On the magnetic structures of 1:1:1 stoichiometric topological phases LnSbTe (Ln = Pr, Nd, Dy and Er)

LnSbTe (Ln - lanthanide) group of materials, belonging to ZrSiS/PbFCl (P4/nmm) structure type, is a platform to study the phenomena originating from the interplay between the electronic correlations, magnetism, structural instabilities and topological electronic structure. Here we report a systematic study of magnetic properties and magnetic structures of LnSbTe materials. The studied materials undergo antiferromagnetic ordering at TN = 2.1 K (Ln = Er), 6.7 K (Ln = Dy), 3.1 K (Ln = Nd). Neutron powder diffraction reveals ordering with k1 = (1/2 + d 0 0) in ErSbTe, k2 = (1/2 0 1/4) in NdSbTe. DySbTe features two propagation vectors k2 and k4 = (0 0 1/2). No long-range magnetic order is observed in PrSbTe down to 1.8 K. We propose the most probable models of magnetic structures, discuss their symmetry and possible relation between the electronic structure and magnetic ordering.Comment: 21 pages, 10 figure

RENiO3 Single Crystals (RE = Nd, Sm, Gd, Dy, Y, Ho, Er, Lu) Grown from Molten Salts under 2000 bar of Oxygen Gas Pressure

The electronic properties of transition-metal oxides with highly correlated electrons are of central importance in modern condensed-matter physics and chemistry, both for their fundamental scientific interest and for their potential for advanced electronic applications. However, the design of materials with tailored properties has been restricted by the limited understanding of their structure−property relationships, which are particularly complex in the proximity of the regime where localized electrons become gradually mobile. RENiO3 perovskites, characterized by the presence of spontaneous metal to insulator transitions, are some of the most widely used model materials for the investigation of this region in theoretical studies. However, crucial experimental information needed to validate theoretical predictions is still lacking due to their challenging high-pressure synthesis, which has prevented to date the growth of sizable bulk single crystals with RE ≠ La, Pr, and Nd. Here we report the first successful growth of single crystals with RE = Nd, Sm, Gd, Dy, Y, Ho, Er, and Lu in sizes up to ∼75 μm, grown from molten salts in a temperature gradient under 2000 bar of oxygen gas pressure. The crystals display regular prismatic shapes with flat facets, and their crystal structures and metal−insulator and antiferromagnetic order transition temperatures are in excellent agreement with previously reported values obtained from polycrystalline samples. The availability of such crystals opens access to measurements that have hitherto been impossible to conduct. This should contribute to a better understanding of the fascinating properties of materials with highly correlated electrons and guide future efforts to engineer transition-metal oxides with tailored functional properties

Short-range magnetic interactions and spin-glass behavior in the quasi-2D nickelate Pr4Ni3O8

The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of three stacked square-planar NiO2 planes, in a similar way to the well-known cuprate superconductors. The mixed-valent nature of Ni and its metallic properties makes it a candidate for potentially unconventional superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of Pr4Ni3O10 in 10 percent hydrogen gas, and report on measurements of powder-neutron diffraction, magnetization and muon-spin rotation (uSR). We find that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic memory effect in the temperature range from 2 to 300 K and a freezing temperature T_s ~ 68 K. Moreover, the analysis of uSR spectra indicates two magnetic processes characterized by remarkably different relaxation rates: a slowly-relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions, and a fast-relaxing signal, whose relaxation rate increases substantially below ~ 70 K which can be ascribed to the presence of short-range correlated regions. We conclude that the complex spin-freezing process in Pr4Ni3O8 is governed by these multiple magnetic interactions. It is possible that the complex magnetism in Pr4Ni3O8 is detrimental to the occurrence of superconductivity

Anisotropic character of the metal-to-metal transition in Pr4Ni3_3O10_{10}

As a member of the Ruddlesden-Popper Ln$_{n+1}$Ni$_n$O$_{3n+1}$ series rare-earth-nickelates, the Pr4Ni$_3$O$_{10}$ consists of infinite quasi-two-dimensional perovskite-like Ni-O based layers. Although a metal-to-metal phase transition at Tpt = 157 K has been revealed by previous studies, a comprehensive study of physical properties associated with this transition has not yet been performed. We have grown single crystals of Pr4Ni3O10 at high oxygen pressure, and report on the physical properties around that phase transition, such as heat-capacity, electric-transport and magnetization. We observe a distinctly anisotropic behavior between in-plane and out-of-plane properties: a metal-to-metal transition at Tpt within the a-b plane, and a metal-to-insulator-like transition along the c-axis with decreasing temperature. Moreover, an anisotropic and anomalous negative magneto-resistance is observed at Tpt that we attribute to a slight suppression of the first-order transition with magnetic field. The magnetic-susceptibility can be well described by a Curie-Weiss law, with different Curie-constants and Pauli-spin susceptibilities between the high-temperature and the low-temperature phases. The single crystal X-ray diffraction measurements show a shape variation of the different NiO6 octahedra from the high-temperature phase to the low-temperature phase. This subtle change of the environment of the Ni sites is likely responsible for the different physical properties at high and low temperatures

Z3_{3}-vestigial nematic order due to superconducting fluctuations in the doped topological insulators Nbx_{x}Bi2_{2}Se3_{3} and Cux_{x}Bi2_{2}Se3_{3}

A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in iron-based and cuprate materials. Here we present the observation of a partially melted superconductivity in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z$_{3}$, i.e., three-state Potts-model symmetry. Thermal expansion, specific heat and magnetization measurements of the doped topological insulators Nb$_{x}$Bi$_{2}$Se$_{3}$ and Cu$_{x}$Bi$_{2}$Se$_{3}$ reveal that this symmetry breaking occurs at T$_{nem}$≃3.8K above T$_{c}$≃3.25K, along with an onset of superconducting fluctuations. Thus, before Cooper pairs establish long-range coherence at T$_{c}$, they fluctuate in a way that breaks the rotational invariance at T$_{nem}$ and induces a crystalline distortion

Phonon promoted charge density wave in topological kagome metal ScV6_{6}Sn6_{6}

Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention due to their unique properties and intricate interplay with exotic correlated phenomena, topological and symmetry-breaking states. However, the origin of the CDW order remains a topic of debate. The discovery of ScV$_{6}$Sn$_{6}$, a vanadium-based bilayer kagome metal exhibiting an in-plane $\sqrt{3}$ x $\sqrt{3}$ $\textit{R}$30${\deg}$ CDW order with time-reversal symmetry breaking, provides a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering measurements and density functional theory to investigate the electronic structures and phonon modes of ScV$_{6}$Sn$_{6}$ and their evolution with temperature. We identify topologically nontrivial Dirac surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS near the K point exhibiting nesting wave vectors in proximity to the $\sqrt{3}$ x $\sqrt{3}$ $\textit{R}$30${\deg}$ CDW wave vector. Additionally, Raman measurements indicate a strong intrinsic electron-phonon coupling in ScV$_{6}$Sn$_{6}$, as evidenced by the presence of a two-phonon mode and a large frequency amplitude mode. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV$_{6}$Sn$_{6}$ and provide important insights into the fascinating correlation phenomena observed in kagome metals

Spin-triplet superconductivity in Weyl nodal-line semimetals

Topological semimetals are three dimensional materials with symmetry-protected massless bulk excitations. As a special case, Weyl nodal-line semimetals are realized in materials either having no inversion or broken time-reversal symmetry and feature bulk nodal lines. The 111-family of materials, LaNiSi, LaPtSi and LaPtGe (all lacking inversion symmetry), belong to this class. Here, by combining muon-spin rotation and relaxation with thermodynamic measurements, we find that these materials exhibit a fully-gapped superconducting ground state, while spontaneously breaking time-reversal symmetry at the superconducting transition. Since time-reversal symmetry is essential for protecting the normal-state topology, its breaking upon entering the superconducting state should remarkably result in a topological phase transition. By developing a minimal model for the normal-state band structure and assuming a purely spin-triplet pairing, we show that the superconducting properties across the family can be described accurately. Our results demonstrate that the 111-family reported here provides an ideal test-bed for investigating the rich interplay between the exotic properties of Weyl nodal-line fermions and unconventional superconductivity

Competing magnetic phases in LnSbTe (Ln = Ho and Tb)

The interplay between topological electronic structure and magnetism may result in intricate physics. In this work, we describe a case of rather peculiar coexistence or competition of several magnetic phases below a seemingly single antiferromagnetic transition in LnSbTe (Ln = Ho and Tb) topological semimetals, the magnetic members of the ZrSiS/PbFCl structure type (space group P4/nmm). Neutron diffraction experiments reveal a complex multi-step order below TN = 3.8 K (Ln = Ho) and TN = 6.4 K (Ln = Tb). Magnetic phases can be described using four propagation vectors: k1 = (1/2 0 0) and k2 = (1/2 0 1/4) at the base temperature of 1.7 K, which transform into incommensurate vectors k1' = (1/2 - d 0 0), k3 = (1/2 - d 0 1/2) at elevated temperatures in both compounds. Together with the refined models of magnetic structures, we present the group-theoretical analysis of the magnetic symmetry of the proposed solutions. These results prompt further investigations of the relation between the electronic structure of those semimetals and the determined antiferromagnetic ordering existing therein

Anisotropic character of the metal-to-metal transition in Pr4Ni3O10

As a member of the Ruddlesden-Popper Ln(n+1)Ni(n)O(3n+1) series rare-earth-nickelates, Pr4Ni3O10 consists of infinite quasi-two-dimensional perovskite-like Ni-O based layers. Although a metal-to-metal phase transition at T-pt approximate to 157K has been revealed by previous studies, a comprehensive study of physical properties associated with this transition has not yet been performed. We have grown single crystals of Pr4Ni3O10 at high oxygen pressure, and report on the physical properties around that phase transition, such as heat-capacity, electrictransport, and magnetization. We observe a distinctly anisotropic behavior between in-plane and out-of-plane properties: a metal-to-metal transition at T-pt within the a-b plane, and a metal-to-insulator-like transition along the c axis with decreasing temperature. Moreover, an anisotropic and anomalous negative magnetoresistance is observed at T-pt that we attribute to a slight suppression of the first-order transition with magnetic field. The magnetic susceptibility can be well described by a Curie-Weiss law, with different Curie constants and Pauli-spin susceptibilities between the high-temperature and the low-temperature phases. The single crystal x-ray diffraction measurements show a shape variation of the different NiO6 octahedra from the high-temperature phase to the low-temperature phase. This subtle change of the environment of the Ni sites is likely responsible for the different physical properties at high and low temperatures

Short-range magnetic interactions and spin-glass behavior in the quasi-two-dimensional nickelate Pr4Ni3O8

The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of three stacked square-planar NiO2 planes, in a similar way to the well-known cuprate superconductors. The mixed-valent nature of Ni and its metallic properties makes it a candidate for potentially unconventional superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of Pr4Ni3O10 in 10% hydrogen gas, and report on measurements of powder-neutron diffraction, magnetization, and muon-spin rotation (µSR). We find that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic memory effect in the temperature range from 2 to 300 K and a freezing temperature Ts≈68K. Moreover, the analysis of µSR spectra indicates two magnetic processes characterized by remarkably different relaxation rates: a slowly relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions, and a fast-relaxing signal, whose relaxation rate increases substantially below ≈70K which can be ascribed to the presence of short-range correlated regions. We conclude that the complex spin-freezing process in Pr4Ni3O8 is governed by these multiple magnetic interactions. It is possible that the complex magnetism in Pr4Ni3O8 is detrimental to the occurrence of superconductivity