arXiv subjects

Oleg Tchernyshyov

Publications and source records attributed to Oleg Tchernyshyov.

64 records · Page 4Linked to original sources

arXiv2001

Planar pyrochlore, quantum ice and sliding ice

We study quantum antiferromagnetism on the highly frustrated checkerboard lattice, also known as the square lattice with crossings. The quantum Heisenberg antiferromagnet on this lattice is of interest as a two-dimensional analog of the pyrochlore lattice magnet. By combining several approaches we conclude that this system is most likely ordered for all values of spin, $S$, with a Neel state for large $S$ giving way to a two-fold degenerate valence-bond solid for smaller $S$. We show next that the Ising antiferromagnet with a weak four-spin exchange, equivalent to square ice with the leading quantum dynamics, exhibits long range ``anti-ferroelectric'' order. As a byproduct of this analysis we obtain, in the system of weakly coupled ice planes, a sliding phase with XY symmetry.

cond-mat.stat-mech↗

arXiv2000

Dispersion of the neutron resonance in cuprate superconductors

We argue that recently measured downward dispersion of the neutron resonance peak in cuprate superconductors is naturally explained if the resonance is viewed as a spin-1 collective mode in a d-wave superconductor. The reduction of the resonant frequency away from the antiferromagnetic wave vector is a direct consequence of the momentum dependence of the d-wave superconducting gap. When the magnetic correlation length becomes large, the dispersion should become magnon-like, i.e., curve upwards from (pi,pi).

cond-mat.supr-con↗

arXiv2000

Parity (and time-reversal) anomaly in a semiconductor

The physics of a parity anomaly, potentially observable in a narrow-gap semiconductor, is revisited. Fradkin, Dagotto, and Boyanovsky have suggested that a Hall current of anomalous parity can be induced by a Peierls distortion on a domain wall. I argue that a perturbation inducing the parity anomaly must break the time reversal symmetry, which rules out the Peierls distortion as a potential cause. I list all possible perturbations that can generate the anomaly.

cond-mat.mes-hall↗

arXiv2000

Holons on a meandering stripe: quantum numbers

We attempt to access the regime of strong coupling between charge carriers and transverse dynamics of an isolated conducting ``stripe'', such as those found in cuprate superconductors. A stripe is modeled as a partially doped domain wall in an antiferromagnet (AF), introduced in the context of two different models: the t-J model with strong Ising anisotropy, and the Hubbard model in the Hartree-Fock approximation. The domain walls with a given linear charge density are supported artificially by boundary conditions. In both models we find a regime of parameters where doped holes lose their spin and become holons (charge Q=1, spin S_z=0), which can move along the stripe without frustrating AF environment. One aspect in which the holons on the AF domain wall differ from those in an ordinary one-dimensional electron gas is their transverse degree of freedom: a mobile holon always resides on a transverse kink (or antikink) of the domain wall. This gives rise to two holon flavors and to a strong coupling between doped charges and transverse fluctuations of a stripe.

cond-mat.str-el↗

arXiv1999

Search for effective models of stripes in the cuprates

We argue that effective 1D models of stripes in the cuprate superconductors can be constructed by studying ground states and elementary excitations of domain walls in 2D model antiferromagnets. This method, applied to the t-J model with Ising anisotropy, yields two such limiting cases: an ordinary 1D electron gas and a 1D gas of holons strongly coupled to transversal fluctuations of the stripe.

cond-mat.str-el↗

arXiv1999

Charged stripes from alternating static magnetic field

We motivate and perform a calculation of the energy of a cold fluid of charged fermions in the presence of a striped magnetic background. We find that a non-trivial value for the doping density on the walls is preferred

cond-mat.str-el↗

arXiv1999

Holons on a meandering stripe

To study a possible effect of transverse fluctuations of a stripe in a 2D antiferromagnet on its charge dynamics, we identify elementary excitations of a weakly doped domain wall in the Hubbard model. Hartree-Fock numerics and analysis of fermion zero modes suggest that for U>=3t charged excitations are mobile holons, Q=1, S=0. Each holon resides on a kink in the position of the domain wall. We construct a simple model in which transverse stripe dynamics is induced solely by motion of the holons. In the absence of spin excitations (spinons, Q=0, S=1/2), stripe fluctuations DO NOT suppress a tendency to form a global charge-density order.

cond-mat.str-el↗

arXiv1998

Pseudogap in 1d revisited

Two decades ago, Sadovskii found an exact solution of a model describing a pseudogap in electron energy spectrum (first introduced by Lee, Rice and Anderson). The discovery of a pseudogap in high-Tc superconductors has revived the interest to his exact solution. I review the model with the emphasis on physical content, point out an error in the original Sadovskii's solution and explain which problem he actually solved. A recent incorporation of Sadovskii's ideas into a description of "hot spots" on the Fermi surface in cuprate superconductors (Schmalian, Pines and Stojkovic) is briefly discussed.

cond-mat↗

arXiv1997

Pseudogaps: A third peak in the fermion spectral function

I present an exactly solvable model of a pseudogap with two zero-energy fermion modes coupled to each other by a classical source of frequency omega_0 and strength |Delta|. A suitably defined fermion propagator has an infinite number of poles at frequencies that are multiple integers of omega_0. In the adiabatic limit, omega_0 << |Δ|, the situation is qualitatively different from the static case omega_0=0: the residue of the pole at omega=0 (a remnant of the bare fermion) vanishes linearly with omega_0, a result that could not be anticipated by perturbation theory; the multiple poles of the propagator coalesce into a continuum instead of forming two single poles at +-|Delta|, which should be interpreted as inhomogeneous broadening of the Bogoliubov quasiparticles.

cond-mat.str-el↗

arXiv1997

Novel Phenomena in Charged Bose Liquid

We investigate charged Bose liquid immersed in uniform background charge at zero temperature. Novel phenomena, such as oscillatory shielding of external localized electric charge, rotons and charge density waves (charge stripes in two dimensions), occur in any dimensions. Oscillatory shielding is caused by mixing between scalar boson exchange and Coulomb interactions, which mediate opposite forces. On the other hand, rotons and charge density waves are due to attractive local self-interaction of bosons. Rotons can be regarded as a finite size charge density wave packet without any back flow. We also comment on charge stripes observed recently in cuprates and nickelates.

cond-mat.supr-con↗