arXiv subjects

Jianhui Dai

Publications and source records attributed to Jianhui Dai.

At least 37 records · Page 2Linked to original sources

arXiv2018

Superconductivity, Electronic Phase Diagram and Pressure Effect in Sr_{1-x}Pr_{x}FBiS_{2}

Based on a combination of X-ray diffraction, electrical transports, magnetic susceptibility, specific heat and pressure effect measurements, we report a series of BiS$_{2}$-based Sr$_{1-x}$Pr$_{x}$FBiS$_{2}$ superconductors with the maximum $T_c$ of 2.7 K for $x =$ 0.5 at ambient pressure. Superconductivity can be only observed at 0.4 $\leq$ x $\leq$ 0.7 while the normal state resistivity shows the semiconducting-like behaviors. $χ(T)$ displays the low superconducting shielding volume fractions and $C(T)$ does not exhibit distinguishable anomaly around $T_c$, suggesting a filamentary superconductivity in the Pr-doped polycrystalline samples. By varying doping concentrations, an electrnoic phase diagram can thus be established. Upon applying pressure on the optimal doping Sr$_{0.5}$Pr$_{0.5}$FBiS$_{2}$ system, $T_c$ is abruptly enhanced, reaches 8.5 K at a critical pressure of $P_c =$ 1.5 GPa and remains a slight increase up to 9.7 K up to 2.5 GPa. Accompanied with the enhancement of superconductivity from the low-$T_c$ phase to the high-$T_c$ phase, the normal state undergoes a semiconductor-to-metal transition under pressure. The scenario can be linked to the enhancement of orbital overlap of Bi-6p and S-p, contributing to the bulk superconductivity above $P_c$. Phase diagram for Sr$_{0.5}$Pr$_{0.5}$FBiS$_{2}$ is also obtained.

cond-mat.supr-con↗

arXiv2018

Giant anomalous Nernst effect in the magnetic Weyl semimetal Co3Sn2S2

In ferromagnetic solids, even in absence of magnetic field, a transverse voltage can be generated by a longitudinal temperature gradient. This thermoelectric counterpart of the Anomalous Hall effect (AHE) is dubbed the Anomalous Nernst effect (ANE). Expected to scale with spontaneous magnetization, both these effects arise because of the Berry curvature at the Fermi energy. Here, we report the observation of a giant ANE in a newly-discovered magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ crystal. Hall resistivity and Nernst signal both show sharp jumps at a threshold field and exhibit a clear hysteresis loop below the ferromagnetic transition temperature. The ANE signal peaks a maximum value of about 5 miuV/K which is comparable to the largest seen in any magnetic material. Moreover, the anomalous transverse thermoelectric conductivity becomes as large as about 10 A/K.m at 70 K, the largest in known semimetals. The observed ANE signal is much larger than what is expected according to the magnetization.

cond-mat.mtrl-sci↗

arXiv2017

Magnetoresistance and robust resistivity plateau in MoAs2

We have grown the MoAs$_2$ single crystal which crystallizes in a monoclinic structure with C2/m space group. Transport measurements show that MoAs$_2$ displays a metallic behavior at zero field and undergoes a metal-to-semiconductor crossover at low temperatures when the applied magnetic field is over 5 T. A robust resistivity plateau appears below 18 K and persists for the field up to 9 T. A large positive magnetoresistance (MR), reaching about 2600\% at 2 K and 9 T, is observed when the field is perpendicular to the current.The MR becomes negative below 40 K when the field is rotated to be parallel to the current. The Hall resistivity shows the non-linear field-dependence below 70 K. The analysis using two-band model indicates a compensated electron-hole carrier density at low temperatures. A combination of the breakdown of Kohler's rule, the abnormal drop and the cross point in Hall data implies that a possible Lifshitz transition has occurred between 30 K and 60 K, likely driving the compensated electron-hole density, the large MR as well as the metal-semiconductor transition in MoAs$_2$. Our results indicate that the family of centrosymmetric transition-metal dipnictides has rich transport behavior which can in general exhibit variable metallic and topological features.

cond-mat.mtrl-sci↗

arXiv2017

Heavy fermion quantum criticality at dilute carrier limit in CeNi$_{2-δ}$(As$_{1-x}$P$_{x}$)$_{2}$

We study the quantum phase transitions in the nickel pnctides, CeNi$_{2-δ}$(As$_{1-x}$P$_{x}$)$_{2}$ ($δ$ $\approx$ 0.07-0.22). This series displays the distinct heavy fermion behavior in the rarely studied parameter regime of dilute carrier limit. We systematically investigate the magnetization, specific heat and electrical transport down to low temperatures. Upon increasing the P-content, the antiferromagnetic order of the Ce-4$f$ moment is suppressed continuously and vanishes at $x_c \sim$ 0.55. At this doping, the temperature dependences of the specific heat and longitudinal resistivity display non-Fermi liquid behavior. Both the residual resistivity $ρ_0$ and the Sommerfeld coefficient $γ_0$ are sharply peaked around $x_c$. When the P-content reaches close to 100\%, we observe a clear low-temperature crossover into the Fermi liquid regime. In contrast to what happens in the parent compound $x$ = 0.0 as a function of pressure, we find a surprising result that the non-Fermi liquid behavior persists over a nonzero range of doping concentration, $x_c<x<0.9$. In this doping range, at the lowest measured temperatures, the temperature dependence of the specific-heat coefficient is logarithmically divergent and that of the electrical resistivity is linear. We discuss the properties of CeNi$_{2-δ}$(As$_{1-x}$P$_{x}$)$_{2}$ in comparison with those of its 1111 counterpart, CeNi(As$_{1-x}$P$_{x}$)O. Our results indicate a non-Fermi liquid phase in the global phase diagram of heavy fermion metals.

cond-mat.str-el↗

arXiv2016

Antiferromagnetic Kondo lattice compound CePt$_{3}$P

A new ternary platinum phosphide CePt$_{3}$P was synthesized and characterized by means of magnetic, thermodynamic and transport measurements. The compound crystallizes in an antiperovskite tetragonal structure similar to that in the canonical family of platinum-based superconductors $A$Pt$_{3}$P ($A$ = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion superconductor CePt$_{3}$Si. In contrast to all the superconducting counterparts, however, no superconductivity is observed in CePt$_{3}$P down to 0.5 K. Instead, CePt$_{3}$P displays a coexistence of antiferromagnetic ordering, Kondo effect and crystalline electric field effect. A field-induced spin-flop transition is observed below the magnetic ordering temperature $T_{N1}$ of 3.0 K while the Kondo temperature is of similar magnitude as $T_{N1}$. The obtained Sommerfeld coefficient of electronic specific heat is $γ_{Ce}$ = 86 mJ/molK$^{2}$ indicating that CePt$_{3}$P is a moderately correlated antiferromagnetic Kondo lattice compound.

cond-mat.str-el↗

arXiv2016

Synthesis, characterization and physical properties of layered bismuthide PtBi$_2$

We report details of single crystal growth of stoichiometric bismuthide PtBi$_2$ whose structure consists of alternate stacking of Pt layer sandwiched by Bi bilayer along the $c$-axis. The compound crystallizes in space group P-3 with a hexagonal unit cell of $a$=$b$=6.553$Å$, $c$=6.165$Å$. The magnetization data show opposite sign for fields parallel and perpendicular to the Pt layers, respectively. The $T$-dependent resistivity is typical of a metal and the magnetic response shows clear two types of charge carriers and the validity of the semi-classical Kohler's rule. Its physical properties was discussed in comparison with recently proposed topological superconductor $β$-PdBi$_2$.

cond-mat.str-el↗

arXiv2016

Dirac-Kondo semimetals and topological Kondo insulators in the dilute carrier limit

Heavy fermion systems contain not only strong electron correlations, which promote a rich set of quantum phases, but also a large spin-orbit coupling, which tends to endow the electronic states a topological character. Kondo insulators are understood in terms of a lattice of local moments coupled to conduction electrons in a half-filled band, i.e., with a dense population of about one electron per unit cell. Here, we propose that a new class of Kondo insulator arises when the conduction-electron band is nearly empty ( or, equivalently, full ) . We demonstrated the effect through a honeycomb Anderson lattice model. In the empty carrier limit, spin-orbit coupling produces a gap in the hybridized heavy fermion band, thereby generating a topological Kondo insulator. This state can be understood in terms of a nearby phase in the overall phase diagram, a Dirac-Kondo semimetal whose quasiparticle excitations exhibit a non-trivial Berry phase. Our results point to the dilute carrier limit of the heavy-fermion systems as a new setting to study strongly correlated insulating and topological states.

cond-mat.str-el↗

arXiv2016

Superconductivity and abnormal pressure effect in Sr0.5La0.5FBiSe2 superconductor

Through the solid state reaction method, we synthesized a new BiSe2-based superconductor Sr0:5La0:5FBiSe2 with superconducting transition temperature Tc?3.8 K. A strong diamagnetic signal below Tc in susceptibility ?(T) is observed indicating the bulk nature of superconductivity. Different to most BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, the present compound exhibits a metallic behavior down to Tc. Under weak magnetic field or pressure, however, a remarkable crossover from metallic to insulating behaviors takes place around Tmin where the resistivity picks up a local minimum. With increasing pressure, Tc decreases monotonously and Tmin shifts to high temperatures, while the absolute value of the normal state resistivity at low temperatures first decreases and then increases with pressure up to 2.5 GPa. These results imply that the electronic structure of Sr0:5La0:5FBiSe2 may be different to those in the other BiS2-based systems.

cond-mat.supr-con↗

arXiv2016

Electronic structures of transition metal dipnictides $XPn_2$ ($X$=Ta, Nb; $Pn$=P, As, Sb)

The electronic structures and topological properties of transition metal dipnictides $XPn_2$ ($X$=Ta, Nb; $Pn$=P, As, Sb) have been systematically studied using first-principles calculations. In addition to small bulk Fermi surfaces, the band anticrossing features near the Fermi level can be identified from band structures without spin-orbit coupling, leading to nodal lines in all these compounds. Inclusion of spin-orbit coupling gaps out these nodal lines leaving only a pair of disentangled electron/hole bands crossing the Fermi level. Therefore, the low energy physics can be in general captured by the corresponding two band model with several isolated small Fermi pockets. Detailed analysis of the Fermi surfaces suggests that the arsenides and NbSb$_2$ are nearly compensated semimetals while the phosphorides and TaSb$_2$ are not. Based on the calculated band parities, the electron and hole bands are found to be weakly topological non-trivial giving rise to surface states. As an example, we presented the surface-direction-dependent band structure of the surfaces states in TaSb$_2$.

cond-mat.mtrl-sci↗

arXiv2016

Field-induced resistivity plateau and unsaturated negative magnetoresistance in topological semimetal TaSb2

Several prominent transport properties have been identified as key signatures of topologicalmaterials. One is the resistivity plateau at low temperatures as observed in several topological insulators (TIs), another is the negative magnetoresistance (MR) when the applied magnetic field is parallel to the current direction as observed in several topological semimetals (TSMs) including Dirac semimetals (DSMs) and Weyl semimetals (WSMs). Usually, these two exotic phenomena emerge in distinct materials with or without time reversal symmetry (TRS), respectively. Here we report the discovery of a new member in TSMs, TaSb2, which clearly exhibits both of these phenomena in a single material. This compound crystallizes in a base-centered monoclinic, centrosymmetric structure, and is metallic with a low carrier density in the zero field. While applying magnetic field it exhibits insulating behavior before appearance of a resistivity plateau below Tc =13 K. In the plateau regime, the ultrahigh carrier mobility and extreme magnetoresistance (XMR) for the field perpendicular to the current are observed as in DSMs and WSMs, in addition to a quantum oscillation behavior with non-trivial Berry phases. In contrast to the most known DSMs and WSMs, the negative MR in TaSb2 does not saturate up to 9 T, which, together with the almost linear Hall resistivity, manifests itself an electron-hole non-compensated TMS. These findings indicate that the resistivity plateau could be a generic feature of topology-protected metallic states even in the absence of TRS and compatible with the negative MR depending on the field direction. Our experiment extends a materials basis represented by TaSb2 as a new platform for future theoretical investigations and device applications of topological materials.

cond-mat.mtrl-sci↗

arXiv2015

Formation of Molecular-Orbital Bands in a Twisted Hubbard Tube: Implications for Unconventional Superconductivity in K2Cr3As3

We study a twisted Hubbard tube modeling the [CrAs] structure of quasi-one-dimensional superconductors A2Cr3As3 (A = K, Rb, Cs). The molecular-orbital bands emerging from the quasi-degenerate atomic orbitals are exactly solved. An effective Hamiltonian is derived for a region where three partially filled bands intersect the Fermi energy. The deduced local interactions among these active bands show a significant reduction compared to the original atomic interactions. The resulting three-channel Luttinger liquid shows various interaction-induced instabilities including two kinds of spin-triplet superconducting instabilities due to gapless spin excitations, with one of them being superseded by the spin-density-wave phase in the intermediate Hund's coupling regime. The implications of these results for the alkali chromium arsenides are discussed.

cond-mat.str-el↗

arXiv2015

Reduced Dimensionality and Magnetic Frustration in KCr$_3$As$_3$

We study the electronic and magnetic structures of the newly-discovered compound KCr$_3$As$_3$. The non-magnetic state has five Fermi surface sheets involving respectively three quasi-one-dimensional and two three-dimensional energy bands. However, the ground state is magnetic, exhibiting a novel interlayer antiferromagnetic order where the basic block-spin state of a unit Cr triangle retains a high spin magnitude. Moreover, its Fermi surface involves three one-dimensional sheets only, providing evidence for local moments in this compound due to the reduced dimensionality. By fitting a twisted spin tube model the magnetic frustrations caused by local moments are found to be relaxed, leading to gapless spin excitations. A frustration-induced transition to the disordered low block-spin state is expected upon increasing the intralayer exchange interaction.

cond-mat.str-el↗

arXiv2015

Upward curvature of the upper critical field and the V-shaped pressure dependence of $T_c$ in the noncentrosymmetric superconductor PbTaSe$_2$

The temperature evolution of the upper critical field $H_{c2}(T)$ in the noncentrosymmetric superconductor PbTaSe$_2$ was determined via resistivity measurements down to 0.5 K. A pronounced positive curvature in the $H_{c2}$-$T$ phase diagram was observed in the whole temperature range below $T_c$. The Seebeck coefficient $S(T)$ in the temperature range 5K$\leq$$T$$\leq$350K was found to be negative in sign, modest in magnitude and non-linear in temperature. In addition, the superconducting transition temperature $T_c$ under hydrostatic pressure shows a marked non-monotonic variation, decreasing initially with the applied pressure up to $P_c$$\sim$5-10 kbar but then rising with further pressurization. The underlying physical mechanisms of all these findings have been discussed.

cond-mat.supr-con↗

arXiv2015

Quasi-linear magnetoresistance and the violation of Kohler's rule in the quasi-one-dimensional Ta$_4$Pd$_3$Te$_{16}$ superconductor

We report on the quasi-linear in field intrachain magnetoresistance in the normal state of a quasi-one-dimensional superconductor Ta$_4$Pd$_3$Te$_{16}$ ($T_c$$\sim$4.6 K). Both the longitudinal and transverse in-chain magnetoresistance shows a power-law dependence, $Δρ$$\propto$B$^α$, with the exponent $α$ close to 1 over a wide temperature and field range. The magnetoresistance shows no sign of saturation up to 50 tesla studied. The linear magnetoresistance observed in Ta$_4$Pd$_3$Te$_{16}$ is found to be overall inconsistent with the interpretations based on the Dirac fermions in the quantum limit, charge conductivity fluctuations as well as quantum electron-electron interference. Moreover, it is observed that the Kohler's rule, regardless of the field orientations, is violated in its normal state. This result suggests the loss of charge carriers in the normal state of this chain-containing compound, due presumably to the charge-density-wave fluctuations.

cond-mat.supr-con↗

arXiv2015

Local Kondo entanglement and its breakdown in an effective two-impurity Kondo model

Competition between the Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction in the two-impurity Kondo problem can be phenomenologically described by the Rasul-Schlottmann spin model. We revisit this model from the quantum entanglement perspective by calculating both the inter-impurity entanglement and the local Kondo entanglement, the latter being the entanglement between a local magnetic impurity and its spatially nearby conduction electron. A groundstate phase diagram is derived and a discontinuous breakdown of the local Kondo entanglement is found at the singular point, associated concomitantly with a jump in the inter-impurity entanglement. An entanglement monogamy holds in the whole phase diagram. Our results identify the important role of the frustrated cross-coupling and demonstrate the local characteristic of the quantum phase transition in the two-impurity Kondo problem. The implications of these results for Kondo lattices and quantum information processing are also briefly discussed.

cond-mat.str-el↗

arXiv2015

Heavy surface state in a possible topological Kondo insulator: Magneto-thermoelectric transport on the (011)-plane of SmB$_6$

Motivated by the high sensitivity to Fermi surface topology and scattering mechanisms in magneto-thermoelectric transport, we have measured the thermopower and Nernst effect on the (011)-plane of the proposed topological Kondo insulator SmB$_6$. These experiments, together with electrical resistivity and Hall effect measurements, demonstrate that the (011)-plane also harbors a metallic surface with the effective mass in the order of 10-10$^2$ $m_0$. The surface and bulk conductances are well distinguished in these measurements and are categorized into metallic and non-degenerate semiconducting regimes, respectively. Electronic correlations play an important role in enhancing scattering and also contribute to the heavy surface state.

cond-mat.str-el↗

arXiv2015

Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2

Through the combination of X-ray diffraction, electrical transport, magnetic susceptibility, and the heat capacity measurements, we studied the effect of Ce doping in the newly discovered SrFBiS${2}$ system. It is found that Sr${0.5}$Ce${0.5}$FBiS${2}$ undergoes a second-order transition below $7.5 K, followed by a superconducting transition with the critical temperature Tc=2.8 K. Our transport, specific heat and DC-magnetization results suggest the presence of bulk ferromagneticcorrelation of Ce ion below 7.5 K that coexist with superconductivity when the temperature is further lowered below 2.8 K.

cond-mat.supr-con↗

arXiv2015

Natural Orbitals Renormalization Group Approach to the Two-Impurity Kondo Critical Point

The problem of two magnetic impurities in a normal metal exposes the two opposite tendencies in the formation of a singlet ground state, driven respectively by the single-ion Kondo effect with conduction electrons to screen impurity spins or the Ruderman-Kittel-Kasuya-Yosida interaction between the two impurities to directly form impurity spin singlet. However, whether the competition between these two tendencies can lead to a quantum critical point has been debated over more than two decades. Here, we study this problem by applying the newly proposed natural orbitals renormalization group method to a lattice version of the two-impurity Kondo model with a direct exchange $K$ between the two impurity spins. The method allows for unbiased accessing the ground state wave functions and low-lying excitations for sufficiently large system sizes. We demonstrate the existence of a quantum critical point, characterized by the power-law divergence of impurity staggered susceptibility with critical exponent $γ= 0.60(1)$, on the antiferromagnetic side of $K$ when the interimpurity distance $R$ is even lattice spacing, while a crossover behavior is recovered when $R$ is odd lattice spacing. These results have ultimately resolved the long-standing discrepancy between the numerical renormalization group and quantum Monte Carlo studies, confirming a link of this two-impurity Kondo critical point to a hidden particle-hole symmetry predicted by the local Fermi liquid theory.

cond-mat.str-el↗