arXiv subjects

Jonathan Lux

Publications and source records attributed to Jonathan Lux.

6 recordsLinked to original sources

arXiv2017

Gigantic negative magnetoresistance in a disordered topological insulator

With the recent discovery of Weyl semimetals, the phenomenon of negative magnetoresistance (MR) is attracting renewed interest. While small negative MR can occur due to the suppression of spin scattering or weak localization, large negative MR is rare in materials, and when it happens, it is usually related to magnetism. The large negative MR in Weyl semimetals is peculiar in that it is unrelated to magnetism and comes from chiral anomaly. Here we report that there is a new mechanism for large negative MR which is not related to magnetism but is related to disorder. In the newly-synthesized bulk-insulating topological insulator TlBi$_{0.15}$Sb$_{0.85}$Te$_2$, we observed gigantic negative MR reaching 98% in 14 T at 10 K, which is unprecedented in a nonmagnetic system. Supported by numerical simulations, we argue that this phenomenon is likely due to the Zeeman effect on a barely percolating current path formed in the disordered bulk. Since disorder can also lead to non-saturating linear MR in Ag$_{2+\delta}$Se, the present finding suggests that disorder engineering in narrow-gap systems is useful for realizing gigantic MR in both positive and negative directions.

cond-mat.mes-hall↗

arXiv2017

Hyers-Ulam stability of elliptic M\"obius difference equation

The linear fractional map $ f(z) = \frac{az+ b}{cz + d} $ on the Riemann sphere with complex coefficients $ ad-bc \neq 0 $ is called M\"obius map. If $ f $ satisfies $ ad-bc=1 $ and $ -2<a+d<2 $, then $ f $ is called $\textit{elliptic}$ M\"obius map. Let $ \{ b_n \}_{n \in \mathbb{N}_0} $ be the solution of the elliptic M\"obius difference equation $ b_{n+1} = f(b_n) $ for every $ n \in \mathbb{N}_0 $. Then the sequence $ \{ b_n \}_{n \in \mathbb{N}_0} $ has no Hyers-Ulam stability.

math.CA↗

arXiv2014

Quench dynamics and statistics of measurements for a line of quantum spins in two dimensions

Motivated by recent experiments, we investigate the dynamics of a line of spin-down spins embedded in the ferromagnetic spin-up ground state of a two-dimensional xxz model close to the Ising limit. In a situation where the couplings in x and y direction are different, the quench dynamics of this system is governed by the interplay of one-dimensional excitations (kinks and holes) moving along the line and single-spin excitations evaporating into the two-dimensional background. A semiclassical approximation can be used to calculate the dynamics of this complex quantum system. Recently, it became possible to perform projective quantum measurements on such spin systems, allowing to determine, e.g., the z-component of each individual spin. We predict the statistical properties of such measurements which contain much more information than correlation functions.

cond-mat.quant-gas↗

arXiv2013

Hydrodynamic long-time tails after a quantum quench

After a quantum quench, a sudden change of parameters, generic many particle quantum systems are expected to equilibrate. A few collisions of quasiparticles are usually sufficient to establish approximately local equilibrium. Reaching global equilibrium is, however, much more difficult as conserved quantities have to be transported for long distances to build up a pattern of fluctuations characteristic for equilibrium. Here we investigate the quantum quench of the one-dimensional bosonic Hubbard model from infinite to finite interaction strength U using semiclassical methods for weak, and exact diagonalization for strong quenches. Equilibrium is approached only slowly, as t^{-1/2} with subleading corrections proportional to t^{-3/4}, consistent with predictions from hydrodynamics. We show that these long-time tails determine the relaxation of a wide range of physical observables.

cond-mat.quant-gas↗

arXiv2012

Interaction dominated transport and Coulomb drag in bilayer graphene

We investigate interaction effects in transport phenomena in bilayer graphene (BLG). For the minimal conductivity in pristine BLG, we find that the conductivity assumes a constant value in the limit $T\to 0$, with the first correction being $\propto \sqrt{T}$. This has to be contrasted from the standard $1/T^2$ in Fermi liquids (neglecting additional logarithms and above all disorder). We furthermore study the Coulomb drag resistivity between two BLGs in the whole range from deep within the Fermi liquid regime all the way to the charge neutrality (CN) point. We find that in the Fermi liquid regime drag behaves very similarly to drag in a standard two-dimensional electron gas. In contrast to monolayer graphene, we find no saturation of drag as a function of the distance $d$ for realistic parameters. In the vicinity of CN, we find an interesting interplay between interaction effects and disorder, like in the case of monolayer graphene. Here the drag resistivity strongly depends upon the ratio of the corresponding scattering times.

cond-mat.mes-hall↗

arXiv2012

Kinetic theory of Coulomb drag in two monolayers of graphene: from the Dirac point to the Fermi liquid regime

We theoretically investigate Coulomb drag in a system of two parallel monolayers of graphene. Using a Boltzmann equation approach we study a variety of limits ranging from the non-degenerate interaction dominated limit close to charge neutrality all the way to the Fermi liquid regime. In the non-degenerate limit we find that the presence of the passive layer can largely influence the conductivity of the active layer despite the absence of drag. This induces a non-trivial temperature behavior of the single layer conductivity and furthermore suggests a promising strategy towards increasing the role of inelastic scattering in future experiments. For small but finite chemical potential we find that the drag resistivity varies substantially as a function of the ratio of inelastic and elastic scattering. We find that an extrapolation from finite chemical potential to zero chemical potential and to the clean system is delicate and the order of limits matters. In the Fermi liquid regime we analyze drag as a function of temperature $T$ and the distance $d$ between the layers and compare our results to existing theoretical and experimental results. In addition to the conventional $1/d^4$-dependence with an associated $T^2$-behavior we find there is another regime of $1/d^5$-dependence where drag varies in linear-in-$T$ fashion. The relevant parameter separating these two regimes is given by $\bar{d}=T d/v_F$ ($v_F$ is the Fermi velocity), where $\bar{d} \ll1$ corresponds to $T^2$-behavior, while $\bar{d}\gg1$ corresponds to $T$-behavior.

cond-mat.mes-hall↗