1,720,967 research outputs found
Dissipative majorana quantum wires
Get PDFIn this paper, we formulate and quantitatively examine the effect of dissipation on topological systems. We use a specific model of Kitaev quantum wire with an onsite Ohmic dissipation and perform a numerically exact method to investigate the effect of dissipation on the topological features of the system (e.g., the Majorana edge mode) at zero temperature. We find that even though the topological phase is robust against weak dissipation as it is supposed to be, it will eventually be destroyed by sufficiently strong dissipation via either a continuous quantum phase transition or a crossover depending on the symmetry of the system. The dissipation-driven quantum criticality has also been discussed.Fil: Huang, Yizhen. Shanghai Jiao Tong University; ChinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Cai, Zi. Shanghai Jiao Tong University; Chin
Parity effect in a mesoscopic Fermi gas
Get PDFWe develop a quantitative analytic theory that accurately describes the odd-even effect observed experimentally in a one-dimensional, trapped Fermi gas with a small number of particles [G. Zürn, Phys. Rev. Lett. 111, 175302 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.175302]. We find that the underlying physics is similar to the parity effect known to exist in ultrasmall mesoscopic superconducting grains and atomic nuclei. However, in contrast to superconducting nanograins, the density (Hartree) correction dominates over the superconducting pairing fluctuations and leads to a much more pronounced odd-even effect in the mesoscopic, trapped Fermi gas. We calculate the corresponding parity parameter and separation energy using both perturbation theory and a path integral framework in the mesoscopic limit, generalized to account for the effects of the trap, pairing fluctuations, and Hartree corrections. Our results are in an excellent quantitative agreement with experimental data and exact diagonalization. Finally, we discuss a few-particle to many-particle crossover between the perturbative mesoscopic regime and nonperturbative many-body physics that the system approaches in the thermodynamic limit.Fil: Hofmann, Johannes. University of Maryland; Estados UnidosFil: Lobos, Alejandro Martin. University of Maryland; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Galitski, Victor. Monash University; Australia. University of Maryland; Estados Unido
Anisotropy and spin-fluctuation effects on the spectral properties of Shiba impurities
Get PDFWe theoretically consider a quantum magnetic impurity coupled to a superconductor, and obtain the local density of states at the position of the impurity taking into account the effect of spinfluctuations and single-ion magnetic anisotropy. We particularly focus on the spectrum of subgap Yu-Shiba-Rusinov (YSR or Shiba) states induced by a quantum impurity with easy- or hard-axis uniaxial anisotropy. Although this is a relevant experimental situation in, e.g., magnetic adatoms on the surface of clean metals, it is customary that theoretical descriptions assume a classical-spin approximation which is not able to account for single-ion anisotropy and other quantum effects. Here, quantum fluctuations of the spin are taken into account in the equations of motion of the electronic Green’s function in the weak-coupling limit, and considerably modify the energy of the Shiba states compared to the classical-spin approximation. Our results point towards the importance of incorporating quantum fluctuations and anisotropy effects for the correct interpretation of scanning tunneling microscopy (STM) experiments.Fil: Andrade, J. A.. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lobos, Alejandro Martin. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Realistic indirect spin interactions between magnetic impurities on a metallic Pb(110) surface
Get PDFMotivated by recent experiments, here we study the indirect interactions between magnetic impurities deposited on top of a clean Pb(110) surface, induced by the underlying conduction electrons. Our approach makes use of ab initio calculations to characterize the clean Pb(110) surface and avoids self-consistency, a feature that greatly reduces the computational cost. In combination with second-order perturbation theory in the microscopic s-d exchange parameter Jsd between a magnetic adatom and the conduction electrons, we are able to systematically derive the Ruderman-Kittel-Kasuya-Yosida, the Dzyaloshinskii-Moriya, and the anisotropic tensor interactions emerging at the Pb(110) surface between magnetic impurities. The only adjustable parameter is Jsd, which is fitted to reproduce the experiments. Our results show important anisotropy effects arising both from the rectangular geometry of the (110) unit cell and from the strong Rashba spin-orbit interaction due to the broken inversion symmetry at the Pb(110) surface. In addition to Pb(110), the characterization of the indirect spin interactions described here could be extended to other realistic metallic surfaces for weakly coupled impurities and would enable us to fabricate atomic-size nanostructures with engineered interactions and on-demand magnetic properties, anticipating useful applications in nanotechnology.Fil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin
Spectral evolution of the SU(4) Kondo effect from the single impurity to the two-dimensional limit
Get PDFWe describe the evolution of the SU(4) Kondo effect as the number of magnetic centers increases from one impurity to the two-dimensional (2D) lattice. We derive a Hubbard-Anderson model which describes a 2D array of atoms or molecules with twofold orbital degeneracy, acting as magnetic impurities and interacting with a metallic host. We calculate the differential conductance, observed typically in experiments of scanning tunneling spectroscopy, for different arrangements of impurities on a metallic surface: a single impurity, a periodic square lattice, and several sites of a rectangular cluster. Our results point towards the crucial importance of the orbital degeneracy and agree well with recent experiments in different systems of iron(II) phtalocyanine molecules deposited on top of Au(111) [N. Tsukahara et al., Phys. Rev. Lett. 106, 187201 (2011)], indicating an experimental realization of an artificial 2D SU(4) Kondo-lattice system.Fil: Lobos, Alejandro Martin. University of Maryland. Department of Physics. Joint Quantum Institute and Condensed Matter Theory Center; Estados UnidosFil: Romero, Marcelo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Física del Litoral; ArgentinaFil: Aligia, Armando Angel. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentin
Tunneling transport in NSN Majorana junctions across the topological quantum phase transition
Get PDFWe theoretically consider transport properties of a normal metal (N)-superconducting semiconductor nanowire (S)-normal metal (N) structure (NSN) in the context of the possible existence of Majorana bound states in semiconductor–superconductor hybrid systems with spin–orbit coupling and external magnetic field. We study in detail the transport signatures of the topological quantum phase transition (TQPT) as well as the existence of the Majorana bound states in the electrical transport properties of the NSN structure. Our treatment includes the realistic non-perturbative effects of disorder, which is detrimental to the topological phase (eventually suppressing the superconducting gap completely), and the effects of the tunneling barriers (or the transparency at the tunneling NS contacts), which affect (and suppress) the zero bias conductance peak associated with the zero-energy Majorana bound states. We show that in the presence of generic disorder and barrier transparency the interpretation of the zero bias peak as being associated with the Majorana bound state is problematic since the non-local correlations between the two NS contacts at two ends may not manifest themselves in the tunneling conductance through the whole NSN structure. We establish that a simple modification of the standard transport measurements using conductance differences (rather than the conductance itself as in a single NS junction) as the measured quantity can allow direct observation of the non-local correlations inherent in the Majorana bound states. We also show that our proposed analysis of transport properties of the NSN junction enables the mapping out of the topological phase diagram (even in the presence of considerable disorder) by precisely detecting the TQPT point. We propose direct experimental studies of NSN junctions (rather than just a single NS junction) in order to establish the existence of Majorana bound states and the topological superconducting phase in semiconductor nanowires of current interest. Throughout the work we emphasize that the NSN transport properties are sensitive to both the bulk topological phase and the end Majorana bound states, and thus the NSN junction is well-suited for studying the non-local correlations between the end Majorana modes as well as the bulk TQPT itself.Fil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. University of Maryland; Estados UnidosFil: Das Sarma, S.. University of Maryland; Estados Unido
Valence fluctuations in a lattice of magnetic molecules: Application to iron(II) phtalocyanine molecules on Au(111)
Get PDFWe study theoretically a square lattice of the organometallic Kondo adsorbate iron(II) phtalocyanine (FePc) deposited on top of Au(111), motivated by recent scanning tunneling microscopy experiments. We describe the system by means of an effective Hubbard-Anderson model, where each molecule has degenerate effective d-orbitals with xz and yz symmetry, which we solve for arbitrary occupation and arbitrary on-site repulsion U. To that end, we introduce a generalized slave-boson mean-field approximation (SBMFA) which correctly describes both the non-interacting limit (NIL) U = 0 and the strongly interacting limit U → ∞, where our formalism reproduces the correct value of the Kondo temperature for an isolated FePc molecule. Our results indicate that while the isolated molecule can be described by an SU(4) Anderson model in the Kondo regime, the case of the square lattice corresponds to the intermediate-valence regime, with a total occupation of nearly 1.65 holes in the FePc molecular orbitals. Our results have important implications for the physical interpretation of the experiment.Fil: Fernández, Joaquín. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (CAB). Grupo de Teoría de Sólidos; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Aligia, Armando Ángel. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (CAB). Grupo de Teoría de Sólidos; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin
Subgap states and quantum phase transitions in one-dimensional superconductor-ferromagnetic insulator heterostructures
Get PDFWe theoretically study the spectral properties of a one dimensional semiconductor-superconductor-ferromagnetic insulator (SE-SU-FMI) hybrid nanostructure, motivated by recent experiments where such devices have been fabricated using epitaxial growing techniques. We model the hybrid structure as a one-dimensional single-channel semiconductor nanowire under the simultaneous effect of two proximity-induced interactions: superconducting pairing and a (spatially inhomogeneous) Zeeman exchange field. The coexistence of these competing mechanisms generates a rich quantum phase diagram and a complex subgap Andreev bound state (ABS) spectrum. By exploiting the symmetries of the problem, we classify the solutions of the Bogoliubov-de Gennes equations into even and odd ABS with respect to the spatial inversion symmetry x → −x. We find the ABS spectrum of the device as a function of the different parameters of the model: the length L of the coexisting SU-FMI region, the induced Zeeman exchange field h0, and the induced superconducting coherence length ξ . In particular we analyze the evolution of the subgap spectrum as a function of the length L. Interestingly, we generically find spin-polarized ABS emerging in the subgap region, which, depending on the ratio h0/, can eventually cross below the Fermi energy at certain critical values Lc, and induce spin- and fermion paritychanging quantum phase transitions. We argue that this type of device constitute a promising highly-tunableplatform to engineer subgap ABS.Fil: Feijoo, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Iucci, Carlos Aníbal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin
Influence of Rashba spin-orbit coupling on the 0-π transition and Kondo temperature in one-dimensional superconductors
No full textUsing the framework of the density-matrix renormalization group (DMRG), we study a quantum dot coupled to a superconducting nanowire with strong Rashba spin-orbit coupling. Regarding the singlet-to-doublet "0-π" transition that takes place when the Kondo effect is overcome by the superconducting gap, we show that the Rashba coupling modifies the critical values at which the transition occurs, favoring the doublet phase. In addition, using a generalized Haldane's formula for the Kondo temperature TK, we show that it is lowered by the Rashba coupling. We benchmark our DMRG results, comparing them with previous numerical renormalization group results. The good agreement obtained opens the possibility of studying chains or clusters of impurities coupled to superconductors by means of DMRG.Fil: Hamad, Ignacio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lisandrini, Franco Thomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Gazza, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin
Intermediate valence behaviour in the new Kondo lattice compound Yb3Ni5Al19
Get PDFThe physical properties of single crystals of the Kondo lattice material Yb3Ni5Al19 have been investigated by means of magnetic susceptibility, specific heat, and electrical resistivity measurements. Single-crystal x-ray diffraction measurements indicate that Yb 3Ni5Al19 adopts the Gd3Ni 5Al19 orthorhombic crystal structure. This compound exhibits intermediate valence behaviour with a characteristic energy scale TK ∼ 500 K. Calculations of ∞(T) based on the Anderson impurity model within the non-crossing approximation including crystalline electric field effects are also presented.Fil: Bauer, E. D.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Bobev, S.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Thompson, J.D.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Hundley, M.F.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Sarrao, J.L.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Aligia, Armando Ángel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin
- …
