An intrinsic magnetic tunnel junction: An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so-called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI ₃ sandwiched between graphite contacts. By varying the number of layers in the samples, Klein et al. and Song et al. found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields. Science , this issue p. 1218 , p. 1214

We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of ${\mathrm{WTe}}_2$, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in ${\mathrm{WTe}}_2$ were proposed to emerge at the crossing points of electron and hole pockets, and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in ${\mathrm{WTe}}_2$ confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in ${\mathrm{WTe}}_2$. We also find that trivial and topological domains coexist on the same surface of the sample due to the presence of inhomogeneous strain detected by scanning electron microscopy data. This is in agreement with the theoretical prediction that strain can drive this system from topological Weyl to trivial semimetal. ${\mathrm{WTe}}_2$ therefore provides a tunable playground for studying exotic topological quantum effects.

Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related and phases and (ii) and .

We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of ${\mathrm{WTe}}_2$, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the $X\text{−}\mathrm{\Gamma }\text{−}X$ direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at $T\simeq 160\mathrm{K}$, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential $\mu (T)$ due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at $T\approx 175\mathrm{K}$ and a breakdown of Kohler’s rule in the 70–140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.

Heavy fermion compounds represent one of the most strongly correlated forms of electronic matter and give rise to low temperature states that range from small moment ordering to exotic superconductivity, both of which are often in close proximity to quantum critical points. These strong electronic correlations are associated with the transfer of entropy from the local moment degrees of freedom to the conduction electrons, and, as such, are intimately related to the low temperature degeneracy of the (originally) moment bearing ion. Here we report the discovery of six closely related Yb-based heavy fermion compounds, YbT ₂ Zn ₂₀ , that are members of the larger family of dilute rare earth bearing compounds: RT ₂ Zn ₂₀ (T = Fe, Co, Ru, Rh, Os, Ir). This discovery doubles the total number of Yb-based heavy fermion materials. Given these compounds' dilute nature, systematic changes in T only weakly perturb the Yb site and allow for insight into the effects of degeneracy on the thermodynamic and transport properties of these model correlated electron systems.

Single-crystalline, single-phase ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ has been grown out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, $T_c=35.0\pm 0.2$ K. Other than superconductivity, there is no indication of any other phase transition for $1.8\text{K}\le T\le 300$ K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped $\left({\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\right){\mathrm{Fe}}_2{\mathrm{As}}_2$, suggesting that stoichiometric ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ is intrinsically close to what is referred to as “optimal-doped” on a generalized, Fe-based superconductor, phase diagram. The anisotropic superconducting upper critical field, $H_{c\text{2}}\left(T\right)$, of ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ was determined up to 630 kOe. The anisotropy parameter $\gamma \left(T\right)=H_{c\text{2}}^{\perp }/H_{c\text{2}}^{\parallel }$, for $H$ applied perpendicular and parallel to the $c$ axis, decreases from $\simeq 2.5$ at $T_c$ to $\simeq 1.5$ at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of $d{H}_{c\text{2}}^{\parallel }/dT\simeq -44$ kOe/K and $d{H}_{c\text{2}}^{\perp }/dT\simeq -109$ kOe/K at $T_c$ yield an electron mass anisotropy of $m_{\perp }/m_{\parallel }\simeq 1/6$ and short Ginzburg-Landau coherence lengths ${\xi }_{\parallel }\left(0\right)\simeq 5.8\text{Å}$ and ${\xi }_{\perp }\left(0\right)\simeq 14.3\text{Å}$. The value of $H_{c\text{2}}^{\perp }\left(0\right)$ can be extrapolated to $\simeq 920$ kOe, well above the BCS paramagnetic limit.