1887
banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Andreev-reflection spectroscopy with superconducting indium—A case study
Rent:
Rent this article for
USD
10.1063/1.4794999
/content/aip/journal/ltp/39/3/10.1063/1.4794999
http://aip.metastore.ingenta.com/content/aip/journal/ltp/39/3/10.1063/1.4794999

Figures

Image of FIG. 1.
FIG. 1.

Schematics of a point contact between two different metals in momentum space with kF 1 > kF 2, see Refs. 31 and 32 . The vertical line symbolizes the interface. At low temperatures and no applied bias voltage only electrons near the Fermi surfaces, indicated by the two circles, take part in transport processes. Flow from left to right requires kz  > 0 for electrons of the left-hand sphere. When the size of the Fermi surfaces differs like in the figure, only electrons in the highlighted region can travel through the contact and find states in the highlighted region of the smaller right-hand sphere. The others are normal reflected. In opposite direction, normal reflection does not occur since all electrons from states of the left-hand sphere with negative kz find states on the left-hand side within an angle Θ c around the negative kz axis. The critical angle is Θ c  = arcsin(kF 2/kF 1) to satisfy conservation of parallel momentum kp .

Image of FIG. 2.
FIG. 2.

Differential resistance spectra dV/dI versus bias voltage V of contacts with In. Normal metal counter electrode and temperature are indicated: an Andreev-reflection double-minimum structure. The two pairs of sharp side peaks make the analysis difficult (a); one pair of side peaks and slightly structured around zero bias (b); no side peaks but a minimum at zero bias, which appears to consist of two separate minima (c). The zero-bias minima in (b) and (c) could result from the proximity effect, while the side peaks in (a) and (b) stem from the self-magnetic field exceeding a critical value in the contact region.

Image of FIG. 3.
FIG. 3.

Differential resistance spectra dV/dI versus bias voltage V of an In–Zn junction at the indicated temperatures. At T = 0.1 K the Josephson-type anomaly at zero bias as well as multiple Andreev reflection within the superconducting gap are clearly visible. At T = 1.5 K the little dip at zero bias could indicate proximity-induced superconductivity in Zn. It is completely suppressed at T = 2.5 K. The spectra of this contact show a side peak (arrow), which moves slightly with temperature and is possibly caused by the self-magnetic field. The inset displays the details of the differential resistance around zero bias with emphasis on the spectra at 1.5 and 2.5 K, respectively.

Image of FIG. 4.
FIG. 4.

Selected differential resistance spectra dV/dI versus bias voltage V of In–Ag contacts at T = 0.7 K (thin lines). The underlying grey curves are fits with the modified BTK model. 37 Fit parameters are shown in Table II .

Image of FIG. 5.
FIG. 5.

Selected differential resistance spectra dV/dI versus bias voltage V of In–Pd contacts at low temperatures (thin lines). The underlying grey curves are fits with the modified BTK model. 37 Temperatures and fit parameters are shown in Table II .

Image of FIG. 6.
FIG. 6.

Selected differential resistance spectra dV/dI versus bias voltage V of In–Pt contacts at low temperatures (thin lines). The underlying grey curves are fits with the modified BTK model. 37 Temperatures and fit parameters are shown in Table II .

Image of FIG. 7.
FIG. 7.

Selected differential resistance spectra dV/dI versus bias voltage V of In–Zn contacts at T = 2.5 K (thin lines). The underlying grey curves are fits with the modified BTK model. 37 Fit parameters are shown in Table II .

Image of FIG. 8.
FIG. 8.

Superconducting energy gap 2Δ0 = 2Δ (T→0) of In extracted from the point-contact spectra using the modified BTK theory 37 versus normal state resistance R. Different symbols mark separate measurement series. For In–Ag contacts we have two measurement series at T = 0.7 K (open symbols) and one at T = 0.1 K. All In–Zn contacts were measured at T = 2.5 K. The In–Pd and the In–Pt contacts were measured at low temperature down to T = 0.1 K. The solid lines at 2Δ0 = 1.20 meV serve as a guide to the eye.

Image of FIG. 9.
FIG. 9.

Dynes lifetime parameter Γ of In in contact with the indicated normal metals extracted from the point-contact spectra using the modified BTK theory 37 versus normal state resistance R. Different symbols mark separate measurement series. For In–Ag contacts we have two measurement series at T = 0.1 K (open symbols) and one at T = 0.1 K. All In–Zn contacts were measured at T = 2.5 K. The In–Pd and the In–Pt contacts were measured at low temperature down to T = 0.1 K.

Image of FIG. 10.
FIG. 10.

Z-parameter of normal reflection of contacts between In and the indicated normal conductors extracted from the point-contact spectra using the modified BTK theory 37 versus normal state resistance R. Different symbols mark separate measurement series. For In–Ag contacts we have two measurement series at T = 0.7 K (open symbols) and one at T = 0.1 K. All In–Zn contacts were measured at T = 2.5 K. The In–Pd and the In–Pt contacts were measured at low temperature down to T = 0.1 K. The solid lines at Z = 0.5 serve as a guide to the eye.

Image of FIG. 11.
FIG. 11.

Schematics of a diffusive point contact between two different metals. The contact (hatched area) has a spatial extension L ≫ l 0. Its elastic electron mean free path l 0 is not necessarily the same as in the bulk electrodes.

Tables

Generic image for table
Table I.

Distribution of contact type: “Andreev” denotes contacts that could be analyzed, “proximity-like” contacts look like those where superconductivity has been induced in the normal metal, and “undefined” are all others which cannot be clearly identified.

Generic image for table
Table II.

Normal contact resistance, measurement temperature, and BTK parameters of the spectra shown in Figures 4–7 .

Loading

Article metrics loading...

/content/aip/journal/ltp/39/3/10.1063/1.4794999
2013-03-27
2014-04-17
Loading

Full text loading...

This is a required field
Please enter a valid email address
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Andreev-reflection spectroscopy with superconducting indium—A case study
http://aip.metastore.ingenta.com/content/aip/journal/ltp/39/3/10.1063/1.4794999
10.1063/1.4794999
SEARCH_EXPAND_ITEM