arXiv subjects

Balazs Ujfalussy

Publications and source records attributed to Balazs Ujfalussy.

6 recordsLinked to original sources

arXiv2026

Transverse Magnetic Response from Orbitally Polarized Cooper Pairs in Elemental Superconductors

We demonstrate how crystalline symmetry lowering, as for instance through strain, allows elemental superconductors such as vanadium and niobium to realize spin-singlet orbitally polarized Cooper pairs composed of electrons with identical orbital moments. Using superconducting density functional theory, we show that lowering of trigonal symmetry to $C_s$, thus keeping only a single mirror plane, activates interorbital pairing in bulk and (111) surfaces, with a pronounced surface enhancement. In a magnetic field, the resulting orbitally polarized superconducting state leads to a novel transverse magnetic response. For in--plane field orientations that break the remaining mirror symmetry, a sizable orbital magnetization emerges perpendicular to the applied field. We show that this effect is a direct consequence of equal--orbital-moment Cooper pairing, providing an experimentally accessible signature of this state. Our results establish strained elemental superconductors as a minimal material platform for superconducting orbitronics.

cond-mat.supr-con↗

arXiv2025

Quantum size effects on Andreev transport in Nb/Au/Nb Josephson junctions: A combined ab-initio and experimental study

We have measured the critical current density, superconducting coherence length, and superconducting transition temperature of single-domain, epitaxially-grown Nb(110)/Au(111)/Nb(110) trilayers, all of which show a non-monotonic dependence on the thickness of the Au layer. These results are compared with the predictions of a relativistic, ab-initio theory, which incorporates superconducting correlations. We find good agreement with experiment, coming from a rich interplay between superconducting proximity - and quantum size effects, mediated by Andreev bound states. These results suggest that quantum size effects could provide a systematic method of controlling the transport properties of superconducting multilayers.

cond-mat.supr-con↗

arXiv2021

Spin-polarized zero-bias peak from a single magnetic impurity at an s-wave superconductor: first-principles study

Magnetic impurities at surfaces of superconductors can induce bound states referred to as Yu-Shiba-Rusinov (YSR) states within superconducting gaps. Understanding of YSR states with spin-orbit coupling (SOC) plays a pivotal role in studies of Majorana zero modes. Spin polarization of a zero-bias peak (ZBP) is used to determine its topological nature. Here we investigate the YSR states of single magnetic impurities at the surface of Pb using the fully relativistic first-principles simulations including band structure of Pb and five 3$d$ orbitals of the impurity in the superconducting state. We show that for single Fe and Co impurities, strong SOC can induce a ZBP with rotation of the impurity magnetic moment and that the ZBP has large spin polarization in contrast to effective model studies. Conditions for a ZBP from a single magnetic impurity are discussed. Our results are relevant to longer atomic chains considering their canting and noncollinear magnetism.

cond-mat.supr-con↗

arXiv2020

Proximity effect in a superconductor-topological insulator heterostructure based on first principles

Superconductor-topological insulator (SC-TI) heterostructures were proposed to be a possible platform to realize and control Majorana zero-modes. Despite experimental signatures indicating their existence, univocal interpretation of the observed features demands theories including realistic electronic structures. To achieve this, we solve the Kohn-Sham-Dirac-Bogoliubov-de Gennes equations for ultrathin Bi$_2$Se$_3$ films on superconductor PdTe, within the fully relativistic Korringa-Kohn-Rostoker method, and investigate quasiparticle spectra as a function of chemical potential and film thickness. We find a strongly momentum-dependent proximity-induced gap feature where the gap sizes highly depend on characteristics of the TI states. The interface TI Dirac state is relevant to the induced gap only when the chemical potential is close to the Dirac-point energy. Otherwise, at a given chemical potential, the largest induced gap arises from the highest-energy quantum-well states, whereas the smallest gap arises from the TI topological surface state with its gap size depending on the TI pairing potential.

cond-mat.supr-con↗

arXiv2016

Prediction of superconducting transition temperatures of heterostructures based on first principles

The prediction of material-specific properties of superconducting systems such as the electronic structure and the transition temperature is one of the major challenge in modern solid-state physics. In this paper we present the first material specific calculations of realistic superconductor -- normal metal heterostructures using density functional theory. In particular, we calculate the quasiparticle spectrum of different normal metal overlayers on a Nb(100) host. We find that the Andreev reflection leads to the formation of momentum dependent quasiparticle bands in the normal metal. As a consequence, the spectrum has a strongly momentum dependent induced gap. From the thickness dependence of the gap size we calculate the superconducting critical temperature of Au/Nb(100) heterostructures where we find very good agreement with experiments. Moreover, predictions are made for similar heterostructures of other compounds.

cond-mat.supr-con↗

arXiv2006

From systems biology to dynamical neuropharmacology: proposal for a new methodology

The concepts and methods of Systems Biology are being extended to neuropharmacology, to test and design drugs against neurological and psychiatric disorders. Computational modeling by integrating compartmental neural modeling technique and detailed kinetic description of pharmacological modulation of transmitter-receptor interaction is offered as a method to test the electrophysiological and behavioral effects of putative drugs. Even more, an inverse method is suggested as a method for controlling a neural system to realize a prescribed temporal pattern. In particular, as an application of the proposed new methodology a computational platform is offered to analyze the generation and pharmacological modulation of theta rhythm related to anxiety is analyzed here in more detail.

q-bio.NC↗