Magnetic and thermodynamic properties of CuxTiSe2 single crystals

Abstract

We present a detailed study of the phase diagram of copper intercalated TiSe2 single crystals, combining local Hall-probe magnetometry, tunnel diode oscillator technique (TDO), and specific heat and angle-resolved photoemission spectroscopy measurements. A series of the CuxTiSe2 samples from three different sources with various copper content x and superconducting critical temperatures Tc have been investigated. We first show that the vortex penetration mechanism is dominated by geometrical barriers enabling a precise determination of the lower critical field, Hc1. We then show that the temperature dependence of the superfluid density deduced from magnetic measurements (both Hc1 and TDO techniques) clearly suggests the existence of a small energy gap in the system, with a coupling strength 2∆s ∼ [2.4 − 2.8]kBTc, regardless of the copper content, in puzzling contradiction with specific heat measurements which can be well described by one single large gap 2∆ l ∼ [3.7 − 3.9]kBTc. Finally, our measurements reveal a non-trivial doping dependence of the condensation energy, which remains to be understood.

Emergent superconductivity upon disordering a charge density wave ground state

“…Surprisingly, the initial rapid decay of CDW order slows down considerably beyond dopings which marks the onset of superconductivity, and an incommensurate charge density wave (ICDW) order survives beyond this point. Such ICDW phase is found to persist along with superconductivity at doping as large as x ≈ 0.11 [31,32].…”

Defect-induced weak collective pinning in superconducting YB6 crystals

“…For example, specially selected single crystals of NbSe 2 with very weak pinning revealed a critical current density of about 1.6 × 10 4 A cm −2 obtained using the width of the magnetization curve [30], but also 2H-NbSe 2 crystals with 500 A cm −2 were prepared [31]. Similarly, such a low critical current density (∼500 A cm −2 ) was observed also in the crystals of Cu x TiSe 2 [32].…”

Critical current in thin flat superconductors with Bean-Livingston and geometrical barriers

“…In this case one cannot use the approximation √ 1 − m ≈ 1 − ms 2 0 ≈ 1 everywhere in Eqs. (37) and (38). The fail of this approximation is also seen from the dependence of the angle θ on u (0) 2 shown in Fig.…”

“…to the current) in the case of the Meissner state. Analogously, equating the ratio of formulas (38) and (37) to the right hand side of expression (36), one arrives at the equation determining s 0 as a functions of u…”