Diamagnetism of metallic nanoparticles as the result of strong spin-orbit interaction

The magnetic susceptibility of an ensemble of clean metallic nanoparticles is shown to change from paramagnetic to diamagnetic one with the onset of spin-orbit interaction. The effect is quantified on the basis of symmetry analysis with the help of the random matrix theory. In particular, the magnetic susceptibility is investigated as the function of symmetry breaking parameter representing magnetic flux in the crossover from symplectic to unitary and from orthogonal to unitary ensembles. Corresponding analytical and numerical results provide a qualitative explanation to the experimental data on diamagnetism of an ensemble of gold nanorods.Comment: 6 pages, 5 figures; extended versio

Enhanced Screening in Chemically Functionalized Graphene

Resonant scatterers such as hydrogen adatoms can strongly enhance the low energy density of states in graphene. Here, we study the impact of these impurities on the electronic screening. We find a two-faced behavior: Kubo formula calculations reveal an increased dielectric function $\varepsilon$ upon creation of midgap states but no metallic divergence of the static $\varepsilon$ at small momentum transfer $q\to 0$. This bad metal behavior manifests also in the dynamic polarization function and can be directly measured by means of electron energy loss spectroscopy. A new length scale $l_c$ beyond which screening is suppressed emerges, which we identify with the Anderson localization length.Comment: 5 pages, 4 figure

Magnon activation by hot electrons via non-quasiparticle states

We consider the situation when a femtosecond laser pulse creates a hot electron state in half-metallic ferromagnet (e. g. ferromagnetic semiconductor) on a picosecond timescale but do not act directly on localized spin system. We show that the energy and magnetic moment transfer from hot itinerant electrons to localized spins is facilitated by the so-called non-quasiparticle states, which are the scattering states of a magnon and spin-majority electron. The magnon distribution is described by a quantum kinetic equation that we derive using the Keldysh diagram technique. In a typical ferromagnetic semiconductor such as EuO magnons remain essentially in non-equilibrium on a scale of the order of microsecond after the laser pulse.Comment: 8 pages, 2 figure

Adhesion and electronic structure of graphene on hexagonal boron nitride substrates

We investigate the adsorption of graphene sheets on h-BN substrates by means of first-principles calculations in the framework of adiabatic connection fluctuation-dissipation theory in the random phase approximation. We obtain adhesion energies for different crystallographic stacking configurations and show that the interlayer bonding is due to long-range van der Waals forces. The interplay of elastic and adhesion energies is shown to lead to stacking disorder and moir\'e structures. Band structure calculations reveal substrate induced mass terms in graphene which change their sign with the stacking configuration. The dispersion, absolute band gaps and the real space shape of the low energy electronic states in the moir\'e structures are discussed. We find that the absolute band gaps in the moir\'e structures are at least an order of magnitude smaller than the maximum local values of the mass term. Our results are in agreement with recent STM experiments.Comment: 8 pages, 8 figures, revised and extended version, to appear in Phys. Rev.

Mechano-electric heterogeneity of the myocardium as a paradigm of its function

Myocardial heterogeneity is well appreciated and widely documented, from sub-cellular to organ levels. This paper reviews significant achievements of the group, led by Professor Vladimir S. Markhasin, Russia, who was one of the pioneers in studying and interpreting the relevance of cardiac functional heterogeneity

Many-Spin Effects and Tunneling Properties of Magnetic Molecules

Spin tunneling in molecular magnets has attracted much attention, however theoretical considerations of this phenomenon up to now have not taken into account the many-spin nature of molecular magnets. We present, to our knowledge, the first successful attempt of a realistic calculation of tunneling splittings for Mn$_{12}$ molecules, thus achieving a quantitatively accurate many-spin description of a real molecular magnet in the energy interval ranging from about 100 K down to 10$^{-12}$ K. Comparison with the results of the standard single-spin model shows that many-spin effects affect the tunneling splittings considerably. The values of ground state splitting given by single-spin and many-spin models differ from each other by a factor of five.Comment: 3REVTeX pages, 2 figure

Transport Properties through Double Barrier Structure in Graphene

The mode-dependent transmission of relativistic ballistic massless Dirac fermion through a graphene based double barrier structure is being investigated for various barrier parameters. We compare our results with already published work and point out the relevance of these findings to a systematic study of the transport properties in double barrier structures. An interesting situation arises when we set the potential in the leads to zero, then our 2D problem reduces effectively to a 1D massive Dirac equation with an effective mass proportional to the quantized wave number along the transverse direction. Furthermore we have shown that the minimal conductivity and maximal Fano factor remain insensitive to the ratio between the two potentials V_2/V_1=\alpha.Comment: 18 pages, 12 figures, clarifications and reference added, misprints corrected. Version to appear in JLT

Thermodynamics of quantum crystalline membranes

We investigate the thermodynamic properties and the lattice stability of two-dimensional crystalline membranes, such as graphene and related compounds, in the low temperature quantum regime $T\rightarrow0$. A key role is played by the anharmonic coupling between in-plane and out-of plane lattice modes that, in the quantum limit, has very different consequences than in the classical regime. The role of retardation, namely of the frequency dependence, in the effective anharmonic interactions turns out to be crucial in the quantum regime. We identify a crossover temperature, $T^{*}$, between classical and quantum regimes, which is $\sim 70 - 90$ K for graphene. Below $T^{*}$, the heat capacity and thermal expansion coefficient decrease as power laws with decreasing temperature, tending to zero for $T\rightarrow0$ as required by the third law of thermodynamics.Comment: 13 pages, 1 figur