arXiv subjects

Jairo Sinova

Publications and source records attributed to Jairo Sinova.

205 records · Page 12Linked to original sources

arXiv2001

The quantum Hall plateau transition at order 1/N

The localization behavior of noninteracting two-dimensional electrons in a random potential and strong magnetic field is of fundamental interest for the physics of the quantum Hall effect. In order to understand the emergence of power-law delocalization near the discrete extended-state energies $E_n = \hbar ω_c (n+{1/2})$, we study a generalization of the disorder-averaged Liouvillian framework for the lowest Landau level to $N$ flavors of electron densities (N=1 for the physical case). We find analytically the large-N limit and 1/N corrections for all disorder strengths: at $N = \infty$ this gives an estimate of the critical conductivity, and at order 1/N an estimate of the localization exponent $ν$. The localization properties of the analytically tractable $N \gg 1$ theory seem to be continuously connected to those of the exact quantum Hall plateau transition at $N = 1$.

cond-mat.mes-hall↗

arXiv2001

Nature and number of distinct phases in the random field Ising model

We investigate the phase structure of the random-field Ising model with a bimodal random field distribution. Our aim is to test for the possibility of an equilibrium spin-glass phase, and for replica symmetry breaking (RSB) within such a phase. We study a low-temperature region where the spin-glass phase is thought to occur, but which has received little numerical study to date. We use the exchange Monte-Carlo technique to acquire equilibrium information about the model, in particular the $P(q)$ distribution and the spectrum of eigenvalues of the spin-spin correlation matrix (which tests for the presence of RSB). Our studies span the range in parameter space from the ferromagnetic to the paramagnetic phase. We find however no convincing evidence for any equilibrium glass phase, with or without RSB, between these two phases. Instead we find clear evidence (principally from the $P(q)$ distribution) that there are only two phases at this low temperature, with a discontinuity in the magnetization at the transition like that seen at other temperatures.

cond-mat.dis-nn↗

arXiv2000

Extensive eigenvalues in spin-spin correlations: a tool for counting pure states in Ising spin glasses

We study the nature of the broken ergodicity in the low temperature phase of Ising spin glass systems, using as a diagnostic tool the spectrum of eigenvalues of the spin-spin correlation function. We show that multiple extensive eigenvalues of the correlation matrix $C_{ij}\equiv< S_i S_j>$ occur if and only if there is replica symmetry breaking. We support our arguments with Exchange Monte-Carlo results for the infinite-range problem. Here we find multiple extensive eigenvalues in the RSB phase for $N \agt 200$, but only a single extensive eigenvalue for phases with long-range order but no RSB. Numerical results for the short range model in four spatial dimensions, for $N\le 1296$, are consistent with the presence of a single extensive eigenvalue, with the subdominant eigenvalue behaving in agreement with expectations derived from the droplet model. Because of the small system sizes we cannot exclude the possibility of replica symmetry breaking with finite size corrections in this regime.

cond-mat.dis-nn↗

arXiv2000

The nature of ergodicity breaking in Ising spin glasses as revealed by correlation function spectral properties

In this work we address the nature of broken ergodicity in the low temperature phase of Ising spin glasses by examining spectral properties of spin correlation functions $C_{ij}\equiv< S_i S_j>$. We argue that more than one extensive (i.e., O(N)) eigenvalue in this matrix signals replica symmetry breaking. Monte-Carlo simulations of the infinite-range Ising spin-glass model, above and below the Almeida-Thouless line, support this conclusion. Exchange Monte-Carlo simulations for the short-range model in four dimensions find a single extensive eigenvalue and a large subdominant eigenvalue consistent with droplet model expectations.

cond-mat.dis-nn↗

arXiv2000

Disorder and interactions in quantum Hall ferromagnets near $ν=1$

We report on a finite-size Hartree-Fock study of the competition between disorder and interactions in a two-dimensional electron gas near Landau level filling factor $ν=1$. The ground state at $ν=1$ evolves with increasing disorder from a fully spin-polarized ferromagnet with a charge gap, to a partially spin-polarized ferromagnetic Anderson insulator, to a quasi-metallic paramagnet at the critical point between $i=0$ and $i=2$ quantum Hall plateaus. Away from $ν=1$, the ground state evolves from a ferromagnetic Skyrmion quasiparticle glass, to a conventional quasiparticle glass, and finally to a conventional Anderson insulator. We comment on signatures of these different regimes in low-temperature transport and NMR lineshape and peak position data.

cond-mat.mes-hall↗

arXiv2000

Skyrmion Dynamics and NMR Line Shapes in QHE Ferromagnets

The low energy charged excitations in quantum Hall ferromagnets are topological defects in the spin orientation known as skyrmions. Recent experimental studies on nuclear magnetic resonance spectral line shapes in quantum well heterostructures show a transition from a motionally narrowed to a broader `frozen' line shape as the temperature is lowered at fixed filling factor. We present a skyrmion diffusion model that describes the experimental observations qualitatively and shows a time scale of $\sim 50 μ{\rm sec}$ for the transport relaxation time of the skyrmions. The transition is characterized by an intermediate time regime that we demonstrate is weakly sensitive to the dynamics of the charged spin texture excitations and the sub-band electronic wave functions within our model. We also show that the spectral line shape is very sensitive to the nuclear polarization profile along the z-axis obtained through the optical pumping technique.

cond-mat.mes-hall↗

arXiv2000

Liouvillian Approach to the Integer Quantum Hall Effect Transition

We present a novel approach to the localization-delocalization transition in the integer quantum Hall effect. The Hamiltonian projected onto the lowest Landau level can be written in terms of the projected density operators alone. This and the closed set of commutation relations between the projected densities leads to simple equations for the time evolution of the density operators. These equations can be used to map the problem of calculating the disorder averaged and energetically unconstrained density-density correlation function to the problem of calculating the one-particle density of states of a dynamical system with a novel action. At the self-consistent mean-field level, this approach yields normal diffusion and a finite longitudinal conductivity. While we have not been able to go beyond the saddle point approximation analytically, we show numerically that the critical localization exponent can be extracted from the energetically integrated correlation function yielding $ν=2.33 \pm 0.05$ in excellent agreement with previous finite-size scaling studies.

cond-mat.mes-hall↗