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Scanning tunneling spectroscopy under large current flow through the sample
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View: Figures


Image of FIG. 1.
FIG. 1.

Support system of the microscope head, made entirely of Cu. The upper flange (A) is gold plated and screwed to the mixing chamber of a dilution refrigerator. The microscope (C) is located at the maximum field position of the superconducting coil. It has a mechanically driven horizontal linear positioning stage as described in Ref. 26 (not shown in the figure for clarity). Here, isolation from the mechanical vibrations has been further improved by decoupling the STM from the support frame by placing fiberglass strands (D) in between. Wires (B) are thermalized along the supporting rods (in addition to the usual thermalization steps in the mixing chamber, still and 1 K pot).

Image of FIG. 2.
FIG. 2.

Schematics of a STS experiment with a constant current I sample applied along a superconducting sample. The same voltage ramp V bias is applied to both sides of the sample, but we add a voltage V sample at one side of the resistance R = 100 Ω, for creating currents I sample up to 30 mA.

Image of FIG. 3.
FIG. 3.

Overview of the electronics used in the STS experiments with a current through the sample. The values for the capacity R filter1 and resistance R filter1 used in the RC filter are and 10 kΩ, respectively. An offset V offset is added to V bias in order to subtract the voltage drop across R wires (here, R wires ≃ 4 Ω) from the one measured in the STS experiment across R tunnel . The value for V offset is discussed in the text. The values for the other elements in the circuitry are and R = 100 Ω. Here R′ and C stand for the resistances and capacitances used in the conventional electronics. Note that both OP27 circuits act as equal and opposed voltage sources, and, if eventually needed, as voltage dividers.

Image of FIG. 4.
FIG. 4.

Schematics of the STS experiment using a normal tip of Au and a type II superconducting sample of . It is shown how the sample is biased separately in both sides and isolated from the sample holder which is grounded. Note that the tunneling current I tunnel is measured, in this case, through the tip electrode. The same schematics can be followed using a superconducting tip and sample of Al.

Image of FIG. 5.
FIG. 5.

STM topography measurements at 100 mK under an applied transport current. (a) Topography images of in surface using a normal tip of Au (left panel) without any transport current and (right panel) under one of 3 mA applied along the sample. (b) We have achieved atomic resolution applying a transport current of 7 mA (left panel), but without notifying any significant change in CDW pattern in the Fourier transform of the topography image shown in the right panel (here a stands for the lattice parameter and for the wavelength of the CDW).

Image of FIG. 6.
FIG. 6.

Normalized tunneling conductance curves taken without and under a transport current of (changing its direction), using a tip and a sample of superconducting Al (1.35 nA of measured tunneling current under a bias voltage of 1.5 mV). The curves have been shifted by 1 for clarity.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Scanning tunneling spectroscopy under large current flow through the sample