arXiv subjects

Xin Gui

Publications and source records attributed to Xin Gui.

At least 55 records · Page 3Linked to original sources

arXiv2021

Ferromagnetic Double Perovskite Semiconductors with Tunable Properties

We successfully dope the magnetically silent double perovskite semiconductor Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and has tunable ferromagnetic ordering temperature and band gap, suggests that magnetic ion doping of double perovskites is a productive avenue towards obtaining materials for application in next-generation oxide-based spintronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Honeycomb-structure RuI3, a new quantum material related to α-RuCl3

The Kitaev model predicts that quantum spin liquids (QSLs) will form at low temperatures under certain special conditions, and materials hosting the QSL state are frequently sought. The layered honeycomb lattice material α-RuCl3 has emerged as a prime candidate for displaying the Kitaev QSL state. Here we describe a new polymorph of RuI3 with a layered honeycomb lattice structure, synthesized at moderately high pressures and stable under ambient conditions. Preliminary characterization reveals metallic, paramagnetic behavior, the absence of long-range magnetic order down to 0.35 K and an unusually large T-linear contribution to the heat capacity at low temperatures. We propose that this RuI3 phase, with a layered honeycomb lattice and strong spin-orbit coupling, provides a new route for the characterization of quantum materials.

cond-mat.mtrl-sci↗

arXiv2021

Ferromagnetic Cr4PtGa17: A Novel Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice

We describe the crystal structure and elementary magnetic properties of a previously unreported ternary intermetallic compound, Cr4PtGa17, which crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group R3m. The crystal structure is closely related to those of XYZ half-Heusler compounds, where X, Y and Z are reported to be single elements only, occupying three different face-centered cubic sublattices. The new material, Cr4PtGa17, can be most straightforwardly illustrated by writing the formula as (PtGa2)(Cr4Ga14)Ga (X=PtGa2, Y = Cr4Ga14, Z = Ga), that is, the X and Y sites are occupied by clusters instead of single elements. The magnetic Cr occupies a breathing pyrochlore lattice. Ferromagnetic ordering is found below TC ~61 K, by both neutron diffraction and magnetometer studies, with a small, saturated moment of ~0.25 muB/Cr observed at 2 K, making Cr4PtGa17 the first ferromagnetically ordered material with a breathing pyrochlore lattice. A magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that the material has a nearly-half-metallic electronic structure. The new material, Cr4PtGa17, the first realization of both a half-Heusler-type structure and a breathing pyrochlore lattice, might pave a new way to achieve novel types of half-Heusler compounds.

cond-mat.mtrl-sci↗

arXiv2021

Crystal Structure, Magnetic Properties and Bonding Analysis of M3Pt23Ge11 (M=Ca, Sr, Ba and Eu)

The properties of Pt-based materials can be intriguing due to the importance of spin-orbit coupling for Pt. Herein, we report four new phases with formulas M3Pt23Ge11 (M = Ca, Sr, Ba and Eu), which adopt the same structure type as Ce3Pt23Si11. Magnetic susceptibility measurements indicate that none of the phases is superconducting above 1.8 K, while for Eu3Pt23Ge11 ferromagnetic ordering is observed at ~ 3 K. The low Curie temperature for that material compared to that of Eu3Pt23Si11 may be due to its larger Eu-Eu distance. One potential factor that destabilizes the structure of other rare-earth based M3Pt23Ge11 is demonstrated through COHP calculations.

cond-mat.mtrl-sci↗

arXiv2021

Magnetic transitions in the 1-D chain compounds NdPd5Ge3 and NdPt5Ge3

We present the structural and initial magnetic characterization of the previously unreported materials NdPd5Ge3 and NdPd5Ge3. These materials, with 1-dimensional Nd chains, crystallize in the orthorhombic YNi5Si3-type structure in space group Pnma. Magnetic ordering is observed for both compounds at ~ 2.2 K for NdPd5Ge3 and ~ 3.0 K for NdPt5Ge3. A magnetic-field-induced transition is clearly observed for NdPd5Ge3 below 2K, at an applied magnetic field of around 1.6 Tesla. The heat capacity data reveals that essentially all the available magnetic entropy is released at the magnetic ordering transition for NdPd5Ge3 but that only 29% is seen for NdPt5Ge3 at temperatures down to 1.5 K, the data implying that a second magnetic transition can be expected at lower temperatures.

cond-mat.str-el↗

arXiv2021

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.

cond-mat.supr-con↗

arXiv2020

Surface Charge Induced Dirac Band Splitting in a Charge Density Wave Material (TaSe4)2I

(TaSe4)2I, a quasi-one-dimensional (1D) crystal, shows a characteristic temperature-driven metal-insulator phase transition. Above the charge density wave (CDW) temperature Tc, (TaSe4)2I has been predicted to harbor a Weyl semimetal phase. Below Tc, it becomes an axion insulator. Here, we performed angle-resolved photoemission spectroscopy (ARPES) measurements on the (110) surface of (TaSe4)2I and observed two sets of Dirac-like energy bands in the first Brillion zone, which agree well with our first-principles calculations. Moreover, we found that each Dirac band exhibits an energy splitting of hundreds of meV under certain circumstances. In combination with core level measurements, our theoretical analysis showed that this Dirac band splitting is a result of surface charge polarization due to the loss of surface iodine atoms. Our findings here shed new light on the interplay between band topology and CDW order in Peierls compounds and will motivate more studies on topological properties of strongly correlated quasi-1D materials.

cond-mat.str-el↗

arXiv2020

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.

cond-mat.mtrl-sci↗

arXiv2020

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.

cond-mat.mtrl-sci↗

arXiv2020

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.

cond-mat.mtrl-sci↗

arXiv2020

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.

cond-mat.mtrl-sci↗

arXiv2020

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.

cond-mat.supr-con↗

arXiv2020

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.

cond-mat.str-el↗

arXiv2020

Bond-breaking Induced Lifshitz Transition in Robust Dirac Semimetal $\mathbf{VAl_3}$

Topological electrons in semimetals are usually vulnerable to chemical doping and environment change, which restricts their potential application in future electronic devices. In this paper we report that the type-II Dirac semimetal $\mathbf{VAl_3}$ hosts exceptional, robust topological electrons which can tolerate extreme change of chemical composition. The Dirac electrons remain intact even after a substantial part of V atoms have been replaced in the $\mathbf{V_{1-x}Ti_xAl_3}$ solid solutions. This Dirac semimetal state ends at $x=0.35$ where a Lifshitz transition to $p$-type trivial metal occurs. The V-Al bond is completely broken in this transition as long as the bonding orbitals are fully depopulated by the holes donated from Ti substitution. In other words, the Dirac electrons in $\mathbf{VAl_3}$ are protected by the V-Al bond whose molecular orbital is their bonding gravity center. Our understanding on the interrelations among electron count, chemical bond and electronic properties in topological semimetals suggests a rational approach to search robust, chemical-bond-protected topological materials.

cond-mat.mtrl-sci↗

arXiv2020

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.

cond-mat.mtrl-sci↗

arXiv2019

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.

physics.app-ph↗

arXiv2019

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.

cond-mat.mtrl-sci↗

arXiv2019

Pressure-Induced Large Volume Collapse, Plane-to-Chain, Insulator to Metal Transition in CaMn$_2$Bi$_2$

In-situ high pressure single crystal X-ray diffraction study reveals that the quantum material CaMn$_2$Bi$_2$ undergoes a unique plane to chain structural transition between 2 and 3 GPa, accompanied by a large volume collapse. CaMn2Bi2 displays a new structure type above 2.3 GPa, with the puckered Mn honeycomb lattice of the trigonal ambient-pressure structure converting to one-dimensional (1D) zigzag chains in the high-pressure monoclinic structure. Single crystal measurements reveal that the pressure-induced structural transformation is accompanied by a dramatic two order of magnitude drop of resistivity; although the ambient pressure phase displays semiconducting behavior at low temperatures, metallic temperature dependent resistivity is observed for the high pressure phase, as, surprisingly, are two resistivity anomalies with opposite pressure dependences. Based on the electronic structure calculations, we hypothesized that the newly emerged electronic state under high pressure is associated with a Fermi surface instability of the quasi-1D Mn chains, while we infer that the other is a magnetic transition. Assessment of the total energies for hypothetical magnetic structures for high pressure CaMn$_2$Bi$_2$ indicates that ferrimagnetism is thermodynamically favored.

cond-mat.mtrl-sci↗