Phonon-limited electronic transport through first principles
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Suppressed ballistic transport of dislocations at strain rates up to 109 s–1 in a stable nanocrystalline alloy
Dislocations are crucial to plastic deformation in crystals. At extreme strain rates, their motion shifts from thermally activated glide to ballistic transport, causing significant drag due to interactions with phonons, which can lead to embrittlement and failure in metals. The concept of dislons, quantized dislocations, has emerged to better understand these types of interactions. Similar to quantum treatment of dislocation-electron interactions, confining dislocations to nanometer scales, especially in nanocrystalline metals, could also yield unique mechanical behaviors different from bulk materials. Here, we present evidence showing that in Cu-3Ta, a thermo-mechanically stable nanocrystalline alloy, the phonon drag effect is entirely suppressed even at ultra-high strain rates (109 s−1). This is due to the stable confinement of dislocations within several-nanometer range, limiting their velocity and interaction with phonons. Our study indicates that in confined environments, the dislocation-phonon drag effect is minimal, potentially improving material performance under extreme conditions.
Ultrafast pump-probe phase-randomized tomography
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Enhanced superconductivity near a pressure-induced quantum critical point of strongly coupled charge density wave order in 2H-Pd0.05TaSe2
Interplay between charge density wave (CDW) order and superconductivity (SC) in quasi-two-dimensional materials remains poorly understood due to their diverse experimental varieties. Here, we investigate the pressure-dependent electrical transport and Raman scattering spectra of 2H-Pd0.05TaSe2, which exhibits a CDW transition at TCDW = 115 K and a superconducting transition at Tc = 2.6 K at ambient pressure conditions. As pressure increases, TCDW, identified by the resistivity anomaly, shifts towards lower temperatures and approaches zero at a critical pressure of Pc ~ 21.5 GPa. At this critical pressure, both Tc and upper critical field Hc2 reach their maximum values of ~ 8.5 K and ~ 6.4 T, respectively. Analysis of the Raman scattering spectra demonstrates that increasing pressure systematically suppresses both the two-phonon spectral weight above TCDW and the CDW amplitudon energies below TCDW, leading to their simultaneous disappearance at Pc. These observations provide direct evidence for the formation of a CDW quantum critical point (QCP) at Pc, indicating that charge and lattice fluctuations associated with the QCP of strongly coupled CDW order may enhance SC in pressurized 2H-Pd0.05TaSe2.
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