arXiv subjects

K. Yu. Povarov

Publications and source records attributed to K. Yu. Povarov.

43 records · Page 3Linked to original sources

arXiv2015

Electron spin resonance in a model S=1/2 chain antiferromagnet with a uniform Dzyaloshinskii--Moriya interaction

The electron spin resonance spectrum of a quasi 1D S=1/2 antiferromagnet K2CuSO4Br2 was found to demonstrate an energy gap and a doublet of resonance lines in a wide temperature range between the Curie--Weiss and Neèl temperatures. This type of magnetic resonance absorption corresponds well to the two-spinon continuum of excitations in S=1/2 antiferromagnetic spin chain with a uniform Dzyaloshinskii--Moriya interaction between the magnetic ions. A resonance mode of paramagnetic defects demonstrating strongly anisotropic behavior due to interaction with spinon excitations in the main matrix is also observed.

cond-mat.str-el↗

arXiv2015

Scaling of temporal correlations in an attractive Tomonaga-Luttinger spin liquid

We report temperature-dependent neutron scattering measurements of the local dynamic structure factor in the quantum spin ladder (C$_{7}$H$_{10}$N)$_{2}$CuBr$_{4}$ in a magnetic field $H=9$~T, in its gapless quantum-critical phase. We show that the measured quantity has a scaling form consistent with expectations for a Tomonaga-Luttinger liquid with attraction. The measured Luttinger parameter $K\approx1.25$ and scaling function are in excellent agreement with density matrix renormalization group numerical calculations for the underlying spin Hamiltonian.

cond-mat.str-el↗

arXiv2014

High-field magnetic resonance of spinons and magnons in a triangular lattice S=1/2 antiferromagnet Cs2CuCl4

The electron spin resonance doublet indicating the width of the two spinon continuum in a spin-1/2 triangular-lattice Heisenberg antiferromagnet Cs2CuCl4 was studied in high magnetic field. The doublet was found to collapse in a magnetic field of a half of the saturation field. The collapse of the doublet occurs via vanishing of the high frequency component in a qualitative agreement with the theoretical prediction for the S=1/2 chain. The field of the collapse is, however, much lower than expected for the S=1/2 chain. This is proposed to be due to the destruction of frustration of interchain exchange bonds in a magnetic field, which restores the 2D character of this spin system. In the saturated phase the mode with the Larmor frequency and a much weaker mode downshifted for 119~GHz are observed. The weak mode is of exchange origin, it demonstrates a positive frequency shift at heating corresponding to the repulsion of magnons in the saturated phase.

cond-mat.str-el↗

arXiv2014

The tunable quantum spin ladder Cu(Qnx)(Cl$_{(1-x)}$Br$_{x}$)$_{2}$

We report magnetic, specific heat and ESR measurements on a series of $S=1/2$ spin ladder compounds Cu(Qnx)(Cl$_{(1-x)}$Br$_{x}$)$_{2}$. Down to $T=2$ K all the observables can be described by the spin ladder model with about 1% of $S=1/2$ impurities in the background, which are present even in a nominally pure Cu(Qnx)Cl$_{2}$ and Cu(Qnx)Br$_{2}$, for the whole range of $0\leq x\leq1$. We extract ladder exchange constants $J_{l}(x)$ and $J_{r}(x)$ as well as the gap value $Δ(x)$ by comparing the experimental data to quantum Monte-Carlo simulations. As the ESR measurements show the $g$-factor of impurities to be precisely equal to $g$-factor of the ladder spins, we suppose the impurities to be the consequence of structural defects resulting in a broken ladder ends.

cond-mat.str-el↗

arXiv2013

Switching of anisotropy and phase diagram of a Heisenberg square lattice S=1/2 antiferromagnet Cu(pz)2(ClO4)2

Experiments in the antiferromagnetic phase of a quasi 2D $S=1/2$ quasi-square lattice antiferromagnet Cu(pz)2(ClO4)2 reveal a biaxial type of the anisotropy, instead of the easy-plane one, considered before. The weak in-plane anisotropy, found by means of electron spin resonance spectroscopy and magnetization measurements, is about an order of magnitude weaker, than the off-plane anisotropy. The weak in-plane anisotropy results in a spin-flop phase transition for the magnetic field aligned along easy axis, and, thereby, in a bicritical point on the phase diagram. A remarkable feature of the weak in-plane anisotropy is the abrupt change of its sign at the spin-flop point. This anisotropy switching disappears at the tilting of magnetic field to the easy axis by the angle of 10$^\circ$ within the plane. The nature of the abrupt anisotropy reversal remains unclear. The phase diagram is characterized by the increase of the ordering temperature in the magnetic field used, except for a dip near the bicritical point.

cond-mat.str-el↗

arXiv2012

Magnetic resonance in the ordered phases of the 2D frustrated quantum magnet Cs2CuCl4

The temperature evolution of the electron spin resonance is studied at cooling the crystal samples of Cs2CuCl4 through the Neel point 0.62 K. A coexistence of the high-frequency spinon type resonance developed in the spin-liquid phase and of the low-frequency antiferromagnetic resonance was found in the ordered phase. The low-frequency magnetic resonance spectrum in the low field range has two gapped branches and corresponds well to the spectrum of spin excitations of a planar spiral spin structure with two axes of the anisotropy. The field induced phase transitions result in a more complicated low-frequency spectra.

cond-mat.str-el↗

arXiv2011

Modes of magnetic resonance in the spin liquid phase of Cs2CuCl4

We report the observation of a frequency shift and splitting of the electron spin resonance (ESR) mode of the low-dimensional S=1/2 frustrated antiferromagnet Cs2CuCl4 in the spin-correlated state below the Curie-Weiss temperature 4 K but above the ordering temperature 0.62 K. The shift and splitting exhibit strong anisotropy with respect to the direction of the applied magnetic field and do not vanish in zero field. The low-temperature evolution of spin resonance response is a result of the specific modification of one-dimensional spinon continuum under the action of the uniform Dzyaloshinskii-Moriya interaction (DM) within the spin chains. Parameters of the uniform DM interaction are derived from the experiment.

cond-mat.str-el↗