Investigations of the superconducting ground state of ${\mathrm{Zr}}_3\mathrm{Ir}$: Introducing a new noncentrosymmetric superconductor

Superconductivity in materials whose crystal structure lacks inversion symmetry is a prime candidate for unconventional superconductivity. A new noncentrosymmetric compound ${\mathrm{Zr}}_3\mathrm{Ir}$ crystallizes in a tetragonal $\alpha -{\mathrm{V}}_3\mathrm{S}$ structure. The magnetization, specific heat, and muon spin rotation confirm s-wave superconductivity, having a transition temperature $T_c=2.3$ K. Muon spin relaxation confirms the preservation of time reversal symmetry in the superconducting ground state.

Figure 1

Powder XRD pattern of the sample recorded at ambient temperature using $\mathrm{Cu}{K}_{\alpha }$ radiation (red line). The Rietveld refined data for the noncentrosymmetric space group $I-42m$ (121) is shown as a dotted black line. The green vertical lines show the calculated reflection positions. The inset displays a unit cell of ${\mathrm{Zr}}_3\mathrm{Ir}$.

Figure 2

Resistivity measurement taken against temperature $\rho \left(T\right)$ at zero field. The inset shows the drop in resistivity at $T_c=2.3$ K. The green line is a fit to low temperature data using power law.

Figure 3

(a) Temperature dependence of magnetic susceptibility collected via both ZFC and FCC mode. Superconducting transition of the sample is observed at $T_c=2.3$ K. (b) Temperature variation of lower critical field ${\mathrm{H}}_{c1}$ collected via magnetization measurement. Extrapolation using G-L equation gives ${\mathrm{H}}_{c1}\left(0\right)=66$ Oe. The inset shows the magnetization curves taken up to 500 Oe at different temperatures. (c) Isothermal magnetization curve taken at different temperatures. The inset shows the enlarged view. ${\mathrm{H}}_{c2}$ is taken at the discontinuity in the gradient as marked in the inset. (d) Determination of upper critical field ${\mathrm{H}}_{c2}$(0) using magnetization and resistivity measurements. The dotted lines indicates the fits to the data using Eq. (2). The inset shows low temperature resistivity data collected at different fields.

Figure 4

C/T Vs $T^2$ shows a jump in specific heat at 2.31 K. An applied field of 20 kOe (green dotted line) which is above ${\mathrm{H}}_{C2}$(0) kills the superconducting transition. (Inset) Variation of electronic specific heat with temperature is fitted by the isotropic s-wave model (green line). The fitting yields the value of superconducting gap as $\frac{\mathrm{\Delta }\left(0\right)}{k_B{T}_c}=1.37$.

Figure 5

$\mu \mathrm{SR}$ spectra collected in zero field configuration at temperatures above (2.6 K) and below (45 mK) the transition temperature. The inset shows no significant change in fit parameters $\mathrm{\Lambda }\left(T\right)$ and $\sigma \left(T\right)$ across the transition temperature.

Figure 6

A representative $\mu \mathrm{SR}$ spectra collected in transverse field configuration at an applied field of 400 Oe. The spectra collected at 0.01 K show significant decay due to flux line lattice formation, while the nondecaying nature of the signal at $T=2.45$ K indicates uniform field distribution above $T_c$.

Figure 7

Temperature dependence of ${\sigma }_{FLL}$ measured at an applied field of 400 Oe. The solid red line is the dirty limit isotropic s-wave fit for the data.

Figure 8

The Uemura plot showing the superconducting transition temperature $T_c$ vs the effective Fermi temperature $T_F$, where ${\mathrm{Zr}}_3\mathrm{Ir}$ is shown as an inverted yellow triangle. Other data points plotted between the blue solid lines are the different families of unconventional superconductors [47, 48].