arXiv subjects

Li Pi

Publications and source records attributed to Li Pi.

51 records · Page 3Linked to original sources

arXiv2016

Pressure induced re-emergence of superconductivity in superconducting topological insulator Sr0.065Bi2Se3

The recent-discovered Sr$_x$Bi$_2$Se$_3$ superconductor provides an alternative and ideal material base for investigating possible topological superconductivity. Here, we report that in Sr$_{0.065}$Bi$_{2}$Se$_3$, the ambient superconducting phase is gradually depressed upon the application of external pressure. At high pressure, a second superconducting phase emerges at above 6 GPa, with a maximum $T_c$ value of $\sim$8.3 K. The joint investigations of the high-pressure synchrotron x-ray diffraction and electrical transport properties reveal that the re-emergence of superconductivity in Sr$_{0.065}$Bi$_{2}$Se$_3$ is closely related to the structural phase transition from ambient rhombohedral phase to high-pressure monoclinic phase around 6 GPa, and further to another high-pressure tetragonal phase above 25 GPa.

cond-mat.supr-con↗

arXiv2016

Single Crystal Growth of the New Pressure-induced-superconductor CrAs via Chemical Vapor Transport

Mono-arsenide CrAs, endures a helical anti-ferromagnetic order transition at~ 265 K under ambient pressure. Recently, pressure-induced-superconductivity was discovered vicinity to the helical anti-ferromagnetic order in CrAs[Wei Wu et al., Nature Communications 5, 5508 (2014).]. However, the size of crystal grown via tin flux method is as small as 1 mm in longest dimension. In this work, we report the single crystal growth of CrAs with size of 1 * 5 * 1 mm3 via chemical vapor transport method and its physical properties.

cond-mat.supr-con↗

arXiv2016

Quantum oscillation and nontrivial transport in the Dirac Semimetal Cd3As2 nanodevice

Here we demonstrate the Shubnikov de Haas oscillation in high-quality Cd3As2 nanowires grown by a chemical vapor deposition approach. The dominant transport of topological Dirac fermions is evident by the nontrivial Berry phase in the Landau Fan diagram. The quantum oscillations rise at a small field of 2 Tesla and preserves till up to 100K, revealing a sizeable Landau level gap and a mobility of over 2000 cm2/V-1s-1. The angle-variable oscillations indicates the isotropy of the bulk Dirac transport. The large estimated mean free path appeals the one-dimensional transport of Dirac semimetals.

cond-mat.mes-hall↗

arXiv2016

Dominant itinerant ferromagnetism in Eu0.5Sr0.5CoO3: evidences from both critical analysis and Rhodes-Wohlfarth's criterion

The critical behaviors of ferromagnet Eu0.5Sr0.5CoO3 arround TC=140.5K have been comprehensively investigated by analyzing a series of isothermal magnetization M(H) curves. Both Modified Arrott plot and Kouvel-Fisher methods give nearly the same critical exponents, which scale nicely the M(H) curves into two different branches below and above TC. The exponents γ=1.044 and δ=3.06 demonstrate the relevance of mean-field characters for this material. The conclusion of mean-field behavior proves a dominant itinerant ferromagnetism (FM) due to a long range exchange interaction in the system. Meanwhile, by using Rhodes-Wohlfarth's criterion [P. Rhodes and E. P. Wohlfarth, Proc. R. Soc. Lond. A 273, 247 (1963)], it is further confirmed that the itinerant FM dominates in the system.

cond-mat.str-el↗

arXiv2015

Rare-earth triangular lattice spin liquid: a single-crystal study of YbMgGaO$_{4}$

YbMgGaO$_{4}$, a structurally perfect two-dimensional triangular lattice with odd number of electrons per unit cell and spin-orbit entangled effective spin-1/2 local moments of Yb$^{3+}$ ions, is likely to experimentally realize the quantum spin liquid ground state. We report the first experimental characterization of single crystal YbMgGaO$_{4}$ samples. Due to 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 the 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 lights on the search of quantum spin liquids in strong spin-orbit coupled insulators.

cond-mat.str-el↗

arXiv2015

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. The analysis of the Shubnikov-de Hass oscillations confirms the 1/2-shift expected from a Dirac spectrum, giving transport evidence of the existence of surface states. Importantly, the SrxBi2Se3superconductor is stable under air, making the SrxBi2Se3 compound an ideal material base for investigating topological superconductivity.

cond-mat.supr-con↗

arXiv2015

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 Tesla. 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.

cond-mat.supr-con↗

arXiv2015

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO$_4$

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 YbMgGaO$_4$ with R$\bar{3}$m 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 $Θ$$_w$ $\sim$ -4 K), the low-T power-law temperature dependence of heat capacity and nonzero susceptibility suggest that YbMgGaO$_4$ is a promising gapless ($\leq$ $|$$Θ$$_w$$|$/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO$_4$, approaches zero ($<$ 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.

cond-mat.str-el↗

arXiv2015

Enhanced quantum coherence in graphene caused by Pd cluster deposition

We report on the unexpected increase in the dephasing lengths of a graphene sheet caused by the deposition of Pd nanoclusters, as demonstrated by weak localization measurements. The dephasing lengths reached saturated values at low temperatures. Theoretical calculations indicate the p-type charge transfer from the Pd clusters, which contributes more carriers. The saturated values of dephasing lengths often depend on both the carrier concentration and mean free path. Although some impurities are increased as revealed by decreased mobilities, the intense charge transfer leads to the improved saturated values and subsequent improved dephasing lengths.

cond-mat.mes-hall↗

arXiv2014

Experimental evidence and control of the bulk-mediated intersurface coupling in topological insulator Bi2Te2Se nanoribbons

Nearly a decade after the discovery of topological insulators (TIs), the important task of identifying and characterizing their topological surface states through electrical transport experiments remains incomplete. The interpretation of these experiments is made difficult by the presence of residual bulk carriers and their coupling to surface states, which is not yet well understood. In this work, we present the first evidence for the existence and control of bulk-surface coupling in Bi2Te2Se nanoribbons, which are promising platforms for future TI-based devices. Our magnetoresistance measurements reveal that the number of coherent channels contributing to quantum interference in the nanoribbons changes abruptly when the film thickness exceeds the bulk phase relaxation length. We interpret this observation as an evidence for bulk-mediated coupling between metallic states located on opposite surfaces. This hypothesis is supported by additional magnetoresistance measurements conducted under a set of gate voltages and in a parallel magnetic field, the latter of which alters the intersurface coupling in a controllable way.

cond-mat.mes-hall↗

arXiv2014

Superconducting properties of novel BiSe$_{2}$-based layered LaO$_{1-x}$F$_{x}$BiSe$_{2}$ single crystals

F-doped LaOBiSe$_{2}$ superconducting single crystals with typical size of 2$\times$4$\times$0.2 mm$^{3}$ are successfully grown by flux method and the superconducting properties are studied. Both the superconducting transition temperature and the shielding volume fraction are effectively improved with fluorine doping. The LaO$_{0.48}$F$_{0.52}$BiSe$_{1.93}$ sample exhibits zero-resistivity at 3.7 K, which is higher than that of the LaO$_{0.5}$F$_{0.5}$BiSe$_{2}$ polycrystalline sample (2.4K). Bulk superconductivity is confirmed by a clear specific-heat jump at the associated temperature. The samples exhibit strong anisotropy and the anisotropy parameter is about 30, as estimated by the upper critical field and effective mass model

cond-mat.supr-con↗

arXiv2014

Bulk superconductivity in single phase Bi3O2S3

We report the synthesis of single phase Bi3O2S3 sample and confirm the occurrence of bulk superconductivity with transition temperature at 5.8 K. The Bi3O2S3 super-conductor is categorized as the typical type-II supercon-ductor based on the results of both temperature and mag-netic field dependences of magnetization. Hall coefficient measurements give evidence of a multiband character, with a dominant conduction mainly by electron-like charge carriers. The charge carrier density is about 1.45 X 1019 cm3, suggesting that the system has very low charge carrier density.

cond-mat.supr-con↗

arXiv2013

Oxygen-Vacancy-Induced Antiferromagnetism to Ferromagnetism Transformation in Multiferroic Thin Films

Oxygen vacancies (VOs) 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-δthin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the VOs. 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 VOs, 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. Our work opens up a new avenue for developing FM-FE materials by manipulating the oxygen deficiency in AFM-FE multiferroics.

cond-mat.mtrl-sci↗

arXiv2013

The effect of Al doping on the structure and magnetism in cobaltite CaBaCo4O7

We report the effects of Al-doping on the structure and magnetic properties in CaBa(Co$_{1-x}$Al$_{x}$)$_4$O$_7$ (0$\leq$x$\leq$0.25). The system exhibits a structural transition from an orthorhombic symmetry to a hexagonal symmetry when the Al content exceeds $x =$ 0.1. The Curie temperature and the value of the magnetization decrease with increasing Al doping level, indicating that the ferrimagnetic ground state is gradually suppressed. The ground state eventually transits into a spin-glass state for $x >$ 0.1. Moreover, the short-range magnetic correlations, which occur at high temperatures in CaBaCo$_4$O$_7$, are found to be gradually suppressed with increasing Al content and eventually disappear for $x =$ 0.25. By comparing our results with other Co-site doping cases, we suggest that the lattice and the spin degrees of freedom are relatively decoupled in CaBaCo$_4$O$_7$.

cond-mat.mtrl-sci↗

arXiv2011

Magnetic properties of the ferrimagnetic cobaltite CaBaCo4O7

The magnetic properties of the ferrimagnetic cobaltite CaBaCo$_4$O$_7$ are systematically investigated. We find that the susceptibility exhibits a downward deviation below $\sim$ 360 K, suggesting the occurrence of short range magnetic correlations at temperature well above $T_C$. The effective moment is determined to be 4.5 $μ_B$/f.u, which is consistent with that expected for the Co$^{2+}$/Co$^{3+}$ high spin species. Using a criterion given by Banerjee [Phys. Lett. \textbf{12}, 16 (1964)], we demonstrate that the paramagnetic to ferrimagnetic transition in CaBaCo$_4$O$_7$ has a first order character.

cond-mat.str-el↗