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Strongly correlated ground states and exotic quasiparticle excitations in low-dimensional systems are central research topics in the solid state research community. The present work develops a new layered material and explores the physical properties. Single crystals of 3R-Na2MnTeO6 were synthesized via a flux method. Single crystal x-ray diffraction and transmission electron microscopy reveal a crystal structure with ABC-type stacking and an R-3 space group, which establishes this material as a stacking polytype to previously reported 2H-Na2MnTeO6. Magnetic and heat capacity measurements demonstrate dominant antiferromagnetic interactions, the absence of long-range magnetic order down to 0.5 K, and field-dependent short range magnetic correlations. A structural transition at ~ 23 K observed in dielectric measurements may be related to displacements of the Na positions. Our results demonstrate that 3R-Na2MnTeO6 displays low-dimensional magnetism, disordered structure and spins, and the system displays a rich structure variety.

When an electron is incident on a superconductor from a metal, it is reflected as a hole in a process called Andreev reflection. If the metal

The single-crystal growth, crystal structure, heat capacity, and anisotropic magnetization characterization of Rb3Yb(PO4)2, a Yb-based triangular lattice material, are presented. Single-crystal X-r...

Pairs on the edge Many materials with topologically nontrivial band structures are characterized by currents that run around the edge of the sample and typically consist of single excitations. It is an open question whether a topological material that is also a superconductor can support an edge current that consists of paired excitations. W. Wang et al. studied the Weyl superconductor molybdenum ditelluride and, using systematic transport measurements in the presence of a magnetic field, revealed the signatures of an edge supercurrent. Science , this issue p. 534

We present the crystallographic analysis, superconducting characterization and theoretical modeling of LiBi, that contains the lightest and the heaviest nonradioactive metal. The compound crystallizes in a tetragonal (CuAu-type) crystal structure with Bi square nets separated by Li planes (parameters a = 3.3636(1) Å and c = 4.2459(2) Å, c/a = 1.26). Superconducting state was studied in detail by magnetic susceptibility and heat capacity measurements. The results reveal that LiBi is a moderately coupled type-I superconductor (λe-p = 0.66) with Tc = 2.48 K and a thermodynamic critical field Hc(0) = 157 Oe. Theoretical studies show that bismuth square net is responsible for superconductivity in this compound, but the coupling between the Li planes and Bi planes makes a significant contribution to the superconductivity.

A previously unreported 1D iridate, K3Ir2O6, has been grown by a flux method in O2-rich environment, and its crystal structure was determined via single crystal structural analysis. It exhibits straight chains of face-sharing [IrO6] octahedra, which are arranged along the crystallographic c axis, separated by nonmagnetic K ions. No magnetic transitions are observed during measured range, and the material is electrically insulating. Potentially interesting electronic behavior for K3Ir2O6 is supported by electronic structure calculations. A structurally related material, K16.3Ir8O30, which displays similar fundamental geometric units but in a different spatial arrangement-zigzag chains-based on edge and face sharing [IrO6] octahedra, is also reported. Both materials are of interest for probing the properties of a 1D system with strong spin-orbit coupling.

KIrO3 in the body-centered cubic variant of the KSbO3-type structure is reported. Black cube-shaped single crystals, obtained from the solid-state reaction in a half-closed silver capsule in a sealed quartz tube, were used for the structural characterization by single-crystal X-ray diffraction. The material, space group Im (no. 204), exhibits a disordered K array and a three-dimensional (3D) IrO6-based tunnel-like framework. Temperature-dependent magnetization and heat capacity measurements suggest a paramagnetic state for KIrO3, with significant contribution of temperature independent paramagnetism and without any sign of long-range magnetic ordering (down to 1.8 K). The 3D motif of this material, based on the 5d Ir5+ ion, is of interest for investigating unconventional magnetism.

We identify candidate loss channels in tantalum by correlating X-ray photoelectron spectroscopy measurements with power and temperature dependent variation of the quality factor of superconducting coplanar waveguide microwave resonators.

When a normal metal $N$ is sandwiched between two superconductors, the energy gaps in the latter act as walls that confine electrons in $N$ in a square-well potential. If the voltage $V$ across $N$ is finite, an electron injected into the well undergoes multiple Andreev reflections (MAR) until it gains enough energy to overcome the energy barrier. Because each reflection converts an electron to a hole (or vice versa), while creating (or destroying) a Cooper pair, the MAR process shuttles a stream of pairs across the junction. An interesting question is, given a finite $V$, what percentage of the shuttled pairs end up as a Josephson supercurrent? This fraction does not seem to have been measured. Here we show that, in high-transparency junctions based on the type II Dirac semimetal MoTe$_2$, the MAR leads to a stair-case profile in the current-voltage ($I$-$V$) response, corresponding to pairs shuttled incoherently by the $n^{th}$-order process. By varying the phase $\varphi$ across the junction, we demonstrate that a Josephson supercurrent ${\bf J}_{\rm s}\sim \sin\varphi$ co-exists with the MAR steps, even at large $V$. The observed linear increase in the amplitude of ${\bf J}_{\rm s}$ with $n$ (for small $n$) implies that ${\bf J}_{\rm s}$ originates from the population of pairs that are coherently shuttled. We infer that the MAR steps and the supercurrent are complementary aspects of the Andreev process. The experiment yields the percentage of shuttled pairs that form the supercurrent. At large $V$, the coherent fraction is initially linear in $n$. However, as $V\to 0$ ($n\gg 1$), almost all the pairs end up as the observed Josephson supercurrent., Comment: 12 pages, 6 figures

Many magnetic materials have quantum disordered magnetic ground states, but it is not always clear what drives them. Here, the authors study the pyrochlore magnet Nd${}_{2}$ScNbO${}_{7}$ using neutron diffraction, heat capacity, and neutron-sampled nuclear hyperfine excitations. The static magnetic moments inferred from these three techniques are inconsistent, pointing to some fraction of spins remaining dynamic to the lowest temperatures -- an observation confirmed by the anomalous low-energy density of states in the specific heat. Similar behavior is seen in Nd${}_{2}$Zr${}_{2}$O${}_{7}$. It could indicate either quantum spin-liquid behavior or local disorder-induced spin singlets.

Triangular Heisenberg antiferromagnets are prototypes of geometric frustration, even if for nearest-neighbor interactions quantum fluctuations are not usually strong enough to destroy magnetic ordering: stronger frustration is required to stabilize a spin-liquid phase. On the basis of static magnetization and electron spin resonance measurements, we demonstrate the emergence of ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{j}}_{\text{eff}}=\frac{1}{2}$ moments in the triangular-lattice magnet ${\mathrm{Na}}_{2}\mathrm{Ba}\mathrm{Co}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$. These moments are subject to an extra source of frustration that causes magnetic correlations to set in far above both the magnetic ordering and Weiss temperatures. Corroborating the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{j}}_{\text{eff}}=\frac{1}{2}$ ground state, theory identifies ferromagnetic Kitaev exchange anisotropy as an additional frustrating agent, altogether putting forward ${\mathrm{Na}}_{2}\mathrm{Ba}\mathrm{Co}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ as a promising Kitaev spin-liquid material.

The layered honeycomb lattice material α-RuCl3 has emerged as a prime candidate for displaying the Kitaev quantum spin liquid state and as such has attracted much research interest. Here we describe a new layered honeycomb lattice polymorph of RuI3 , a material that is strongly chemically and structurally related to α-RuCl3. The material is synthesized at moderately elevated pressures and is stable under ambient conditions. Preliminary characterization reveals that it is a metallic conductor, with the absence of long-range magnetic order down to 0.35 K and an unusually large T-linear contribution to the heat capacity. We propose that this phase, with a layered honeycomb lattice and strong spin-orbit coupling, provides a new route for the characterization of quantum materials. This article is protected by copyright. All rights reserved.

Quantum spin liquids (QSLs) are topologically ordered states of matter that host fractionalized excitations. A particular route towards a QSL is via strongly bond-dependent interactions on the hexagonal lattice. A number of Ru- and Ir-based candidate Kitaev QSL materials have been pursued, but all have appreciable non-Kitaev interactions. Using time-domain terahertz spectroscopy, we observed a broad magnetic continuum over a wide range of temperatures and fields in the honeycomb cobalt-based magnet BaCo

We report the synthesis and physical properties of a full Heusler compound, $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$, which we found to show superconductivity below ${T}_{c}=2.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure [$Fm\text{\ensuremath{-}}3m, a=6.4523(1)\phantom{\rule{0.16em}{0ex}}\AA{}$] were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ is a type-II, weak coupling superconductor (${\ensuremath{\lambda}}_{e\text{\ensuremath{-}}p}=0.53$). The observed pressure dependence of ${T}_{c}$ ($\mathrm{\ensuremath{\Delta}}{T}_{c}/p\ensuremath{\approx}--0.23\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{GPa}$) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in $\mathrm{Mg}{\mathrm{Pd}}_{2}\mathrm{Sb}$ were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters to those of all reported Heusler-type superconductors.

We present the synthesis, structure, and magnetic properties of the novel borate LaNiB3O7 – the first magnetically ordered compound reported in the CaAlB3O7 structure type. This material is made of alternating sheets of corner-sharing borate tetrahedra and planes of La and Ni ions, with distorted nickel oxide [NiO6] octahedra and lanthanum oxide [LaO10] polyhedra. Temperature-dependent magnetic susceptibility data reveal dominantly antiferromagnetic interactions and an antiferromagnetic transition with a Neel temperature of 19 K, confirmed by specific heat data. The magnetic moment per nickel ion is 3.06 μB. This compound uncovers a new family of rare-earth transition-metal borates to probe for magnetic interactions.

A recurring theme in topological matter is the protection of unusual electronic states by symmetry, for example, protection of the surface states in Z2 topological insulators by time reversal symmetry [1-3]. Recently interest has turned to unusual surface states in the large class of nonsymmorphic materials [4-11]. In particular KHgSb is predicted to exhibit double quantum spin Hall (QSH) states [10]. Here we report observation of a novel feature of the Hall conductivity in KHgSb in strong magnetic field B. In the quantum limit, the Hall conductivity is observed to fall exponentially to zero, but the diagonal conductivity is finite. A large gap protects this unusual zero-Hall state. We propose that, in this limit, the chemical potential drops into the bulk gap, intersecting equal numbers of right and left-moving QSH surface modes to produce the zero-Hall state., 7 pages, 4 figures

A previously unreported family of electrically insulating rare-earth borates, RbBaR(BO3)2 (R = Y, Gd–Yb), was designed and then successfully obtained by traditional solid-state reaction. They crystallize in a monoclinic crystal system space group P21/m (No. 11). They feature triangular planar rare-earth (R) lattices, which are part of, for example, [Yb(BO3)2]3– infinite 2D layers. These R-based triangular lattices are stacked with layers of crystallographically ordered Rb and Ba atoms to build the 3D structures. Polycrystalline samples of RbBaR(BO3)2 were used to study the elementary magnetic properties, and millimeter-size RbBaYb(BO3)2 single crystals were grown by spontaneous nucleation for further anisotropic magnetic characterization. Antiferromagnetic spin interactions are observed for all magnetic compounds, and no long-range magnetic ordering is found down to 1.8 K. Our results suggest that this RbBaR(BO3)2 (R = Gd–Yb) family may be of further interest both experimentally and theoretically as highl...

We show that the previously unreported ternary σ phases Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are both superconductors with Tc values of approximately 1.9 K. The superconducting transitions were characterized through temperature-dependent magnetic susceptibility, electrical resistance, and specific heat measurements. The Sommerfeld constants, γ, for Nb20.4Rh5.7Ge3.9 and Nb20.4Rh5.7Si3.9 are 89(1) mJ mol-f.u.−1K−2 and 86(1) mJ mol-f.u.−1K−2 (about 3.0 and 2.9 mJ mol-atom−1 K−2), respectively. The normalized specific heat jumps at Tc, ΔC/γTc, are approximately 1.39 for Nb20.4Rh5.7Ge3.9 and 1.30 for Nb20.4Rh5.7Si3.9, consistent with both materials being weakly coupled BCS type superconductors.

Radio-frequency (14.6 MHz) AC magnetic susceptibility, $\chi^{\prime}_{AC}$, of \dytio\ was measured using a self-oscillating tunnel-diode resonator. Measurements were made with the excitation AC field parallel to the superimposed DC magnetic field up 5 T in a wide temperature range from 50 mK to 100 K. At 14.6 MHz a known broad peak of $\chi^{\prime}_{AC}(T)$ from kHz - range audio-frequency measurements around 15~K for both [111] and [110] directions shifts to 45~K, continuing the Arrhenius activated behavior with the same activation energy barrier of $E_a \approx 230$~K. Magnetic field dependence of $\chi^{\prime}_{AC}$ along [111] reproduces previously reported low-temperature two-in-two-out to three-in-one-out spin configuration transition at about 1~T, and an intermediate phase between 1 and 1.5~T. The boundaries of the intermediate phase show reasonable overlap with the literature data and connect at a critical endpoint of the first-order transition line, suggesting that these low-temperature features are frequency independent. An unusual upturn of magnetic susceptibility at $T \to 0$ was observed in magnetic fields between 1.5~T and 2~T for both magnetic field directions, before fully polarized configuration sets in above 2~T.

Radio-frequency (14.6 MHz) AC magnetic susceptibility,χAC', of Dy

The realization of quantum spin liquids on a triangular lattice magnet remains challenging due to quenched disorders present in real materials. Here, we report local-probe signatures of spin-liquid-like excitations in the structurally perfect triangular antiferromagnet ${\mathrm{Na}}_{2}\mathrm{BaCo}{({\mathrm{PO}}_{4})}_{2}$. Our zero-field and longitudinal-field muon spin relaxation measurements reveal both spatially and temporally correlated spins with no hint of static magnetism down to 80 mK, consistent with a quantum spin liquid. Comprehensive $^{23}\mathrm{Na}$ nuclear magnetic resonance experiments enable us to identify a field-induced crossover of magnetic excitations from a spinonlike to a gapped magnon at the critical field ${\ensuremath{\mu}}_{0}{H}_{C}=1.65$ T. Our findings uncover the temporal, thermal, and magnetic-field characteristics of the magnetic excitations in the triangular-lattice quantum spin liquid candidate ${\mathrm{Na}}_{2}\mathrm{BaCo}{({\mathrm{PO}}_{4})}_{2}$.

KIrO3 in the body-centered cubic variant of the KSbO3-type structure is reported. Black cube-shaped single crystals, obtained from the solid-state reaction in a half-closed silver capsule in a sealed quartz tube, were used for the structural characterization by single-crystal X-ray diffraction. The material, space group Im3[combining macron] (no. 204), exhibits a disordered K array and a three-dimensional (3D) IrO6-based tunnel-like framework. Temperature-dependent magnetization and heat capacity measurements suggest a paramagnetic state for KIrO3, with significant contribution of temperature independent paramagnetism and without any sign of long-range magnetic ordering (down to 1.8 K). The 3D motif of this material, based on the 5d Ir5+ ion, is of interest for investigating unconventional magnetism.

A study of the layered triangular lattice materials ${\mathrm{K}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{2}$ and ${\mathrm{Rb}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{2}$ is reported. These isostructural compounds crystallize in the trigonal space group $R\ensuremath{-}3m$ (No. 166). The magnetic $\mathrm{C}{\mathrm{o}}^{2+}$ ions form a spin-1/2 triangular lattice and display strongly frustrated magnetism. We find no evidence in the susceptibility or heat capacity for in-plane ordering of the spins; rather the in-plane inverse susceptibility is typical of that seen for frustrated magnets. At around 10 K, a ferromagnetic component appears in the magnetic susceptibility perpendicular to the triangular planes. The heat capacity at low applied fields does not show sharp features, but in larger applied fields a sharp ferromagneticlike transition appears. Field- and direction-dependent magnetization measurements at 2 K indicate that both materials have a magnetic easy axis perpendicular to the triangular planes. The magnetic properties are sensitive to the field applied perpendicular to the triangular planes, which induces a metamagnetization transition at 0.75 T. Spin polarization develops along with the increasing out-of-plane field, resulting in a saturated ferromagnetic state at high fields. In contrast, the magnetic properties are resistant to the in-plane field. Our results suggest that these materials are embodiments of Ising spins on triangular lattices with easy-axis anisotropy.

Here, the authors perform ultrasound velocity measurements in the frustrated pyrochlore fluoride NaCaCo${}_{2}$F${}_{7}$, which exhibits spin freezing below ${T}_{f}$ $\ensuremath{\sim}$ 2.4 K with the inherent presence of exchange disorder. In this cubic magnet, the bulk modulus and the trigonal shear modulus exhibit anomalies at temperatures below $\ensuremath{\sim}$20 K down to ${T}_{f}$, which reveal an occurrence of magnetic field induced crossover from an isostructural lattice instability toward the spin freezing to a trigonal lattice instability arising from the emergent dynamical spin-cluster state.

The crystal structures of the $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{Ru}{\mathrm{O}}_{3}(0\ensuremath{\le}x\ensuremath{\le}1)$ perovskites are investigated using both long-range and local structural probes. High-resolution synchrotron powder x-ray-diffraction characterization at ambient temperature shows that the materials have orthorhombic long-range crystal structures to high precision, and we support previous work showing that $\mathrm{C}{\mathrm{a}}^{2+}$ substitution for $\mathrm{S}{\mathrm{r}}^{2+}$ primarily changes the tilting of rigid corner-sharing $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedra at their shared oxygen vertices. X-ray pair-distribution function analysis for $\mathrm{SrRu}{\mathrm{O}}_{3},\mathrm{CaRu}{\mathrm{O}}_{3}$, and one intermediate composition show them to display monoclinic symmetry at the local level; when averaged over different domain orientations this yields orthorhombic symmetry in the long range, and no long-range or local phase transitions are observed between 80 and 300 K for materials with intermediate compositions. High-resolution transmission electron microscopy shows that the Sr/Ca distribution is random at the nanoscale. We plot magnetic characteristics such as the ferromagnetic $T\text{c}$, Curie-Weiss theta, effective moment, and ambient temperature susceptibility vs the octahedral tilt and unit-cell volume.

After the recent finding that CrI

After the recent finding that CrI3, displays ferromagnetic order down to its monolayer, extensive studies have followed to pursue new two-dimensional (2D) magnetic materials. In this article, we report on the growth of single crystal CrCl3 in the layered monoclinic phase. The system after mechanical exfoliation exhibits stability in ambient air (the degradation occurs on a time scale at least four orders of magnitude longer than is observed for CrI3). By means of mechanical cleavage and atomic force microscopy (AFM) combined with optical identification, we demonstrate the systematic isolation of single and few layer flakes onto 270 nm and 285 nm SiO2/Si (100) substrates with lateral size larger than graphene flakes isolated with the same method. The layer number identification has been carried with statistically significant data, quantifying the optical contrast as a function of the number of layers for up to six layers. Layer dependent optical contrast data have been fitted within the Fresnel equation formalism determining the real and imaginary part of the wavelength dependent refractive index of the material. A layer dependent (532 nm) micro-Raman study has been carried out down to two layers with no detectable spectral shifts as a function of the layer number and with respect to the bulk.

The magnetic properties of transparent pink Na2Mn3Cl8 and NaMnCl3 are presented. For both phases, the effective magnetic moments are large, while the Curie-Weiss thetas are below 10 K. The compounds crystallize in the Trigonal R-3m and R-3 space groups, respectively. A Kagome plane of Mn2+ octahedrally coordinated to Cl− is found in Na2Mn3Cl8 and the material has no apparent magnetic ordering above 1.8 K, while the octahedrally coordinated, honeycomb network of Mn2+ in NaMnCl3 orders antiferromagnetically at 6.3 ± 0.2 K. The heat capacity of NaMnCl3 has one transition, consistent with the susceptibility; while Na2Mn3Cl8 exhibits a more complex heat capacity with two peaks, at 0.7 K and 1.2 K. A third, broad peak near 6.2 K in the heat capacity of Na2Mn3Cl8 is problematic but may be due to the intergrowth of domains of NaMnCl3.

We report the magnetic structure and electronic properties of the honeycomb antiferromagnet $\rm NaNi_2BiO_{5.66}$. We find magnetic order with moments along the $c$ axis for temperatures below $T_{c1}=6.3(1)\>{\rm K}$ and then in the honeycomb plane for $T {\rm K}$ with a counterrotating pattern and an ordering wave vector ${\bf q}=(\frac{1}{3},\> \frac{1}{3},\> 0.15(1))$. Density functional theory and electron spin resonance indicate this is high-spin Ni$^{3+}$ magnetism near a high to low spin transition. The ordering wave vector, in-plane magnetic correlations, missing entropy, spin state, and superexchange pathways are all consistent with bond-dependent Kitaev-$\Gamma$-Heisenberg exchange interactions in $\rm NaNi_2BiO_{6-\delta}$.

The indium-rich intermetallic compound LaPdIn 4 is reported, prepared by arc-melting and annealing at 600 °C. Single crystal X-ray diffraction found the material to be orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.5462(3) A, b = 16.9208(10) A, and c = 7.3100(5) A. This previously unreported indide is isostructural with LaNiIn 4 and LaPtIn 4 . It is demonstrated that all three compounds in the La T In 4 ( T = Ni, Pd, Pt) family display metallic behavior with resistivity values between 20 and 30 μΩ-cm at 250 K. In addition, temperature and field-dependent magnetization measurements between 2 and 250 K show all to be weak paramagnets or diamagnets, with very small amounts of spin-bearing impurities present. The field-dependent magnetization showed evidence of de Haas-van Alphen quantum oscillations in the Pd and Pt containing compounds near applied fields of 5 T.

Following the predictions of total energy calculations, a tetragonal SrMn2P2 phase is proposed and successfully formed under high pressure. At ambient pressure, SrMn2P2 adopts the primitive trigonal La2O3 structure type (space group P3[combining macron]m1). However, the results of total energy calculations indicate that SrMn2P2 should be more stable in the tetragonal ThCr2Si2 structure type (space group I4/mmm) than in its known trigonal structure, thus motivating our synthetic experiments. Guided by these calculations, a new tetragonal polymorph of SrMn2P2 was found under the relatively mild conditions of 5 GPa applied pressure at a temperature of 900 °C through the transformation of the ambient pressure trigonal form. The new polymorph has the body centered tetragonal ThCr2Si2 structure type, as predicted. The electronic structure calculations indicate the likelihood of antiferromagnetic, semiconducting properties for the high pressure SrMn2P2 phase.