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The bi-component ZnO/ZnCo 2 O 4 nanocomposites are prepared via a facile and scalable synthesis method by controlling the ratio of Zn to Co in the synthesis stage. The ZnO/ZnCo 2 O 4 nanocomposites built from the interconnecting porous nanosheets possess loose porous nanostructures with abundant open space and electroactive surface sites. When evaluated as an anode material for lithium ion batteries, the ZnO/ZnCo 2 O 4 nanocomposite electrode exhibits high capacity, good cycling stability (1086 mAh g −1 at 100 mA g −1 after 80 cycles and 847 mAh g −1 at 500 mA g −1 after 200 cycles), and excellent rate capability (∼538 mAh g −1 at 3200 mA g −1 ), which is superior to most of the previously-reported ZnO-based or ZnCo 2 O 4 -based electrode materials. The superior electrochemical performances of the ZnO/ZnCo 2 O 4 nanocomposites are attributed to the loose porous structure, which can buffer the volume expansion and increase the contact area between the electrode and electrolyte. Moreover, a strong synergistic effect between the Zn and Co occurs during the lithiation/delithiation process, where the Zn and Co are acting as mutually beneficial matrix ions to effectively alleviate the large mechanical stress caused by the severe volume change, and thus bring about high and stable capacity.

Bi 2− x Ca x Ir 2 O 7− δ ( x =0, 0.1, 0.2, 0.3, and 0.4) pyrochlore iridates were prepared by the solid-state reaction method in air. In this paper we reported a systematic study of hole-doped Bi 2− x Ca x Ir 2 O 7− δ by performing crystal structure, electrical transport and magnetic measurements. A high-crystallized Bi 2– x Ca x Ir 2 O 7– δ with a cubic structure was obtained. Because Bi 3+ was substituted in a random way by Ca 2+ which has relatively smaller ionic radius, disorder and phononic oscillations were induced and the the length of Ir–O bands were reduced. The doped samples were found to exhibit metal–insulator transition. Magnetic measurements on the doping samples indicated a shift towards nonmagnetic Ir 5+ , and the anti-ferromagnetism was weakened.

We have studied the vortex dynamics of the Tl0.4 K 0.41Fe2−y Se2 single crystal through the measurements of temperature and magnetic field dependencies of electrical resistivity. Due to the existence of intra-layer Fe-site vacancy and inter-layer Josephson coupling, it is found that the pinning of vortices is very strong, which hinders the flux flow. A very high upper critical field H c2 value and a moderate anisotropy parameter γ are obtained, similar to those found in YBa2Cu3O7−δ superconductor. These results suggest that the Tl0.4 K 0.41Fe2−y Se2 superconductor has a good sustainability under high magnetic field, indicating a good potential for application.

The B20 compound MnSi exhibits a skyrmion phase in a certain range of temperature (T) and external magnetic field (H) in addition to the helimagnetic ordering. In this work, the magnetic entropy change (ΔSM) in the single crystal helimagnet MnSi has been investigated by the scaling analysis. The ΔSM(T,H) curves in higher field range (2 kOe [ Δ S M s k X ( T , H ) ] can be derived by subtraction of the calculated Δ S M c a l ( T , H ) from the experimental Δ S M e x p ( T , H ) . The obtained results show that Δ S M s k X reaches the maximum at ∼1.6 kOe, which indicates the highest number of skyrmion vortices at that field.

We report a detailed study of magnetic properties in double perovskite iridate ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal, which exhibits an antiferromagnetic (AFM) ground state. The field- and angle-dependent magnetizations $[M(H)$ and $M(\ensuremath{\varphi})]$ suggest strong magnetic anisotropy in this system. The magnetization of ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ is isotropic in the $ab$ plane, while it is much stronger than that along the $c$ axis. A field-induced magnetic transition from AFM to ferromagnetic (FM) state is found, which is of a first-order type. The critical behavior is investigated, where critical exponents $\ensuremath{\beta}=0.2317(1),\phantom{\rule{0.28em}{0ex}}\ensuremath{\gamma}=0.9783(2)$, and $\ensuremath{\delta}=5.0071(5)$ are obtained. The critical exponents belong to the universality class of the tricritical mean-field model, which indicates a field-induced tricritical phenomenon. Based on the scaling equations, we construct the $H\text{\ensuremath{-}}T$ phase diagram for ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal with $H//b$. A tricritical point is revealed at the intersection point between the AFM, FM, and paramagnetic phases (${T}_{tr}\ensuremath{\approx}8$ K; ${H}_{tr}\ensuremath{\approx}170$ Oe).

A giant planar Hall effect (PHE) and anisotropic magnetoresistance (AMR) is observed in TaP, a nonmagnetic Weyl semimetal with ultrahigh mobility. The perpendicular resistivity (i.e., the planar magnetic field applied normal to the current) far exceeds the zero-field resistivity, which thus rules out the possible origin of negative longitudinal magnetoresistance. The giant PHE/AMR is finally attributed to the large anisotropic orbital magnetoresistance that stems from the ultrahigh mobility. Furthermore, the mobility-enhanced current jetting effects are found to strongly deform the line shape of the curves, and their evolution with the changing magnetic field and temperature is also studied. Although the giant PHE/AMR suggests promising applications in spintronics, the enhanced current jetting shows the other side of the coin, which needs to be considered in the future device design., Physical Review Materials

We report the experimental realization of a Dirac semimetal state in NdSb, a material with antiferromagnetic ground state. The occurrence of a topological semimetal state has been well supported by our band structure calculations and the experimental observation of chiral-anomaly-induced negative magnetoresistance. A field-induced Fermi surface reconstruction is observed in response to the change of spin polarization. The observation of a topological semimetal state in a magnetic material provides an opportunity to investigate the magnetotopological phenomena.

Whether or not epitaxially grown superconducting films have the same bulk-like superconducting properties is an important concern. We report the structure and the electronic properties of epitaxially grown Ba(Fe1-xCox)2As2 films using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). This film showed a different surface structure, (2sqrtx2sqrt2)R45 reconstruction, from those of as-cleaved surfaces from bulk crystals. The electronic structure of the grown film is different from that in bulk, and it is notable that the film exhibits the same superconducting transport properties. We found that the superconducting gap at the surface is screened at the Ba layer surface in STS measurements, and the charge density wave was observed at the surface in sample in the superconducting state., Comment: 24 pages 8 figures

The electronic structures of a representative rare earth monopnictide (i.e., DySb) under high magnetic field (i.e., in the ferromagnetic state) are studied from both experimental and theoretical aspects. A non-saturated extremely large positive magnetoresistance (XMR) is observed (as large as 3.7 × 104% at 1.8 K and 38.7 T), along with the Shubnikov-de Haas oscillations that are well reproduced by our first principles calculations. Three possible origins of XMR are examined. Although a band inversion is found theoretically, suggesting that DySb might be topologically nontrivial, it is deeply underneath the Fermi level, which rules out a topological nature of the XMR. The total densities of electron-like and hole-like carriers are not fully compensated, showing that compensation is unlikely to account for the XMR. The XMR is eventually understood in terms of high mobility that is associated with the steep linear bands. This discovery is important to the intensive studies on the XMR of rare earth monopnictides.The electronic structures of a representative rare earth monopnictide (i.e., DySb) under high magnetic field (i.e., in the ferromagnetic state) are studied from both experimental and theoretical aspects. A non-saturated extremely large positive magnetoresistance (XMR) is observed (as large as 3.7 × 104% at 1.8 K and 38.7 T), along with the Shubnikov-de Haas oscillations that are well reproduced by our first principles calculations. Three possible origins of XMR are examined. Although a band inversion is found theoretically, suggesting that DySb might be topologically nontrivial, it is deeply underneath the Fermi level, which rules out a topological nature of the XMR. The total densities of electron-like and hole-like carriers are not fully compensated, showing that compensation is unlikely to account for the XMR. The XMR is eventually understood in terms of high mobility that is associated with the steep linear bands. This discovery is important to the intensive studies on the XMR of rare earth monopnictides.

The pyrochlore iridate has been investigated by means of the electron paramagnetic resonance spectroscopy. A magnetic transition at 20 K is found in addition to the transition at 130 K, which has not been reported previously. The phase transition at , which corresponds to a resistivity transition, is resulted from the long-range spin ordering of ions in all-in/all-out state. However, the magnetic transition at , which is regardless of resistivity transition, is not caused by but ions. Both of the magnetic transitions are irrelevant to the lattice distortion. We suggest that the competition between the enhanced paramagnetism of ions and the f–d interaction should be responsible for the magnetic transition at .

We have studied the magnetic properties of spin-frustrated compound Dy 2 Ti 2− x V x O 7 single crystals. Bulk magnetization data show that ferromagnetic interaction enhances with increasing content of V, resulting from the ferromagnetic interactions between Dy and V ions. It is also found from ac susceptibility that the modestly doped samples ( x ≤0.4) still keep ice state, demonstrating the robustness of spin ice. When the doped concentration increases up to 0.5, more disorder on B site and internal field associated with V 4+ ions would affect the macroscopic ground-state degeneracy and relieve the frustration, leading to the disappearance of spin ice and occurrence of a spin-glass-like transition. The magnetic properties of the system are related to magnetic frustration and local structural disorder.

One-dimensional porous anhydrous cobalt oxalate nanorods are prepared via a facile water-controlled coprecipitate method followed by thermal annealing treatment under N 2 at 300 °C. The nanorods are characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. When evaluated as an anode material for lithium ion batteries, the nanorods exhibit high reversible specific capacity and excellent cycling stability (924 mA h g −1 at 50 mA g −1 after 100 cycles and 709 mA h g −1 at 200 mA g −1 after 220 cycles). This remarkable electrochemical performance is attributed to the one-dimensional porous nanostructure that can provide large electrode/electrolyte contact area and short lithium-ion diffusion pathway, meanwhile reduce the volume expansion during the repeated discharge/charge process.

The magnetic studies have been carried out on the R-doped La0.5Ba0.5Co0.9R0.1O3 (R = Cu, Zn, Cr, Ni, Ti and Ru) cobaltites. X-ray absorption near-edge structure (XANES) proves these ions are in the valence state of Cu2+, Zn2+, Cr3+, Ni3+, Ti4+ and Ru4+. Magnetic moment calculation shows both Co3+ and Co4+ hold in the intermediate spin state. Based on the ratio of Co3+/Co4+, the average B-site size, the tolerance factor and electron itinerancy, the different influence of these ions on the magnetism were discussed. Among all these ions, Cr3+ gives an extraordinary effect of enhancing TC a lot. It is attributed to the Co-O-Cr exchange interaction, which is confirmed by the electron spin resonance spectra. The typical magnetotransport behavior implies a double-exchange property of this exchange interaction.

Superconductor–insulator transition (SIT) in one-dimensional (1D) nanowires attracts great attention in the past decade and remains an open question since contrasting results were reported in nanowires with different morphologies (i.e., granular, polycrystalline, or amorphous) or environments. Nb2PdS5 is a recently discovered low-dimensional superconductor with typical quasi-1D chain structure. By decreasing the wire diameter in the range of 100–300 nm, we observed a clear SIT with a 1D transport character driven by both the cross-sectional area and external magnetic field. We also found that the upper critical magnetic field (Hc2) decreases with the reduction of nanowire cross-sectional area. The temperature dependence of the resistance below Tc can be described by the thermally activated phase slip (TAPS) theory without any signature of quantum phase slips (QPS). These findings demonstrated that the enhanced Coulomb interactions with the shrinkage of the wire diameter competes with the interchain Joseph...

The orbitally-induced Peierls phase transition in the Na-doped Cu 1− x Na x Ir 2 S 4 has been investigated. The phase transition temperature on warming T M W increases while that on cooling T M C decreases with x increasing, which means that the phase transition is broadened by the doping of Na ions. However, the average phase transition temperature T M A is not changed. The Raman spectroscopy and X-ray diffraction studies demonstrate that no structural distortion is induced by the doping of Na in Cu 1− x Na x Ir 2 S 4 , which excludes the lattice distortion effect. The tendency to metallic behavior with the doping of Na indicates a hybridization between Na + and surrounding S 2− ions via the outer shell p electrons, which enhances the itinerant characteristic of electrons. It is suggested that the scattering from itinerant electrons and lattice defects may be responsible for the broadening of the orbitally-induced Peierls phase transition.

We have studied the magnetic and dynamical properties of spin-frustrated magnet Dy2Ti2−x FexO7 single crystals. Bulk magnetization data of the heavily Fe doped samples give a negative Curie–Weiss temperature, probably suggesting the existence of short-range antiferromagnetic interaction in Fe-doped samples. Dynamical analyses show that the doped system still freezes into an ice-like state but it is more dynamical than that in pure spin ice Dy2Ti2O7. Furthermore, the dynamic freezing of the spins is suppressed to lower temperatures, which is caused by the Dy-Fe spin interactions and the altered crystalline electric field. It is also found that the coordination number of Fe decreases at high doping level (x=0.15), leading to the change of the spin state of Fe3+.

In this paper, the magnetism of the single-crystal ${\mathrm{Cr}}_{1/3}{\mathrm{NbS}}_{2}$, which exhibits a chiral magnetic soliton lattice (CSL) state, is investigated. The magnetization displays strong magnetic anisotropy when the field is applied perpendicularly and parallel to the $c$ axis in the low-field region ($Hl{H}_{S},\phantom{\rule{0.28em}{0ex}}{H}_{S}$ is the saturation field). The critical exponents of ${\mathrm{Cr}}_{1/3}{\mathrm{NbS}}_{2}$ are obtained as $\ensuremath{\beta}=0.370(4),\phantom{\rule{0.28em}{0ex}}\ensuremath{\gamma}=1.380(2)$, and $\ensuremath{\delta}=4.853(6)$, which are close to the theoretical prediction of the three-dimensional Heisenberg model. Based on the scaling equation and the critical exponents, the $H\ensuremath{-}T$ phase diagram in the vicinity of the phase transition is constructed where two critical points are determined. One is a tricritical point which locates at the intersection across the CSL, the forced ferromagnetic, and the paramagnetic (PM) states. The other one is a critical point situated at the boundaries across the CSL, the helimagnetic, and the PM states.

The iso-spinel structural systems CuIr

The half-wave rectifiers have been adopted in the wound field doubly salient generators (WFDSGs). To improve the output power, a new half-wave rectifier with the controllable conduction angle for the WFDSM is presented in this paper. With a 12/8-pole WFDSM prototype, the finite element method is used in the simulation. The operation process with the new control scheme is analyzed. The simulation curves are compared with the half-wave rectifier mode. And the energy conversion loops are plotted and investigated too. The experiment waveforms show the good coincidence with the simulation. Furthermore, the external characteristics curves with different conduction angles and different field currents are also presented. It can be concluded that a WFDSG with the proposed rectifier has higher power output than the half-wave rectifier.

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fittings to a two-carrier model show that the magnetoresistance is strongly dependent on the residual resistivity ratio (i.e., the degree of non-stoichiometry), which is eventually understood in terms of electron doping which not only breaks the balance between electron-type and hole-type carrier densities but also reduces the average carrier mobility. Thus, compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe2.

The low-energy behaviors of gapless double- and triple-Weyl fermions caused by the interplay of long-range Coulomb interaction and quenched disorder are studied by performing a renormalization group analysis. It is found that an arbitrarily weak disorder drives the double-Weyl semimetal to undergo a quantum phase transition into a compressible diffusive metal, independent of the disorder type and the Coulomb interaction strength. In contrast, the nature of the ground state of triple-Weyl fermion system relies sensitively on the specific disorder type in the noninteracting limit: The system is turned into a compressible diffusive metal state by an arbitrarily weak random scalar potential or $z$ component of random vector potential but exhibits stable critical behavior when there is only $x$ or $y$ component of random vector potential. In case the triple-Weyl fermions couple to random scalar potential, the system becomes a diffusive metal in the weak interaction regime but remains a semimetal if Coulomb interaction is sufficiently strong. Interplay of Coulomb interaction and $x$, or $y$, component of random vector potential leads to a stable infrared fixed point that is likely to be characterized by critical behavior. When Coulomb interaction coexists with the $z$ component of random vector potential, the system flows to the interaction-dominated strong coupling regime, which might drive a Mott insulating transition. It is thus clear that double- and triple-Weyl fermions exhibit distinct low-energy behavior in response to interaction and disorder. The physical explanation of such distinction is discussed in detail. The role played by long-range Coulomb impurity in triple-Weyl semimetal is also considered., Comment: 22 pages, 17 figures

The effects of isovalent Sm doping and bivalent Pb doping at the Bi site on the superconductivity of Bi4O4S3 superconductor are studied and compared. It is found that the bivalent Pb doping results in much faster decrease of superconducting transition temperature and upper critical field, compared with the isovalent Sm doping. Hall effect measurements suggest that bivalent Pb doping gives rise to rapid decrease in electron-like charge carrier concentration. Our results indicate that the bivalent Pb ions not only act as the impurity scatterers but also introduce hole-type charge carriers, which is harmful to the superconductivity in Bi4O4S3 system.

We report the synthesis of single phase Bi3O2S3 sample and confirm the occurrence of bulk superconductivity with transition temperature at 5.8 K. The Bi3O2S3 super-conductor is categorized as the typical type-II supercon-ductor based on the results of both temperature and mag-netic field dependences of magnetization. Hall coefficient measurements give evidence of a multiband character, with a dominant conduction mainly by electron-like charge carriers. The charge carrier density is about 1.45 X 1019 cm3, suggesting that the system has very low charge carrier density.

Critical behaviors of the half-doped perovskite cobaltites Pr0.5Sr0.5 CoO 3 - Δ ( Δ = 0 and ∼0.16) are investigated around the critical temperatures by bulk magnetization study, where the critical exponents (β, γ and δ) are obtained. These critical exponents fulfill the Widom scaling law δ = 1 + γ β - 1 , indicating self-consistency and reliability of the obtained results. With the critical exponents, M – T – H curves collapse onto two independent universal branches below and above the critical temperatures. The critical exponents of the oxygen-nonstoichiometric Pr0.5Sr0.5 CoO 3 - Δ accord with the mean-field model exactly. However, for the oxygen-stoichiometric Pr 0.5 Sr 0.5 CoO 3 , β deviates to the theoretical prediction of three-dimensional Heisenberg model while γ and δ are close to that of mean-field model. These results indicate long-range ferromagnetic coupling in Pr0.5Sr0.5CoO3−Δ ( Δ = 0 and ∼0.16), which cannot be explained by the nearest-neighbor interaction proposed for the double-exchange mechanism. Instead, the collective effect of p - d hybridization and RKKY interaction of Pr 3 + f-electrons with the conduction electrons is suggested to be responsible for the long-range interaction. In addition, the discrepancy of β in the oxygen-stoichiometric Pr0.5Sr0.5CoO3 may be due to a short-range interaction corresponding to the extra crystalline phases in the oxygen-stoichiometric sample.

In the present paper, we report the bulk magnetization, electron-spin-resonance spectra and transport properties of Y2Ir2O7. It is found that Y2Ir2O7 exhibits a magnetic transition at Tc=150 K and coexistence of antiferromagnetic and ferromagnetic component due to geometrical frustration. The antiferromagnetic order is due to Ir–O–Ir superexchange interactions and the ferromagnetic component is caused by canting of the moments from the antiferromagnetic state. The behavior of spin dynamics confirms that antiferromagnetic ordering with all-in/all-out structure is responsible for the existence of ferromagnetic component. The resistivity reveals that this compound is a semiconductor and the variable-range hopping process dominates the transport mechanism.

In this paper, the dilution effects of non-magnetic Y ions on spin-ice compound Dy2Ti2O7 by infrared and Raman spectra and magnetization measurements were investigated. An anomalous phonon softening with temperature decreasing is found in both the parent and diluted compounds, and Y doping can relax the softening of phonons except that of the IR mode near 233 cm−1, indicating a strong phonon–phonon coupling in the spin-ice material. The magnetization measurements reveal that the non-magnetic impurities do not severely influence the spin-ice rules in the ground state when the level of dilution is not very high. However, a large amount of dilution enhance the disorder and break the spin-ice state because the collective spin-flip clusters are no longer available.

The magnetic order and dynamical properties of spin-frustrated magnet Dy 2− x Yb x Ti 2 O 7 single crystals have been studied by dc and ac susceptibility measurements. It is found that the substitution of the Dy 3+ by the Yb 3+ in Dy 2 Ti 2 O 7 relaxes ferromagnetic coupling. In low Yb 3+ doping samples, a spin freezing peak at T f (T f T s associated with Dy 3+ are observed. With increasing Yb 3+ doping, a new peak marked by T ⁎ associated with Yb 3+ appears. We suggest that T ⁎ originates from the thermally activated spin fluctuations of Yb 3+ . It is also found that the relaxation process for T s becomes both thermally activated and quantum tunneled in x ≥1.0 samples. The low-temperature dynamical behaviors of Dy 2− x Yb x Ti 2 O 7 are dominated by the Dy–Yb spin interactions and the altered crystalline electric field. Moreover, crystal field-phonon coupling may contribute to the spin dynamic properties.

In this work, we successfully synthesize the single crystal Cr11Ge19. The magnetism of the noncentrosymmetric Cr11Ge19 with itinerant ferromagnetic ground state is thoroughly investigated on the single crystal. Based on the variation measurements including the angular rotation, temperature, and magnetic field dependence of magnetization, we find that this material exhibits strong magnetic anisotropy along the c-axis. To clearly reveal the magnetic interactions, the critical behavior is studied using the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm technique. Combining these different methods, three main critical exponents (β, γ, and δ) are obtained. The critical exponent β is close to the theoretical prediction of a three-dimensional XY model with spin-dimensionality n = 2, indicating two-dimensional magnetic coupling. Meanwhile, the critical exponent γ suggests that the magnetic interaction is of long-range type with magnetic exchange distance decaying as J(r) ≈ r−4.61. We propose that the ferromagnetic ground state of Cr11Ge19 is formed by the polarized magnetic moments along the c-axis, while the long-range magnetic coupling is established within the ab plane.

The influence of weak disorder on the superconductivity in ordinary metals can be formally described by the Abrikosov-Gorkov diagrammatic approach. The vertex correction is ignored in this approach because an inequality $k_F l \gg 1$, where $k_F$ is the Fermi momentum and $l$ mean free path, is satisfied in ordinary metals with a large Fermi surface. In a Dirac semimetal that has discrete Fermi points, this inequality may break down even for arbitrarily weak disorder since $k_F \rightarrow 0$, and thus the vertex correction could be important. We incorporate the vertex correction into the self-consistent equations of the superconducting gap and the disorder scattering rate, and then apply the generalized approach to study how $s$-wave superconductivity is affected by random chemical potential in two- and three-dimensional Dirac semimetals, as well as two-dimensional semi-Dirac semimetal. In the clean limit, superconductivity is formed only when the pairing interaction strength is greater than some critical value in these materials. Adding random chemical potential to the system promotes superconductivity by generating a finite fermionic density of states at the Fermi level. In three-dimensional Dirac semimetal, the critical attraction strength is reduced by weak disorder, but remains finite. In the other two cases, superconductivity is induced by arbitrarily weak attraction. Including the vertex correction does not change these qualitative results, and actually could further promote superconductivity in the weak-attraction regime. Bilayer graphene is quite special in that its zero-energy density of states is nonzero despite the existence of Fermi points. Due to this peculiar property, superconductivity is always slightly suppressed by random chemical potential, and the impact of vertex correction is nearly negligible., 35pages, 20 figures, the paper is entirely re-written

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the absence of negative MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed., Comment: 14 pages, 4 figures

The transport and thermoelectric properties together with annealing of the new layered Bi-chalcogenide LaOBiHgS3 are studied. On the transport part, the insulating behavior of the as-grown sample is evidently depressed by post annealing. A hump-like abnormality appears around 170 K. The thermoelectric performance of the sample is observably improved by the annealing, mainly because of the enhanced electrical conductance. The present results suggest that the physical properties of LaOBiHgS3 are sensitive to post annealing and the possible micro adjustments that follow, indicating the layered Bi-chalcogenide family to be an ideal platform for designing novel functional materials.

In this work, we perform a systematic study of the lattice dynamics of IrTe using temperature dependence of X-ray diffraction experiment. It is found that the lattice structural symmetry of IrTe changes from trigonal (space group ) into monoclinic () below the phase transition temperature (). Remarkably, experimental results show that the trigonal cell still insists below , which coexists intrinsically with the monoclinic cell. After the phase transition, the proportion of the monoclinic cell almost remains unchanged. The structure phase transition temperatures determined from cooling and warming are 240 K and 265 K, respectively. Moreover, the superlattice phase is found with 13.5 , which is suggested to be caused by the destabilization of polymeric Te–Te bonds.

We report the observation of giant negative anisotropic magnetoresistance and planar Hall effect in superconducting topological insulator Sr0.06Bi2Se3. It is found that giant anisotropic magnetoresistance and planar Hall effect with non-zero transverse voltage are developed by tilting the in-plane magnetic field away from the direction of the electrical current. Quantitative analyses of the measured data suggest that the observed anisotropic magnetoresistance and planar Hall effect originate from the chiral anomaly behavior of the material. The large anisotropic magnetoresistance and planar Hall effect demonstrate that this material has potential to be utilized in magnetoresistive devices with low power consumption.

Critical behavior of the single-layered Sr2IrO4, which exhibits weak ferromagnetism in the ab plane, is investigated by the bulk magnetization study. Critical exponents β = 0.284 ± 0.008 and γ = 1.726 ± 0.004 with the critical temperature TC=230.8±0.9 are obtained by the Kouvel–Fisher method, and δ = 4.443 ± 0.008 is generated by the critical isotherm analysis at TC=231 K. The obtained critical exponents of Sr2IrO4 are close to prediction of the theoretical model with { d : n } = { 2 : 1 } (where d is the partial dimensionality and n is the spin dimensionality), which indicates one-dimensional ferromagnetic interaction in the two-dimensional layered material. On the other hand, the critical exponents lie between the prediction of long-range and short-range models, indicating that the short-range Heisenberg interaction alone cannot totally describe the critical behavior. It is suggested that the Dzialoshinsky–Moriya interaction caused by rotation of the octahedra and the symmetric anisotropy result into a lower spatial short-range interaction, which competes with the long-range interaction caused by expansion of 5d orbits.

A spinel sulphide CuIr2S4 single crystal, which exhibits an orbitally induced Peierls phase transition at ∼230 K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir4+ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir4+ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir4+ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE JT is much smaller than the spin-dimerization gap.

In this work, we investigate the polycrystalline CuIr 2 S 4 , which exhibits an orbitally induced Peierls phase transition at T MI ≈ 230 K , by the electron spin resonance (ESR) spectroscopy. A corresponding change occurs to the ESR spectra, as well as in the obtained ESR parameters such as resonance field Hr and g-factor ( g eff ) . It is suggested that the ESR signals originate from the paramagnetic moments caused by lattice defects, which are affected by the spin-dimerization transition. However, ESR signals from a few non-dimerized Ir 4 + maybe also exist. In addition, an anomalous change below ∼ 50 K is detected by the ESR parameters. A possible explanation was proposed to interpret the experimental results.

Research on two-dimensional transition metal dichalcogenides (TMDs) has grown rapidly over the past several years, from fundamental studies to the development of next generation technologies. Recently, it has been reported that the MX2-type PdTe2 exhibits superconductivity with topological surface state, making this compound a promising candidate for investigating possible topological superconductivity. However, due to the multi-band feature of most of TMDs, the investigating of magnetoresistance and quantum oscillations of these TMDs proves to be quite complicated. Here we report a combined de Hass-van Alphen effect and magnetoresistance studies on the PdTe2 single crystal. Our high-field de Hass-van Alphen data measured at different temperature and different tilting angle suggest that though these is a well-defined multi-band feature, a predominant oscillation frequency has the largest oscillation magnitude in the fast Fourier transformation spectra, which is at least one order of magnitude larger than other oscillation frequencies. Thus it is likely that the transport behavior in PdTe2 system can be simplified into a single-band model. Meanwhile, the magnetoresistance results of the PdTe2 sample can be well-fitted according to the single-band models. The present results could be important in further investigation of the transport behaviors of two-dimensional TMDs.

Topological superconductors are a very interesting and frontier topic in condensed matter physics. Despite the tremendous efforts in exploring topological superconductivity, its presence is however still under heavy debate. The Dirac electrons have been proven to exist on the surface of a topological insulator. It remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. Here we show the systematic study of scanning tunnelling microscope/spectroscopy on the possible topological superconductor SrxBi2Se3. We first demonstrate that only the intercalated Sr atoms can induce superconductivity. Then we show the full superconducting gaps without any in-gap density of states as expected theoretically for a bulk topological superconductor. Finally, we find that the surface Dirac electrons will simultaneously condense into the superconducting state within the superconducting gap. This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs., Whether and how the Dirac electrons can be driven into superconducting state remains unclear. Here, Du et al. present systematic study to demonstrate the Dirac electrons condensing into Cooper pairs on the surface of a possible topological superconductor Sr x Bi2Se3.

At the nematic quantum critical point that exists in the $d_{x^2-y^2}$-wave superconducting dome of cuprates, the massless nodal fermions interact strongly with the quantum critical fluctuation of nematic order. We study this problem by means of renormalization group approach and show that, the fermion damping rate $\left|\mathrm{Im}\Sigma^R(\omega)\right|$ vanishes more rapidly than the energy $\omega$ and the quasiparticle residue $Z_f\rightarrow 0$ in the limit $\omega \rightarrow 0$. The nodal fermions thus constitute an unconventional non-Fermi liquid that represents an even weaker violation of Fermi liquid theory than a marginal Fermi liquid. We also investigate the interplay of quantum nematic critical fluctuation and gauge-potential-like disorder, and find that the effective disorder strength flows to the strong coupling regime at low energies. Therefore, even an arbitrarily weak disorder can drive the system to become a disorder controlled diffusive state. Based on these theoretical results, we are able to understand a number of interesting experimental facts observed in curpate superconductors., Comment: 29 pages, 6 figures

Angle-resolved upper critical field ${H}_{c2}$ provides an efficient tool to probe the gap symmetry of unconventional superconductors. We revisit the behavior of in-plane ${H}_{c2}$ in $d$-wave superconductors by considering both the orbital effect and Pauli paramagnetic effect. After carrying out systematic analysis, we show that the maxima of ${H}_{c2}$ could be along either nodal or antinodal directions of a $d$-wave superconducting gap, depending on the specific values of a number of tuning parameters. This behavior is in contrast to the common belief that the maxima of in-plane ${H}_{c2}$ are along the direction where the superconducting gap takes its maximal value. Therefore, identifying the precise $d$-wave gap symmetry through fitting experiments results of angle-resolved ${H}_{c2}$ with model calculations at a fixed temperature, as widely used in previous studies, is difficult and practically unreliable. However, our extensive analysis of angle-resolved ${H}_{c2}$ show that there is a critical temperature ${T}^{*}$: in-plane ${H}_{c2}$ exhibits its maxima along nodal directions at $Tl{T}^{*}$ and along antinodal directions at ${T}^{*}lTl{T}_{c}$. The concrete value of ${T}^{*}$ may change as other parameters vary, but the existence of $\ensuremath{\pi}/4$ shift of ${H}_{c2}$ at ${T}^{*}$ appears to be a general feature. Thus a better method to identify the precise $d$-wave gap symmetry is to measure ${H}_{c2}$ at a number of different temperatures, and examine whether there is a $\ensuremath{\pi}/4$ shift in its angular dependence at certain ${T}^{*}$. We further show that Landau level mixing does not change this general feature. However, in the presence of Fulde-Ferrell-Larkin-Ovchinnikov state, the angular dependence of ${H}_{c2}$ becomes quite complicated, which makes it more difficult to determine the gap symmetry by measuring ${H}_{c2}$. Our results indicate that some previous studies on the gap symmetry of ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$ are unreliable and need to be reexamined, and also provide a candidate solution to an experimental discrepancy in the angle-resolved ${H}_{c2}$ in ${\mathrm{CeCoIn}}_{5}$.

Mono-arsenide CrAs, endures a helical anti-ferromagnetic order transition at ∼265 K under ambient pressure. Recently, pressure-induced-superconductivity was discovered vicinity to the helical anti-ferromagnetic order in CrAs [Wei Wu et al., Nature Communications 5, 5508 (2014).]. However, the size of crystal grown via tin flux method is as small as 1 mm in longest dimension. In this work, we report the single crystal growth of CrAs with size of 1 × 5 × 1 mm3 via chemical vapor transport method and its physical properties.

Topological superconductor is a very interesting and frontier topic in condensed matter physics1. Despite the tremendous efforts in exploring the topological superconductivity, its presence is however still under heavy debates. The Dirac electrons are supposed to exist in a thin layer of the surface of a topological insulator. Due to the finite spin-orbital coupling, these electrons will have a spin-momentum locking effect. In this case, the superfluid with the spin singlet Cooper pairing is not completely comforted by the Dirac electrons. It thus remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. In this work, we show the systematic study of scanning tunneling microscope/spectroscopy on the possible topological superconductor SrxBi2Se3. We first show that only the intercalated (or inserted), not the substituted Sr atoms can induce superconductivity. Then we show the full superconducting gaps without any abnormal in-gap density of states as expected theoretically for the bulk topological superconductivity. However, we find that the surface Dirac electrons will simultaneously condense into the superconducting state when the energy is smaller than the bulk superconducting gap. This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs., 28 pages, 7 figures, including Supplementary Information

The recently discovered ${\mathrm{Sr}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ superconductor provides an alternative and ideal material base for investigating possible topological superconductivity. Here, we report that in ${\mathrm{Sr}}_{0.065}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, the ambient superconducting phase is gradually depressed upon the application of external pressure. At high pressure, a second superconducting phase emerges at above 6 GPa, with a maximum ${T}_{c}$ value of $\ensuremath{\sim}8.3$ K. The joint investigations of the high-pressure synchrotron x-ray diffraction and electrical transport properties reveal that the reemergence of superconductivity in ${\mathrm{Sr}}_{0.065}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is closely related to the structural phase transition from an ambient rhombohedral phase to a high-pressure monoclinic phase around 6 GPa, and further to another high-pressure tetragonal phase above 25 GPa.

The cubic B20 compound FeGe, which exhibits a near room temperature skyrmion phase, is of great importance not only for fundamental physics such as nonlinear magnetic ordering and solitons but also for future application of skyrmion states in spintronics. In this work, the critical behavior of the cubic FeGe is investigated by means of bulk dc-magnetization. We obtain the critical exponents (β = 0.336 ± 0.004, γ = 1.352 ± 0.003 and β = 5.276 ± 0.001), where the self-consistency and reliability are verified by the Widom scaling law and scaling equations. The magnetic exchange distance is found to decay as "Equation missing" r−4.9, which is close to the theoretical prediction of 3D-Heisenberg model (r−5). The critical behavior of FeGe indicates a short-range magnetic interaction. Meanwhile, the critical exponents also imply an anisotropic magnetic coupling in this system.

The ${122}^{\ensuremath{\star}}$ series of iron chalcogenide superconductors, for example ${\mathrm{K}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2}$, only possesses electron Fermi pockets. Their distinctive electronic structure challenges the picture built upon iron pnictide superconductors, where both electron and hole Fermi pockets coexist. However, partly due to the intrinsic phase separation in this family of compounds, many aspects of their behavior remain elusive. In particular, the evolution of the ${122}^{\ensuremath{\star}}$ series of iron chalcogenides with chemical substitution still lacks a microscopic and unified interpretation. Using angle-resolved photoemission spectroscopy, we studied a major fraction of ${122}^{\ensuremath{\star}}$ iron chalcogenides, including the isovalently ``doped'' ${\mathrm{K}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{S}}_{z},{\mathrm{Rb}}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{Te}}_{z}$, and ${(\text{Tl},\mathrm{K})}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{\mathrm{S}}_{z}$. We found that the bandwidths of the low energy Fe $3d$ bands in these materials depend on doping; and more crucially, as the bandwidth decreases, the ground state evolves from a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven insulator found here with small band filling may be a novel insulating phase. Our study shows that almost all the known ${122}^{\ensuremath{\star}}\text{-series}$ iron chalcogenides can be understood via one unifying phase diagram which implies that moderate correlation strength is beneficial for the superconductivity.

At zero temperature, the Lorentz invariance is strictly preserved in three-dimensional quantum electrodynamics. This property ensures that the velocity of massless fermions is not renormalized by the gauge interaction. At finite temperature, however, the Lorentz invariance is explicitly broken by the thermal fluctuation. The longitudinal component of gauge interaction becomes short ranged due to thermal screening, whereas the transverse component remains long ranged because of local gauge invariance. The transverse gauge interaction leads to singular corrections to the fermion self energy and thus results in an unusual renormalization of the fermion velocity. We calculate the renormalized fermion velocity ${v}^{R}({p}_{0},\mathbf{p},T)$ by employing a renormalization group analysis, and discuss the influence of the anomalous dimension ${\ensuremath{\eta}}_{n}$ on the fermion specific heat.

A sufficiently strong long-range Coulomb interaction can induce excitonic pairing in gapless Dirac semimetals, which generates a finite gap and drives semimetal-insulator quantum phase transition. This phenomenon is in close analogy to dynamical chiral symmetry breaking in high energy physics. In most realistic Dirac semimetals, including suspended graphene, Coulomb interaction is too weak to open an excitonic gap. The Coulomb interaction plays a more important role at low energies in a two-dimensional semi-Dirac semimetal, in which the fermion spectrum is linear in one component of momenta and quadratic in the other, than a Dirac semimetal, and indeed leads to breakdown of Fermi liquid theory. We study dynamical excitonic gap generation in a two-dimensional semi-Dirac semimetal by solving the Dyson-Schwinger equation, and show that a moderately strong Coulomb interaction suffices to induce excitonic pairing. Additional short-range four-fermion coupling tends to promote excitonic pairing. Among the available semi-Dirac semimetals, we find that TiO$_{2}$/VO$_{2}$ nanostructure provides a promising candidate for the realization of excitonic insulator. We also apply the renormalziation group method to analyze the strong coupling between the massless semi-Dirac fermions and the quantum critical fluctuation of excitonic order parameter at the semimetal-insulator quantum critical point, and reveal non-Fermi liquid behaviors of semi-Dirac fermions., Comment: 25 pages, 11 figures

Mono-arsenide CrAs, endures a helical anti-ferromagnetic order transition at~ 265 K under ambient pressure. Recently, pressure-induced-superconductivity was discovered vicinity to the helical anti-ferromagnetic order in CrAs[Wei Wu et al., Nature Communications 5, 5508 (2014).]. However, the size of crystal grown via tin flux method is as small as 1 mm in longest dimension. In this work, we report the single crystal growth of CrAs with size of 1 * 5 * 1 mm3 via chemical vapor transport method and its physical properties., Comment: 9 pages, 3 figures