arXiv subjects

Y. M. Xiong

Publications and source records attributed to Y. M. Xiong.

At least 19 recordsLinked to original sources

arXiv2022

Evidence of orbit-selective electronic kagome lattice with planar flat-band in correlated paramagnetic YCr6Ge6

Electronic properties of kagome lattice have drawn great attention recently. In associate with flat-band induced by destructive interference and Dirac cone-type dispersion, abundant exotic phenomena have been theoretically discussed. The material realization of electronic kagome lattice is a crucial step towards comprehending kagome physics and achieving novel quantum phases. Here, combining angle-resolved photoemission spectroscopy, transport measurements and first-principle calculations, we expose a planar flat-band in paramagnetic YCr6Ge6 as a typical signature of electronic kagome lattice. We unearth that the planar flat-band arises from the d_(z^2 ) electrons with intra-kagome-plane hopping forbidden by destructive interference. On the other hand, the destructive interference and flatness of the d_(x^2-y^2 ) and d_xy bands are decomposed possibly due to additional in-plane hopping terms, but the Dirac cone-type dispersion is reserved near chemical potential. We explicitly unveil that orbital character plays an essential role to realize electronic kagome lattice in bulk materials with transition metal kagome layers. Paramagnetic YCr6Ge6 provides an opportunity to comprehend intrinsic properties of electronic kagome lattice as well as its interplays with spin orbit coupling and electronic correlation of Cr-3d electrons, and be free from complications induced by strong local moment of ions in kagome planes.

cond-mat.mtrl-sci↗

arXiv2018

Topological semimetal state and field-induced Fermi surface reconstruction in antiferromagnetic monopnictide NdSb

We report the experimental realization of Dirac semimetal state in NdSb, a material with antiferromagnetic ground state. The occurrence of topological semimetal state has been well supported by our band structure calculations and the experimental observation of chiral anomaly induced negative magnetoresistance. A field-induced Fermi surface reconstruction is observed, in response to the change of spin polarization. The observation of topological semimetal state in a magnetic material provides an opportunity to investigate the magneto-topological phenomena.

cond-mat.mtrl-sci↗

arXiv2013

Ferromagnetic Quantum Critical Point in FeGa3 Tuned by Mixed-Valence Fe Dimers

The magnetic, transport, and thermal properties of single crystals of the series Fe(Ga1-xGex)3 are reported. Pure FeGa3 is a nonmagnetic semiconductor, that when doped with small concentrations of Ge (extrinsic electrons), passes through an insulator-to-metal transition and displays non-Fermi liquid (NFL) behavior. Moreover, we observer clear signatures of a ferromagnetic quantum critical point (FM-QCP) in this system at x = 0.052. The mechanism of the local moment formation is consistent with a one-electron reduction of Fe dimer singlets, a unique structural feature in FeGa3, where the density of these mixed valence (Fe(III)-Fe(II)) dimers provides a unique tuning parameter of quantum criticality.

cond-mat.str-el↗

arXiv2013

Superconducting and Critical Current Properties of NiBi3 Thin Films on Carbon Microfibers and Sapphire

The superconducting and critical current properties of thin films of NiBi3 formed on the surface of carbon microfibers and sapphire substrates are reported. The NiBi3 coated carbon microfibers were prepared by reacting 7 μm diameter Ni-coated (~ 80 nm) carbon fibers with Bi vapor, and thin films on sapphire were formed by exposing electron-beam deposited Ni films (~ 40 - 120 nm) to Bi vapor. The microfibers and films show Tc = 4.3 K and 4.4 K,respectively, which were slightly higher than that reported for bulk polycrystalline NiBi3. The critical current density (Jc) was measured below the transition temperature and is well described by the Ginzburg-Landau power-law.

cond-mat.supr-con↗

arXiv2013

Thermoelectric Properties of Intermetallic Semiconducting RuIn3 and Metallic IrIn3

Low temperature (<400 K) thermoelectric properties of semiconducting RuIn3 and metallic IrIn3 are reported. RuIn3 is a narrow band gap semiconductor with a large n-type Seebeck coefficient at room temperature (S(290K)~400 μV/K), but the thermoelectric Figure of merit (ZT(290K) = 0.007) is small because of high electrical resistivity and thermal conductivity (κ(290 K) ~ 2.0 W/m K). IrIn3 is a metal with low thermopower at room temperature (S(290K)~20 μV/K) . Iridium substitution on the ruthenium site has a dramatic effect on transport properties, which leads to a large improvement in the power factor and corresponding Figure of merit (ZT(380 K) = 0.053), improving the efficiency of the material by an over of magnitude.

cond-mat.mtrl-sci↗

arXiv2012

Exchange Field-Mediated Magnetoresistance in the Correlated Insulator Phase of Be Films

We present a study of the proximity effect between a ferromagnet and a paramagnetic metal of varying disorder. Thin beryllium films are deposited onto a 5 nm-thick layer of the ferromagnetic insulator EuS. This bilayer arrangement induces an exchange field, $H_{ex}$, of a few tesla in low resistance Be films with sheet resistance $R\ll R_Q$, where $R_Q=h/e^2$ is the quantum resistance. We show that $H_{ex}$ survives in very high resistance films and, in fact, appears to be relatively insensitive to the Be disorder. We exploit this fact to produce a giant low-field magnetoresistance in the correlated insulator phase of Be films with $R\gg R_Q$.

cond-mat.mes-hall↗

arXiv2011

Mystery of Excess Low Energy States in a Disordered Superconductor in a Zeeman Field

Tunneling density of states measurements of disordered superconducting (SC) Al films in high Zeeman fields reveal a significant population of subgap states which cannot be explained by standard BCS theory. We provide a natural explanation of these excess states in terms of a novel disordered Larkin-Ovchinnikov (dLO) phase that occurs near the spin-paramagnetic transition at the Chandrasekhar-Clogston critical field. The dLO superconductor is characterized by a pairing amplitude that changes sign at domain walls. These domain walls carry magnetization and support Andreev bound states, which lead to distinct spectral signatures at low energy.

cond-mat.supr-con↗

arXiv2011

Spin-Resolved Tunneling Studies of the Exchange Field in EuS/Al Bilayers

We use spin-resolved electron tunneling to study the exchange field in the Al component of EuS/Al bilayers, in both the superconducting and normal-state phases of the Al. Contrary to expectation, we show that the exchange field, Hex, is a non-linear function of applied field, even in applied fields that are well beyond the EuS coercive field. Furthermore the magnitude Hex is unaffected by the superconducting phase. In addition, Hex decreases significantly with increasing temperature in the temperature range of 0.1-1 K. We discuss these results in the context of recent theories of generalized spin-dependent boundary conditions at a superconductor/ferromagnet interface.

cond-mat.supr-con↗

arXiv2011

Structural and Physical Properties of CaFe4As3 Single Crystals

We report the synthesis, and structural and physical properties of CaFe4As3 single crystals. Needle-like single crystals of CaFe4As3 were grown out of Sn flux and the compound adopts an orthorhombic structure as determined by X-ray diffraction measurements. Electrical, magnetic, and thermal properties indicate that the system undergoes two successive phase transitions occurring at TN1 ~ 90 K and TN2 ~ 26 K. At TN1, electrical resistivities (ρ(b) and ρ(ac)) are enhanced while magnetic susceptibilities (χ(b) and χ(ac)) are reduced in both directions parallel and perpendicular to the b-axis, consistent with the scenario of antiferromagnetic spin-density-wave formation. At TN2, specific heat reveals a slope change, and χ(ac) decreases sharply but χ(b) has a clear jump before it decreases again with decreasing temperature. Remarkably, both ρ(b) and ρ(ac) decrease sharply with thermal hysteresis, indicating the first-order nature of the phase transition at TN2. At low temperatures, ρ(b) and ρ(ac) can be described by ρ = ρ0 + AT^α(ρ0, A, and α are constants). Interestingly, these constants vary with applied magnetic field. The ground state of CaFe4As3 is discussed.

cond-mat.supr-con↗

arXiv2011

Effect of Chemical Doping on the Thermoelectric Properties of FeGa3

Thermoelectric properties of the chemically-doped intermetallic narrow-band semiconductor FeGa3 are reported. The parent compound shows semiconductor-like behavior with a small band gap (Eg = 0.2 eV), a carrier density of ~ 10(18) cm-3 and, a large n-type Seebeck coefficient (S ~ -400 μV/K) at room temperature. Hall effect measurements indicate that chemical doping significantly increases the carrier density, resulting in a metallic state, while the Seebeck coefficient still remains fairly large (~ -150 μV/K). The largest power factor (S2/ρ = 62 μW/m K2) and corresponding figure of merit (ZT = 0.013) at 390 K were observed for Fe0.99Co0.01(Ga0.997Ge0.003)3.

cond-mat.mtrl-sci↗

arXiv2010

Structure and physical properties of the noncentrosymmetric superconductor Mo3Al2C

We have synthesized polycrystalline samples of the noncentrosymmetric superconductor Mo3Al2C by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at Tc ~ 9.2 K, while the density of states at the Fermi surface is found to be dominated by Mo d-orbitals. Using the measured values for the lower critical field Hc1, upper critical field Hc2, and the specific heat C, we estimated the thermodynamic critical field Hc(0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ(0). The specific heat jump at Tc, ΔC/γTc = 2.14, suggests that Mo3Al2C is moderately-to-strongly coupled, consistent with the fast opening of the gap, as evidenced by the rapid release of entropy below Tc from our electronic specific heat measurements. Above 2K the electronic specific heat exhibits the power law behavior, suggesting that synthesis of single crystals and measurements at lower temperature are needed to establish whether the gap is anisotropic. The estimated value of the upper critical field Hc2(0) is close to the calculated Pauli limit, therefore further studies are needed to determine whether the absence of an inversion center results in a significant admixture of the triplet component of the order parameter.

cond-mat.supr-con↗

arXiv2010

Saturation of the Anomalous Hall Effect in Critically Disordered Ultra-thin CNi3 Films

We demonstrate that a distinct high-disorder anomalous Hall effect phase emerges at the correlated insulator threshold of ultra-thin, amorphous, ferromagnetic CNi3 films. In the weak localization regime, where the sheet conductance G >> e^2/h, the anomalous Hall resistance of the films increases with increasing disorder and the Hall conductance scales as Gxy ~ G^1.6. However, at sufficiently high disorder the system begins to enter the 2D correlated insulator regime, at which point the Hall resistance Rxy abruptly saturates and the scaling exponent becomes 2. Tunneling measurements show that the saturation behavior is commensurate with the emergence of the 2D Coulomb gap, suggesting that e-e interactions mediate the high-disorder phase.

cond-mat.str-el↗

arXiv2009

Pairing resonance as a normal-state spin probe in ultra-thin Al films

We present a quantitative analysis of the low-temperature, high parallel field pairing resonance in ultra-thin superconducting Al films with dimensionless conductance g>>1. In this regime we derive an analytical expression for the tunneling density-of-states spectrum from which a variety of normal-state spin parameters can be extracted. We show that by fitting tunneling data at several supercritical parallel magnetic fields we can determine all of the relevant parameters that have traditionally been obtained via fits to tunneling data in the superconducting phase. These include the spin-orbit scattering rate, the antisymmetric Landau parameter G^0, and the orbital pair-breaking parameter.

cond-mat.supr-con↗

arXiv2009

Temperature dependence of resistivity and Hall-coefficient in a strongly disordered metal: NbN

We report the temperature dependence of resistivity (rho) and Hall coefficient (R_H) in the normal state of homogeneously disordered epitaxial NbN thin films with kFl~3.27-10.12. The superconducting transition temperature (Tc) of these films varies from 8.13K to 16.8K. While our least disordered film displays usual metallic behavior, for all the films with kFl<8.13, both and are negative up to 300K. We observe that R_H(T) varies linearly with rho(T) for all the films. Measurements performed on a 2nm thick Be film shows similar behavior >. This behavior is inconsistent with existing theories of localization and e-e interactions in a disordered metal.

cond-mat.dis-nn↗

arXiv2009

Measurement of Conduction Electron Polarization Via the Pairing Resonance

We show that the pairing resonance in the Pauli-limited normal state of ultra-thin superconducting Al films provides a spin-resolved probe of conduction electron polarization in thin magnetic films. A superconductor-insulator-ferromagnet tunneling junction is used to measure the density of states in supercritical parallel magnetic fields that are well beyond the Clogston-Chandresekhar limit, thus greatly extending the field range of the tunneling density of states technique. The applicability and limitations of using the pairing resonance as a spin probe are discussed.

cond-mat.supr-con↗

arXiv2009

Spin-Orbit Scattering and Quantum Metallicity in Ultra-Thin Be Films

We compare and contrast the low temperature magnetotransport properties of ultra-thin, insulating, Be films with and without spin-orbit scattering (SOS). Beryllium films have very little intrinsic SOS, but by "dusting" them with sub-monolayer coverages of Au, one can introduce a well controlled SOS rate. Pure Be films with sheet resistance R >R_Q exhibit a low-temperature negative magnetoresistance (MR) that saturates to the quantum resistance R_Q = h/e^2. This high-field quantum metal phase is believed to represent a new ground state of the system. In contrast, the corresponding negative MR in Be/Au films is greatly diminished, suggesting that, in the presence of strong SOS, the quantum metal phase can only be reached at field scales well beyond those typically available in a low temperature laboratory.

cond-mat.str-el↗

arXiv2006

Magnetic and transport properties in Gd$_{1-x}$Sr$_x$CoO$_{3}$ ($x$= 0.10-0.70)

Magnetic and transport properties of polycrystalline Gd$_{1-x}$Sr$_x$CoO$_{3}$ ($x$= 0.10-0.70) are investigated systemically. Cluster-glass magnetism for $x \leq$ 0.45 and long-range ferromagnetic order in higher doping level are observed. Transport measurements indicate insulator-like behaviors for the samples with $x \leq$ 0.30, and an insulator-metal (IM) transition around $x$ = 0.35, and metallic behaviors for higher $x$ samples. In contrast to La$_{1-x}$Sr$_{x}$COO$_{3}$, the striking feature is that the system reenters insulator-like state for $x \geq$ 0.60, and the long-range ferromagnetic order and IM transition take place in samples with higher Sr content. It could be attributed to the enhancement of low-spin state stability for the trivalent Co ions due to the small radius of Gd$^{3+}$ ion.

cond-mat.str-el↗

arXiv2004

Anomalous Magnetoresistance in Pb-doped Bi$_2$Sr$_2$Co$_2$O$_y$ Single Crystals

Magnetoresistance (MR) of the Bi$_{2-x}$Pb$_x$Sr$_2$Co$_2$O$_y$ ($x$=0, 0.3, 0.4) single crystals is investigated systematically. A nonmonotonic variation of the isothermal in-plane and out-of-plane MR with the field is observed. The out-of-plane MR is positive in high temperatures and increases with decreasing $T$, and exhibits a pronounced hump, and changes the sign from positive to negative at a centain temperature. These results strongly suggest that the observed MR consists of two contributions: one \emph{negative} and one \emph{positive} component. The isothermal MR in high magnetic fields follows a $H^2$ law. While the negative contribution comes from spin scattering of carriers by localized-magnetic-moments based on the Khosla-Fischer model.

cond-mat.str-el↗