Superconductivity and Charge Density Wave in ZrTe3−xSex

Charge density wave (CDW) and superconductivity (SC), both Fermi surface instabilities and low-temperature collective orders in solids, are commonly believed to compete with each other1,2. Recently, dynamic CDW fluctuations have also been discussed in copper oxide superconductors3 in connection with quantum critical transition between CDW and superconductivity. CDW favors low dimensional systems, especially transition metal (M) MX2 and MX3 chalcogenides (X represents S, Se and Te)1,4. Among them, ZrTe3 is of interest since its crystal structure (Fig. 1a) is quasi-two dimensional (2D), yet it contains two quasi-one dimensional (1D) trigonal prismatic ZrTe6 chains with inversion symmetry along the b-axis5. From the view along c-axis (Fig. 1b), the top Te2/Te3 atoms form a rectangular network with the distances of 0.279/0.310 nm along the a axis and 0.393 nm along the b-axis. The first principle calculation gives evidence that the electron-type band (Te2/Te3 5px in origin) provides the major contribution, whereas the contribution of the partially filled hole-type band that originates in Te1 5py and orbitals is minor at the Fermi surface5. Angular resolved photoemission (ARPES) demonstrates that CDW originates from the Te2/Te3 5px band6. Figure 1 (a) Crystal structure of ZrTe3. (b) Top Te2/Te3 rectangular network layer viewed from c-axis. The quasi 1D ZrTe6 chains run along the b-axis, with the shortest Zr-Zr distance and Te1-Te1 distance of 0.393 nm. Solid line denotes the alternately ... ZrTe3 features not only a CDW transition temperature (TCDW) ~63 K with a CDW vector but also a nearly isotropic in-plane and quasi-two-dimensional (2D) electronic transport5,7,8. There is a filamentary SC in a stoichiometric single crystal with higher onset of Tc for a-axis from resistivity measurement than for b-axis5,9. Heat capacity data suggest that SC transitions in ZrTe3 are successive from filamentary-to-bulk with local pair fluctuations above Tc; SC phase first condenses into filaments along a-axis, becoming phase coherent below 2 K9. Pressure(P), intercalation, and disorder can tune ZrTe3 into bulk SC with suppression of CDW order10,11,12. Here we provide evidence for the pronounced upper critical field Hc2(T) anisotropy and emerging 1D electronic transport along the ZrTe6 chain-direction b axis in ZrTe3−xSex (0 ≤ x ≤ 0.1). The Hc2(T) anisotropy and new Raman modes suggest coexistence of local CDW modes and enhanced superconducting Tc(x) in ZrTe3−xSex.