Abstract
In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.
Highlights
An insulator-to-metal transition is visible in the form of a broad maximum at 76 K, which we associate with the antiferromagnetic transition of the bulk Fe1+yTe layer
It is important to note that the resistance is composed of 3 parallel components: the Bi2Te3 layer, the bulk Fe1+yTe layer and the intermediate thin interfacial layer
Until 15 K, the gap is rounded at low energy, but at 12 K the conductance flattens around Vb = 0 prior to the emergence of a zero bias conductance peak (ZBCP) below ~10 K
Summary
To fabricate a point-contact device on the edge of the bilayer, a thin slab was attached to a silicon substrate with one edge facing upwards. The maximum contact area is ~100 × 149 nm[2] (from the width of the Au strip and the total thickness of the FeTe/Bi2Te3 bilayer, respectively). In our contacts we consistently achieve Z ≥ 0.35 and our nanoscale contact area ensures that our experimental tunneling regime is ballistic and not thermal or diffusive, i.e. the applied bias voltage Vb corresponds to the electron injection energy. This is confirmed by the temperature-independent value of the normal-state contact resistance. A standard lock-in technique in combination with a DC multimeter was used to measure dI/dV and Vb =VDC across the junction
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