ion conductivity increase along c-axis and the conductivity enhancement in the grain boundaries. [ABSTRACT FROM AUTHOR]

Influence of heavy ions irradiation on magnetic properties of CuGeO3 single crystals is presented. Magnetization data for the irradiated sample are analyzed in the frame of the Bonner–Fisher model. The contribution of broken-chain effects to the susceptibility of the damaged volume fraction of the sample is considered. It is shown that irradiation leads to the breaking of dimerized Cu–O chains and to the collapse of spin dimerization. [ABSTRACT FROM AUTHOR]

A quantum spin liquid is a state of matter characterized by quantum entanglement and the absence of any broken symmetry. In condensed matter, the frustrated rare-earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7, so-called spin ices, exhibit a classical spin liquid state with fractionalized thermal excitations (magnetic monopoles). Evidence for a quantum spin ice, in which the magnetic monopoles become long range entangled and an emergent quantum electrodynamics arises, seems within reach. The magnetic properties of the quantum spin ice candidate Yb2Ti2O7 have eluded a global understanding and even the presence or absence of static magnetic order at low temperatures is controversial. Here we show that sensitivity to pressure is the missing key to the low temperature behaviour of Yb2Ti2O7. By combining neutron diffraction and muon spin relaxation on a stoichiometric sample under pressure, we evidence a magnetic transition from a disordered, non-magnetic, ground state to a splayed ferromagnetic ground state. [ABSTRACT FROM AUTHOR]

Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga3+,Mn2+) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semiconductor (Ba1?xKx)(Zn1?yMny)2As2, which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr2Si2 (122) structure. Holes are doped via (Ba2+, K1+) replacements, while spins via isovalent (Zn2+,Mn2+) substitutions. Bulk samples with x=0.1?0.3 and y=0.05?0.15 exhibit ferromagnetic order with TC up to 180?K, which is comparable to the highest TC for (Ga,Mn)As and significantly enhanced from TC up to 50?K of the '111'-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn)2As2 shares the same 122 crystal structure with semiconducting BaZn2As2, antiferromagnetic BaMn2As2 and superconducting (Ba,K)Fe2As2, which makes them promising for the development of multilayer functional devices. [ABSTRACT FROM AUTHOR]

The discovery of the spin-ice phase in Dy2Ti2O7 numbers among the most significant findings in magnetic materials in over a decade. Spin ice has since been associated with the manifestation of magnetic monopoles and may even inform our understanding of emergent quantum electrodynamics. The spin-ice model is based on an elegant analogy to Pauling's model of geometrical frustration in water ice, and predicts the same residual entropy, as confirmed by numerous measurements. Here we present results for the specific heat of Dy2Ti2O7, demonstrating why previous measurements were unable to correctly capture its low-temperature behaviour. By carefully tracking the flow of heat into and out of the material, we observe a non-vanishing specific heat that has not previously been detected. This behaviour is confirmed in two samples of Dy2Ti2O7, in which cooling below 0.6 K reveals a deviation from Pauling's residual entropy, calling into question the true magnetic ground state of spin ice. [ABSTRACT FROM AUTHOR]