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Magnetic toroidicity is an uncommon type of magnetic structure in solid-state materials. Here, we experimentally demonstrate that collinear spins in a material with R-3 lattice symmetry can host a significant magnetic toroidicity, even parallel to the ordered spins. Taking advantage of a single crystal sample of CoTe6O13 with an R-3 space group and a Co2+ triangular sublattice, temperature-dependent magnetic, thermodynamic, and neutron diffraction results reveal A-type antiferromagnetic order below 19.5 K, with magnetic point group -3′ and k = (0,0,0). Our symmetry analysis suggests that the missing mirror symmetry in the lattice could lead to the local spin canting for a toroidal moment along the c axis. Experimentally, we observe a large off-diagonal magnetoelectric coefficient of 41.2 ps/m that evidences the magnetic toroidicity. In addition, the paramagnetic state exhibits a large effective moment per Co2+, indicating that the magnetic moment in CoTe6O13 has a significant orbital contribution. CoTe6O13 embodies an excellent opportunity for the study of next-generation functional magnetoelectric materials. © 2023, The Author(s).

The intrinsic condensate in the superconducting state of MoTe2 is incompatible with supercurrent injected from Nb contacts, as evidenced by strong stochasticity observed in the current-voltage curves. In a magnetic field H, competition between the two pair fields produces hysteresis with an anomalous sign. The differential resistance exhibits a long train of periodic peaks with a history-dependent phase noise. By tailoring the contact geometry, we demonstrate that the periodic peaks represent the fluxoid quantization of the edge supercurrent. From the oscillations we infer the existence of a condensate blockade mechanism. The intrinsic condensate is capable of blocking the pairing action of the injected supercurrent depending on the history. The blockade leads to the antihysteretic curves in both the bulk and edge states as H is cycled.

Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles density-functional theory calculations are used to study the structure, relative stability and electronic properties of Nb12O29. The optimized crystal structures are in good agreement with experimental observations and total energy calculations show similar stability of the two phases, while a magnetic electronic state is slightly favoured for m-Nb12O29. The unusual magnetism of the monoclinic phase originates from a Stoner instability that can be attributed to the Nb atoms with valence states close to Nb5+, i.e., the atoms with an electronic configuration of [similar]d0. This is in clear contradiction to current models in which the magnetism is attributed to the presence of localized Nb4+ ions with a formal d1 configuration. Our study demonstrates that in complex structures, magnetic properties are best not inferred from ionic models, but require a full quantum mechanical calculation over the whole unit cell., Quantum Nanoscience, Applied Sciences

Nb12O29 is a 4d transition metal oxide that occurs in two forms with different symmetries, monoclinic (m) and orthorhombic (o). The monoclinic form has unusual magnetic properties; below a temperature of 12 K, it exhibits both metallic conductivity and antiferromagnetic ordering. Here, first-principles density-functional theory calculations are used to study the structure, relative stability and electronic properties of Nb12O29. The optimized crystal structures are in good agreement with experimental observations and total energy calculations show similar stability of the two phases, while a magnetic electronic state is slightly favoured for m-Nb12O29. The unusual magnetism of the monoclinic phase originates from a Stoner instability that can be attributed to the Nb atoms with valence states close to Nb5+, i.e., the atoms with an electronic configuration of [similar]d0. This is in clear contradiction to current models in which the magnetism is attributed to the presence of localized Nb4+ ions with a formal d1 configuration. Our study demonstrates that in complex structures, magnetic properties are best not inferred from ionic models, but require a full quantum mechanical calculation over the whole unit cell., Quantum Nanoscience, Applied Sciences

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a ?7-doublet ground state and a ?8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a ?6-excited state resides at 32 meV; however, the ?8/?6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the ?7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound., QN/Quantum Nanoscience, Applied Sciences

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a ?7-doublet ground state and a ?8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a ?6-excited state resides at 32 meV; however, the ?8/?6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the ?7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound., QN/Quantum Nanoscience, Applied Sciences

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2, which shows a charge-density wave transition and no superconductivity. The crystal structure, characterized by high-resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers., Kavli Institute of Nanoscience, Applied Sciences

Bi2Se3 is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the Bi2Se3 layers, yielding an electron concentration of ?2×1020??cm-3, results in superconductivity at 3.8 K in CuxBi2Se3 for 0.12?x?0.15. This demonstrates that Cooper pairing is possible in Bi2Se3 at accessible temperatures, with implications for studying the physics of topological insulators and potential devices., Kavli Institute of Nanoscience, Applied Sciences

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2, which shows a charge-density wave transition and no superconductivity. The crystal structure, characterized by high-resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers., Kavli Institute of Nanoscience, Applied Sciences

Bi2Se3 is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the Bi2Se3 layers, yielding an electron concentration of ?2×1020??cm-3, results in superconductivity at 3.8 K in CuxBi2Se3 for 0.12?x?0.15. This demonstrates that Cooper pairing is possible in Bi2Se3 at accessible temperatures, with implications for studying the physics of topological insulators and potential devices., Kavli Institute of Nanoscience, Applied Sciences

Although many materials display the transition from insulating to metallic behavior on doping, only a few, such as VO2, have the right combination of crystal structure and physical properties to serve as model systems. Here we report the electronic and structural characteristics of the insulator to metal transition in V1?xMoxO2, which we have studied over the range 0.0?x?0.50 through characterization of the electrical resistivity, magnetic susceptibility, specific heat, and average- and short-range crystal structures. We find that metal-metal pairing exists in small domains in the doped metallic phases and an unexpected phenomenology for the crossover between a Curie-Weiss insulating regime and an intermediate mass metallic regime. An electronic phase diagram is presented., Kavli Institute of Nanoscience, Applied Sciences

The recently discovered iron arsenide superconductors appear to display a universal set of characteristic features, including proximity to a magnetically ordered state and robustness of the superconductivity in the presence of disorder. Here we show that superconductivity in Fe1+?Se, which can be considered the parent compound of the superconducting arsenide family, is destroyed by very small changes in stoichiometry. Further, we show that nonsuperconducting Fe1+?Se is not magnetically ordered down to 5 K. These results suggest that robust superconductivity and immediate instability against an ordered magnetic state should not be considered as intrinsic characteristics of iron-based superconducting systems., Kavli Institute of Nanoscience, Applied Sciences

Although many materials display the transition from insulating to metallic behavior on doping, only a few, such as VO2, have the right combination of crystal structure and physical properties to serve as model systems. Here we report the electronic and structural characteristics of the insulator to metal transition in V1?xMoxO2, which we have studied over the range 0.0?x?0.50 through characterization of the electrical resistivity, magnetic susceptibility, specific heat, and average- and short-range crystal structures. We find that metal-metal pairing exists in small domains in the doped metallic phases and an unexpected phenomenology for the crossover between a Curie-Weiss insulating regime and an intermediate mass metallic regime. An electronic phase diagram is presented., Kavli Institute of Nanoscience, Applied Sciences

We report the characterization of layered 2H-type CuxTaS2 for 0?x?0.12. The charge density wave (CDW), at 70 K for TaS2, is destabilized with Cu doping. The sub-1 K superconducting transition in undoped 2H-TaS2 jumps quickly to 2.5 K at low x, increases to 4.5 K at the optimal composition Cu0.04TaS2, and then decreases at higher x. The electronic contribution to the specific heat, first increasing and then decreasing as a function of Cu content, is 12 mJ mol?1 K?2 at Cu0.04TaS2. Electron-diffraction studies show that the CDW remains present at the optimal superconducting composition but with both a changed q vector and decreased coherence length. We present an electronic phase diagram for the system., Kavli Institute of Nanoscience, Applied Sciences

We report the characterization of layered 2H-type CuxTaS2 for 0?x?0.12. The charge density wave (CDW), at 70 K for TaS2, is destabilized with Cu doping. The sub-1 K superconducting transition in undoped 2H-TaS2 jumps quickly to 2.5 K at low x, increases to 4.5 K at the optimal composition Cu0.04TaS2, and then decreases at higher x. The electronic contribution to the specific heat, first increasing and then decreasing as a function of Cu content, is 12 mJ mol?1 K?2 at Cu0.04TaS2. Electron-diffraction studies show that the CDW remains present at the optimal superconducting composition but with both a changed q vector and decreased coherence length. We present an electronic phase diagram for the system., Kavli Institute of Nanoscience, Applied Sciences

Applied Sciences

Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3 blocks. These TeBi antisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1?xMnx]Te and [Bi1?2xTexMnx]Te series; in the former, the solubility is limited to x=0.067, while the latter has xmax=0.125. The magnetism in [Bi1?xMnx]Te changes little with x, while that for [Bi1?2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x>0.067. Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples., Kavli Institute of Nanoscience, Applied Sciences

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a=10.568 Å, displaying a structure type for which no previous superconductors have been reported., Kavli Institute of Nanoscience, Applied Sciences

type:text, Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation+Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.

Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation+Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.

Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation+Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.

Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3 blocks. These TeBi antisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1?xMnx]Te and [Bi1?2xTexMnx]Te series; in the former, the solubility is limited to x=0.067, while the latter has xmax=0.125. The magnetism in [Bi1?xMnx]Te changes little with x, while that for [Bi1?2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x>0.067. Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples., Kavli Institute of Nanoscience, Applied Sciences

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a=10.568 Å, displaying a structure type for which no previous superconductors have been reported., Kavli Institute of Nanoscience, Applied Sciences

Applied Sciences

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Mechanical, Maritime and Materials Engineering

Applied Sciences

Applied Sciences

Mechanical, Maritime and Materials Engineering

Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation+Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.