Immediately after the discovery of high temperature superconductivity in the cuprates in 1987, properties in the metallic state above Tc were discovered that violated the reigning paradigm in ...condensed matter physics: the quasiparticle concept due to Landau. The most discussed of such properties is the linear in temperature resistivity down to asymptotically low temperatures, sometimes called Planckian resistivity, above the region of the highest Tc . Similar anomalies have since also been discovered in the heavy-fermion compounds and in the Fe-based superconducting metals, and most recently in twisted bilayer graphene. Innumerable papers in the past three decades have pointed out that the linear in T resistivity and associated properties are a mystery and the most important unsolved problem in condensed matter physics; superconductivity itself is a corollary to the normal state properties. Even in this prolifically investigated field, quantitative experimental results on crucial normal state and superconducting state properties have only recently become available. It is now possible to compare some of the detailed predictions of a theory for the normal and superconductive state in cuprates and in heavy fermions with the experiments. The theory gives the frequency and temperature dependence of various normal state properties and also their measured magnitudes in terms of the same values of two parameters. It also resolves the paradox of d-wave symmetry of superconductivity in the cuprates given that the scattering rate of fermions in the normal state is nearly momentum independent. The same parameters that govern the normal state anomalies are also deduced from the quantitative analysis of data in the superconducting state in cuprates. The simplicity of the results depends on the discovery of a new class of quantum-critical fluctuation in which orthogonal topological excitations in space and time determine the spectra, such that the correlations of the critical spectra are a product of a function of space and a function of time with the spatial correlation length proportional to the logarithm of the temporal correlation length. The fermions scattering with such fluctuations form a marginal Fermi liquid.
Bright and efficient blue emission is key to further development of metal halide perovskite light-emitting diodes. Although modifying bromide/chloride composition is straightforward to achieve blue ...emission, practical implementation of this strategy has been challenging due to poor colour stability and severe photoluminescence quenching. Both detrimental effects become increasingly prominent in perovskites with the high chloride content needed to produce blue emission. Here, we solve these critical challenges in mixed halide perovskites and demonstrate spectrally stable blue perovskite light-emitting diodes over a wide range of emission wavelengths from 490 to 451 nanometres. The emission colour is directly tuned by modifying the halide composition. Particularly, our blue and deep-blue light-emitting diodes based on three-dimensional perovskites show high EQE values of 11.0% and 5.5% with emission peaks at 477 and 467 nm, respectively. These achievements are enabled by a vapour-assisted crystallization technique, which largely mitigates local compositional heterogeneity and ion migration.
Whereas the discovery of Dirac- and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and ...technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, angle-resolved photoemission spectroscopy measurements have shown an unusually robust linear dispersion (up to ∼2 eV) with multiple nondegenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (WHM with W = Zr, Hf; H = Si, Ge, Sn; M = O, S, Se, Te) with identical band topology. Along with extremely large and nonsaturating magnetoresistance (MR), ∼1.4 × 10⁵% at 2 K and 9 T, it shows strong anisotropy, depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. A nontrivial π Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as the Adler–Bell–Jackiw chiral anomaly, has also been observed.
The electron-phonon interaction and related transport properties are investigated in monolayer silicene and MoS2 by using a density functional theory calculation combined with a full-band Monte Carlo ...analysis. In the case of silicene, the results illustrate that the out-of-plane acoustic phonon mode may play the dominant role unlike its close relative, graphene. The small energy of this phonon mode, originating from the weak $sp^2 π$ bonding between Si atoms, contributes to the high scattering rate and significant degradation in electron transport. In MoS2, the longitudinal acoustic phonons show the strongest interaction with electrons. The key factor in this material appears to be the $Q$ valleys located between the $Γ$ and $K$ points in the first Brillouin zone as they introduce additional intervalley scattering. The analysis also reveals the potential impact of extrinsic screening by other carriers and/or adjacent materials. The effective deformation potential constants are extracted for all relevant intrinsic electron-phonon scattering processes in both materials.
Monopoles are intriguing topological objects, which play a central role in gauge theories and topological states of matter. While conventional monopoles are found in odd-dimensional flat spaces, such ...as the Dirac monopole in three dimensions and the non-Abelian Yang monopole in five dimensions, more exotic objects were predicted to exist in even dimensions. This is the case of "tensor monopoles," which are associated with tensor (Kalb-Ramond) gauge fields, and which can be defined in four-dimensional flat spaces. In this work, we investigate the possibility of creating and measuring such a tensor monopole in condensed-matter physics by introducing a realistic three-band model defined over a four-dimensional parameter space. Our probing method is based on the observation that the topological charge of this tensor monopole, which we relate to a generalized Berry curvature, can be directly extracted from the quantum metric. We propose a realistic three-level atomic system, where tensor monopoles could be generated and revealed through quantum-metric measurements.
Moiré lattices consist of two superimposed identical periodic structures with a relative rotation angle. Moiré lattices have several applications in everyday life, including artistic design, the ...textile industry, architecture, image processing, metrology and interferometry. For scientific studies, they have been produced using coupled graphene-hexagonal boron nitride monolayers
, graphene-graphene layers
and graphene quasicrystals on a silicon carbide surface
. The recent surge of interest in moiré lattices arises from the possibility of exploring many salient physical phenomena in such systems; examples include commensurable-incommensurable transitions and topological defects
, the emergence of insulating states owing to band flattening
, unconventional superconductivity
controlled by the rotation angle
, the quantum Hall effect
, the realization of non-Abelian gauge potentials
and the appearance of quasicrystals at special rotation angles
. A fundamental question that remains unexplored concerns the evolution of waves in the potentials defined by moiré lattices. Here we experimentally create two-dimensional photonic moiré lattices, which-unlike their material counterparts-have readily controllable parameters and symmetry, allowing us to explore transitions between structures with fundamentally different geometries (periodic, general aperiodic and quasicrystal). We observe localization of light in deterministic linear lattices that is based on flat-band physics
, in contrast to previous schemes based on light diffusion in optical quasicrystals
, where disorder is required
for the onset of Anderson localization
(that is, wave localization in random media). Using commensurable and incommensurable moiré patterns, we experimentally demonstrate the two-dimensional localization-delocalization transition of light. Moiré lattices may feature an almost arbitrary geometry that is consistent with the crystallographic symmetry groups of the sublattices, and therefore afford a powerful tool for controlling the properties of light patterns and exploring the physics of periodic-aperiodic phase transitions and two-dimensional wavepacket phenomena relevant to several areas of science, including optics, acoustics, condensed matter and atomic physics.
We present an analog of the phenomenon of orthogonality catastrophe in quantum many-body systems subject to a local dissipative impurity. We show that the fidelity F(t), giving a measure for distance ...of the time-evolved state from the initial one, displays a universal scaling form F(t)∝t^{θ}e^{-γt}, when the system supports long-range correlations, in a fashion reminiscent of traditional instances of orthogonality catastrophe in condensed matter. An exponential falloff at rate γ signals the onset of environmental decoherence, which is critically slowed down by the additional algebraic contribution to the fidelity. This picture is derived within a second-order cumulant expansion suited for Liouvillian dynamics, and substantiated for the one-dimensional transverse field quantum Ising model subject to a local dephasing jump operator, as well as for XY and XX quantum spin chains, and for the two-dimensional Bose gas deep in the superfluid phase with local particle heating. Our results hint that local sources of dissipation can be used to inspect real-time correlations and to induce a delay of decoherence in open quantum many-body systems.
A variety of nickel oxide compounds have long been studied for their manifestation of various correlated electron phenomena. Recently, superconductivity was observed in nanoscale infinite layer ...nickelate thin films of Nd0.8Sr0.2NiO2, epitaxially stabilized on SrTiO3 substrates via topotactic reduction from the perovskite precursor phase. Here, we present the synthesis and properties of PrNiO2 thin films on SrTiO3. Upon doping in Pr0.8Sr0.2NiO2, we observe superconductivity with a transition temperature of 7–12 K and robust critical current density at 2 K of 334 kA/cm2. These findings indicate that superconductivity in the infinite layer nickelates is relatively insensitive to the details of the rare earth 4f configuration. Furthermore, they motivate the exploration of a broader family of compounds based on two-dimensional NiO2 planes, which will enable systematic investigation of the superconducting and normal state properties and their underlying mechanisms.
PDF
