arXiv subjects

Lijie Hao

Publications and source records attributed to Lijie Hao.

16 recordsLinked to original sources

arXiv2026

Vacancy Order and Physical Properties of a Ternary Compound Fe0.68Pd0.80Te with an α-Fe1+xTe-Type Structure

We report the identification and characterization of a new compound Fe0.68Pd0.80Te with an α-Fe1+xTe prototype structure. Different from the Fe-square net and minor occupancy of interstitial Fe-sites in Fe1+xTe, Fe0.68Pd0.80Te is featured by a Pdsquare net and near 68% occupancy of the corresponding interstitial Fe-sites. Furthermore, noncontact atomic force microscopy and X-ray diffraction provide evidence for the existence of a 3*3*3 Pd-vacancy order in this layered material. A spin-glass ground state below Tg 40 K is identified via magnetic characterization. Electrical transport measurements show that Fe0.68Pd0.80Te is a semiconductor with a very small band gap below 10 meV. It has weak negative magnetoresistance and holelike charge carriers below room temperature. Our results demonstrate its potentials for further exploring various quantum phenomena.

cond-mat.mtrl-sci↗

arXiv2026

Noncollinear antiferromagnetic structure and physical properties of CrRhAs with distorted kagome lattice

CrRhAs was theoretically proposed to be a kagome metal with unusual magnetic ground states; however, little is known about its magnetic structure and physical properties experimentally. Here, we present an experimental investigation of CrRhAs with ZrNiAl-type structure and a distorted Cr kagome lattice. CrRhAs is an antiferromagnet with TN = 149 K. Powder neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector k = (1/3, 1/3, 1/2), which features a ferromagnetic second nearest neighbor coupling in the kagome plane that is different from the prediction in previous density functional theory calculations. Furthermore, CrRhAs exhibits anomalous electrical transport properties which are possibly related to multiband effects and strong spin fluctuations. For the temperature-dependent longitudinal resistivity \r{ho}xx, it is semiconductinglike above TN and becomes metallic below TN . The Hall coefficients exhibit two sign changes near 70 and 300 K. Combined with the results of heat capacity measurements, a large Kadowaki-Woods ratio α = 33.9 μΩ cm mol2 K2/J2 is obtained. The above results suggest CrRhAs is a strongly correlated kagome metal with multiband and noncollinear magnetic structure features.

cond-mat.str-el↗

arXiv2024

FePd2Te2: An Anisotropic Two-Dimensional Ferromagnet with One-Dimensional Fe Chains

Two-dimensional (2D) magnets have attracted significant attentions in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with one-dimensional Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter-size could be grown. Density functional theory calculations, mechanical exfoliation and atomic force microscopy on these crystals reveal that they are 2D materialsthat can be thinned down to 5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with Tc 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and anomalous Hall effect demonstrate that ferromagnetism could maintain in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right-angle bent in the cleavage plane and creates an intriguing spin texture. Our results show that FePd2Te2 is a correlated anisotropic 2D magnets that may attract multidisciplinary research interests.

cond-mat.mtrl-sci↗

arXiv2024

Magnetic properties of van der Waals layered single crystals DyOBr and SmOCl

Two-dimensional van der Waals single crystals DyOBr and SmOCl have been grown by flux method and their anisotropic magnetic properties are reported. DyOBr orders antiferromagnetically at T$_{N}$=9.5 K with magnetic moments lying along $a$-axis, similar as DyOCl. Its magnetic susceptibility shows an anomaly at T$^{*}$=30 K possibly due to the crystal field effect. Furthermore a 1/3 magnetization plateau is clearly observed under H$\parallel$a and H$\parallel$[110], which might be a field-induced spin-flop phase or some exotic quantum magnetic state. On the other hand, isostructural SmOCl undergoes an antiferromagnetic transition at T$_{N}$=7.1 K and exhibits a contrasting Ising-like perpendicular $c$-axis magnetic anisotropy, which could be well explained by our crystal field calculations. Both DyOBr and SmOCl are insulators with band gap of $\sim$5 eV, our results suggest they are promising in building van der Waals heterostructures and applications in multifunctional devices.

cond-mat.mtrl-sci↗

arXiv2024

Strong electron-phonon coupling in Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$

The charge density wave (CDW) or nematicity has been found to coexist with superconductivity in many systems. It is thus interesting that the superconducting transition temperature $T_c$ in the doped BaNi$_2$As$_2$ system can be enhanced up to six times as the CDW or nematicity in the undoped compound is suppressed. Here we show that the transverse acoustic phonons of Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$ are strongly damped in a wide doping range and over the whole $Q$ range, which excludes its origin from either CDW or nematicity. The damping of TA phonons can be understood as large electron-phonon coupling and possible strong hybridization between acoustic and optical phonons as shown by the first-principle calculations. The superconductivity can be quantitatively reproduced by the change of electron-phonon coupling constant calculated by the McMillan equation in the BCS framework, which suggests that no quantum fluctuations of any order is needed to promote the superconductivity. On the contrary, the change of $T_c$ in this system should be understood as the six-fold suppression of superconductivity in undoped compounds.

cond-mat.supr-con↗

arXiv2024

Pressure tunable magnetic skyrmion phase in Co8Zn8Mn4 single crystals

In a magnetic skyrmion phase, magnetic moments form vortex-like topological textures which are of both fundamental and industrial interests. In $β$-Mn-type Co-Zn-Mn alloys, chrial magnetic skyrmions emerge above room temperature, providing a unique system for studying the skrymion physics and exploring spintronics applications. However, the magnetic skyrmion phase is typically confined in a narrow and limited temperature ($T$) and magnetic field ($H$) range. Here, we demonstrate that hydrostatic pressure can expand the skyrmion phase in the $T-H$ phase diagram of single-crystalline Co$_8$Zn$_8$Mn$_4$. At ambient pressure, signatures of skyrmions are seen within $T\sim302-308$ K and $H\sim50-100$ Oe. Applying a moderate pressure of 6 kbar extends this range to $T\sim300-310$ K and $H\sim50-150$ Oe. However, further escalation of pressure to 10 kbar results in a slight contraction of the skyrmion phase. These findings underscore the sensitivity of the skyrmion phase in Co$_8$Zn$_8$Mn$_4$ to external pressures, and hint at the potential of strain engineering, particularly in $β$-Mn-type Co-Zn-Mn thin films, as a promising avenue to customize the skyrmion phase.

cond-mat.mtrl-sci↗

arXiv2023

FeGe1-xSbx:a series of novel kagome metals with noncollinear antiferromagnetism

Kagome metals are important for exploring emergent phenomena due to the interplay between band topology and electron correlation.Motivated by the recent discovery of charge density wave in a kagome lattice antiferromagnetic FeGe,we investigate the impact of Sb doping on the structural,charge and magnetic order of FeGe.The charge density wave is rapidly suppressed by Sb doping(~1.5%) and the antiferromagnetic ordering temperature gradually shifts to 280K for FeGe0.7Sb0.3.For FeGe1-xSbx with x>0.1,crystal structures with slightly distorted Fe kagome lattice are formed.Their magnetic anisotropy has significant change,temperature driven spin-reorientation and field-induced spin-flop transition are identified from magnetization measurement.Interestingly,neutron diffraction reveals noncollinear antiferromagnetic structures widely exist below TN for all sample with x>0.1.This noncollinear magnetic orders could possibly be unconventional and resulted from onsite repulsion and filling condition of kagome flat band,as predicted by a recent theoretical work.

cond-mat.str-el↗

arXiv2023

Multiple magnetic transitions and complex magnetic structures in Fe$_2$SiSe$_4$ with the sawtooth lattice

The sawtooth lattice shares some structural similarities with the kagome lattice and may attract renewed research interest. Here, we report a comprehensive study on the physical properties of Fe$_2$SiSe$_4$, an unexplored member in the olivine chalcogenides with the sawtooth lattice of Fe. Our results show that Fe$_2$SiSe$_4$ is a magnetic semiconductor with band gap of 0.66~eV. It first undergoes an antiferromagnetic transition at T$_{m1}$=110~K, then an ferrimagnetic-like one at T$_{m2}$=50~K and finally a magnetic transition at T$_{m3}$=25~K which is likely driven by the thermal populations of spin-orbit manifold on the Fe site. Neutron diffraction analysis reveals a non-collinear antiferromagnetic structure with propagation vector $\mathbf{q_1}$=(0,0,0) at T$_{m2}$<T<T$_{m1}$. Interestingly, below T$_{m2}$, an additional antiferromagnetic structure with $\mathbf{q_2}$=(0,0.5,0) appears and Fe$_2$SiSe$_4$ exhibits a complex double-$\mathbf{q}$ magnetic structure which has never been observed in sawtooth olivines. Density functional theory calculations suggest this complex noncollinear magnetic structure may originate from the competing antiferromagnetic interactions for both intra- and inter-chain in the sawtooth lattice. Furthermore, band structural calculations show that Fe$_2$SiSe$_4$ has quasi-flat band features near the valence and conduction bands. Based on the above results, we propose Fe$_2$SiSe$_4$ as a new material platform to condensed matter researches.

cond-mat.mtrl-sci↗

arXiv2022

Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe2

We report high pressure studies on the C-type antiferromagnetic semiconductor EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to C2/m space group is identified at ~16 GPa. Superconductivity is discovered above ~5 GPa in both the I4/mcm and C2/m space groups. In the low-pressure phase (< 16 GPa), the antiferromagnetic transition temperature is enhanced with increasing pressure due to the enhanced magnetic exchange interactions. Magnetoresistance measurements indicate an interplay between the local moments of Eu2+ and the conduction electrons of Te 5p orbits. The upper critical field of the superconductivity is well above the Pauli limit. Across the structural transition to the high-pressure phase (> 16 GPa), EuTe2 becomes nonmagnetic and the superconducting transition temperature evolves smoothly with the upper critical field below the Pauli limit. Therefore, the high upper critical field of EuTe2 in the low-pressure phase is due to the exchange field compensation effect of the Eu magnetic order and the superconductivity in both structures may arise in the framework of the BCS theory.

cond-mat.supr-con↗

arXiv2022

Antiferromagnetic structure and magnetic properties of Dy2O2Te: An isostructural analog of the rare-earth superconductors R2O2Bi

The rare-earth compounds R2O2Bi (R=Tb, Dy, Er, Lu, Y) are newly discovered superconductors in the vicinity of a rare-earth magnetic long-range order. In this work, we determine the magnetic order of the parent compound Dy2O2Te by neutron scattering as the A-type antiferromagnetic structure below the Néel temperature TN=9.7K. The large staggered magnetic moment 9.4(1) μB per Dy at T=3.5K lies in the basal ab plane. In a magnetic field, anomalous magnetic properties including the bifurcation between zero-field- and field-cooling magnetization, a butterfly-shaped magnetic hysteresis, and slow magnetic relaxation emerge, which are related to the field-induced metamagnetic transitions in Dy2O2Te. Our experimental findings could stimulate further research on the relation between antiferromagnetism and superconductivity in these rare-earth compounds.

cond-mat.supr-con↗

arXiv2021

DyOCl: a rare-earth based two-dimensional van der Waals material with strong magnetic anisotropy

Comparing with the widely known transitional metal based van der Waals (vdW) materials, rare-earth based ones are rarely explored in the research of intrinsic two-dimensional (2D) magnetism. In this work, we report the physical properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by neutron scattering as the $A$-type antiferromagnetic structure below the Néel temperature $T_N=10~$K. The large magnetic moment near 10.1 $ μ_{B} $/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At $2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state. Density functional theory calculations reveal an extremely large magnetic anisotropy energy ($-5850~μeV/Dy$) for DyOCl, indicating the great potentials to realize magnetism in 2D limit. Furthermore, the mechanical exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated. Our findings suggest DyOCl is a promising material playground to investigate 2D $f$-electron magnetism and spintronic applications at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2017

Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed `spinon'). Here, we report neutron scattering measurements that reveal broad spin excitations covering a wide region of the Brillouin zone in a triangular antiferromagnet YbMgGaO4. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, which is consistent with the particle-hole excitation of a spinon Fermi surface. Our results therefore point to a QSL state with a spinon Fermi surface in YbMgGaO4 that has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.

cond-mat.str-el↗

arXiv2017

Crystal growth and phase diagram of 112-type iron pnictide superconductor Ca1-yLayFe1-xNixAs2

We report a systematic crystal growth and characterization of Ca$_{1-y}$La$_{y}$Fe$_{1-x}$Ni$_{x}$As$_{2}$, the newly discovered 112-type iron-based superconductor. After substituting Fe by a small amount of Ni, bulk superconductivity is successfully obtained in high quality single crystals sized up to 6 mm. Resistivity measurements indicate common features for transport properties in this 112-type iron pnictide, suggest strong scattering from chemical dopants. Together with the superconducting transition temperature $T_c$, and the Neel temperature $T_N$ determined by the elastic neutron scattering, we sketch a three-dimensional phase diagram in the combination of both Ni and La dopings.

cond-mat.supr-con↗

arXiv2016

Effect of nematic order on the low-energy spin fluctuations in detwinned BaFe$_{1.935}$Ni$_{0.065}$As$_2$

The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,$π$) should decrease with decreasing temperature below the structural transition temperature $T_s$. Here we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe$_{1.935}$Ni$_{0.065}$As$_2$ under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,$π$) happens just below $T_s$, suggesting strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.

cond-mat.supr-con↗

arXiv2005

Evolution of 4f-Electron States in the Metal-Insulator Transition of PrRu$_4$P$_{12}$

Magnetic excitations of the filled skutterudite PrRu4P12 exhibiting a metal-insulator (M-I) transition at TM-I= 63 K were studied by inelastic neutron scattering experiment. The spectra at temperatures much lower than TM-I are described as well-defined crystal-field excitations. With approaching TM-I, the excitation peaks broaden and shift considerably together with the temperature variation of the carrier number and the atomic displacement in the transition. The 4f-electron state evolve from the well localized state in the insulator phase to the strongly hybridized itinerant state by p-f mixing near TM-I. The hybridization is responsible for the M-I transition of PrRu4P12.

cond-mat.str-el↗

arXiv2005

Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12

Electronic state evolution in the metal-non-metal transition of PrRu4P12 has been studied by X-ray and polarized neutron diffraction experiments. It has been revealed that, in the low-temperature non-metallic phase, two inequivalent crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2) ground states are located at Pr1 and Pr2 sites forming the bcc unit cell surrounded by the smaller and larger cubic Ru-ion sublattices, respectively. This modulated electronic state can be explained by the p-f hybridization mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f hybridization effect plays an important role for the electronic energy gain in the metal-non-metal transition originated from the Fermi surface nesting.

cond-mat.str-el↗