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Results for “weakness”
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Weak phase stiffness and nature of the quantum critical point in underdoped cuprates
We demonstrate that the zero-temperature superconducting phase diagram of underdoped cuprates can be quantitatively understood in the strong binding limit, using only the experimental spectral function of the “normal” pseudogap phase without any free parameter. In the prototypical (La 1–x Sr x ) 2 CuO 4 , a kinetics-driven d-wave superconductivity is obtained above the critical doping δ c ~ 5.2%, below which complete loss of superfluidity results from local quantum fluctuation involving local p-wave pairs. Near the critical doping, an enormous mass enhancement of the local pairs is found responsible for the observed rapid decrease of phase stiffness. Lastly, a striking mass divergence is predicted at δ c that dictates the occurrence of the observed quantum critical point and the abrupt suppression of the Nernst effects in the nearby region.
Competing magnetic instabilities in the weak itinerant antiferromagnetic TiAu
The binary intermetallic compound TiAu is distinguished by an extremely sharp and narrow density of states peak at the Fermi level that has been proposed, via scattering between mirrored van Hove singularities, to be the mechanism for antiferromagnetic ordering versus the more fundamental ferromagnetic Stoner instability. Here we study, using density functional theory methods, magnetic tendencies and effects of doping, the latter within the virtual crystal approximation (VCA). Ferromagnetic tendencies are quantified using the fixed spin moment approach, illustrating the strong Stoner instability that does not, however, provide the ground state. Use of VCA results allows the identification of the value of the Stoner exchange constant I = 0.74eV for Ti. Magnetic fluctuations not included with semilocal density functionals are quantified with the procedure provided by Ortenzi and coauthors, with alloy concentrations corresponding to the quantum critical points reduced by a factor of three to five. Furthermore, our results provide useful guidelines for experimental doping studies of TiAu.
Quasistatic remanence in Dzyaloshinskii-Moriya interaction driven weak ferromagnets and piezomagnets
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Superconductor to weak-insulator transitions in disordered tantalum nitride films
Here, we study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents zν ≈ 1.3, with a corresponding critical field H c << H c2 , the upper critical field. The Hall effect exhibits a crossing point near H c , but with a nonuniversal critical value ρ c xy comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.
Weak exchange striction between the 4 f and 3 d ions in the multiferroic GdMn 2 O 5
We used single-crystal neutron diffraction to investigate the magnetic structures of the multiferroic GdMn 2 O 5 . The system undergoes a first-order incommensurate to commensurate magnetic transition below 33 K, accompanied by the appearance of electric polarization P . Upon cooling, P increases smoothly while the magnetic order shows an abrupt enhancement in intensity below 20 K owing to the large increase of the rare-earth Gd moment. The contrasting temperature evolution of the magnetic order and polarization indicates the polarization is mainly driven by the exchange striction between the magnetic Mn ions. The incommensurate phase in the intermediate temperature range has a cycloidal modulation along the c axis, with spin configuration projected in the ab plane similar to the commensurate phase. The lack of observable bulk polarization suggests the exchange striction is not the dominant mechanism for the polarization in the incommensurate phase.
Weak antilocalization in quasi-two-dimensional electronic states of epitaxial LuSb thin films
Observation of large nonsaturating magnetoresistance in rare-earth monopnictides has raised enormous interest in understanding the role of its electronic structure. Here, by a combination of molecular-beam epitaxy, low-temperature transport, angle-resolved photoemission spectroscopy, and hybrid density functional theory we have unveiled the band structure of LuSb, where electron-hole compensation is identified as a mechanism responsible for large magnetoresistance in this topologically trivial compound. In contrast to bulk single crystal analogues, quasi-two-dimensional behavior is observed in our thin films for both electron and holelike carriers, indicative of dimensional confinement of the electronic states. Introduction of defects through growth parameter tuning results in the appearance of quantum interference effects at low temperatures, which has allowed us to identify the dominant inelastic scattering processes and elucidate the role of spin-orbit coupling. Our findings open up possibilities of band structure engineering and control of transport properties in rare-earth monopnictides via epitaxial synthesis.
Intensity of a weak 519-keV γ ray following β decay of the superallowed emitter 34 Ar determined via the 33 S(p,γ) 34 Cl reaction
The predominant branch in the β decay of 34 Ar is the superallowed 0 + → 0 + transition to the ground state of 34 Cl. To determine its important branching ratio one must first establish the ratios for the competing Gamow-Teller branches based on the measured intensities of γ rays subsequently emitted from the excited states they populate in 34 Cl. The strongest of these branches populates the 1 + state at 666 keV in 34 Cl, which has three possible γ-decay paths. Here, we report here a measurement of the decay of this state, which we populated via resonant proton capture in the reaction 33 S(p,γ) 34 Cl. We find that the intensity of the 519-keV γ-ray path is 1.46(19)% relative to that of the 666-keV path. This result is critical to new precise measurements of the superallowed decay of 34 Ar.
Incorporating the weak mixing angle dependence to reconcile the neutron skin measurement on Pb 208 by PREX-II
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F t values of the mirror β transitions and the weak-magnetism-induced current in allowed nuclear β decay
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Power of two: Assessing the impact of a second measurement of the weak-charge form factor of Pb 208
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Quantum Monte Carlo calculations of weak transitions in A = 6 – 10 nuclei
{\it Ab initio} calculations of the Gamow-Teller (GT) matrix elements in the $\beta$ decays of $^6$He and $^{10}$C and electron captures in $^7$Be are carried out using both variational and Green's function Monte Carlo wave functions obtained from the Argonne $v_{18}$ two-nucleon and Illinois-7 three-nucleon interactions, and axial many-body currents derived from either meson-exchange phenomenology or chiral effective field theory. The agreement with experimental data is excellent for the electron captures in $^7$Be, while theory overestimates the $^6$He and $^{10}$C data by $\sim 2\%$ and $\sim 10\%$, respectively. We show that for these systems correlations in the nuclear wave functions are crucial to explain the data, while many-body currents increase by $\sim 2$--$3\%$ the one-body GT contributions. These findings suggest that the longstanding $g_A$-problem, {\it i.e.}, the systematic overprediction ($\sim 20 \%$ in $A\le 18$ nuclei) of GT matrix elements in shell-model calculations, may be resolved, at least partially, by correlation effects.
Supersymmetric S U ( 5 ) × U ( 1 ) χ and the weak gravity conjecture
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Analytic transport from weak to strong coupling in the O ( N ) model
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Measurements of weak decay asymmetries of Λ c + → p K s 0 , Λ π + , Σ + π 0 , and Σ 0 π +
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Thermal free energy of large N f QED in 2 + 1 dimensions from weak to strong coupling
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