Miklos Gulacsi

Electron spin resonance signal of Luttinger liquids and single-wall carbon nanotubes

A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.

Spin Gap and Luttinger Liquid Description of the NMR Relaxation in Carbon Nanotubes

Recent NMR experiments by Singer et al. [Singer, Phys. Rev. Lett. 95, 236403 (2005).] showed a deviation from Fermi-liquid behavior in carbon nanotubes with an energy gap evident at low temperatures. Here, a comprehensive theory for the magnetic field and temperature dependent NMR 13C spin-lattice relaxation is given in the framework of the Tomonaga-Luttinger liquid. The low temperature properties are governed by a gapped relaxation due to a spin gap ( approximately 30 K), which crosses over smoothly to the Luttinger liquid behavior with increasing temperature.

Inelastic Scattering from Local Vibrational Modes

We study a nonuniversal contribution to the dephasing rate of conduction electrons due to local vibrational modes. The inelastic-scattering rate is strongly influenced by multiphonon excitations, exhibiting oscillatory behavior. For higher frequencies, it saturates to a finite, coupling dependent value. In the strong-coupling limit, the phonon is almost completely softened and the inelastic cross section reaches its maximal value. This represents a magnetic-field insensitive contribution to the dephasing time in mesoscopic systems, in addition to magnetic impurities.

Incomplete protection of the surface Weyl cones of the Kondo insulator SmB 6 : Spin exciton scattering

The compound

Majorana zero modes in graphene with trigonal warping

{mathrm{SmB}}_{6}

RPA approach to supersolidity

is a Kondo insulator, where the lowest-energy bulk electronic excitations are spin-excitons. It also has surface states that are subjected to strong spin-orbit coupling. It has been suggested that

RPA Green's functions of the anisotropic Heisenberg model

{mathrm{SmB}}_{6}

Luther-Emery liquid in the NMR relaxation rate of carbon nanotubes

is also a topological insulator. Here we show that, despite the absence of time-reversal symmetry breaking and the presence of strong spin-orbit coupling, the chiral spin texture of the Weyl cone is not completely protected. In particular, we show that the spin-exciton-mediated scattering produces features in the surface electronic spectrum at energies separated from the surface Fermi energy by the spin-exciton energy. Despite the features being far removed from the surface Fermi energy, they are extremely temperature dependent. The temperature variation occurs over a characteristic scale determined by the dispersion of the spin-exciton. The structures may be observed by electron spectroscopy at low temperatures.

Ordering of correlated electrons in rare-earth compounds

We study the low energy properties of warped monolayer graphene, where the symmetry of the original honeycomb lattice reveals itself. The zero energy solutions are Majorana fermions, whose wavefunction, originating from the corresponding modified Dirac equation is spatially localized. Experimental consequences are discussed.

Pseudospin Exchange in Rare Earth Alloys

We investigate the newly discovered supersolid phase by solving in random phase approximation the anisotropic Heisenberg model of the hard-core boson He lattice. We include nearest and nextnearest neighbor interactions and calculate exactly all pair correlation functions in a cumulant expansion scheme. We describe the properties of the normal solid and supersolid phases and argue that based on analogies to the fermionic half filled extended Hubbard model the supersolid state corresponds to a bond-ordered-wave.We investigate the newly discovered supersolid phase by solving in random phase approximation the anisotropic Heisenberg model of the hard-core boson 4He lattice. We include nearest- and next-nearest-neighbor interactions and calculate exactly all pair correlation functions in a cumulant expansion scheme. Here we clarify the controversy over the role of the vacancies and defects, which have long been proposed to have a crucial role in the formation of a SS phase. We show that vacancies and interstitials will be present even at zero temperature in the supersolid phase. This phase is characterized by Bose condensation of the vacancies as well as the interstitials and may be regarded as a bond-ordered wave as it exhibits alternating strength of the expectation value of the kinetic energy term on bonds. We also show that the superfluid-to-supersolid transition is triggered by a collapsing roton minimum, however, the supersolid phase is stable against spontaneously induced superflow.