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The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe 0.55 Se 0.45 . However, the topological features and superconducting properties are not observed uniformly across the sample surface. The understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications. Here, we combine neutron scattering, scanning angle-resolved photoemission spectroscopy, and microprobe composition and resistivity measurements to characterize the electronic state of Fe 1+ y Te 1− x Se x . We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, whereas the coexisting topological surface state occurs only at sufficiently high Te concentration. We find that FeTe 0.55 Se 0.45 is located very close to both phase boundaries, which explains the inhomogeneity of superconducting and topological states. Our results demonstrate the compositional control required for use of topological MZMs in practical applications. The compositional dependence of magnetic, superconducting and topological surface states on an iron-based superconductor is reported.

We present a comprehensive study on anisotropic magnetocaloric porperties of the van der Waals weak-itinerant ferromagnet Fe 3− x GeTe 2 that features gate-tunable room-temperature ferromagnetism in few-layer device. Intrinsic magnetocrystalline anisotropy is observed to be temperature-dependent and most likely favors the long-range magnetic order in thin Fe 3− x GeTe 2 crsytal. The magnetic entropy change Δ S M also reveals an anisotropic characteristic between H // ab and H // c , which could be well scaled into a universal curve. The peak value − Δ S M max of 1.20 J kg −1 K −1 and the corresponding adiabatic temperature change Δ T ad of 0.66 K are deduced from heat capacity with out-of-plane field change of 5 T. By fitting of the field-dependent parameters of − Δ S M max and the relative cooling power RCP, it gives − ∆ S M max  ∝  H n with n  = 0.603(6) and RCP  ∝  H m with m  = 1.20(1) when H // c . Given the high and tunable T c , Fe 3− x GeTe 2 crystals are of interest for fabricating the heterostructure-based spintronics device.

Visualizing atomic-orbital degrees of freedom is a frontier challenge in scanned microscopy. Some types of orbital order are virtually imperceptible to normal scattering techniques because they do not reduce the overall crystal lattice symmetry. A good example is d xz / d yz (π,π) orbital order in tetragonal lattices. For enhanced detectability, here we consider the quasiparticle scattering interference (QPI) signature of such (π,π) orbital order in both normal and superconducting phases. The theory reveals that sublattice-specific QPI signatures generated by the orbital order should emerge strongly in the superconducting phase. Sublattice-resolved QPI visualization in superconducting CeCoIn 5 then reveals two orthogonal QPI patterns at lattice-substitutional impurity atoms. We analyze the energy dependence of these two orthogonal QPI patterns and find the intensity peaked near E  = 0, as predicted when such (π,π) orbital order is intertwined with d -wave superconductivity. Sublattice-resolved superconductive QPI techniques thus represent a new approach for study of hidden orbital order. Orbital order that does not break the overall crystal lattice symmetry is difficult to observe. Here, the authors use scanning tunneling microscopy on the superconductor CeCoIn 5 to detect a signature of the orbital order in quasiparticle interference which is enhanced in the superconducting state, as predicted theoretically.

We investigate the voltage control of magnetism in a van der Waals (vdW) heterostructure device consisting of two distinct vdW materials, the ferromagnetic Fe 3- x GeTe 2 and the ferroelectric In 2 Se 3 . It is observed that gate voltages applied to the Fe 3- x GeTe 2 /In 2 Se 3 heterostructure device modulate the magnetic properties of Fe 3- x GeTe 2 with significant decrease in coercive field for both positive and negative voltages. Raman spectroscopy on the heterostructure device shows voltage-dependent increase in the in-plane In 2 Se 3 and Fe 3- x GeTe 2 lattice constants for both voltage polarities. Thus, the voltage-dependent decrease in the Fe 3- x GeTe 2 coercive field, regardless of the gate voltage polarity, can be attributed to the presence of in-plane tensile strain. This is supported by density functional theory calculations showing tensile-strain-induced reduction of the magnetocrystalline anisotropy, which in turn decreases the coercive field. Our results demonstrate an effective method to realize low-power voltage-controlled vdW spintronic devices utilizing the magnetoelectric effect in vdW ferromagnetic/ferroelectric heterostructures. The control of magnetism by electric field is an important goal for future development of low-power spintronics. Here, the authors demonstrate voltage control of magnetism in van der Waals ferromagnetic/ferroelectric heterostructure devices via the strain-mediated magnetoelectric effect.

Electrical transport in 2D materials exhibits unique behaviors due to reduced dimensionality, broken symmetries, and quantum confinement. It serves as both a sensitive probe for the emergence of coherent electronic phases and a tool to actively manipulate many-body correlated states. Exploring their interplay and interdependence is crucial but remains underexplored. This review integratively cross-examines the atomic and electronic structures and transport properties of van der Waals-layered crystals ZrTe3, 2H-TaS2, and Cr2Si2Te6, providing a comprehensive understanding and uncovering new discoveries and insights. A common observation from these crystals is that modifying the atomic and electronic interface structures of 2D van der Waals interfaces using heteroatoms significantly influences the emergence and stability of coherent phases, as well as phase-sensitive transport responses. In ZrTe3, substitution and intercalation with Se, Hf, Cu, or Ni at the 2D vdW interface alter phonon–electron coupling, valence states, and the quasi-1D interface Fermi band, affecting the onset of CDW and SC, manifested as resistance upturns and zero-resistance states. We conclude here that these phenomena originate from dopant-induced variations in the lattice spacing of the quasi-1D Te chains of the 2D vdW interface, and propose an unconventional superconducting mechanism driven by valence fluctuations at the van Hove singularity, arising from quasi-1D lattice vibrations. Short-range in-plane electronic heterostructures at the vdW interface of Cr2Si2Te6 result in a narrowed band gap. The sharp increase in in-plane resistance is found to be linked to the emergence and development of out-of-plane ferromagnetism. The insertion of 2D magnetic layers such as Mn, Fe, and Co into the vdW gap of 2H-TaS2 induces anisotropic magnetism and associated transport responses to magnetic transitions. Overall, 2D vdW interface modification offers control over collective electronic behavior, transport properties, and their interplays, advancing fundamental science and nanoelectronic devices.

The Berry curvature dipole (BCD) serves as a one of the fundamental contributors to emergence of the nonlinear Hall effect (NLHE). Despite intense interest due to its potential for new technologies reaching beyond the quantum efficiency limit, the interplay between BCD and NLHE has been barely understood yet in the absence of a systematic study on the electronic band structure. Here, we report NLHE realized in NbIrTe 4 that persists above room temperature coupled with a sign change in the Hall conductivity at 150 K. First-principles calculations combined with angle-resolved photoemission spectroscopy (ARPES) measurements show that BCD tuned by the partial occupancy of spin-orbit split bands via temperature is responsible for the temperature-dependent NLHE. Our findings highlight the correlation between BCD and the electronic band structure, providing a viable route to create and engineer the non-trivial Hall effect by tuning the geometric properties of quasiparticles in transition-metal chalcogen compounds. Previous work proposed the Berry curvature dipole as the mechanism of the nonlinear Hall effect. Lee et al. establish the sign-changing Berry curvature hot spots from spin-orbit split bands as the origin of the Berry curvature dipole and link it to the nonlinear Hall effect in the topological semimetal NbIrTe 4 .

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We report neutron scattering measurements which reveal spin-liquid polymorphism in an “11” iron chalcogenide superconductor. It occurs when a poorly metallic magnetic state of FeTe is tuned toward superconductivity by substitution of a small amount of tellurium with isoelectronic sulfur. We observe a liquid-like magnetic response, which is described by the coexistence of two disordered magnetic phases with different local structures whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe, which preserves the C₄ symmetry of the underlying square lattice and is favored at high temperatures, whereas the other is the antiferromagnetic plaquette phase with broken C₄ symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest the coexistence of and competition between two distinct liquid states, and a liquid–liquid phase transformation between these states, in the electronic spin system of FeTe1–x(S,Se)ₓ. We have thus discovered the remarkable physics of competing spin-liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors. In particular, the phase with lower C₂ local symmetry, whose emergence precedes superconductivity, naturally accounts for a propensity for forming electronic nematic states which have been observed experimentally, in cuprate and iron-based superconductors alike.

Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe 3 when the long range CDW order is gradually suppressed. Superconducting critical temperature T c ( x ) in ZrTe 3− x Se x (0 ≤  x  ≤ 0.1) increases up to 4 K plateau for 0.04 ≤  x  ≤ 0.07. Further increase in Se content results in diminishing T c and filametary superconductivity. The CDW modes from Raman spectra are observed in x  = 0.04 and 0.1 crystals, where signature of ZrTe 3 CDW order in resistivity vanishes. The electronic-scattering for high T c crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T  = 300 K and contributes to substantial in-plane anisotropy.

We report on the emergence of robust superconducting order in single crystal alloys of TaSe 2 − x S x (0 ≤ × ≤ 2). The critical temperature of the alloy is surprisingly higher than that of the two end compounds TaSe 2 and TaS 2 . The evolution of superconducting critical temperature T c ( x ) correlates with the full width at half maximum of the Bragg peaks and with the linear term of the high-temperature resistivity. The conductivity of the crystals near the middle of the alloy series is higher or similar than that of either one of the end members 2H-TaSe 2 and/or 2H-TaS 2 . It is known that in these materials superconductivity is in close competition with charge density wave order. We interpret our experimental findings in a picture where disorder tilts this balance in favor of superconductivity by destroying the charge density wave order. Condensed matter physics: crystallographic disorder enhances superconductivity Substituting sulfur into TaSe 2 induces disorder, which further helps to enhance superconductivity, with a higher transition temperature. It is higher than that of either TaSe 2 or TaS 2 . An international team of researchers led by Cedomir Petrovic at Brookhaven national laboratory of USA synthesized single crystal alloys of TaSe 2 − x S x and measured the electrical conductivity and superconducting transition temperature as a function of x . They found that the transition temperature optimally increased when a maximal disorder is introduced by substituting sulfur into TaSe 2 . The role of such a disorder was understood as to suppress other competing orders while keeping superconductivity intact. By breaking other orders, conducting carriers were released so that they contributed further to superconductivity. These results highlight a benefit role of disorder and provide a possible way to enhance superconductivity.