Search

Using X-ray emission spectroscopy, we find appreciable local magnetic moments until 30 GPa to 40 GPa in the high-pressure phase of iron; however, no magnetic order is detected with neutron powder diffraction down to 1.8 K, contrary to previous predictions. Our first-principles calculations reveal a “spin-smectic” state lower in energy than previous results. This state forms antiferromagnetic bilayers separated by null spin bilayers, which allows a complete relaxation of the inherent frustration of antiferromagnetism on a hexagonal close-packed lattice. The magnetic bilayers are likely orientationally disordered, owing to the soft interlayer excitations and the near-degeneracy with other smectic phases. This possible lack of long-range correlation agrees with the null results from neutron powder diffraction. An orientationally disordered, spin-smectic state resolves previously perceived contradictions in high-pressure iron and could be integral to explaining its puzzling superconductivity.

Hybrid van der Waals heterostructures comprising ultrathin layers of different materials and offering the possibility of novel properties and unusual charge transport characteristics have become a reality in recent years. Here, we vertically stack graphene, a transition metal dichalcogenide and a III–VI semiconductor together and report a novel self-driven photodetector based on a graphene/InSe/MoS2 heterostructure. The device shows rectifying and bipolar behavior. In the self-driven mode it exhibits high photoresponsivity (110 mA W−1), fast photo-response (less than 1 ms) and high detectivity (over 1010 Jones). It also shows ambient operational stability over one month of operation and nearly uniform photocurrent distribution because of the efficient electron–hole pair separation arising from the large built-in potential at the interface of MoS2 and InSe. Our graphene/InSe/MoS2 heterostructure holds promise for novel self-driven optoelectronics based on III–VI/transition metal dichalcogenide heterojunctions.

We monitor the dynamics of hot carriers in InSe by means of two-photon photoelectron spectroscopy (2PPE). The electrons excited by photons of 3.12 eV experience a manifold relaxation. First, they thermalize to electronic states degenerate with the $\overline{M}$ valley. Subsequently, the electronic cooling is dictated by Fr\"ohlich coupling with phonons of small momentum transfer. Ab initio calculations predict cooling rates that are in good agreement with the observed dynamics. We argue that electrons accumulating in states degenerate with the $\overline{M}$ valley could travel through a multilayer flake of InSe with a lateral size of 1 $\ensuremath{\mu}\mathrm{m}$. The hot carriers pave a viable route to the realization of below-band-gap photodiodes and Gunn oscillators. Our results indicate that these technologies may find a natural implementation in future devices based on layered chalcogenides.

New data on Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) reveal interesting aspects of photoexcited superconductors. The electrons dynamics show that inelastic scattering by nodal quasiparticles decreases when the temperature is lowered below the critical value of the superconducting phase transition. This drop of electronic dissipation is astonishingly robust and survives to photoexcitation densities much larger than the value sustained by long-range superconductivity. The unconventional behavior of quasiparticle scattering is ascribed to superconducting correlations extending on a length scale comparable to the inelastic mean-free path. Our measurements indicate that strongly driven superconductors enter in a regime without phase coherence but finite pairing amplitude.

The spin-polarized transport properties of nonmagnetic (metallic Al and nonmetallic C) atomic chains adsorbed on zigzag graphene nanoribbons (ZGNRs) are investigated by the density functional theory (DFT) combined with the nonequilibrium Green’s function method. We find that the spin polarization of ZGNRs is sensitive to the adsorption sites and atomic types of the chains. As an Al chain is adsorbed on the middle of ZGNR, no spin-polarized transport arises. As the Al chain is adsorbed on the edge of ZGNR, high spin polarization is produced around the Fermi level. The different transport behaviors are originated from the fact that the edge adsorption of Al chain breaks the magnetization symmetry of two edges while the middle adsorption of Al chain only modifies the magnetizations of two edges equally. More prominent spin polarization is generated as a C chain is adsorbed on the edge of ZGNR. The complete spin polarization emerges not only around the Fermi level but also far from the Fermi level, owing to the edge states and the localized states. These results indicate that one can effectively modulate the spin-polarized transports of ZGNRs through adsorbing different nonmagnetic atomic chains.

The spin-polarized transport properties of Fe atomic chain adsorbed on zigzag graphene nanoribbons (ZGNRs) are investigated using the density-functional theory in combination with the nonequilibrium Green's function method. We find that the Fe chain has drastic effects on spin-polarized transport properties of ZGNRs compared with a single Fe atom adsorbed on the ZGNRs. When the Fe chain is adsorbed on the centre of the ZGNR, the original semiconductor transforms into metal, showing a very wide range of spin-polarized transport. Particularly, the spin polarization around the Fermi level is up to 100%. This is because the adsorbed Fe chain not only induces many localized states but also has effects on the edge states of ZGNR, which can effectively modulate the spin-polarized transports. The spin polarization of ZGNRs is sensitive to the adsorption site of the Fe chain. When the Fe chain is adsorbed on the edge of ZGNR, the spin degeneracy of conductance is completely broken. The spin polarization is found to be more pronounced because the edge state of one edge is destroyed by the additional Fe chain. These results have direct implications for the control of the spin-dependent conductance in ZGNRs with the adsorption of Fe chains.