arXiv subjects

Andrey V. Chubukov

Publications and source records attributed to Andrey V. Chubukov.

202 records · Page 12Linked to original sources

arXiv1994

On the contrasting spin dynamics of $La_{2-x}Sr_xCuO_4$, $Nd_{2-x}Ce_xCuO_4$ and $YBa_2Cu_3O_{6+x}$ near half filling

We present simple calculations which show that incommensurability upon doping and the width of the magnetically ordered phase in Mott-Hubbard insulators depend strongly on the location of the hole/electron pockets in the Brillouin zone. For $LaSrCuO$ systems, we found the pockets at $(\pm π/2,\pm π/2)$, in which case the corrections to the antiferromagnetic spin stiffness grow with doping and destroy the commensurate antiferromagnetic ordering already at a very small doping. On the other hand, in $NdCeCuO$, the hole pockets are located at $(π,0)$ and the symmetry related points, in which case the corrections to the stiffness scale linearly with the density of carriers and do not destroy commensurate spin ordering. For $YBCuO$, systems the situation is less certain, but our results favor hole pockets at $(π/2,π/2)$. We also discuss briefly the tendency towards phase separation.

cond-mat↗

arXiv1994

Theory of Two-Dimensional Quantum Heisenberg Antiferromagnets with a Nearly Critical Ground State

We present the general theory of clean, two-dimensional, quantum Heisenberg antiferromagnets which are close to the zero-temperature quantum transition between ground states with and without long-range Néel order. For Néel-ordered states, `nearly-critical' means that the ground state spin-stiffness, $ρ_s$, satisfies $ρ_s \ll J$, where $J$ is the nearest-neighbor exchange constant, while `nearly-critical' quantum-disordered ground states have a energy-gap, $Δ$, towards excitations with spin-1, which satisfies $Δ\ll J$. Under these circumstances, we show that the wavevector/frequency-dependent uniform and staggered spin susceptibilities, and the specific heat, are completely universal functions of just three thermodynamic parameters. Explicit results for the universal scaling functions are obtained by a $1/N$ expansion on the $O(N)$ quantum non-linear sigma model, and by Monte Carlo simulations. These calculations lead to a variety of testable predictions for neutron scattering, NMR, and magnetization measurements. Our results are in good agreement with a number of numerical simulations and experiments on undoped and lightly-doped $La_{2-δ} Sr_δCu O_4$.

cond-mat↗

arXiv1994

Quantum Phase Transition in Frustrated Two-Dimensional Antiferromagnets

We study frustrated, two-dimensional, quantum antiferromagnets in the vicinity of a quantum transition from a non-collinear, magnetically-ordered ground state to a quantum disordered phase. The general scaling properties of this transition are described. A detailed study of a particular field-theoretic model of the transition, with bosonic spin-1/2 spinon fields, is presented. Explicit universal scaling forms for a variety of observables are obtained and the results are compared with numerical data on the spin-1/2 triangular antiferromagnet. Universal properties of an alternative field-theory, with confined spinons, are also briefly noted.

cond-mat↗

arXiv1993

Universal Magnetic Properties of $La_{2-δ} Sr_δ Cu O_4$ at Intermediate Temperatures

We present the theory of two-dimensional, clean quantum antiferromagnets with a small, positive, zero temperature ($T$) stiffness $ρ_s$, but with the ratio $k_B T / ρ_s $ arbitrary. Universal scaling forms for the uniform susceptibility ($χ_u$), correlation length($ξ$), and NMR relaxation rate ($1/T_1$) are proposed and computed in a $1/N$ expansion and by Monté-Carlo simulations. For large $k_B T/ρ_s$, $χ_u (T)/T$ and $Tξ(T)$ asymptote to universal values, while $1/T_{1}(T)$ is nearly $T$-independent. We find good quantitative agreement with experiments and some numerical studies on $La_{2-δ} Sr_δ Cu O_4$.

cond-mat↗