Raman scattering as a probe of the superconducting proximity effect (original) (raw)

Observation of the superconducting proximity effect in Nb/InAs and NbN_ {x}/InAs by Raman scattering

2002

High-quality thin Nb and NbN films ͑60-100 Å͒ are grown on ͑100͒ n ϩ-InAs (nϭ10 19 cm Ϫ3) substrates by dc-magnetron sputter deposition. Studies of the electronic properties of interfaces between the superconductor and the semiconductor are done by Raman scattering measurements. The superconducting proximity effect at superconductor-semiconductor interfaces is observed through its impact on inelastic light scattering intensities originating from the near-interface region of InAs. The InAs longitudinal optical phonon LO mode (237 cm Ϫ1) and the plasmon-phonon coupled modes L Ϫ (221 cm Ϫ1) and L ϩ ͑1100 to 1350 cm Ϫ1), for n ϩ ϭ1ϫ10 19 Ϫ2ϫ10 19 cm Ϫ3 are measured. The intensity ratio of the LO mode ͑associated with the near-surface charge accumulation region, in InAs͒ to that of the L Ϫ mode ͑associated with bulk InAs͒, is observed to increase by up to 40% below the superconducting transition temperature. This temperature-dependent change in light scattering properties is only observed with high quality superconducting films and when the superconductor and the semiconductor are in good electrical contact. A few possible mechanisms of the observed effect are proposed.

Observation of the superconducting proximity effect in Nb/InAs and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:mrow mml:msub mml:mrow<mml:mi mathvariant="normal">NbNmml:mrow mml:mixmml:mo/</mml...

Physical review, 2002

Raman Scattering in High Temperature Superconductors

The detailed study of Raman Scattering in high temperature Superconductors (HTS) via using the quantum dynamical approach of double time temperature dependent phonon-Green's functions. The theory of first-order Raman scattering, second-order Raman scattering, third-order Raman scattering and electron-phonon contribution Raman scattering is investigated for high temperature superconductors. Raman tensor, intensity of Raman lines and differential cross-sections of various orders of scattering have been investigated. It has been developed using almost complete Hamiltonian which consists of the contributions due to the unperturbed phonons and electrons, anharmonic phonon fields, localized phonon fields and that of electron-phonon interactions. The temperature and defect dependencies are discussed in detail along with the nature of continues and line spectra. The phonon Raman scattering spectral density function has been obtained and analyzed for high temperature superconductors.

Phase sensitive electron-phonon coupling in a superconducting proximity structure

Physical Review B, 2009

We study the role of the superconducting proximity effect on the electron-phonon energy exchange in diffusive normal metals (N) attached to superconductors (S). The proximity effect modifies the spectral response of the normal metal, in particular the local density of states. This leads to a weakening of the electron-phonon energy relaxation. We show that the effect is easily observable with modern thermometry methods, and predict that it can be tuned in structures connected to multiple superconductors by adjusting the phase difference between superconducting order parameters at the two NS interfaces.

Near-surface InAs 2DEG on a GaAs substrate: characterization and superconducting proximity effect

2022

We have studied a near-surface two-dimensional electron gas based on an InAs quantum well on a GaAs substrate. In devices without a dielectric layer we estimated large electron mobilities on the order of 10 5 cm 2 /Vs. We have observed quantized conductance in a quantum point contact, and determined the g-factor. Using samples with an epitaxial Al layer, we defined multiple Josephson junctions and found the critical current to be gate tunable. Based on multiple Andreev reflections the semiconductor-superconductor interface is transparent, with an induced gap of 125 µeV. Our results demonstrate the viability of this platform for hybrid topological superconductor devices.

Raman scattering study of phonons in Bi-based superconductor thin films

Physica C: Superconductivity, 2004

Raman spectra were obtained from samples of Bi-Pb-Sr-Ca-Cu-O (BPSCCO) thin films after varying several growth parameters, such as covering material, annealing time (t R), annealing temperature (T R), and nominal lead content (x). Thin films with the nominal composition Bi 1.4 Pb x Sr 2 Ca 2 Cu 3 O d were grown on MgO substrates by a spray pyrolysis technique, followed by a solid state reaction. The results of Raman scattering measurements at room temperature show a series of vibrational optical modes within the range 300-900 cm À1. The assignment of these modes was made by involving mainly the 2212 and 2223 phases and was confirmed by both X-ray diffraction and resistance in dependence of the temperature (R-T) measurements as well.

Superconducting Proximity Effect in InAsSb Surface Quantum Wells with In Situ Al Contacts

We demonstrate a robust superconducting proximity effect in InAs 0.5 Sb 0.5 quantum wells grown with epitaxial Al contacts, which has important implications for mesoscopic and topological superconductivity. Unlike more commonly studied InAs and InSb semiconductors, bulk InAs 0.5 Sb 0.5 supports stronger spin−orbit coupling and a larger g-factor. However, these potentially desirable properties have not been previously measured in epitaxial heterostructures with superconductors, which could serve as a platform for fault-tolerant topological quantum computing. Through structural and transport characterization, we observe highquality interfaces and a strong spin−orbit coupling. We fabricate Josephson junctions based on InAs 0.5 Sb 0.5 quantum wells and observe a strong proximity effect. With a contact separation of 500 nm, these junctions exhibit products I c R N = 270 μV and I ex R N = 230 μV of normal resistance R N , critical current I c , and excess current I ex. Both of these quantities demonstrate a robust and long-range proximity effect with highly transparent contacts.

Anomalous Raman Scattering From Phonons and Electrons of Superconducting

Solid State …, 2010

We report interesting anomalies in the temperature dependent Raman spectra of FeSe 0.82 measured from 3K to 300K in the spectral range from 60 to 1800 cm -1 and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm -1 exhibits a sharp increase by ~ 5% in frequency below a temperature T s (~ 100K) attributed to strong spin-phonon coupling and onset of shortrange antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm -1 and 1600 cm -1 , attributed to electronic Raman scattering from (x 2 -y 2 )to xz / yz d-orbitals of Fe.

Superconductivity induced phonon anomalies in the Raman spectra of Zn and Ni doped YBa2Cu3O7

European Physical Journal B, 1994

Here we present Raman spectra of YBa2(Cul_xZnx)30 7 and YBa2(Cul_~Nix)307 as a function of temperature and Zn or Ni content. The temperature dependence of two modes at 340 and 440 cm-1 is analyzed. Similarly to the infrared measurements it is found that Zn substantially suppresses the superconductivity induced phonon softening whereas, Ni does not affect much that effect. Moreover, the superconductivity induced phonon stiffening of the 440 cm 1 mode completely disappeared with the Zn doping. We find this behaviour might support the model where Zn acts effectively as a magnetic pair breaker.

Measurement of junction conductance and proximity effect at superconductor/semiconductor junctions

Eprint Arxiv 1402 6055, 2014

The superconducting proximity effect has played an important role in recent work searching for Majorana modes in thin semiconductor devices. Using transport measurements to quantify the changes in the semiconductor caused by the proximity effect provides a measure of dynamical processes such as screening and scattering. However, in a two terminal measurement the resistance due to the interface conductance is in series with resistance of transport in the semiconductor. Both of these change, and it is impossible to separate them without more information. We have devised a new three terminal device that provides two resistance measurements that are sufficient to extract both the junction conductance and the two dimensional sheet resistance under the superconducting contact. We have compared junctions between Nb and InAs and Nb and 30% InGaAs all grown before being removed from the ultra high vacuum molecular beam epitaxy growth system. The most transparent junctions are to InAs, where the transmission coefficient per Landauer mode is greater than 0.6. Contacts made with ex-situ deposition are substantially more opaque. We find that for the most transparent junctions, the largest fractional change as the temperature is lowered is to the resistance of the semiconductor.

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