Sergey Slizovskiy

Magnetic fluctuations and specific heat in NaxCoO2 near a Lifshitz transition

We analyze the temperature and doping dependence of the specific heat C(T) in Na(x)CoO(2). This material was conjectured to undergo a Lifshitz-type topological transition at x=x(c)=0.62, in which a new electron Fermi pocket emerges at the Γ point, in addition to the existing hole pocket with large k(F). The data show that near x=x(c), the temperature dependence of C(T)/T at low T gets stronger as x approaches x(c) from below and then reverses the trend and changes sign at x≥x(c). We argue that this behavior can be quantitatively explained within the spin-fluctuation theory. We show that magnetic fluctuations are enhanced near x(c) at momenta around k(F), and their dynamics changes between x≤x(c) and x>x(c), when the new pocket forms. We demonstrate that this explains the temperature dependence of C(T)/T. We show that at larger x (x>0.65) the system enters a magnetic quantum critical regime where C(T)/T roughly scales as logT. This behavior extends to progressively lower T as x increases towards a magnetic instability at x≈0.75.

Cooling of chiral heat transport in the quantum Hall effect graphene

In the quantum Hall effect (QHE) regime, heat is carried by electrons in the edge states of Landau levels. Here, we study cooling of hot electrons propagating along the edge of graphene at the filling factor

Effect of paramagnetic fluctuations on a Fermi-surface topological transition in two dimensions

\nu=\pm2

Suppressed compressibility of quantum Hall effect edge states in epitaxial graphene on SiC

, mediated by acoustic phonons. We determine the temperature profile extended from a hot spot, where the Hall current is injected into graphene from a metallic contact, taking into account specifics of boundary conditions for lattice displacements in graphene in a van der Waals heterostructure with an insulating substrate. Our calculations, performed using generic boundary conditions for Dirac electrons, show that emission of phonons can explain a short cooling length observed in graphene-based QHE devices by Nahm, Hwang and Lee [PRL 110, 226801 (2013)].

Bound states of charges on top of graphene in a magnetic field

We study the Fermi-surface topological transition of the pocket-opening type in a two-dimensional Fermi liquid. We find that the paramagnetic fluctuations in an interacting Fermi liquid typically drive the transition first order at zero temperature. We first gain insight from a calculation using second-order perturbation theory in the self-energy. This is valid for weak interaction and far from instabilities. We then extend the results to stronger interaction, using the self-consistent fluctuation approximation. Experimental signatures are given in light of our results.

Nonlinear magnetization of graphene

We determine conditions for the formation of compressible stripes near the quantum Hall effect (QHE) edges of top-gated epitaxial graphene on Si-terminated SiC (G/SiC) and compare those to graphene exfoliated onto insulating substrate in the field-effect-transistor (GraFET) geometry. For G/SiC, a large density of localised surface states on SiC just underneath graphene layer and charge transfer between them lead both to doping of graphene and to screening of potential profile near its edge. This suppresses formation of compressible stripes near QHE edges in graphene, making them much narrower than the corresponding compressible stripes in GraFETs.

Magnetoresistance in Co-hBN-NiFe tunnel junctions enhanced by resonant tunneling through single defects in ultrathin hBN barriers.

We show theoretically that in the external magnetic field like charges on top of graphene monolayer may be mutually attracted to form macro-molecules. For this to happen graphene needs to be in Quantum Hall plateau state with local chemical potential being between the Landau levels. Graphene electron(s) gets localized in the middle between charges and provides overscreening of Coulomb repulsion between the charges. The size of the resulting macro-molecules is of the order of the magnetic length (

Nematic phase in a two-dimensional Hubbard model at weak coupling and finite temperature

\sim 10

Stable bound states of like charges on top of graphene in magnetic field

nm for magnetic field 10 T). The possible stable macro-molecules that unit charges can form on graphene in magnetic field are classified. The binding survives significant temperatures, exceeding mobility barriers for many ionically bond impurities. The influence of possible lattice-scale effects of valley-mixing are discussed. Tuning the doping of graphene or the magnetic field, the binding of impurities can be turned on and off and the macro-molecule size may be tuned. This opens the perspective to nanoscopic manipulation of ions on graphene by using magnetic field and gating.

Magnetic fluctuations and specific heat in Na

We compute the magnetization of graphene in amagnetic field, taking into account for generality the possibility of a mass gap. We concentrate on the physical regime where quantum oscillations are not observed due to the effect of the temperature or disorder and show that the magnetization exhibits nonlinear behavior as a function of the applied field, reflecting the strong nonanalyticity of the two-dimensional effective action of Dirac electrons. The necessary values of the magnetic field to observe this nonlinearity vary from a few teslas for very clean suspended samples to 20–30 T for good samples on substrate. In the light of these calculations, we discuss the effects of disorder and interactions as well as the experimental conditions under which the predictions can be observed.