Singlegap superconductivity in βBi_{2}Pd
The βBi_{2}Pd compound has been proposed as another example of a multigap superconductor [Imai et al., J. Phys. Soc. Jpn. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable of showing a presence of multiple energy gaps on our superconducting single crystals of βBi_{2}Pd with the critical temperature T_{c} close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at
the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred
from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature
and angular dependence of the upper critical magnetic field point unequivocally to standard single swave gap
superconductivity. The Hallprobe magnetometry provides the same result from the analysis of the temperature
dependence of the lower critical field. A singlegapped BCS density of states is detected by the scanning
tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard
conventional superconductivity in this system where the topologically protected surface states have been recently
detected by angleresolved photoemission spectroscopy [Sakano et al., Nat. Commun. 6, 8595 (2015).].
J. Kačmarčík, Z. Pribulová, T. Samuely, P. Szabó, V. Cambel, J. Šoltýs, E. Herrera, H. Suderow, A. CorreaOrellana,
D. Prabhakaran, and P. Samuely: Singlegap superconductivity in βBi_{2}Pd
Physical Review B 93, 144502 (2016).
Figure 1: Total heat capacity of the sample plus addenda in superconducting (0 T) and normal (1 T) states. The upper inset: the difference in entropy (purple line, right axis applies) and the thermodynamic critical field (black line, left axis). The lower inset: electronic specific heat from experimental data and theoretical curve from α model with the coupling ratio 2Δ/k_{B}T_{c} = 4.1.
Figure 2: Temperature dependence of the upper critical field for H in the c direction (closed symbols) and parallel to the ab planes (open symbols). Lines are fit to the WHH model. The lower inset: angular dependence of Tc2 measured at a fixed field of 0.1 T (symbols) and the theoretical curve from the GinzburgLandau model (line). The upper inset: deviation function of our measurements (red symbols) compared to those of Welp et al. (open circles) for a two gap superconductor,(Ba,K)Fe_{2}As_{2}.
Figure 3: The phase diagram of βBi_{2}Pd showing H^{c}_{c1} (blue
squares, the data are multiplied by a factor of 10 to be in scale) with the best fit (blue line) corresponding to 2Δ/k_{B}T_{c} = 4.1; H_{c2} from heat capacity (circles) and resistivity (lozenges) for both Hc
(filled symbols) and Hab (open symbols) together with the WHH theoretical curves (gray full lines) as well as a H_{c3} line (gray dashed line). (b) Local magnetic induction B as a function of applied field H measured by a Hall probe at selected temperatures with the field first increasing and then decreasing back to zero. (c) Superconducting transitions for H ⊥ ab revealed by the heat capacity (left axis) and resistivity measurements (right axis) at magnetic fields 0, 0.2, and 0.4 T, respectively.
