BZPEERPapers, people, evidence and research paths
Menu

Discover

SearchFind papers, people, topics, institutions and opportunities from one place.GraphSee how papers, authors, topics and evidence connect.

Research tools

HomeContinue from the papers, people and topics that matter now.CollectionsTurn saved papers into reading lists, evidence maps and shareable context.ResearchReconstruct the path that led you from search to paper to question.CollaborationMove from a paper, topic or expert request into a focused thread.PublishCreate full-text research articles with metadata, formulas and versions.

Network

ExpertsFind specialists whose work and reviews explain why they can help.CommunitiesJoin research groups organized around papers, topics and shared evidence.

Opportunities

ListingsBrowse roles, calls and collaborations connected to real research context.

Account

Log inReturn to your saved papers, graph views and active threads.Create accountStart saving papers, building a research trail and joining teams.
Log inCreate account

Source author record

Weiwei Xie

Weiwei Xie appears in the imported research catalog. Authorship, coauthor and topic links are available while profile ownership is still unclaimed.

ResearcherUnclaimed source record
cond-mat.mtrl-scicond-mat.supr-concond-mat.str-elcond-mat.mes-hallArtificial Intelligencecond-mat.otherMachine LearningNeural and Evolutionary Computingphysics.app-ph

Catalog footprint

What is connected

36works
9topics
4close collaborators

Actions

Connect this record

Log in to claim
Open graphBrowse works

Research graph

See the researcher in context

Open full explorer

Inspect adjacent papers, topics, institutions and collaborators without losing the researcher page.

Building this map preview

BZPEER is loading the nearby papers, people, topics and institutions for this page.

Published work

36 published item(s)

preprint2026arXiv

Frustrated Magnetism in FeGe$_3$O$_4$ with a Chiral Trillium Network

The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-trillium lattice with nearest-neighbor Fe--Fe distances of $\sim$4.2~Å, while Ge$^{2+}$ ions mediate magnetic interactions through Fe-Ge-Fe pathways. Field-dependent magnetization at 2~K shows a pronounced nonlinearity, reaching a maximum moment of 2.55(3)~$μ_\mathrm{B}$/Fe$^{2+}$ at 70~kOe without evidence of saturation. Magnetic susceptibility, heat capacity, and neutron scattering collectively reveal the onset of short-range magnetic interactions near 5~K, with no long-range ordering detected down to 0.06~K. Specific heat measurements demonstrate strong frustration: only $\sim$34\% of the expected magnetic entropy is recovered at 2.4~K. Taken together, these results establish FeGe$_3$O$_4$ as a rare example of a geometrically frustrated trillium-lattice magnet, offering a promising platform for exploring exotic quantum magnetic phenomena.

0 citations0 reviewsNo code linkedOpen access
preprint2026arXiv

Scalable Learning in Structured Recurrent Spiking Neural Networks without Backpropagation

Spiking Neural Networks (SNNs) provide a promising framework for energy-efficient and biologically grounded computation; however, scalable learning in deep recurrent architectures with sparse connectivity remains a major challenge. In this work, we propose a structured multi-layer recurrent SNN architecture composed of locally dense recurrent layers augmented with sparse small-world long-range projections to a readout population. The long-range connectivity is largely fixed, preserving routing efficiency and hardware scalability, while synaptic adaptation is performed using strictly local plasticity mechanisms. To enable supervised learning without backpropagation or surrogate gradients, we introduce a biologically motivated learning framework that combines: (i) population-based winner-take-all (WTA) teaching signals at the output layer, (ii) fixed random broadcast alignment feedback pathways, and (iii) low-dimensional modulatory neuron populations that gate synaptic updates through three-factor learning rules with eligibility traces. This design supports deep recurrent computation with sparse global communication and purely local synaptic updates. We analyze the algorithmic properties, computational complexity, and hardware feasibility of the proposed approach, and demonstrate stable learning and competitive performance on benchmark classification tasks. The results highlight the potential of structured recurrence and neuromodulatory learning to enable scalable, hardware-compatible SNN training beyond gradient-based methods.

0 citations0 reviewsNo code linkedOpen access
preprint2024arXiv

Insulator to Metal Transition, Spin-Phonon Coupling, and Potential Magnetic Transition Observed in Quantum Spin Liquid Candidate LiYbSe$_2$ under High Pressure

Metallization of quantum spin liquid (QSL) materials has long been considered as a potential route to achieve unconventional superconductivity. Here we report our endeavor in this direction by pressurizing a three-dimensional QSL candidate, LiYbSe$_2$, with a previously unreported pyrochlore structure. High-pressure X-ray diffraction and Raman studies up to 50 GPa reveal no appreciable changes of structural symmetry or distortion in this pressure range. This compound is so insulating that its resistance decreases below 10$^5$ $Ω$ only at pressures above 25 GPa in the corresponding temperature range accompanying the gradual reduction of band gap upon compression. Interestingly, an insulator-to-metal transition takes place in LiYbSe$_2$ at about 68 GPa and the metallic behavior remains up to 123.5 GPa, the highest pressure reached in the present study. A possible sign of magnetic or other phase transition was observed in LiYbSe$_2$. The insulator-to-metal transition in LiYbSe$_2$ under high pressure makes it an ideal system to study the pressure effects on QSL candidates of spin-1/2 Yb$^{3+}$ system in different lattice patterns.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

High-throughput screening assisted discovery of a stable layered anti-ferromagnetic semiconductor: CdFeP2Se6

Recent advances in two-dimensional (2D) magnetism have heightened interest in layered magnetic materials due to their potential for spintronics. In particular, layered semiconducting antiferromagnets exhibit intriguing low-dimensional semiconducting behavior with both charge and spin as carrier controls. However, synthesis of these compounds is challenging and remains rare. Here, we conducted firstprinciples based high-throughput search to screen potentially stable mixed metal phosphorous trichalcogenides (MM'P2X6, where M and M' are transition metals and X is a chalcogenide) that have a wide range of tunable bandgaps and interesting magnetic properties. Among the potential candidates, we successfully synthesized a stable semiconducting layered magnetic material, CdFeP2Se6, that exhibits a short-range antiferromagnetic order at TN = 21 K with an indirect band gap of 2.23 eV. Our work suggests that highthroughput screening assisted synthesis be an effective method for layered magnetic materials discovery.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3

Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrachain and interchain excitons, and possibly trions. The thresholds for the formation of a photo-hole together with an exciton appear as side valence bands with dispersions nearly parallel to the main valence band, but shifted to lower excitation energies. The energy separation between side and main valence bands can be controlled by surface doping, enabling the tuning of certain exciton properties.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

The honeycomb and hyperhoneycomb polymorphs of IrI$_3$

The synthesis of IrI$_3$ at high pressure in its layered honeycomb polymorph is reported. Its crystal structure is refined by single crystal X-ray diffraction. Faults in the honeycomb layer stacking are observed by single crystal diffraction, synchrotron powder diffraction, and transmission electron microscopy. A previously unreported hyperhoneycomb polymorph of IrI$_3$ ($β$-IrI$_3$), is also described. Its structure in space group Fddd is determined by single crystal XRD. Both materials are highly-resistive diamagnetic semiconductors, consistent with a low spin d$^6$ configuration for Ir(III). The two- and three-dimensional Ir arrays in these polymorphs of IrI$_3$ are analogous to those found in the $α$- and $β$- polymorphs of Li$_2$IrO$_3$, although the Ir electron configurations are different.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Theory-guided investigation on magnetic evolution of MnPt$_{5-x}$Pd$_x$P and discovery of anti-CeCoIn$_5$-type ferromagnetic MnPd$_5$P

We report the magnetic changes from canted antiferromagnetic to ferromagnetic orderings in anti-115-type MnPt$_{5-x}$Pd$_x$P ($x$ = 1, 2, 2.5, 3, 4, and 5) and the discovery of a new rare-earth-free ferromagnet, MnPd$_5$P by both theoretical prediction and experimental investigation. The family compounds were synthesized using high temperature solid state method and characterized to crystalize in the anti-CeCoIn$_5$ type with the space group P4/mmm exhibiting a two-dimensional layered structural feature. The magnetic property measurements indicate that the compounds ordered from canted A-type antiferromagnet in MnPt$_5$P to ferromagnet above the room temperature with varying degrees of coercivity and magnetic moments in MnPd$_5$P by reducing the spin orbital coupling. The results of the MnPt$_{5-x}$Pd$_x$P have been analyzed in comparison to the other candidates of the 151 family of Mn(Pt/Pd)$_5$(P/As) to understand the complex structure-magnetism relationships.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Unusual electrical and magnetic properties in layered EuZn2As2

Eu-based compounds often exhibit unusual magnetism, which is critical for nontrivial topological properties seen in materials such as EuCd2As2. We investigate the structure and physical properties of EuZn2As2 through measurements of the electrical resistivity, Hall effect, magnetization, and neutron diffraction. Our data show that EuZn2As2 orders antiferromagnetically with an A-type spin configuration below TN = 19 K. Surprisingly, there is strong evidence for dominant ferromagnetic fluctuations above TN, as reflected by positive Curie-Weiss temperature and extremely large negative magnetoresistance (MR) between TN and Tfl » 200 K. Furthermore, the angle dependence of the MRab indicates field-induced spin reorientation from the ab-plane to a direction approximately 45° from the ab plane. Compared to EuCd2As2, the doubled TN and Tfl make EuZn2As2 a better platform for exploring topological properties in both magnetic fluctuation (TN < T < Tfl) and ordered (T < TN) regimes.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

Annihilation and Control of Chiral Domain Walls with Magnetic Fields

The control of domain walls is central to nearly all magnetic technologies, particularly for information storage and spintronics. Creative attempts to increase storage density need to overcome volatility due to thermal fluctuations of nanoscopic domains and heating limitations. Topological defects, such as solitons, skyrmions, and merons, may be much less susceptible to fluctuations, owing to topological constraints, while also being controllable with low current densities. Here, we present the first evidence for soliton/soliton and soliton/antisoliton domain walls in the hexagonal chiral magnet Mn1/3NbS2 that respond asymmetrically to magnetic fields and exhibit pair-annihilation. This is important because it suggests the possibility of controlling the occurrence of soliton pairs and the use of small fields or small currents to control nanoscopic magnetic domains. Specifically, our data suggest that either soliton/soliton or soliton/antisoliton pairs can be stabilized by tuning the balance between intrinsic exchange interactions and long-range magnetostatics in restricted geometries

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

NbIr$_2$B$_2$ and TaIr$_2$B$_2$ -- new low symmetry noncentrosymmetric superconductors with strong spin orbit coupling

Superconductivity was first observed more than a century ago, but the search for new superconducting materials remains a challenge. The Cooper pairs in superconductors are ideal embodiments of quantum entanglement. Thus, novel superconductors can be critical for both learning about electronic systems in condensed matter and for possible application in future quantum technologies. Here two previously unreported materials, NbIr$_2$B$_2$ and TaIr$_2$B$_2$, are presented with superconducting transitions at 7.2 and 5.2 K, respectively. They display a unique noncentrosymmetric crystal structure, and for both compounds the magnetic field that destroys the superconductivity at 0 K exceeds one of the fundamental characteristics of conventional superconductors (the Pauli limit), suggesting that the superconductivity may be unconventional. Supporting this experimentally based deduction, first-principle calculations show a spin split Fermi surface due to the presence of strong spin-orbit coupling. These materials may thus provide an excellent platform for the study of non-BCS superconductivity in intermetallic compounds.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

A Novel Magnetic Material by Design: Observation of Yb3+ with Spin-1/2 and Possible Superconducting Trace in YbxPt5P

The localized f-electrons enrich the magnetic properties in rare-earth-based intermetallics. Among those, compounds with heavier 4d and 5d transition metals are even more fascinating because anomalous electronic properties may be induced by the hybridization of 4f and itinerant conduction electrons primarily from the d orbitals. Here, we describe the observation of trivalent Yb3+ with S = 1/2 at low temperatures in YbxPt5P, the first of a new family of materials. YbxPt5P (0.20< x <1) phases were synthesized and structurally characterized. They exhibit a large homogeneity width with the Yb ratio exclusively occupying the 1a site in the anti-CeCoIn5 structure. Moreover, the resistivity measurement of a sample analyzed as Yb0.25Pt5P shows it to exist a complete zero-resistance transition with a critical transition temperature of ~0.6 K, possible superconductivity. However, the zero-resistivity transition was not observed in YbPt5P with antiferromagnetic ordering existing solely. First-principles electronic structure calculations substantiate the antiferromagnetic ground state and indicate that 2D nesting around the Fermi level may give rise to exotic physical properties, such as superconductivity. YbxPt5P appears to be a unique case among materials.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Chemical Bonding Governs Complex Magnetism in MnPt5P

Subtle changes in chemical bonds may result in dramatic revolutions in magnetic properties in solid state materials. MnPt5P, a new derivative of the rare-earth-free ferromagnetic MnPt5As, was discovered and is presented in this work. MnPt5P was synthesized and its crystal structure and chemical composition were characterized by X-ray diffraction as well as energy-dispersive X-ray spectroscopy. Accordingly, MnPt5P crystallizes in the layered tetragonal structure with the space group P4/mmm (No. 123), in which the face-shared Mn@Pt12 polyhedral layers are separated by P layers. In contrast to the ferromagnetism observed in MnPt5As, the magnetic properties measurements on MnPt5P show antiferromagnetic ordering occurs at ~188 K with a strong magnetic anisotropy in and out of the ab-plane. Moreover, a spin-flop transition appears when a high magnetic field is applied. An A-type antiferromagnetic structure was obtained from the analysis of powder neutron diffraction (PND) patterns collected at 150 K and 9 K. Calculated electronic structures imply that hybridization of Mn-3d and Pt-5d orbitals are critical for both the structural stability and observed magnetic properties. Semi-empirical molecular orbitals calculations on both MnPt5P and MnPt5As indicate that the lack of 4p character on the P atoms at the highest occupied molecular orbital (HOMO) in MnPt5P may cause the different magnetic behavior in MnPt5P compared to MnPt5As. The discovery of MnPt5P, along with our previously reported MnPt5As, parametrizes the end points of a tunable system to study the chemical bonding which tunes the magnetic ordering from ferromagnetism to antiferromagnetism with strong spin-orbit coupling (SOC) effect.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Crystal Structure, Magnetism, and Electronic Properties of New Rare-Earth-Free Ferromagnetic MnPt5As

The design and synthesis of targeted functional materials have been a long-term goal for material scientists. Although a universal design strategy is difficult to generate for all types of materials, however, it is still helpful for a typical family of materials to have such design rules. Herein, we incorporated several significant chemical and physical factors regarding magnetism, such as structure type, atom distance, spin-orbit coupling, and successfully synthesized a new rare-earth-free ferromagnet, MnPt5As, for the first time. MnPt5As can be prepared by using high-temperature pellet methods. According to X-ray diffraction results, MnPt5As crystallizes in a tetragonal unit cell with the space group P4/mmm (Pearson symbol tP7). Magnetic measurements on MnPt5As confirm ferromagnetism in this phase with a Curie temperature of ~301 K and a saturated moment of 3.5 uB per formula. Evaluation by applying the Stoner Criterion also indicates that MnPt5As is susceptible to ferromagnetism. Electronic structure calculations using the WIEN2k program with local spin density approximation imply that the spontaneous magnetization of this phase arises primarily from the hybridization of d orbitals on both Mn and Pt atoms. The theoretical assessments are consistent with the experimental results. Moreover, the spin-orbit coupling effects heavily influence on magnetic moments in MnPt5As. MnPt5As is the first high-performance magnetic material in this structure type. The discovery of MnPt5As offers a platform to study the interplay between magnetism and structure.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Enhanced Anomalous Hall Effect in Magnetic Topological Semimetal Co$_3$Sn$_{2-x}$In$_x$S$_2$

We study the anomalous Hall Effect (AHE) of single-crystalline Co$_3$Sn$_{2-x}$In$_x$S$_2$ over a large range of indium concentration x from 0 to 1. Their magnetization reduces progressively with increasing x while their ground state evolves from a ferromagnetic Weyl semimetal into a nonmagnetic insulator. Remarkably, after systematically scaling the AHE, we find that their intrinsic anomalous Hall conductivity (AHC) features an unexpected maximum at around x = 0.15. The change of the intrinsic AHC corresponds with the doping evolution of Berry curvature and the maximum arises from the magnetic topological nodal-ring gap. Our experimental results show a larger AHC in a fundamental nodal-ring gap than that of Weyl nodes.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Structural distortion and incommensurate noncollinear magnetism in EuAg4As2

Layered pnictide materials have provided a fruitful platform to study various emergent phenomena, including superconductivity, magnetism, charge density waves, etc. Here we report the observation of structural distortion and noncollinear magnetism in layered pnictide EuAg$_4$As$_2$ via transport, magnetization, single crystal X-ray and neutron diffraction data. EuAg$_4$As$_2$ single crystal shows a structural distortion at 120 K, where two sets of superlattice peaks with the propagation vectors of $q_1=\pm$(0, 0.25, 0.5) and $q_2=\pm$(0.25, 0, 1) emerge. Between 9 K to 15 K, the hexagonal Eu$^{2+}$ sub-lattice enters an unpinned state, with magnetic Bragg reflections pictured as circular-sectors. Below 9 K, it orders in an incommensurate noncollinear antiferromagnetic state with a well-defined propagation wavevector of (0, 0.1, 0.12), where the magnetic structure is helical along the $c$ axis and cycloidal along the $b$ axis with a moment of 6.4 $μ_B$/Eu$^{2+}$. Furthermore, rich magnetic phases under magnetic fields, large magnetoresistance, and strong coupling between charge carriers and magnetism in EuAg$_4$As$_2$ are revealed.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Superconductivity in Metal-Rich Chalcogenide Ta2Se

The metal-metal bond in metal-rich chalcogenide is known to exhibit various structures and dominate interesting physical properties. Ta2Se can be obtained by both arc-melting and solid-state pellet methods. Ta2Se crystallizes a layered tetragonal structure with space group P4/nmm (S.G.129, Pearson symbol tP6). Each unit cell consists of four layers of body-centered closed packing Ta atoms sandwiched between two square nets of Se atoms, forming the Se-Ta-Ta-Ta-Ta-Se networks. A combined result of magnetic susceptibility, resistivity, and heat capacity measurements on Ta2Se indicate the bulk superconductivity with Tc = 3.8 (1) K. According to the first-principal calculations, the d orbitals in Ta atoms dominate the Fermi level in Ta2Se. The flat bands at gamma-point in the Brillouin zone (BZ) yield to the van Hove singularities in density of states (DOS) around the Fermi level, which is intensified by introducing spin-orbit coupling (SOC) effect, thus, could be critical for the superconductivity in Ta2Se. The physical properties especially superconductivity is completely different from Ta-rich alloys or transition metal dichalcogenide TaSe2.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Topological Hall effect and the magnetic states of Nowotney chimney ladder compound Cr$_{11}$Ge$_{19}$}

We have investigated the magnetic and charge transport properties of single crystals of Nowotney Chimney Ladder compound Cr$_{11}$Ge$_{19}$ and mapped out a comprehensive phase diagram reflecting the complicated interplay between the Dzyaloshinskii-Moriya (DM) interaction, the dipolar interaction, and the magnetic anisotropy. We have identified a set of interesting magnetic phases and attributed a finite topological Hall effect to the recently discovered bi-skyrmion phase. These data also suggest the existence of an anti-skyrmion state at finite fields for temperatures just below the magnetic ordering temperature, $T_c$, as indicated by a distinct change in sign of the topological Hall effect. Above $T_c$, we discovered a region of enhanced magnetic response corresponding to a disordered phase likely existing near the ferromagnetic critical point under small magnetic fields. Strong spin chirality fluctuations are demonstrated by the large value of the topological Hall resistivity persisting up to 1 T which is most likely due to the existence of the DM interaction. We argue that changes to the topological Hall effect correspond to different topological spin textures that are controlled by magnetic dipolar and DM interactions that vary in importance with temperature.

0 citations0 reviewsNo code linkedOpen access
preprint2019arXiv

Highly Mobile Carriers in a Candidate of Quasi-Two-Dimensional Topological Semimetal AuTe$_2$Br

We report the crystal and electronic structures of a non-centrosymmetric quasi-two-dimensional (2D), candidate of topological semimetal AuTe2Br. The Fermi surface of this layered compound consists of 2D-like, topological trivial electron and non-trivial hole pockets which host a Dirac cone along the kz direction. Our transport measurements on the single crystals show highly anisotropic, compensated low-density electrons and holes, both of which exhibit ultrahigh mobility at a level of 10^5cm^2V^-1s^-1 at low temperature. The highly mobile, compensated carriers lead a non-saturated, parabolic magnetoresistance as large as 3*10^5 in single-crystalline AuTe2Br in a magnetic field up to 58 T.

0 citations0 reviewsNo code linkedOpen access
preprint2019arXiv

Transport evidence of triply degenerate nodal semimetal YRh6Ge4

We have investigated magnetotransport properties of YRh6Ge4, which was recently predicted to be a triply degenerate nodal semimetal. We find it exhibits remarkable signatures of a chiral anomaly, manifested by large negative longitudinal magnetoresistance, quadratic field dependence of magnetoconductance and planar Hall effect. Furthermore, we have also observed Shubnikov-de Haas (SdH) quantum oscillations in the magnetoresistivity measurements on this material. The analyses of the SdH data reveal two point-like Fermi surfaces and these pockets are found to host nearly massless fermions. The small size of these Fermi pockets is in a good agreement with the theoretical prediction that the triply degenerate point in YRh6Ge4 is much closer to the Fermi level than previously demonstrated triply degenerate nodal semimetals such as MoP and WC. These results suggest YRh6Ge4 may serve as a model system to probe exotic properties of three-component fermions and understand their underlying physics.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

Differences in chemical doping matter - Superconductivity in Ti1-xTaxSe2 but not in Ti1-xNbxSe2

We report that 1T-TiSe2, an archetypical layered transition metal dichalcogenide, becomes superconducting when Ta is substituted for Ti but not when Nb is substituted for Ti. This is unexpected because Nb and Ta should be chemically equivalent electron donors. Superconductivity emerges near x = 0.02 for Ti1-xTaxSe2, while for Ti1-xNbxSe2, no superconducting transitions are observed above 0.4 K. The equivalent chemical nature of the dopants is confirmed by X-ray photoelectron spectroscopy. ARPES and Raman scattering studies show similarities and differences between the two systems, but the fundamental reasons why the Nb and Ta dopants yield such different behavior are unknown. We present a comparison of the electronic phase diagrams of many electron-doped 1T-TiSe2 systems, showing that they behave quite differently, which may have broad implications in the search for new superconductors. We propose that superconducting Ti0.8Ta0.2Se2 will be suitable for devices and other studies based on exfoliated crystal flakes.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

Influence of structural distortions on the Ir magnetism in Ba2-xSrxYIrO6 double perovskites

We explore the relative strengths of spin orbit coupling and crystal field splitting in the Ir5+ compounds Ba2-xSrxYIrO6. In the case of strong spin orbit coupling and regular Ir5+ octahedra, one expects a nonmagnetic J = 0 state; in the case of distorted octahedra where crystal field effects dominate, the t2g manifold splits into a magnetic ground state. We report the results of continuously transitioning from the cubic Ba2YIrO6 double perovskite with ideal octahedra to the monoclinic Sr2YIrO6 double perovskite with distorted octahedra. We see no emergence of an enhanced Ir5+ magnetic moment in the series on increasing the structural distortions, as would have been the case for significant crystal field splitting. The near-constant magnetic moment observed through the Ba2-xSrxYIrO6 series reinforces the notion that spin-orbit coupling is the dominant force in determining the magnetism of iridium-oxygen octahedra in perovskite-like structures

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

MoTe2: A Type-II Weyl Topological Metal

Based on the ab initio calculations, we show that MoTe2, in its low-temperature orthorhombic structure characterized by an X-ray diffraction study at 100 K, realizes 4 type-II Weyl points between the N-th and N+1-th bands, where N is the total number of valence electrons per unit cell. Other WPs and nodal lines between different other bands also appear close to the Fermi level due to a complex topological band structure. We predict a series of strain-driven topological phase transitions in this compound, opening a wide range of possible experimental realizations of different topological semimetal phases. Crucially, with no strain, the number of observable surface Fermi arcs in this material is 2 - the smallest number of arcs consistent with time-reversal symmetry.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

Superconducting properties of Rh$_{9}$In$_4$S$_4$ single crystals

The synthesis and crystallographic, thermodynamic and transport properties of single crystalline Rh$_{9}$In$_4$S$_4$ were studied. The resistivity, magnetization and specific heat measurements all clearly indicate bulk superconductivity with a critical temperature, $T_{c}\sim$ 2.25 K. The Sommerfeld coefficient $γ$ and the Debye temperature($\varTheta_{\textrm{D}}$) were found to be 34 mJ mol$^{-1}$ K$^{-2}$ and 217 K respectively. The observed specific heat jump, $ΔC/γT_{c}$ = 1.66, is larger than the expected BCS weak coupling value of 1.43. Ginzburg-Landau (GL) ratio of the low temperature GL-penetration depth, $λ_\text{GL}$$\approx$ 5750Å, to the GL-coherence length, $ξ_\text{GL}$$\approx$ 94Å, is large: $κ$ $\sim$ 60. Furthermore, we observed a peak effect in the resistivity measurement as a function of both temperature and magnetic field.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

Superconductivity in a misfit phase combining a topological crystalline insulator and a layered transition metal dichalcogenide

We report the characterization of the misfit compound (Pb1-xSnxSe2)1.16(TiSe2)2, in which a [100] rocksalt bilayer of Pb1-xSnxSe, which is a topological crystalline insulator in bulk form, alternates with a double layer of the normally non-superconducting layered transition metal dichalcogenide TiSe2. The x dependence of Tc displays a weak dome-like shape with a maximum Tc of 4.5 K at x = 0.2; there is only a subtle change in Tc corresponding to the expected trivial to topological transition in the Pb1-xSnxSe bi-layer. We present a more detailed characterization of the superconductor at x = 0.4, for which the bulk Pb1-xSnxSe phase is in the topological crystalline insulator regime. For this material, the Sommerfeld parameter gamma =11.06 mJ mol-1 K-2, the Debye temperature delta D = 161 K, the normalized specific heat jump value delta C/ gamma Tc = 1.38 and the electron-phonon constant value lambda ep = 0.72, suggesting that (Pb0.6Sn0.4Se)1.16(TiSe2)2 is a BCS-type weak coupling superconductor. This material is of interest for probing the interaction of superconductivity with the surface states of a topological crystalline insulator.

0 citations0 reviewsNo code linkedOpen access
preprint2016arXiv

The New Superconductor tP-SrPd2Bi2: Structural Polymorphism and Superconductivity in Intermetallics

We consider a system where structural polymorphism suggests the possible existence of superconductivity through the implied structural instability. SrPd2Bi2 has two poly-morphs which can be controlled by the synthesis temperature: a tetragonal form (CaBe2Ge2-type) and a monoclinic form (BaAu2Sb2-type). Though the crystallographic difference between the two forms may at first seem trivial, we show that tetragonal SrPd2Bi2 is superconducting at 2.0 K whereas monoclinic SrPd2Bi2 is not. We rationalize this finding and place it in context with other 1-2-2 phases

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

A large new family of filled skutterudites stabilized by electron count

Based on the interplay of theory and experiment, a large new family of filled group 9 (Co, Rh and Ir) skutterudites is designed and synthesized. The new materials fill the empty cages in the structures of the known binary CoSb3, RhSb3 and IrSb3 skutterudites with alkaline, alkaline earth, and rare earth atoms to create compounds of the type AyB4X12; A atoms fill the cages to a fraction y, B are the group 9 transition metals, and X is a mixture of electronegative main group elements chosen to achieve chemical stability by adjusting the electron counts to electron-precise values. Forty-three new compounds are reported, antimony-tin and phosphorous-silicon based, with 63 compositional variations presented. The new family of compounds is large and general. The results described here can be extended to the synthesis of hundreds of new group 9 filled skutterudites.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

A new material for probing spin-orbit coupling in Iridates

We report the structure and magnetic properties of a new iridate compound, SrxLa11-xIr4O24, where the d-electron count of Ir and therefore its number of unpaired electrons can be tuned continuously from 5d5 Ir4+ to 5d4 Ir5+, i.e. from SrLa10Ir4O24 to Sr5La6Ir4O24. The IrO6 octahedra in SrxLa11-xIr4O24 are isolated from each other and from other transition elements, minimizing band effects, and the doping is on the framework sites, not the Ir sites, minimizing the effects of disorder. Measurements of the temperature dependent magnetic susceptibility are employed to determine the evolution of the Ir magnetic moment on progressing from 5d5 Ir4+ to 5d4 Ir5+, and are clearly best described by a transition from a J=1/2 to a J=0 Ir magnetic state; that is, the evolution of the magnetic susceptibility shows the dominance of spin-orbit coupling in determining the magnetic properties of a material with highly isolated IrO6 octahedra.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Gold-Gold Bonding: The Key to Stabilizing the 19-Electron Ternary Phases LnAuSb (Ln = La-Nd and Sm) as New Dirac Semimetals

We report a new family of ternary 111 hexagonal LnAuSb (Ln = La-Nd, Sm) compounds that, with a 19 valence electron count, has one extra electron compared to all other known LnAuZ compound. The "19th" electron is accommodated by Au-Au bonding between the layers; this Au-Au interaction drives the phases to crystallize in the YPtAs-type structure rather than the more common LiGaGe-type. This is critical, as the YPtAs structure type has the symmetry-allowed band crossing necessary for the formation of Dirac semimetals. Band structure, density of stats, and crystal orbital calculations confirm this picture, which results in a nearly complete band gap between full and empty electronic states and stable compounds; we can thus present a structural stability phase diagram for the LnAuZ (Ln = Ge, As, Sn, Sb, Pb, Bi) family of phases. Those calculations also show that LaAuSb has a bulk Dirac cone below the Fermi level. The YPtAs-type LnAuSb family reported here is an example of the uniqueness of gold chemistry applied to a rigidly closed shell system in an unconventional way.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Polytypism, polymorphism and superconductivity in TaSe2-xTex

Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe2, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe2-xTex solid solution, and find that the 3R polytype shows a superconducting transition temperature that is nearly 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Potential ring of Dirac nodes in a new polymorph of Ca$_3$P$_2$

We report the crystal structure of a new polymorph of Ca$_3$P$_2$, and an analysis of its electronic structure. The crystal structure was determined through Rietveld refinements of powder synchrotron x-ray diffraction data. Ca$_3$P$_2$ is found to be a variant of the Mn$_5$Si$_3$ structure type, with a Ca ion deficiency compared to the ideal 5:3 stoichiometry to yield a charge-balanced compound. We also report the observation of a secondary phase, Ca$_5$P$_3$H, in which the Ca and P sites are fully occupied and the presence of interstitial hydride ions creates a closed-shell electron-precise compound. We show via electronic structure calculations of Ca$_3$P$_2$ that the compound is stabilized by a gap in the density of states compared to the hypothetical compound Ca$_5$P$_3$. Moreover, the calculated band structure of Ca$_3$P$_2$ indicates that it should be a three-dimensional Dirac semimetal with a highly unusual ring of Dirac nodes at the Fermi level. The Dirac states are protected against gap opening by a mirror plane in a manner analogous to graphene. The results suggest that further study of the electronic properties of Ca$_3$P$_2$ will be of interest.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Resonance-state-induced superconductivity at high Indium contents in In-doped SnTe

We report a reinvestigation of superconducting Sn$_{1-x}$In$_{x}$Te at both low and high In doping levels. Analysis of the superconductivity reveals a fundamental change as a function of \textit{x}: the system evolves from a weakly coupled to a strongly coupled superconductor with increasing indium content. Hall Effect measurements further show that the carrier density does not vary linearly with Indium content; indeed at high Indium content, the samples are overall \textit{n}-type, which is contrary to expectations of the standard picture of In$^{1+}$ replacing Sn$^{2+}$ in this material. Density functional theory calculations probing the electronic state of In in SnTe show that it does not act as a trivial hole dopant, but instead forms a distinct, partly filled In 5\textit{s} - Te 5\textit{p} hybridized state centered around E$_F$, very different from what is seen for other nominal hole dopants such as Na, Ag, and vacant Sn sites. We conclude that superconducting In-doped SnTe therefore cannot be considered as a simple hole doped semiconductor.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Superconducting NbRuB derived through the fragment formalism

We employ the chemical fragment formalism to perform a targeted superconductor search in the Nb-Ru-B system, yielding the orthorhombic metal-rich boride NbRuB, which displays BCS-like superconductivity with a Tc = 3.1 K. NbRuB is derived from the chemical fragments Nb3B2 + Ru3B, in which the Nb3B2 fragment contains B-B dimers and the Ru3B fragment contains isolated B atoms. A charge transfer occurs between the fragments. The results indicate that the fragment formalism is a useful chemical tool for the design of new intermetallic superconductors much the same way as the charge reservoir concept has been a useful chemical tool for the design of new copper oxide superconductors.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Superconductivity in 3R-Ta1-xMxSe2 (M = W, Mo)

The 3-layer (3R) polytype of TaSe2-xTex shows a superconducting transition temperature that is between 6 and 17 times higher than that of the two-layer (2H) polytype. The remarkable difference in Tc, although clearly associated with a difference in polytype, could have been due to an electronic effect specific to the Te-Se substitution. Here we report that small amounts of Mo or W doping lead to a 2H to 3R polytype transition in Ta1-xMoxSe2 and Ta1-xWxSe2. The 3R polytype materials are again found to have substantially higher Tcs (~ 2 K for Ta0.9W0.1Se2 and Ta0.9Mo0.1Se2) than the 2H material (0.15 K). This eliminates the possibility that any special characteristics of the Te/Se substitution are responsible for the dramatic difference in Tc, and instead shows that a three-layer stacking sequence is strongly preferred for superconductivity over a two-layer stacking sequence in the TaSe2 system.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Superconductivity in Hf$_5$Sb$_3$$_-$$_x$Ru$_x$: Are Ru and Sb a critical charge-transfer pair for superconductivity?

We address the hypothesis that in intermetallic compounds, contrary to a long-standing view that considers electron count and crystal structure type as the only significant chemical criteria for the occurrence of superconductivity, consideration of the actual elements present is a third equally important factor. The importance of chemical identity may seem obvious, especially to chemists, but it has not previously been explicitly tested for intermetallic superconductors. Here we test the hypothesis by searching for and finding a new superconductor in the tetragonal symmetry Hf5Sb3-xMx solid solution. This phase is ideal for this study, because M can be many 3d, 4d and 5d transition metals in an M-Sb chain and is a minor elemental constituent. We find superconductivity for M = Ru only. This is the case even when the electron count can be adjusted to the same value with a different transition element within the same structure type. This leads us to propose that, like Cu-O (cuprate superconductors) and Fe-As (iron-pnictide superconductors) in different classes of compounds, Ru and Sb may be a critical element pair for superconductivity in intermetallic phases.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Superconductivity versus structural phase transition in the closely related Bi$_{2} $Rh$ _{3.5}$S$ _{2}$ and Bi$_{2} $Rh$ _{3}$S$ _{2}$

Single crystals of Bi$_{2} $Rh$ _{3}$S$ _{2}$ and Bi$_{2} $Rh$ _{3.5}$S$ _{2}$ were synthesized by solution growth and the crystal structures, thermodynamic and transport properties of both compounds were studied. In the case of Bi$_{2} $Rh$ _{3}$S$ _{2}$, a structural first-order transition at around 165 K is identified by single crystal diffraction experiments, with clear signatures visible in resistivity, magnetization and specific heat data. No superconducting transition for Bi$_{2} $Rh$ _{3}$S$ _{2}$ was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi$_{2} $Rh$ _{3.5}$S$ _{2}$, however bulk superconductivity with a critical temperature, $T_{c}\approx$ 1.7 K was observed. The Sommerfeld coefficient $γ$\ and the Debye temperature($\varTheta_{\textrm{D}}$) were found to be 9.4 mJ mol$^{-1}$ K$^{-2}$ and 209 K respectively for Bi$_{2} $Rh$ _{3}$S$ _{2}$, and 22 mJ mol$^{-1}$ K$^{-2}$ and 196 K respectively for Bi$_{2} $Rh$ _{3.5}$S$ _{2}$. Study of the specific heat in the superconducting state of Bi$_{2} $Rh$ _{3.5}$S$ _{2}$ suggests that Bi$_{2} $Rh$ _{3.5}$S$ _{2}$ is a weakly coupled, BCS superconductor.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

Zr$_5$Sb$_3$$_-$$_x$Ru$_x$, a new superconductor in the W$_5$Si$_3$ structure type

We report that at low Ru contents, up to x = 0.2, the Zr$_5$Sb$_3$$_-$$_x$Ru$_x$ solid solution forms in the hexagonal Mn$_5$Si$_3$ structure type of the host (x = 0), but that at higher Ru contents (x = 0.4 - 0.6) the solid solution transforms into the tetragonal W$_5$Si$_3$ structure type. We find that tetragonal Zr$_5$Sb$_2$$_.$$_4$Ru$_0$$_.$$_6$ is superconducting at 5 K, significantly higher than the transition temperature of hexagonal Zr$_5$Sb$_3$ (x = 0), which has a T$_c$ of 2.3 K. In support of a hypothesis that certain structure types are favorable for superconductivity, we describe how the W$_5$Si$_3$ and Tl$_5$Te$_3$ structure types, both of which support superconductivity, are derived from the parent Al$_2$Cu type structure, in which superconductors are also found. Electronic structure calculations show that in Zr$_1$$_0$Sb$_5$Ru, a model for the new superconducting compound, the Fermi level is located on a peak in the electronic density of states.

0 citations0 reviewsNo code linkedOpen access