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Misfit layer compounds, heterostructures composed by a regular alternating stacking of rocksalt monochalcogenides bilayers and few-layer transition metal dichalchogenides, are an emergent platform to investigate highly doped transition metal dichalcogenides. Among them, (LaSe)$_{1.14}$(NbSe$_2$)$_2$ displays Ising superconductivity, while the presence of a charge density wave (CDW) in the material is still under debate. Here, by using polarized Raman spectroscopy and first-principles calculations, we show that NbSe$_2$ undergoes a doping-driven collapse of the CDW ordering within the misfit, and no signature of the CDW is detected down to 8~K. We provide a complete experimental and theoretical description of the lattice dynamics of this misfit compound. We show that the vibrational properties are obtained from those of the two subunits, namely the LaSe unit and the NbSe$_2$ bilayer, in the presence of a suitable field-effect doping, and then highlight the 2D nature of the lattice dynamics of NbSe$_2$ within the (LaSe)$_{1.14}$(NbSe$_2$)$_2$ 3D structure., Comment: First version of the manuscript (before revisions)

Low-dimensional materials have remarkable properties that are distinct from their bulk counterparts. A paradigmatic example is Ising superconductivity that occurs in monolayer materials such as NbSe2 which show a strong violation of the Pauli limit. In monolayers, this occurs due to a combination of broken inversion symmetry and spin-orbit coupling that locks the spins of the electrons out-of-plane. Bulk NbSe2 is centrosymmetric and is therefore not an Ising superconductor. We show that bulk misfit compound superconductors, (LaSe)1.14(NbSe2) and (LaSe)1.14(NbSe2)2, comprised of monolayers and bilayers of NbSe2, exhibit unexpected Ising protection with a Pauli-limit violation comparable to monolayer NbSe2, despite formally having inversion symmetry. We study these misfit compounds using complementary experimental methods in combination with first-principles calculations. We propose theoretical mechanisms of how the Ising protection can survive in bulk materials. We show how some of these mechanisms operate in these bulk compounds due to a concerted effect of charge-transfer, defects, reduction of interlayer hopping, and stacking. This highlights how Ising superconductivity can, unexpectedly, arise in bulk materials, and possibly enable the design of bulk superconductors that are resilient to magnetic fields., Comment: 14 pages, 4 figures, 4 extended data items

We have developed a phenomenological turbulent model with one-dimensional (1D) simulation based on Reynolds decomposition. Using this method, we have systematically studied models with different effects of compression, mixing length parameters, and diffusion coefficient of internal energy, turbulence energy and electron fraction. With employed turbulent effects, supernova explosion can be achieved in 1D geometry, which can mimic the evolution of shock in the 3D simulations. We found that enhancement of turbulent energy by compression affects the early shock evolution. The diffusion coefficients of internal energy and turbulent energy also affect the explodability. The smaller diffusion makes the shock revival faster. Our comparison between the two reveals that the diffusion coefficients of internal energy has a greater impact. These simulations would help understand the role of turbulence in core-collapse supernovae., Comment: 13 pages, 18 figures, accepted in MNRAS

Transition metal dichalcogenides (TMDs) display a rich variety of instabilities such as spin and charge orders, Ising superconductivity and topological properties. Their physical properties can be controlled by doping in electric double-layer field-effect transistors (FET). However, for the case of single layer NbSe$_2$, FET doping is limited to $\approx 1\times 10^{14}$ cm$^{-2}$, while a somewhat larger charge injection can be obtained via deposition of K atoms. Here, by performing ARPES, STM, quasiparticle interference measurements, and first principles calculations we show that a misfit compound formed by sandwiching NbSe$_2$ and LaSe layers behaves as a NbSe$_2$ single layer with a rigid doping of $0.55-0.6$ electrons per Nb atom or $\approx 6\times 10^{14}$ cm$^{-2}$. Due to this huge doping, the $3\times3$ charge density wave is replaced by a $2\times2$ order with very short coherence length. As a tremendous number of different misfit compounds can be obtained by sandwiching TMDs layers with rock salt or other layers, our work paves the way to the exploration of heavily doped 2D TMDs over an unprecedented wide range of doping.

Fourier transformation of atomically resolved STM topography of $(LaSe)_{1.14}(NbSe_2)$ revealed a surface modulation along the hexagonal surface lattice of $NbSe_2$ layer, but with a two times larger period. We compare it to the modified charge density wave found on plain $NbSe_2$ under strain., Comment: Withdrawn due to data re-evaluation

Chalcogenides (Q = S, Se, Te), one of the most important family of materials in solid-state chemistry, differ from oxides by their ability to form covalently-bonded (Qn)2- oligomers. Each chalcogen atom within such entity fulfills the octet rule by sharing electrons with other chalcogen atoms but some antibonding levels are vacant. This makes these oligomers particularly suited for redox reactions in solid state, namely towards elemental metals with a low redox potential that may be oxidized. We recently used this strategy to design, at low temperature and in an orientated manner, materials with 2D infinite layers through the topochemical insertion of copper into preformed precursors containing (S2)2- and/or (Se2)2- dimers (i.e. La2O2S2, Ba2F2S2 and LaSe2). Herein we extend the validity of the concept to the redox activity of (S2)2- and (S3)2- oligomers towards 3d transition metal elements (Cu, Ni, Fe) and highlight the strong relationship between the structures of the precursors, BaS2 and BaS3, and the products, BaCu2S2, BaCu4S3, BaNiS2 and BaFe2S3. Clearly, beyond the natural interest for the chemical reactivity of oligomers to generate compounds, this soft chemistry route may conduct to the rational conception of materials with a predicted crystal structure.

For a higher order linear ordinary differential operator P, its Stokes curve bifurcates in general when it hits another turning point of P. This phenomenon is most neatly understandable by taking into account Stokes curves emanating from virtual turning points, together with those from ordinary turning points. This understanding of the bifurcation of a Stokes curve plays an important role in resolving a paradox recently found in the Noumi-Yamada system, a system of linear differential equations associated with the fourth Painleve equation., Comment: 7 pages, 4 figures