Langsheng Ling

Investigation of critical behavior in Pr0.55Sr0.45MnO3 by using the field dependence of magnetic entropy change

One method of calculating critical exponents based on the field dependence on magnetic entropy change was applied to study critical behavior in Pr0.55Sr0.45MnO3. By using the obtained critical exponents, the modified Arrott plot [A. Arrott and J. E. Noakes, Phys. Rev. Lett. 19, 786 (1967)] is consistent with that by using conventional method. The calculated critical exponents not only obey the scaling theory, but also inosculate the deduced results from the Kouvel–Fisher method [J. S. Kouvel and M. E. Fisher, Phys. Rev. 136, A1626 (1964)]. It eliminates the drawback due to utilization of multistep nonlinear fitting in a conventional manner. Therefore, this means can be applied to investigate critical behavior.

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ −4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

Detection of a superconducting phase in a two-atom layer of hexagonal Ga film grown on semiconducting GaN(0001).

The recent observation of the superconducting state at atomic scale has motivated the pursuit of exotic condensed phases in two-dimensional (2D) systems. Here we report on a superconducting phase in two-monolayer crystalline Ga films epitaxially grown on wide-band-gap semiconductor GaN(0001). This phase exhibits a hexagonal structure and only 0.552 nm in thickness, nevertheless, brings about a superconducting transition temperature Tc as high as 5.4 K, confirmed by in situ scanning tunneling spectroscopy and ex situ electrical magnetotransport and magnetization measurements. The anisotropy of critical magnetic field and Berezinski-Kosterlitz-Thouless-like transition are observed, typical for the 2D superconductivity. Our results demonstrate a novel platform for exploring atomic-scale 2D superconductors, with great potential for understanding the interface superconductivity.

Fe-doping–induced superconductivity in the charge-density-wave system 1T-TaS2

We report the interplay between charge-density-wave (CDW) and superconductivity of 1T-FexTa1−xS2 (0≤x≤0.05) single crystals. The CDW order is gradually suppressed by Fe-doping, accompanied by the disappearance of pseudogap/Mott-gap as shown by the density functional theory (DFT) calculations. The superconducting state develops at low temperatures within the CDW state for the samples with the moderate doping levels. The superconductivity strongly depends on x within a narrow range, and the maximum superconducting transition temperature is 2.8 K as x=0.02. For high doping level (x> 0.04), the Anderson localization (AL) state appears, resulting in a large increase of resistivity. We present a complete electronic phase diagram of the 1T-FexTa1−xS2 system that shows a dome-like Tc(x).

Superconductivity enhancement in the S-doped Weyl semimetal candidate MoTe2

Two-dimensional (2D) transition-metal dichalcogenide (TMDs) MoTe2 has attracted much attention due to its predicted Weyl semimetal (WSM) state and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that the superconductivity in MoTe2 single crystal can be much enhanced by the partial substitution of the Te ions by the S ones. The maximum of the superconducting temperature TC of MoTe1.8S0.2 single crystal is about 1.3 K. Compared with the parent MoTe2 single crystal (TC=0.1 K), nearly 13-fold in TC is improved in MoTe1.8S0.2 one. The superconductivity has been investigated by the resistivity and magnetization measurements. MoTe2-xSx single crystals belong to weak coupling superconductors and the improvement of the superconductivity may be related to the enhanced electron-phonon coupling induced by the S-ion substitution. A dome-shape superconducting phase diagram is obtained in the S-doped MoTe2 single crystals. MoTe2-xSx materials may provide a new platform for our understanding of superconductivity phenomena and topological physics in TMDs.

Oxygen-Vacancy-Induced Antiferromagnetism to Ferromagnetism Transformation in Eu0.5Ba0.5TiO3−δ Multiferroic Thin Films

Oxygen vacancies (VO) effects on magnetic ordering in Eu0.5Ba0.5TiO3−δ (EBTO3−δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO3−δ thin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the VO. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperature of 1.85 K has been found in the EBTO3−δ thin films. Spin-polarized Ti3+ ions, which originated from the VO, has been proven to mediate a FM coupling between the local Eu 4f spins and were believed to be responsible for the great change of the magnetic ordering. Considering the easy formation of VO, our work opens up a new avenue for achieving co-existence of FM and FE orders in oxide materials.

Griffiths phase and magnetic polaronic behavior in B-site disordering manganites

We report a detailed study of magnetic and transport properties in perovskite manganites Nd0.55Sr0.45Mn1−xGaxO3 (0.00⩽x⩽0.20). The Ga substitution induces the B-site disorder together with a distinct suppression of the metal-insulator transition and ferromagnetic-paramagnetic transition. Due to an appearance of inhomogeneous magnetic clusters, the Griffiths-like phase is observed in 0.08⩽x⩽0.10 compounds. Meanwhile, with the increase of Ga concentration, the carriers self-trap into magnetic polarons. Because the oxygen sublattice distortion causes the variation of the phonon density of state, an additional Raman vibrative mode appears in the system.

Critical properties of the 3D-Heisenberg ferromagnet \chem{CdCr_{2}Se_{4}}

The critical properties of the ferromagnet CdCr2Se4 around the paramagnetic-ferromagnetic phase transition have been investigated. It is found that the 3D-Heisenberg model is the best one to describe the critical phenomena around the critical point. Critical exponents β=0.337±0.03 and γ=1.296±0.109 at TC=130.48±0.34 are obtained. In addition, the critical exponent δ=4.761±0.129 is determined separately from the isothermal magnetization at TC. These critical exponents fulfill the Widom scaling relation δ=1+γ/β. Based on these critical exponents, the magnetization-field-temperature (M-H-T) data around TC collapses into two curves obeying the single scaling equation M(H, e)=eβf±(H/eβ+γ). Although the 3D-Heisenberg model is the most satisfactory model to describe this system, critical exponents for CdCr2Se4 are slightly smaller than the theoretical exponents (β=0.36, γ=1.39 and δ=4.8). This indicates that the exchange interaction J(r) decays slower than r− 5 in this system, which can be attributed to the spin-lattice coupling.

3D-Heisenberg ferromagnetic characteristics in CuCr2Se4

The critical properties of the spinel selenide CuCr2Se4 around TC have been investigated by the modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis. Reliable critical exponents β = 0.372±0.007, γ = 1.277±0.044, and δ = 4.749±0.016 with TC = 430 K are obtained. Based on these critical exponents, the magnetization-field-temperature (M-H-T) data around TC collapses into two independent curves obeying the single scaling equation M(H,ɛ)=ɛβf±(H/ɛβ+γ). Moreover, the critical exponents are confirmed by the field dependence of the magnetic entropy change relation ΔSM|T=TC∝Hn with n = 1 + (β-1)/(β+γ). The obtained critical exponents are in good agreement with the prediction of the 3D-Heisenberg model except that γ is smaller than the theoretical value. The smallness of γ may be due to the delocalization of holes produced by Se1-, which gives evidence for the model of the ferrimagnetic hybridization between localized electrons of the Cr3+ ions and delocalized holes of the Se 4p band proposed f...

Giant anisotropic magnetoresistance in bilayered La1.2Sr1.8Mn2O7 single crystals

We report an observation of anomalous anisotropic magnetoresistance (AMR) in bilayered La1.2Sr1.8Mn2O7 single crystals. A giant AMR is found to be 80% under a magnetic field of 1 T near the metal-insulator transition temperature, where AMR is defined as AMR=[ρ(H⊥c)−ρ(H∥c)]/ρ(H⊥c)×100%, and ρ(H⊥c) and ρ(H∥c) are the resistivity with the magnetic field perpendicular and parallel to c-axis, respectively. The AMR effect shows strong temperature and magnetic field dependences, and indicates a close interrelation with the anisotropic field-tuned metal-insulator transition.