Dephasing-enabled triplet Andreev conductance

Béri, Benjámin

doi:10.1103/physrevb.79.245315

Cited by 50 publications

(93 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3d), suggesting significant Andreev reflection. This conundrum may be resolved by spin-flip Andreev reflections resulting from spin-orbit coupling in the superconductor 32 , dephasing 33 , magnetization gradients 34 , and/or impurities 35 . Such processes would restore a BTK-like lineshape for split peaks on the e 2 /h plateau (Supplementary Information).…”

mentioning

confidence: 99%

Gate-tunable superconducting weak link and quantum point contact spectroscopy on a strontium titanate surface

et al. 2014

View full text Add to dashboard Cite

Two-dimensional electron systems in gallium arsenide and graphene have enabled ground-breaking discoveries in condensed-matter physics, in part because they are easily modulated by voltages on nanopatterned gate electrodes. Electron systems at oxide interfaces hold a similarly large potential for fundamental studies of correlated electrons and novel device technologies 1-3 , but typically have carrier densities too large to control by conventional gating techniques. Here we present a quantum transport study of a superconducting strontium titanate (STO) interface, enabled by a combination of electrolyte 4-7 and metal-oxide gating. Our structure consists of two superconducting STO banks flanking a nanoscale STO weak link, which is tunable at low temperatures from insulating to superconducting behaviour by a local metallic gate. At low gate voltages, our device behaves as a quantum point contact that exhibits a minimum conductance plateau of e 2 /h in zero applied magnetic field, half the expected value for spin-degenerate electrons, but consistent with predictions 8-12 and experimental signatures 13-18 of a magnetically ordered ground state. The quantum point contact mediates tunnelling between normal and superconducting regions, enabling lateral tunnelling spectroscopy of the local superconducting state. Our work provides a generic scheme for quantum transport studies of STO and other surface electron liquids.Transition metal oxides exhibit electronic ground states not seen in conventional semiconductors 2,3 . For instance, the interface between lanthanum aluminate and strontium titanate 19 -two non-magnetic band insulators-hosts superconductivity 20 and magnetism [13][14][15][16][17][18] . Rashba spin-orbit coupling at conductive STO interfaces 21 has led to predictions of unconventional superconducting states 10 , and of helical wires and Majorana fermions in nanoscale STO channels 11 . Furthermore, nanoscale lateral control of carriers could allow fabrication of gate-tunable, single-material Josephson junctions and superconducting quantum interference devices, as well as mesoscopic devices. However, few experiments on nanostructures in STO systems exist: superconductivity has been demonstrated in submicron regions tunable with a global back gate 22 , and channels sketched by a nanoscale tip show superconducting features 23 . In this work, we demonstrate the first realization of an all-STO, gate-tunable superconducting weak link. We tune our device to the ballistic 1D limit and perform superconducting spectroscopy that agrees with BCS weak-coupling expectations and previous work 24 .Undoped STO is a band insulator. Inducing a two-dimensional (2D) electron density near 10 13 cm −2 creates a metal, and several times that density creates an optimally doped superconducting state 4 . To modulate the density on this scale, we use the electric double-layer transistor technique [4][5][6][7] . A schematic of our sample is shown in Fig. 1a. A single crystal of TiO 2 -terminated (100) SrTiO 3 is patterned with ohmic conta...

show abstract

mentioning

confidence: 99%

Gate-tunable superconducting weak link and quantum point contact spectroscopy on a strontium titanate surface

et al. 2014

View full text Add to dashboard Cite

show abstract

“…Our finding can be seen in a broader context as a manifestation of Béri degeneracy of Andreev reflection eigenvalues: 29 The charge-conjugation symmetry (5.3), with (a,b) ∈ {(y,z),(x,0),(z,0)}, enforces a twofold degeneracy of the Andreev reflection eigenvalues ρ n = λ 2 n that can only be avoided if ρ n equals 0 or 1.…”

Section: Appendix C: Equality Of Conductance and Topological Invarianmentioning

confidence: 82%

Scattering theory of topological invariants in nodal superconductors

2012

View full text Add to dashboard Cite

Time-reversal invariant superconductors having nodes of vanishing excitation gap support zero-energy boundary states with topological protection. Existing expressions for the topological invariant are given in terms of the Hamiltonian of an infinite system. We give an alternative formulation in terms of the Andreev reflection matrix of a normal-metal-superconductor interface. This allows us to relate the topological invariant to the angle-resolved Andreev conductance also when the boundary state in the superconductor has merged with the continuum of states in the normal metal. A variety of symmetry classes is obtained, depending on additional unitary symmetries of the reflection matrix. We derive conditions for the quantization of the conductance in each symmetry class and test these on a model for a two-or three-dimensional superconductor with spin-singlet and spin-triplet pairing, mixed by Rashba spin-orbit interaction.

show abstract

“…This canonical form has been used in the physics context for example to prove the Kramer's degeneracy of transmission eigenvalues [17] and the degeneracy of Andreev reflection eigenvalues [18]. The problem of computing the canonical form of an even-dimensional skew-symmetric tridiagonal matrix has been discussed in [19][20][21], the reduction of the problem with on odd-dimensional matrix to the even-dimensional case in [19].…”

Section: B Tridiagonalization and The Canonical Form Of Skew-symmetrmentioning

confidence: 99%

Algorithm 923

Wimmer

2012

ACM Trans. Math. Softw.

149

View full text Add to dashboard Cite

Computing the Pfaffian of a skew-symmetric matrix is a problem that arises in various fields of physics. Both computing the Pfaffian and a related problem, computing the canonical form of a skewsymmetric matrix under unitary congruence, can be solved easily once the skew-symmetric matrix has been reduced to skew-symmetric tridiagonal form. We develop efficient numerical methods for computing this tridiagonal form based on Gauss transformations, using a skew-symmetric, blocked form of the Parlett-Reid algorithm, or based on unitary transformations, using block Householder transformations and Givens rotations, that are applicable to dense and banded matrices, respectively. We also give a complete and fully optimized implementation of these algorithms in Fortran, and also provide Python, Matlab and Mathematica implementations for convenience. Finally, we apply these methods to compute the topological charge of a class D nanowire, and show numerically the equivalence of definitions based on the Hamiltonian and the scattering matrix.

show abstract

Dephasing-enabled triplet Andreev conductance

Cited by 50 publications

References 42 publications

Gate-tunable superconducting weak link and quantum point contact spectroscopy on a strontium titanate surface

Gate-tunable superconducting weak link and quantum point contact spectroscopy on a strontium titanate surface

Scattering theory of topological invariants in nodal superconductors

Algorithm 923

Contact Info

Product

Resources

About