Materials discovery lays the foundation for many technological advancements. The prediction and of new materials are not simple tasks. Here, we outline some basic principles solid-state chemistry, which might help to advance both, discuss pitfalls challenges in discovery. Using recent work Szymanski [Nature 624, 86 (2023)], reported autonomous 43 novel materials, as an example, problems that can arise unsupervised hope by addressing these, be brought closer reality. We all synthetic products...

The electronic properties of the carbon substituted MgB$_2$ single crystals are reported. substitution drops T$_c$ below 2 K. In-plane resistivity shows a remarkable increase in residual by C-substitution, while change in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that E$_{2g}$-phonon frequency radically hardens with increasing carbon-content, suggesting weakening electron-phonon coupling. Another striking C-effect increases second critical fields...

We report on the study of electronic anisotropy ${\mathrm{MgB}}_{2}$ superconductor using in-plane resistivity measurements in magnetic field applied perpendicular and parallel to Mg B planes single crystals. The results show temperature dependent upper critical with ratio $\ensuremath{\gamma}{=H}_{c2\ensuremath{\parallel}}{/H}_{c2\ensuremath{\perp}}$ increasing from 2.2 close ${T}_{c}$ up about 3 below 30 K. Our estimation out-of-plane coherence length...

Polarization-resolved Raman scattering measurements were performed on MgB(2) single crystals to determine the magnitude, symmetry, and temperature dependence of superconducting gap. A sharp peak due Cooper pair breaking appears in electronic continuum below T(c), reaching a maximum shift 105 +/- 1 cm(-1) [2 Delta(0)/k(B)T(c) = 3.96 0.09] showing up 5 anisotropy between polarized depolarized spectra. The 2 Delta follows that predicted from BCS theory, while decreases with decreasing...

The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching Fermi energy. These can be assigned to theoretically predicted sigma (B 2p(x,y)) pi 2p(z)) bands. In addition, a small parabolic-like band is detected around Gamma point, which attributed surface-derived state. overall agreement between our calculations suggests that electronic structure of...

We report observations of quantum oscillations in single crystals the high temperature superconductor MgB2. Three de Haas-van Alphen frequencies are clearly resolved. Comparison with band structure calculations strongly suggests that two these come from a warped Fermi surface tube along c direction, and third arises cylindrical sections an in-plane honeycomb network. The measured values effective mass range (0.44-0.68)m(e). By comparing to calculated masses, we find electron-phonon coupling...

Doped lead apatite (LK-99) has been proposed as a candidate ambient temperature and pressure superconductor, dramatic claim requiring careful investigation from experiment theory. Here, the authors synthesize an LK-99 sample find multiphase, transparent material that does not support high-temperature superconductivity. This is in agreement with $a\phantom{\rule{0}{0ex}}b$...

We have studied the phase diagram of MgB(2) superconductor using a single crystal for H parallel c-axis. For first time we report existence peak effect in screening current In magnetic field regime 10<H<13.5 kOe local fundamental diamagnetic moment displays very narrow step. higher fields this step is transformed to (peak effect) and, finally, H<10 gradual transition.

We study phonons in ${\mathrm{MgB}}_{2}$ using inelastic x-ray scattering (1.6 and 6 meV resolution). clearly observe the softening broadening of crucial ${E}_{2g}$ mode through Kohn anomaly along $\ensuremath{\Gamma}M$, excellent agreement with ab initio calculations. Low temperature measurements (just above below ${T}_{c}$) show negligible changes for momentum transfers investigated no change at $A$ between room 16 K. report presence a longitudinal $\ensuremath{\Gamma}A$ near energy to...

In a series of recent reports, doped lead apatite (LK-99) has been proposed as candidate ambient temperature and pressure superconductor. However, from both an experimental theoretical perspective, these claims are largely unsubstantiated. To this end, our synthesis subsequent analysis LK-99 sample reveals multiphase material that does not exhibit high-temperature superconductivity. We study the structure phase with single-crystal X-ray diffraction (SXRD) find consistent...

``Sub-meV'' resolution photoemission spectroscopy was used to study carbon-substitution dependence on the multiple superconducting gap of Mg(B$_{1 - x}$C$_{x})_{2}$. Two features corresponding $\sigma $ and $\pi gaps are clearly observed in raw spectra up carbon concentration x = 7.5 {%}. The two shows a qualitatively different behavior: marked change proportional $T_{c}$ variation negligible one gap. This as well temperature can be explained with two-band mean-field theory. Implications...

We report resistivity and the Hall-effect measurements in normal superconducting states of ${\mathrm{MgB}}_{2}$ single crystals. The has been found to be anisotropic with slightly temperature-dependent ratio about 3.5. Hall constant, a magnetic field parallel Mg B sheets, is negative contrast holelike response directed along c axis, indicating presence both types charge carriers and, thus, multiband electronic structure ${\mathrm{MgB}}_{2}.$ effect mixed state shows no sign change anomaly,...

We report measurements of the de Haas-van Alphen effect for single crystals MgB$_2$, in magnetic fields up to 32 Tesla. In contrast our earlier work, dHvA orbits from all four sheets Fermi surface were detected. Our results are good overall agreement with calculations electronic structure and electron-phonon mass enhancements various orbits, but there some small quantitative discrepancies. particular, systematic differences relative volumes magnitudes coupling constants could be large enough...

Raman scattering spectra from the ac face of thick MgB2 single crystals were measured in zz, xz, and xx polarizations. In zz xz polarizations a threshold at around 29 cm(-1) forms below T(c) continuum but no pair-breaking peak is seen, contrast to sharp 100 polarization. The are consistent with dirty superconductor while argues for clean system. Analysis resolves this contradiction, placing larger smaller gap magnitudes sigma pi bands indicating that relatively strong impurity restricted bands.

We present measurements of H$_{c2}(T)$ under pressure in MgB$_2$ and YNi$_2$B$_2$C. The changes the shape are interpreted within current models show evolution main Fermi surface velocities $v_F$ electron-phonon coupling parameters $\lambda$ with pressure. In strength nearly two dimensional $\sigma$ band, responsible for high critical temperature, is more affected by than $\pi$ band coupling, hole doping decreases. YNi$_2$B$_2$C, peculiar positive curvature weakened

We extract phonon contributions from the transport properties of a ${\mathrm{MgB}}_{2}$ single crystal. The temperature dependence in-plane resistivity is well explained by Bloch-Gr\"uneisen formula with Debye ${\ensuremath{\Theta}}_{D}\ensuremath{\sim}400 \mathrm{K},$ taking into account an additional contribution ${E}_{2g}$ mode $(\ensuremath{\sim}890 \mathrm{K}).$ In thermoelectric power, we find drag peak around 70 K, which gives consistent estimation ${\ensuremath{\Theta}}_{D}$ result....

The flux flow resistivity ${\ensuremath{\rho}}_{f}$ associated with purely viscous motion of vortices in high-quality ${\mathrm{MgB}}_{2}$ was measured by microwave surface impedance. Flux exhibits unusual field dependence strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover separates two distinct regimes having slopes clearly observed $\mathit{H}\ensuremath{\Vert}\mathrm{ab}$ plane. H indicates that very differently sized...

Two-phonon contributions to meV-resolved inelastic x-ray scattering spectra of MgB2 at 300K are identified, in good agreement, both intensity and energy, with a harmonic calculation using the force constant matrix from ab-inito LDA calculations. This contribution impacts determination linewidth E2g phonon mode that is so important for high Tc this material. To best our knowledge, first observation peaks measurements dispersion (q>0) due 2-phonon non-rare-gas solid.

1D charge transport offers great insight into strongly correlated physics, such as Luttinger liquids, electronic instabilities, and superconductivity. Although is observed in nanomaterials quantum wires, examples bulk crystalline solids remain elusive. In this work, it demonstrated that spin-orbit coupling (SOC) can act a mechanism to induce quasi-1D the Ln

A method is presented herein to correct for laser sheet extinction effects in performing Planar Liquid Laser Induced Fluorescence (PLLIF) dense sprays. The involves sequential illumination of the spray by counterpropagating sheets, and assumes only that occurs according Beer's law. Spray symmetry not jired. experimentally evaluated us ig a hollow cone flat fan spray. Introduction For non-fluorescing fluids, means achieving (PLLIF), dissolve fluorescent dye fluid be sprayed. When later...

The electron density distribution in ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{B}}_{2}$ has been obtained by the precise x-ray structure analysis on high-quality single crystals. A slight deficiency $(x\ensuremath{\sim}0.04)$ of Mg observed. sectional Fourier map B plane shows triangle-shaped extended along B-B bonds, which indicates typical ${\mathrm{sp}}^{2}$ orbitals boron atom. Further, difference maps clearly reveal $\mathrm{B}\ensuremath{\sigma}{(sp}^{2})$ covalent bonds within and...

The in-plane and the out-of-plane optical spectra of small single crystals Mg(B1-xCx)2 were directly determined by a microscope spectroscopy technique. Contrary to previous reports, estimated plasma frequencies for both directions are quite consistent with band calculation. A multi-Drude picture corresponding multiband system is necessary explain whole spectral profile. changes carbon substitution indicate decrease carrier concentration as well an increase scattering rate, particularly, in...