Quasiclassical theory of charge transport across mesoscopic normal-metal–superconducting heterostructures with current conservation

Seja, Kevin Marc; Löfwander, Tomas

doi:10.1103/physrevb.104.104502

Cited by 13 publications

(21 citation statements)

References 58 publications

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“…For finite transparency, there is a jump between reservoir temperatures and right-and left-mover temperatures, determined by the thermal resistance of the barrier. The temperatures T eff, → ← are analogues of the right-moving and left-moving quasipotentials, φ→ ← (x), appearing in a voltage bias set-up [41]. We note that the example in Fig.…”

Section: Calculation Schemementioning

confidence: 94%

“…In this paper, however, we assume a spin-degenerate system and spin singlet d-wave superconductivity. In practice [41][42][43], we use the so-called Riccati parametrization of all elements in Eqs. ( 3)-( 4), to solve Eq.…”

Section: B Methodsmentioning

confidence: 99%

“…There is a freedom to parameterize the Keldysh Green's function ĝK (p F , R, ε) in terms of different distribution functions. As we discussed in Ref [41], one choice that is appealing when interpreting results is to use the distribution matrix f (p F , R, ε),…”

Section: B Methodsmentioning

confidence: 99%

“…As we discussed in some detail in Ref. [41], this means that the dwell time for injected non-equilibrium quasiparticles is short compared to time scales of inelastic scattering processes in the superconductor, and final relaxation takes place far inside the normal metal contact reservoirs. Here we consider relatively small nano-devices with L S < 100ξ 0 , where this can be met.…”

Section: A Modelmentioning

confidence: 99%

“…In this work we consider the thermoelectric effect in d-wave superconductors with impurities scattering with an intermediate phase shift [34,40]. Building on our recent, fully self-consistent calculations of charge flow and charge imbalance in superconducting devices with normal metal leads [41], we study a d-wave superconductor between two normal metal reservoirs with a temperature bias ∆T , see Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

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Thermopower and thermophase in a $d$-wave superconductor

Seja,

Jacob,

Löfwander

2021

Preprint

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In an unconventional superconductor impurities may scatter electron-like and hole-like quasiparticles differently. Such electron-hole asymmetry appears when the impurity scattering phase shift is intermediate between the Born and unitary limits and leads to an expectation for large thermoelectric effects. Here, we examine the thermoelectric response of a d-wave superconductor connected to normal-metal reservoirs under a temperature bias using a fully self-consistent quasiclassical theory. The thermoelectrically induced quasiparticle current is cancelled by superflow in an open circuit set-up, but at the cost of a charge imbalance induced at the contacts and extending across the structure. We investigate the resulting thermopower and thermophase and their dependencies on scattering phase shift, mean free path, and interface transparency. For crystal-axis orientations such that surface-bound zero-energy Andreev states are formed, the thermoelectric effect is reduced as a result of locally reduced electron-hole asymmetry. For a semiballistic superconductor with good contacts we find thermopowers of order several µV /K, suggesting a thermovoltage measurement as a promising path to investigate thermoelectricity in unconventional superconductors.

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Section: Calculation Schemementioning

confidence: 94%

Section: B Methodsmentioning

confidence: 99%

Section: B Methodsmentioning

confidence: 99%

Section: A Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermopower and thermophase in a $d$-wave superconductor

Seja,

Jacob,

Löfwander

2021

Preprint

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Self-consistent theory of current injection into d and d + is superconductors

Seja

Löfwander

2022

J. Phys.: Condens. Matter

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We present results for the steady-state nonlinear response of a dx2-y2 superconducting ﬁlm connected to normal-metal reservoirs under voltage bias, allowing for a subdominant s-wave component appearing near the interfaces. Our investigation is based on a current-conserving theory that self-consistently includes the non-equilibrium distribution functions, charge imbalance, and the voltage-dependencies of order parameters and scalar impurity self-energies. For a pure d-wave superconductor with [110] orientation of the interfaces to the contacts, the conductance contains a zero-bias peak reﬂecting the large density of zero-energy interface Andreev bound states. Including a subdominant s-wave pairing channel, it is in equilibrium energetically favorable for an s-wave order parameter component ∆sto appear near the interfaces in the time-reversal symmetry breaking combination d + is. The Andreev states then shift to ﬁnite energies in the density of states. Under voltage bias, we ﬁnd that the non-equilibrium distribution in the contact area causes a rapid suppression of the s-wave component to zero as the voltage eV → ∆s. The resulting spectral rearrangements and voltage-dependent scattering amplitudes lead to a pronounced non-thermally broadened split of the zero-bias conductance peak that is not seen in a non-selfconsistent Landauer-Büttiker scattering approach.

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Feasibility of a Fulde-Ferrell-Larkin-Ovchinnikov superfluid Fermi atomic gas

Taira

Ōhashi²

2022

Phys. Rev. A

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We theoretically investigate a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type superfluid phase transition in a driven-dissipative two-component Fermi gas. The system is assumed to be in the non-equilibrium steady state, which is tuned by adjusting the chemical potential difference between two reservoirs that are coupled with the system. Including pairing fluctuations by extending the strong-coupling theory developed in the thermal-equilibrium state by Nozières and Schmitt-Rink to this non-equilibrium case, we show that a non-equilibrium FFLO (NFFLO) phase transition can be realized without spin imbalance, under the conditions that (1) the two reservoirs imprint a two-edge structure on the momentum distribution of Fermi atoms, and (2) the system is loaded on a threedimensional cubic optical lattice. While the two edges work like two Fermi surfaces with different sizes, the role of the optical lattice is to prevent the NFFLO long-range order from destruction by NFFLO pairing fluctuations. We also draw the non-equilibrium mean-field phase diagram in terms of the chemical potential difference between the two reservoirs, a fictitious magnetic field to tune the spin imbalance of the system, and the environmental temperature of the reservoirs, to clarify the relation between the NFFLO state and the ordinary thermal-equilibrium FFLO state discussed in spin-imbalanced Fermi gases.

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Quasiclassical theory of charge transport across mesoscopic normal-metal–superconducting heterostructures with current conservation

Cited by 13 publications

References 58 publications

Thermopower and thermophase in a $d$-wave superconductor

Thermopower and thermophase in a $d$-wave superconductor

Self-consistent theory of current injection into d and d + is superconductors

Feasibility of a Fulde-Ferrell-Larkin-Ovchinnikov superfluid Fermi atomic gas

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