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Register a new userSuperconductivity and Charge Density Wave in ZrTe$_{3-x}$Se$_{x}$
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Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe$_{3}$ when the long range CDW order is gradually suppressed. Superconducting critical temperature $T_c(x)$ in ZrTe$_{3-x}$Se$_x$ (${0leq}xleq0.1$) increases up to 4 K plateau for $0.04$$leq$$x$$leq$$0.07$. Further increase in Se content results in diminishing $T_{c}$ and filametary superconductivity. The CDW modes from Raman spectra are observed in $x$ = 0.04 and 0.1 crystals, where signature of ZrTe$_{3}$ CDW order in resistivity vanishes. The electronic-scattering for high $T_{c}$ crystals is dominated by local CDW fluctuations at high temperures, the resistivity is linear up to highest measured $T=300K$ and contributes to substantial in-plane anisotropy.
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We carried out a comprehensive study of the electronic, magnetic, and thermodynamic properties of Ni-doped ZrTe$_2$. High quality Ni$_{0.04}$ZrTe$_{1.89}$ single crystals show a possible coexistence of charge density waves (CDW, T$_{CDW}approx287$,K) with superconductivity (T$_capprox 4.1$,K), which we report here for the first time. The temperature dependence of the lower (H$_{c_1}$) and upper (H$_{c_2}$) critical magnetic fields both deviate significantly from the behaviors expected in conventional single-gap s-wave superconductors. However, the behaviors of the normalized superfluid density $rho_s(T)$ and H$_{c_2}(T)$ can be described well using a two-gap model for the Fermi surface, in a manner consistent with conventional multiband superconductivity. Electrical resistivity and specific heat measurements show clear anomalies centered near 287,K suggestive of CDW phase transition. Additionally, electronic-structure calculations support the coexistence of electron-phonon multiband superconductivity and CDW order due to the compensated disconnected nature of the electron- and hole-pockets at the Fermi surface. Our calculations also suggest that ZrTe$_2$ is a non-trivial topological type-II Dirac semimetal. These findings highlight that Ni-doped ZrTe2 is uniquely important for probing the coexistence of superconducting and CDW ground states in an electronic system with non-trivial topology.
A Weyl semimetal with strong electron-phonon interaction can show axionic coupling in its insulator state at low temperatures, owing to the formation of a charge density wave (CDW). Such a CDW emerges in the linear chain compound Weyl semimetal Ta$_2$Se$_8$I below 263 K, resulting in the appearance of the dynamical condensed-matter axion quasiparticle. In this study, we demonstrate that the interchain coupling in Ta$_2$Se$_8$I can be varied to suppress the CDW formation with pressure, while retaining the Weyl semimetal phase at high temperatures. Above 17 GPa, the Weyl semimetal phase does not survive and we induce superconductivity, due to the amorphization of the iodine sub-lattice. Structurally, the one-dimensional Ta-Se-chains remain intact and provide a superconducting channel in one dimension. We highlight that our results show a near-complete suppression of the gap induced by the axionic charge-density wave at pressures inaccessible to previous studies. Including this CDW phase, our experiments and theoretical predictions and analysis reveal the complete topological phase diagram of Ta$_2$Se$_8$I and its relationship to the nearby superconducting state. The results demonstrate Ta$_2$Se$_8$I to be a distinctively versatile platform for exploring correlated topological states.
We report the interplay between charge-density-wave (CDW) and superconductivity of 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ ($0leq x leq 0.05$) 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 $x=0.02$. We propose that the induced superconductivity and CDW phases are separated in real space. 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 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ system that shows a dome-like $T_{c}(x)$.
We have performed an isovalent substitution study in a layered titanium oxypnictide system BaTi$_{2}$(Sb$_{1-x}$Bi$_{x}$)$_{2}$O (0$leq xleq$ 0.40) by the measurements of x-ray diffraction, electrical resistivity and magnetic susceptibility. The parent compound BaTi$_{2}$Sb$_{2}$O is confirmed to exhibit superconductivity at 1.5 K as well as charge- or spin-density wave (CDW/SDW) ordering below 55 K. With the partial substitution of Sb by Bi, the lattice parameters $a$, $c$ and $c/a$ all increase monotonically, indicating negative chemical pressure and lattice distortion on the (super)conducting Ti$_2$Sb$_2$O-layers. The Bi doping elevates the superconducting transition temperature to its maximum $T_c$=3.7 K at $x=$0.17, and then $T_c$ decreases gradually with additional Bi doping. A metal-to-nonmetal transition takes place around $x$=0.3, and superconductivity at $sim$1K exists at the nonmetal side. The CDW/SDW anomaly, in comparison, is rapidly suppressed by the Bi doping, and vanishes for $xgeq$0.17. The results are discussed in terms of negative chemical pressure and disorder effect.
Superconductivity in topological kagome metals has recently received great research interests. Here, charge density wave (CDW) orders and the evolution of superconductivity under various pressures in CsV3Sb5 single crystal with V kagome lattice are investigated. By using high-resolution scanning tunnelling microscopy /spectroscopy (STM/STS), two CDW orders in CsV3Sb5 are observed which correspond to 4a*1a and 2a*2a superlattices. By applying pressure, the superconducting transition temperature Tc is significantly enhanced and reaches a maximum value of 8.2 K at around 1 GPa. Accordingly, CDW state is gradually declined as increasing the pressure, which indicates the competing interplay between CDW and superconducting state in this material. The broad superconducting transitions around 0.4 - 0.8 GPa can be related to the strong competition relation among two CDW states and superconductivity. These results demonstrate that CsV3Sb5 is a new platform for exploring the interplay between superconductivity and CDW in topological kagome metals.
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