Physical properties and magnetic structure of a layered antiferromagnet PrPd0.82Bi2

We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic(AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at TN^7K. A large Sommerfeld coefficient of 329.23 m J·mol-1·K-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k =(0 0 0) is formed below TN. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μBat 4K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μB.PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.

Magnetic-field modulation of topological electronic state and emergent magneto-transport in a magnetic Weyl semimetal

The modulation of topological electronic state by an external magnetic field is highly desired for condensed-matter physics.Schemes to achieve this have been proposed theoretically,but few can be realized experimentally.Here,combining transverse transport,theoretical calculations,and scanning tunneling microscopy/spectroscopy(STM/S)investigations,we provide an observation that the topological electronic state,accompanied by an emergent magneto-transport phenomenon,was modulated by applying magnetic field through induced non-collinear magnetism in the magnetic Weyl semimetal EuB6.A giant unconventional anomalous Hall effect(UAHE)is found during the magnetization re-orientation from easy axes to hard ones in magnetic field,with a UAHE peak around the low field of 5 kOe.

Topological electronic states in HfRuP family superconductors

Based on the first-principles calculations and experimental measurements,we report that the hexagonal phase of ternary transition metal pnictides TT’X(T=Zr,Hf;T’=Ru;X=P,As),which are well-known noncentrosymmetric superconductors with relatively high transition temperatures,host nontrivial bulk topology.Before the superconducting phase transition,we find that HfRuP belongs to a Weyl semimetal phase with 12 pairs of type-II Weyl points,while ZrRuAs,ZrRuP and HfRuAs belong to a topological crystalline insulating phase with trivial Fu-Kane Z_(2) indices but nontrivial mirror Chern numbers.High-quality single crystal samples of the noncentrosymmetric superconductors with these two different topological states have been obtained and the superconductivity is verified experimentally.The wide-range band structures of ZrRuAs have been identified by ARPES and reproduced by theoretical calculations.Combined with intrinsic superconductivity,the nontrivial topology of the normal state may generate unconventional superconductivity in both bulk and surfaces.Our findings could largely inspire the experimental searching for possible topological superconductivity in these compounds.

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co_(3)Sn_(2)S_(2)

Co_(3)Sn_(2)S_(2) is a recently identified magnetic Weyl semimetal in Shandite compounds. Upon cooling, Co_(3)Sn_(2)S_(2) undergoes a ferromagnetic transition with c-axis polarized moments(0.3 μ_(B)/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 TC with a maximum of anomalous Hall angle near T_(A). Here, we report an elastic neutron scattering on the crystalline lattice of Co_(3)Sn_(2)S_(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_(3)Sn_(2)S_(2) lattice and its related topological states.

Experimental evidence for field-induced metamagnetic transition of EuCd_(2)As_(2)

Recent studies have shown that layered compound EuCd_(2)As_(2) could exhibit diverse topological states depending on the different magnetic structures,such as Weyl semimetal,Dirac semimetal and topological insulato r.In order to further study the interplay between magnetism and topology of EuCd_(2)As_(2),it is necessary to figure out its magnetic structure.Here,by magnetization(M) measurements and negative magnetostriction(λ) along the [001] direction measured by scanning tunneling microscopy on EuCd_(2)As_(2) single crystals,we observe field-induced metamagnetic phase transition from A-type antiferromagnetic(AFM) ground state to field-polarized state,with canted AFM(CAFM) state in between.Magnetization and magnetostriction are more sensitive to the in-plane field than the out-of-plane field,indicating the magnetic moments lying in the ab plane.The absence of abrupt jump on M-H and λ-H curves demonstrates that the phase transition is a second-order type.In CAFM state,M increases linearly with the field and λ is proportional to M~2.Tunneling conductance spectra show the field-induced evolution of the electronic density of states.Our results provide experimental evidence for understanding the magnetic structure of EuCd_(2)As_(2).

Spin excitations and spin wave gap in the ferromagnetic Weyl semimetal Co3Sn2S2

We report a comprehensive neutron scattering study on the spin excitations in the magnetic Weyl semimetal Co3Sn2S2 with a quasi-two-dimensional structure.Both in-plane and out-of-plane dispersions of the spin waves were revealed in the ferromagnetic state.Similarly,dispersive but damped spin excitations were found in the paramagnetic state.The effective exchange interactions were estimated using a semi-classical Heisenberg model to consistently reproduce the experimental TCand spin stiffness.However,a full spin wave gap below Eg=2.3 meV was observed at T=4 K.This value was considerably larger than the estimated magnetic anisotropy energy(~0.6 meV),and its temperature dependence indicated a significant contribution from the Weyl fermions.These results suggest that Co3Sn2S2 is a three-dimensional correlated system with a large spin stiffness,and the low-energy spin dynamics can interplay with the topological electron states.