Li Pi

Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride

Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.

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.

Superconductivity with Topological Surface State in SrxBi2Se3

By intercalation of alkaline earth metal Sr in Bi2Se3, superconductivity with large shielding volume fraction (∼91.5% at 0.5 K) has been achieved in Sr0.065Bi2Se3. Analysis of the Shubnikov-de Hass oscillations confirms the half-shift expected from a Dirac spectrum, giving transport evidence of the existence of surface states. Importantly, SrxBi2Se3 superconductor is stable under air, making SrxBi2Se3 an ideal material base for investigating topological superconductivity.

Rare-Earth Triangular Lattice Spin Liquid: A Single-Crystal Study of YbMgGaO4.

YbMgGaO4, a structurally perfect two-dimensional triangular lattice with an odd number of electrons per unit cell and spin-orbit entangled effective spin-1/2 local moments for the Yb(3+) ions, is likely to experimentally realize the quantum spin liquid ground state. We report the first experimental characterization of single-crystal YbMgGaO4 samples. Because of the spin-orbit entanglement, the interaction between the neighboring Yb(3+) moments depends on the bond orientations and is highly anisotropic in the spin space. We carry out thermodynamic and the electron spin resonance measurements to confirm the anisotropic nature of the spin interaction as well as to quantitatively determine the couplings. Our result is a first step towards the theoretical understanding of the possible quantum spin liquid ground state in this system and sheds new light on the search for quantum spin liquids in strong spin-orbit coupled insulators.

Exchange bias-like phenomenon in SrRuO3

Exchange bias-like phenomenon is observed in the SrRuO3 polycrystalline. After the sample is cooled down to 4K in a magnetic field, the magnetic hysteresis loop shifts in the opposite direction to the applied biasing field. The shift decreases as the sweeping range of the measuring field increases. This phenomenon may arise from the spin glass property of SrRuO3. Since SrRuO3 is widely used in spintronics devices, the observation of exchange bias-like shift in SrRuO3 itself suggests that the application of SrRuO3 should be more carefully considered.

Effect of Ru doping in La 0.5 Sr 0.5 Mn O 3 and La 0.45 Sr 0.55 Mn O 3

We investigated the structural, magnetic, and transport properties of polycrystalline doping systems La0.5Sr0.5Mn1−xRuxO3 0 x 0.15 with ferromagnetic matrix and La0.45Sr0.55Mn1−yRuyO3 0 y 0.5 with antiferromagnetic matrix. X-ray photoelectron spectroscopy shows that Ru ions exist mainly in the form of Ru4+ while there also exist a small quantity of Ru5+. For the low doping samples 0.05 x y 0.15 0.2 , the ferromagnetism is enhanced and Curie temperature TC rises with increasing Ru doping level, but TC is much higher than the temperature TIM corresponding to insulating-metallic transition. For the high doping samples 0.3 y 0.5 , oppositely the ferromagnetism is suppressed and the insulating property is enhanced with further increasing Ru doping level. These results show that there is an exchange interaction between Mn3+ and Ru4+ Ru5+ . The electron spin resonance spectra clearly and directly inspect that the interaction between Mn3+ and Ru4+ Ru5+ is ferromagnetic. Furthermore, the electron spin resonance spectra also show that a Ru-Ru antiferromagnetic interaction takes place in the high doping region y=0.4,0.5 . We explained the disagreement between TC and TIM.

Evolution of the intrinsic electronic phase separation in La 0.6 Er 0.1 Sr 0.3 MnO 3 perovskite

Magnetic and electronic transport properties of perovskite manganite La0.6Er0.1Sr0.3MnO3 have been thoroughly examined through the measurements of magnetization, electron paramagnetic resonance(EPR), and resistivity. It was found that the substitution of Er3+ for La3+ ions introduced the chemical disorder and additional strain in this sample. An extra resonance signal occurred in EPR spectra at high temperatures well above TC gives a strong evidence of electronic phase separation(EPS). The analysis of resistivity enable us to identify the polaronic transport mechanism in the paramagnetic region. At low temperature, a new ferromagnetic interaction generates in the microdomains of Er3+-disorder causing the second increase of magnetization. However, the new ferromagnetic interaction does not improve but decreases electronic transport due to the enhancement of interface resistance among neighboring domains. In view of a really wide temperature region for the EPS existence, this sample provides an ideal platform to uncover the evolution law of different magnetic structures in perovskite manganites.

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.

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.