Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures

Abstract

The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.

Figure 1

(a) Normalized temperature dependent resistances and (b) dR/dT curves of sample Bi₂Te₃(7 nm)/FeTe in as-grown and after-two-years cases. The as-grown and after-two-years normal state resistances at 18 K are 21.0 Ω and 25.3 Ω, respectively. The T_max, T_mid, T_zero of after-two-years case are indicated with dash lines and arrows. Normalized temperature dependent resistances of samples Bi₂Te₃(14 nm)/FeTe, Bi₂Te₃(7 nm)/FeTe, Bi₂Te₃(5 nm)/FeTe and Bi₂Te₃(3 nm)/FeTe in (c) as-grown and (d) after-two-years case, respectively. The corresponding dR/dT curves are given in their insets.

Figure 2

Normalized temperature dependent resistances of sample Bi₂Te₃(14 nm)/FeTe in magnetic fields ranging from 0 T to 14 T in (a) as-grown and (b) after-two-years cases, respectively. The magnetic field is perpendicular to the ab plane as shown in the insets.

Figure 3

Magnetic field-temperature phase diagram of samples (a) Bi₂Te₃(7 nm)/FeTe and (b) Bi₂Te₃(14 nm)/FeTe. The upper critical field H_max and H_zero in the as-grown case are plotted as triangle symbols, and the H_max, H_mid and H_zero in the after-two-years case are presented as circle symbols. The solid and hollow symbols represent the perpendicular and parallel fields’ situations, respectively.

Figure 4

lnR_sq(T) vs. 1/T in different perpendicular magnetic fields for sample (a) Bi₂Te₃(7 nm)/FeTe in as-grown case, (b) Bi₂Te₃(7 nm)/FeTe in after-two-years case, (d) Bi₂Te₃(14 nm)/FeTe in as-grown case, (e) Bi₂Te₃(14 nm)/FeTe in after-two-years case. The solid lines in (a,b,d,e) are fitting results from the Arrhenius relation, whose slopes give the values of U in (c,f). The solid lines in (c,f) are fitting results from the function U = U₀ ln(H₀/H).