arXiv subjects

Mikhail S. Kalenkov

Publications and source records attributed to Mikhail S. Kalenkov.

28 records · Page 2Linked to original sources

arXiv2011

Crossed Andreev reflection and spin-resolved non-local electron transport

The phenomenon of crossed Andreev reflection (CAR) is known to play a key role in non-local electron transport across three-terminal normal-superconducting-normal (NSN) devices. Here we review our general theory of non-local charge transport in three-terminal disordered ferromagnet-superconductor-ferromagnet (FSF) structures. We demonstrate that CAR is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary voltages, temperature, degree of disorder, spin-dependent interface transmissions and their polarizations. We demonstrate that magnetic effects have different implications: While strong exchange field suppresses disorder-induced electron interference in ferromagnetic electrodes, spin-sensitive electron scattering at SF interfaces can drive the total non-local conductance negative at sufficiently low energies. At higher energies magnetic effects become less important and the non-local resistance behaves similarly to the non-magnetic case. Our results can be applied to multi-terminal hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.

cond-mat.supr-con↗

arXiv2011

Triplet superconductivity in a ferromagnetic vortex

We argue that odd-frequency triplet superconductivity can be conveniently realized in hybrid superconductor-ferromagnet (SF) structures with a ferromagnetic vortex. We demonstrate that due to proximity-induced long-range triplet pairing such SFS junctions can sustain appreciable supercurrent which can be directly measured in experiments.

cond-mat.supr-con↗

arXiv2010

Non-local spin-sensitive electron transport in diffusive proximity heterostructures

We formulate a quantitative theory of non-local electron transport in three-terminal disordered ferromagnet-superconductor-ferromagnet structures. We demonstrate that magnetic effects have different implications: While strong exchange field suppresses disorder-induced electron interference in ferromagnetic electrodes, spin-sensitive electron scattering at superconductor-ferromagnet interfaces can drive the total non-local conductance negative at sufficiently low energies. At higher energies magnetic effects become less important and the non-local resistance behaves similarly to the non-magnetic case. Our predictions can be directly tested in future experiments on non-local electron transport in hybrid FSF structures.

cond-mat.supr-con↗

arXiv2009

Josephson current in ballistic heterostructures with spin-active interfaces

We develop a general microscopic theory of dc Josephson effect in hybrid SNS structures with ballistic electrodes and spin-active NS interfaces. We establish a direct relation between the spectrum of Andreev levels and the Josephson current which contains complete information about non-trivial interplay between Andreev reflection and spin-dependent interface scattering. The system exhibits a rich structure of properties sensitive to spin-dependent barrier transmissions, spin-mixing angles, relative magnetization orientation of interfaces and the kinematic phase of scattered electrons. We analyze the current-phase relations and identify the conditions for the presence of a pi-junction state in the systems under consideration. We also analyze resonant enhancement of the supercurrent in gate-voltage-driven nanojunctions. As compared to the non-magnetic case, this effect can be strongly modified by spin-dependent scattering at NS interfaces.

cond-mat.supr-con↗

arXiv2008

Josephson current and Andreev states in superconductor-half metal-superconductor heterostructures

We develop a detailed microscopic theory describing dc Josephson effect and Andreev bound states in superconducting junctions with a half-metal. In such systems the supercurrent is caused by triplet pairing states emerging due to spin-flip scattering at the interfaces between superconducting electrodes and the half-metal. For sufficiently clean metals we provide a detailed non-perturbative description of the Josephson current at arbitrary transmissions and spin-flip scattering parameters for both interfaces. Our analysis demonstrates that the behavior of both the Josephson current and Andreev bound states crucially depends on the strength of spin-flip scattering showing a rich variety of features which can be tested in future experiments.

cond-mat.supr-con↗

arXiv2007

Non-local electron transport and cross-resistance peak in NSN heterostructures

We develop a microscopic theory describing the peak in the temperature dependence of the non-local resistance of three-terminal NSN devices. This peak emerges at sufficiently high temperatures as a result of a competition between quasiparticle/charge imbalance and subgap (Andreev) contributions to the conductance matrix. Both the height and the shape of this peak demonstrate the power law dependence on the superconductor thickness $L$ in contrast to the zero-temperature non-local resistance which decays (roughly) exponentially with increasing $L$. A similar behavior was observed in recent experiments.

cond-mat.supr-con↗

arXiv2007

Spin-resolved crossed Andreev reflection in ballistic heterostructures

We theoretically analyze non-local effects in electron transport across three-terminal ballistic normal-superconducting-normal (NSN) structures with spin-active interfaces. Subgap electrons entering S-electrode from one N-metal may form Cooper pairs with their counterparts penetrating from another N-metal. This phenomenon of crossed Andreev reflection is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary interface transmissions, voltages and temperatures. Our results can be applied to hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.

cond-mat.supr-con↗

arXiv2007

Crossed Andreev reflection at spin-active interfaces

With the aid of the quasiclassical Eilenberger formalism we develop a theory of non-local electron transport across three-terminal ballistic normal-superconducting-normal (NSN) devices with spin-active NS interfaces. The phenomenon of crossed Andreev reflection (CAR) is known to play the key role in such transport. We demonstrate that CAR is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary voltages, temperature, spin-dependent interface transmissions and their polarizations. Our results can be applied to multi-terminal hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.

cond-mat.supr-con↗

arXiv2007

Nonlocal Andreev reflection at high transmissions

We analyze non-local effects in electron transport across three-terminal normal-superconducting-normal (NSN) structures. Subgap electrons entering S-electrode from one N-metal may form Cooper pairs with their counterparts penetrating from another N-metal. This phenomenon of crossed Andreev reflection -- combined with normal scattering at SN interfaces -- yields two different contributions to non-local conductance which we evaluate non-perturbatively at arbitrary interface transmissions. Both these contributions reach their maximum values at fully transmitting interfaces and demonstrate interesting features which can be tested in future experiments.

cond-mat.supr-con↗

arXiv2006

Minigap, Parity Effect and Persistent Currents in SNS Nanorings

We have evaluated a proximity-induced minigap in the density of states (DOS) of SNS junctions and SNS nanorings at an arbitrary concentration of non-magnetic impurities. We have demonstrated that an isotropic energy minigap in the electron spectrum opens up already at arbitrarily weak disorder, while angle resolved DOS at higher energies can remain strongly anisotropic. The minigap value $ε_g$ can be tuned by passing a supercurrent through an SNS junction or by applying a magnetic flux $Φ$ to an SNS ring. A non-monotonous dependence of $ε_g$ on $Φ$ has been found at weak disorder. We have also studied persistent currents in isolated SNS nanorings. For odd number of electrons in the ring we have found a non-trivial current-phase (current-flux) relation which -- at relatively high disorder -- may lead to a $π$-junction state and spontaneous currents in the ground state of the system.

cond-mat.supr-con↗