arXiv subjects

T. Micklitz

Publications and source records attributed to T. Micklitz.

28 records · Page 2Linked to original sources

arXiv2009

Microscopic theory of the Andreev gap

We present a microscopic theory of the Andreev gap, i.e. the phenomenon that the density of states (DoS) of normal chaotic cavities attached to superconductors displays a hard gap centered around the Fermi energy. Our approach is based on a solution of the quantum Eilenberger equation in the regime $t_D\ll t_E$, where $t_D$ and $t_E$ are the classical dwell time and Ehrenfest-time, respectively. We show how quantum fluctuations eradicate the DoS at low energies and compute the profile of the gap to leading order in the parameter $t_D/t_E$ .

nlin.CD↗

arXiv2009

Odd Parity and Line Nodes in Non-Symmorphic Superconductors

Group theory arguments have been invoked to argue that odd parity order parameters cannot have line nodes in the presence of spin-orbit coupling. In this paper we show that these arguments do not hold for certain non-symmorphic superconductors. Specifically, we demonstrate that when the underlying crystal has a twofold screw axis, half of the odd parity representations vanish on the Brillouin zone face perpendicular to this axis. Many unconventional superconductors have non-symmorphic space groups, and we discuss implications for several materials, including UPt3, UBe13, Li2Pt3B and Na4Ir3O8.

cond-mat.supr-con↗

arXiv2009

Conductance of fully equilibrated quantum wires

We study the conductance of a quantum wire in the presence of weak electron-electron scattering. In a sufficiently long wire the scattering leads to full equilibration of the electron distribution function in the frame moving with the electric current. At non-zero temperature this equilibrium distribution differs from the one supplied by the leads. As a result the contact resistance increases, and the quantized conductance of the wire acquires a quadratic in temperature correction. The magnitude of the correction is found by analysis of the conservation laws of the system and does not depend on the details of the interaction mechanism responsible for equilibration.

cond-mat.mes-hall↗

arXiv2009

Kondo decoherence: finding the right spin model for iron impurities in gold and silver

We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a longstanding question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin and orbital degrees of freedom? Previous studies suggest a fully screened spin $S$ Kondo model, but the value of $S$ remained ambiguous. We perform density functional theory calculations that suggest $S = 3/2$. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi 1-dimensional wires to numerical renormalization group predictions for $S=1/2,1$ and 3/2, finding excellent agreement for $S=3/2$.

cond-mat.str-el↗

arXiv2009

How to measure a spinon Fermi surface

We propose an experiment to identify the potential existence of a spinon Fermi surface by looking for oscillatory coupling between two ferromagnets via a spin liquid spacer. Three candidate spin liquids are investigated, and it is found that in all cases, long period oscillations should be present, the period of which would identify the Fermi wavevector of the spinon surface.

cond-mat.str-el↗

arXiv2008

Low-energy theory of disordered interacting quantum wires

We derive an effective low-energy theory of disordered interacting quantum wires. Our theory describes Anderson localization in the limit of vanishing dephasing and reduces to standard abelian bosonization in the limit of vanishing disorder. In a system with many transport channels, it exhibits the diffusive physics characteristic for multi-channel quantum wires.

cond-mat.mes-hall↗

arXiv2007

Interface dependence of the Josephson-current fluctuations in short SNS junctions

We discuss the dependence of the Josephson current correlations in mesoscopic superconductor/normal-conductor/superconductor (SNS) devices on the transparency of the superconductor/normal-conductor (SN) interfaces. Focusing on short junctions we apply the supersymmetry method to construct an effective field theory for mesoscopic SNS devices which is evaluated in the limit of highly and weakly transparent interfaces. We show that the two-point Josephson-current correlator differs by an universal factor 2 in these two cases.

cond-mat.mes-hall↗

arXiv2007

Magnetic Field Dependence of Dephasing Rate due to Diluted Kondo Impurities

We investigate the dephasing rate, 1/tau_phi, of weakly disordered electrons due to scattering from diluted dynamical impurities. Our previous result for the weak-localization dephasing rate is generalized from diluted Kondo impurities to arbitrary dynamical defects with typical energy transfer larger than 1/tau_phi. For magnetic impurities, we study the influence of magnetic fields on the dephasing of Aharonov-Bohm oscillations and universal conductance fluctuations both analytically and using the numerical renormalization group. These results are compared to recent experiments.

cond-mat.mes-hall↗

arXiv2006

Scaling of the low temperature dephasing rate in Kondo systems

We present phase coherence time measurements in quasi-one-dimensional Ag wires doped with Fe Kondo impurities of different concentrations $n_s$. Due to the relatively high Kondo temperature $T_{K}\approx 4.3K$ of this system, we are able to explore a temperature range from above $T_{K}$ down to below $0.01 T_{K}$. We show that the magnetic contribution to the dephasing rate $γ_m$ per impurity is described by a single, universal curve when plotted as a function of $(T/T_K)$. For $T>0.1 T_K$, the dephasing rate is remarkably well described by recent numerical results for spin $S=1/2$ impurities. At lower temperature, we observe deviations from this theory. Based on a comparison with theoretical calculations for $S>1/2$, we discuss possible explanations for the observed deviations.

cond-mat.mes-hall↗

arXiv2006

Universal dephasing rate due to diluted Kondo impurities

We calculate the dephasing rate due to magnetic impurities in a weakly disordered metal as measured in a weak localization experiment. If the density n_S of magnetic impurities is sufficiently low, the dephasing rate 1/tau_phi is a universal function, 1/tau_phi = (n_S/nu) f(T/T_K), where T_K is the Kondo temperature and nu the density of states. We show that inelastic vertex corrections with a typical energy transfer Delta E are suppressed by powers of 1/(tau_phi Delta E) proportional to n_S. Therefore the dephasing rate can be calculated from the inelastic cross section proportional to pi nu Im T- |pi nu T|^2, where T is the T-matrix which is evaluated numerically exactly using the numerical renormalization group.

cond-mat.mes-hall↗