International Conference on Condensed Matter Physics
Calculations motivated by the successful prediction of the nickelate phase diagram suggest that palladates might hit the sweet spot for high-temperature superconductivity.
Copper-based (cuprate) superconductors have long held the record for the highest superconducting critical temperature (Tc) at ambient pressure. In 2019, after decades of theoretical and experimental effort, researchers reported a nickel-based (nickelate) analog to cuprate superconductors (see Trend: Entering the Nickel Age of Superconductivity). Since then, others have sought to pinpoint the factors that control superconductivity in such single-orbital-dominated systems. Motoharu Kitatani of the University of Hyogo in Japan and his colleagues now identify some of these factors and suggest that swapping out nickel for palladium could deliver a material that superconducts at even higher temperatures than cuprate superconductors [1]. The study could help guide the ongoing search for novel superconducting materials and establish “palladates” as the new kid on the block.
Kitatani and his colleagues previously had used a standard condensed-matter-physics model, called the single-band Hubbard model, to predict Tc for nickelates and had validated their predictions using measurements in defect-free nickelate films. Now, by simulating this system while varying the electrons’ interaction strength, filling factor, and energy-momentum dispersion, the researchers have tracked the strength of electron–electron pairing that leads to the emergence of superconductivity. This allows them to determine the electronic configuration that optimizes Tc. However, according to their results, neither nickelates nor cuprates come close to these optimized conditions. Instead, the researchers have found that palladates, thanks to somewhat weaker interactions and thus weaker correlations, could more closely approach the optimal “Goldilocks” conditions that maximize Tc. The researchers hope their theoretical results will encourage experimentalists to grow and examine palladates as new candidates for higher-Tc options.
In recent years, physicists have been trying to attain the control of chemical reactions in the quantum degenerate regime, where de Broglie wavelength of particles becomes comparable to the spacing between them. Theoretical predictions suggest that many-body reactions between bosonic reactants in this regime will be marked by quantum coherence and Bose enhancement, yet this has been difficult to validate experimentally. Researchers at University of Chicago recently set out to observe these elusive many-body chemical reactions in the quantum degenerate regime. Their paper, published in Nature Physics, presents the observation of coherent, collective reactions between Bose-condensed atoms and molecules. "The quantum control of molecular reactions is a fast-progressing research area in atomic and molecular physics," Cheng Chin, one of the researchers who carried out the study, told Phys.org. "People envision applications of cold molecules in precision metrology, quantum i...
International Conference on Condensed Matter Physics National University of Singapore (NUS) physicists have demonstrated a new way of controlling Rashba interactions in oxide systems. Tuning and controlling Rashba interactions is a particularly promising technology, as it can potentially be integrated directly into functional logic and memory devices. Scientists and engineers need devices that can process information efficiently with ultra-low power consumption. Recently, there have been new developments in logic and memory devices that use the spin of electrons, in addition to their electronic charge, to store and process information. To accomplish this, the device architecture needs a strong interaction between the spin of electrons and their orbital moments. This coupling, known as Rashba effect, allows for easy manipulation of spin currents and can lead to lower energy consumption. In particular, it can facilitate voltage-driven magnetization switching for logic and memory co...
Germanene undergoes a topological phase transition and then becomes a normal insulator when the strength of an applied electric field is dialed up. Graphene’s valence and conduction bands meet at a point, making the single-layer crystal a semimetal. Researchers have predicted that spin-orbit coupling of carbon’s outer electrons opens a narrow gap between these bands—but only for the crystal’s bulk. Along the edges, spin-dependent states bridge the band gap, allowing the resistance-free flow of electrons: a quantum spin Hall effect. The weakness of carbon’s spin-orbit coupling means that this quantum spin Hall effect is too fragile to observe, however. Now Pantelis Bampoulis of the University of Twente in the Netherlands and his collaborators have seen the quantum spin Hall effect in graphene’s germanium (Ge) analog, germanene [ 1 ]. Furthermore, they show that germanene’s structure—a honeycomb like graphene’s, but lightly buckled—allows the quantum spin Hall effect to be turned o...
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