Magneto-Transport and Shubnikov–de Haas Oscillations in the Type-Ⅱ Weyl Semimetal Candidate NbIrTe_4 Flake

We report on magnetoresistance, Hall effect, and quantum Shubnikov–de Haas oscillation(SdH) experiments in NbIrTe4 single crystals, which was recently predicted to be a type-II Weyl semimetal. NbIrTe_4 manifests a non-saturating and parabolic magnetoresistance at low temperatures. The magneto-transport measurements show that NbIrTe_4 is a multiband system. The analysis of the SdH oscillations reveals four distinct oscillation frequencies. Combined with the density-functional theory calculations, we show that they come from two types of Fermi surfaces: electron pocket E_1 and hole pocket H_2.     

Magnetoresistivity and filamentary superconductivity in nickel-doped BaFe_2As_2

We present magnetotransport studies on a series of BaFe_(2-x)Ni_xAs_2(0.03 ≤ x ≤ 0.10) single crystals. In the underdoped(x = 0.03) non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity(FLSC). FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped(x = 0.10) compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.     

Anisotropic and mutable magnetization in Kondo lattice CeSb_2

We have systematically studied the behaviors of the resistivity and magnetization of CeSb_2 single crystals as a function of temperature and external field. Four anomalies in the resistivity/magnetization-versus-temperature curves are observed at low magnetic field. They are located at 15.5 K, 11.5 K, 9.5 K, and 6.5 K, corresponding to the paramagnetic–magnetically ordered state(MO), MO-antiferromagnetic(AFM), AFM–AFM, and AFM–ferromagnetic(FM) transitions, respectively.The anomaly at 9.5 K is only visible with H‖[010] by magnetic susceptibility measurements, indicating that the AFM–AFM transition only happens along [010] direction in ab-plane. The four magnetic transitions are strongly suppressed by high external field. Finally, the field-temperature phase diagrams of CeSb_2 with different orientations of the applied field in ab-plane are constructed and indicate the highly anisotropic nature of the magnetization of CeSb_2.     

Temperature Dependent In-Plane Anisotropic Magnetoresistance in HfTe_5 Thin Layers

We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe₅ thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T_p.Below T_p,the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe₅ thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.     

Anisotropy Properties of Mn_2P Single Crystals with Antiferromagnetic Transition

Single crystals of hexagonal structure Mn_2P are synthesized by Sn flux for the first time. Transport and magnetic properties have been performed on the single crystals, which is an antiferromagnet with Neel temperature 103 K.Obvious anisotropy of resistivity is observed below the Neel temperature, which is manifested by metallic behavior with a current along the C-axis and semiconducting behavior with a current along the α-axis. The negative slope of temperature-dependent resistivity is observed above the Neel temperature in both α and C directions. Strong anisotropy of magnetic susceptibility is also evident from the magnetization measurements. A weak metamagnetic transition is observed only in α-axis plane at high magnetic field near 50–60 K compared to the C-axis. We believe these strong anisotropies of magnetic and transport properties are due to the anisotropy of spin arrangement.Mn_2P could be a candidate for exploration of possible superconductivity due to the low spin state.     

Magnetotransport Properties of a Nodal Line Semimetal TiSi

We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.     

Large linear magnetoresistance in a new Dirac material BaMnBi_2

Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles.Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials.In this paper,we report the synthesis of high quality single crystals of BaMnBi_2 and investigate the transport properties of the samples.BaMnBi_2 is a metal with an antiferromagnetic transition at T_N = 288 K.The temperature dependence of magnetization displays different behavior from CaMnBi_2 and SrMnBi_2,which suggests the possible different magnetic structure of BaMnBi_2.The Hall data reveals electron-type carriers and a mobility μ(5K)= 1500 cm~2/V·s.Angle-dependent magnetoresistance reveals the quasi-two-dimensional(2D) Fermi surface in BaMnBi_2- A crossover from semiclassical MR~H~2dependence in low field to MR~H dependence in high field,which is attributed to the quantum limit of Dirac fermions,has been observed in magnetoresistance.Our results indicate the existence of Dirac fermions in BaMnBi_2.     

Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe_(3-x)Se_x

It was found that selenium doping can suppress the charge-density-wave(CDW) order and induce bulk superconductivity in ZrTe_3. The observed superconducting dome suggests the existence of a CDW quantum critical point(QCP) in ZrTe_3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe_(3-x)Se_x single crystals(x = 0.044 and 0.051) down to 80 m K. For both samples, the residual linear term κ_0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ_0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe_(3-x)Se_x,which indicates conventional superconductivity despite of the existence of a CDW QCP.     

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co_3Sn_2S_2

Co_3Sn_2S_2 is a recently identified magnetic Weyl semimetal in Shandite compounds. Upon cooling, Co_3Sn_2S_2 undergoes a ferromagnetic transition with c-axis polarized moments(~0.3 μB/Co) around T_C= 175 K, followed by another magnetic anomaly around T_A≈ 140 K. A large intrinsic anomalous Hall effect is observed in the magnetic state below T_C with a maximum of anomalous Hall angle near T_A. Here, we report an elastic neutron scattering on the crystalline lattice of Co_3Sn_2S_2 in a magnetic field up to 10 T. A strongly anisotropic magnetoelastic response is observed, while only a slight enhancement of the Bragg peaks is observed when B//c. The in-plane magnetic field(B//ab) dramatically suppresses the Bragg peak intensity probably by tilting the moments and lattice toward the external field direction. The in-plane magnetoelastic response commences from T_C, and as it is further strengthened below T_A, it becomes nonmonotonic against the field between T_A and T_C because of the competition from another in-plane magnetic order. These results suggest that a magnetic field can be employed to tune the Co_3Sn_2S_2 lattice and its related topological states.     

Growth and characterization of CaCu_3Ru_4O_(12) single crystal

High-quality single crystals of A-site ordered perovskite oxides CaCu3Ru4O12 were synthesized by flux method with Cu O serving as a flux. The typical size of these single crystals was around 1 × 1 × 1 mm3 and the lattice constant was determined to be 7.430 ± 0.0009 ?A by using x-ray single crystal diffraction. The surfaces of the samples were identified to be(100) surface. The high quality of the single crystal samples was confirmed by the rocking curve data which have a full width at half maximum of approximately 0.02 degree. The x-ray photoelectron spectroscopy measurement was performed and the temperature-dependent specific heat, magnetic susceptibility, and electric resistivity were measured along the [100]direction of the single crystals. All these measurements showed that the physical properties of Ca Cu3Ru4O12 single crystals are similar to that of polycrystals. However, the single crystals have a lower Curie susceptibility tail and a smaller residual resistivity than polycrystals, which indicates that the amount of paramagnetic impurities can be controlled by tuning the number of defects in CaCu3Ru4O12 samples.     

Large and anisotropic linear magnetoresistance in bulk stoichiometric Cd3As2 crystals

Cd3As2 was recently identified as a novel three-dimensional(3D)topological semimetal hosting the long-pursuing 3D Dirac Fermion.Crystals of Cd3As2 grown preferentially along the[100]and[112]directions were obtained through the modified chemical vapor transfer growth method,thus allowing the examination of transport anisotropy.The resistivity and magnetoresistance(MR)are basically linear with respect to magnetic field(H)in the measured temperature range of 2–300 K irrespective of the directions.The linear resistivity and MR are significantly anisotropic not only along[100]and[112]directions but also with respect to tilt angle between the growth directions and H,thus providing transport signatures of the 3D Dirac Fermion as well as the possible linear and anisotropic change of Weyl Fermi surface in H.Very large MR along the[100]direction is observed,even approaching 3100%at 2 K and 14 k Oe(1 Oe=79.5775 A m-1).The results would be helpful in renewing interest in studying emergent phenomena arising from bulk 3D Dirac Fermion as well as in paving the way for Cd3As2 to be used in magnetoelectronic sensors.     

Superconductivity and Normal-State Properties of Kagome Metal RbV_3Sb_5 Single Crystals

We report the discovery of superconductivity and detailed normal-state physical properties of RbV_3Sb_5 single crystals with V kagome lattice.RbV_3Sb_5 single crystals show a superconducting transition at T_c～0.92 K.Meanwhile,resistivity,magnetization and heat capacity measurements indicate that it exhibits anomalies of properties at T~*～102-103 K,possibly related to the formation of charge ordering state.When T is lower than T*,the Hall coefficient R_H undergoes a drastic change and sign reversal from negative to positive,which can be partially explained by the enhanced mobility of hole-type carriers.In addition,the results of quantum oscillations show that there are some very small Fermi surfaces with low effective mass,consistent with the existence of multiple highly dispersive Dirac band near the Fermi energy level.     

New family of Dirac and Weyl semimetals in XAuTe (X = Na,K, Rb) ternary honeycomb compounds

We propose a new family of 3D Dirac semimetals based on XAuTe(X = K, Na, Rb) ternary honeycomb compounds, determined based on first-principles calculations, which are shown to be topological Dirac semimetals in which the Dirac points are induced by band inversion. Dirac points with four-fold degeneracy that are protected by C3 rotation symmetry and located on the Γ-A high-symmetry path are found. Through spatial-inversion symmetry breaking, a K(Au0.5 Hg0.5)(Te0.5As0.5) superlattice structure composed of KHgAs and KAuTe compounds is proven to be a Weyl semimetal with type-II Weyl points, which connect electronand hole-like bands. In this superlattice structure, the six pairs of Weyl nodes are distributed along the K-Γ high-symmetry path on the kz = 0 plane. Our research expands the family of topological Dirac and type-II Weyl semimetals.     

Large Magnetoresistance and Nontrivial Berry Phase in Nb_3Sb Crystals with A15 Structure

Compounds with the A15 structure have attracted extensive attention due to their superconductivity and nontrivial topological band structures.We have successfully grown Nb_3 Sb single crystals with the A15 structure and systematically measured the longitudinal resistivity,Hall resistivity and quantum oscillations in magnetization.Similar to other topological trivial/nontrivial semimetals,Nb_3 Sb exhibits large magnetoresistance(MR) at low temperatures(717%,2 K and 9 T),unsaturating quadratic field dependence of MR and up-turn behavior inρx_x(T) curves under magnetic field,which is considered to result from a perfect hole-electron compensation,as evidenced by the Hall resistivity measurements.The nonzero Berry phase obtained from the de-Hass van Alphen(dHvA) oscillations demonstrates that Nb_3 Sb is topologically nontrivial.These results indicate that Nb_3 Sb superconductor is also a semimetal with large MR and nontrivial Berry phase.This indicates that Nb_3 Sb may be another platform to search for the Majorana zero-energy mode.     

Magnetoresistance and Kondo Effect in Nodal-Line Semimetal VAs_2

We performed calculations of the electronic band structure and the Fermi surface,measured the longitudinal resistivity ρxx(T,H),Hall resistivity ρxy(T,H),and magnetic susceptibility as a function of temperature at various magnetic fields for VAs₂ with a monoclinic crystal structure.The band structure calculations show that VAs₂ is a nodal-line semimetal when spin-orbit coupling is ignored.The emergence of a minimum at around11 K in ρxx(T) measured at H=0 demonstrates that some additional magnetic impurities(V⁴⁺,S=1/2)exist in VAs₂ single crystals,inducing Kondo scattering,evidenced by both the fitting of ρxx(T) data and the susceptibility measurements.It is found that a large positive magnetoresistance(MR) reaching 649% at 10 K and 9 T,its nearly quadratic field dependence,and a field-induced up-turn behavior of ρxx(T) also emerge in VAs₂,although MR is not so large due to the existence of additional scattering compared with other topological nontrivial/trivial semimetals.The observed properties are attributed to a perfect charge-carrier compensation,which is evidenced by both the calculations relying on the Fermi surface and the Hall resistivity measurements.These results indicate that the compounds containing V(3d³4s²) element can be as a platform for studying the influence of magnetic impurities to the topological properties.     

Low field induced giant anisotropic magnetocaloric effect in DyFeO_3 single crystal

We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in Dy FeO3 single crystal. A giant rotating field entropy change of -ΔS R M= 16.62 J/kg·K was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 k Oe. The large anisotropic magnetic entropy change is mainly accounted for the 4 f electron of rare-earth Dy3+ ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite Dy FeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region.     

General equation describing viscosity of metallic melts under horizontal magnetic field

Viscosities of pure Ga, Ga_(80)Ni_(20), and Ga_(80)Cr_(20) metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as η_B = η +(2H/πΩ)B~2(η_B is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample,? is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of ηB and quadratic B, which is related to the electrical resistivity,conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field.     

Unusual Normal and Superconducting State Properties Observed in Hydrothermal Fe_(1-δ)Se Flakes

The electronic and superconducting properties of Fe_(1-δ)Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T. The results contrast sharply with those previously reported for nematically ordered Fe Se by chemical-vapor-transport(CVT) growth. No signature of the electronic nematicity, but an evident metal-to-nonmetal crossover with increasing temperature,is detected in the normal state of the present hydrothermal samples. Interestingly, a higher superconducting critical temperature T_c of 13.2 K is observed compared to a suppressed T_c of 9 K in the presence of the nematicity in the CVT Fe Se. Moreover, the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of ~42 T, which breaks the Pauli limit by a factor of 1.8.     

Magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics driven by DC/AC magnetic field

The response of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to alternating current(AC) or direct current(DC) bias magnetic field is evaluated by the reaction–diffusion equation for the probability distribution function of the molecular concentration in the spherical coordinate system. The magnetization function and the probability distribution function of the magnetic particles in the reaction system are derived by using the Legendre polynomials and Laplace transform. We discuss the characteristics of magnetization and probability distribution of the magnetic particles with different anisotropic parameters driven by a DC and AC magnetic fields, respectively. It is shown that both the magnetization and the probability distribution decrease with time increasing due to the reaction process. The uniformity of the probability distribution and the amplitude of the magnetization are both affected by the anisotropic parameters.Meanwhile, the difference between the case with linear reaction dynamics and the non-reaction case is discussed.     

Butterfly-Like Anisotropic Magnetoresistance and Angle-Dependent Berry Phase in a Type-Ⅱ Weyl Semimetal WP_2

The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-Ⅱ Weyl semimetal WP_2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP_2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.