The relation between enhanced superconductivity in monolayer FeSe grown on SrTiO3 and the large nematicity in multilayer FeSe on SrTiO3 remains not well understood. Here, the authors observe a ...long-range smectic phase in bilayer FeSe films but vanishes in monolayer FeSe, providing a new instability to help enhance the superconductivity.
Precisely probing heavy metal ions in water is important for molecular biology, environmental protection, and healthy monitoring. Although many methods have been reported in the past decade, ...developing a quantitative approach capable of detecting sub-ppt level heavy metal ions with high selectivity is still challenging. Here we report an extremely sensitive and highly selective nanoporous gold/aptamer based surface enhanced resonance Raman scattering (SERRS) sensor. The optical sensor has an unprecedented detection sensitivity of 1 pM (0.2 ppt) for Hg2+ ions, the most sensitive Hg2+ optical sensor known so far. The sensor also exhibits excellent selectivity. Dilute Hg2+ ions can be identified in an aqueous solution containing 12 metal ions as well as in river water and underground water. Moreover, the SERRS sensor can be reused without an obvious loss of the sensitivity and selectivity even after 10 cycles.
We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi2Te3 using a scanning tunneling microscope. The interference fringes are caused by the ...scattering of the topological states off Ag impurities and step edges on the Bi2Te3(111) surface. By studying the voltage-dependent standing wave patterns, we determine the energy dispersion E(k), which confirms the Dirac cone structure of the topological states. We further show that, very different from the conventional surface states, backscattering of the topological states by nonmagnetic impurities is completely suppressed. The absence of backscattering is a spectacular manifestation of the time-reversal symmetry, which offers a direct proof of the topological nature of the surface states.
We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall ...conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to a quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.
Abstract
Interface charge transfer and electron–phonon coupling have been suggested to play a crucial role in the recently discovered high-temperature superconductivity of single unit-cell FeSe films ...on SrTiO
3
. However, their origin remains elusive. Here, using ultraviolet photoemission spectroscopy and element-sensitive X-ray photoemission spectroscopy, we identify the strengthened Ti–O bond that contributes to the interface enhanced electron–phonon coupling and unveil the band bending at the FeSe/SrTiO
3
interface that leads to the charge transfer from SrTiO
3
to FeSe films. We also observe band renormalization that accompanies the onset of superconductivity. Our results not only provide valuable insights into the mechanism of the interface-enhanced superconductivity, but also point out a promising route toward designing novel superconductors in heterostructures with band bending-induced charge transfer and interfacial enhanced electron–phonon coupling.
Thin films of magnetically doped topological insulators Cr0.22(BixSb1‐x)1.78Te3 are found to possess carrier‐independent long‐range ferromagnetic order with perpendicular magnetic anisotropy. The ...anomalous Hall resistance is greatly enhanced, up to one quarter of quantum Hall resistance, by depletion of the carriers. The results demonstrate this material as a promising system to realize the quantized anomalous Hall effect.
The discovery that potassium-doped iron selenide undergoes phase separation into a defect-free superconducting phase and an iron-vacancy-ordered insulating phase resolves many questions about the ...unusual behaviour of this iron-based superconductor.
The evolution of the quantum anomalous Hall effect with the thickness of Cr‐doped (Bi,Sb)2Te3 magnetic topological insulator films is studied, revealing how the effect is caused by the interplay of ...the surface states, band‐bending, and ferromagnetic exchange energy. Homogeneity in ferromagnetism is found to be the key to high‐temperature quantum anomalous Hall material.
The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to ...observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions.
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