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Register a new userThermal effects versus spin nematicity in a frustrated spin-1/2 chain
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The spin-nematic phase is an intriguing state of matter that lacks usual long-range dipolar order, yet it exhibits higher multipolar order. This makes its detection extremely difficult and controversial. Recently, nuclear magnetic resonance (NMR) has been proposed as one of the most suitable techniques to confirm its existence. We report a $^{17}$O NMR observation of the reduction of the local magnetization in the polarized state of the frustrated spin-1/2 chain $beta$-TeVO$_4$, which was previously proposed to be a fingerprint of the spin-nematic behavior. However, our detailed study shows that the detected missing fraction of the magnetization, probed by NMR frequency shift, is thermally activated, thus undermining the presence of the spin-nematic phase in the investigated compound. This highlights the importance of careful considerations of temperature-dependent NMR shift that has been overlooked in previous studies of spin nematicity.
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Motifs of periodic modulations are encountered in a variety of natural systems, where at least two rival states are present. In strongly correlated electron systems such behaviour has typically been associated with competition between short- and long-range interactions, e.g., between exchange and dipole-dipole interactions in the case of ferromagnetic thin films. Here we show that spin-stripe textures may develop also in antiferromagnets, where long-range dipole-dipole magnetic interactions are absent. A comprehensive analysis of magnetic susceptibility, high-field magnetization, specific heat, and neutron diffraction measurements unveils $beta$-TeVO$_4$ as a nearly perfect realization of a frustrated (zigzag) ferromagnetic spin-1/2 chain. Strikingly, a narrow spin stripe phase develops at elevated magnetic fields due to weak frustrated short-range interchain exchange interactions possibly assisted by the symmetry allowed electric polarization. This concept provides an alternative route for the stripe formation in strongly correlated electron systems and may help understanding other widespread, yet still elusive, stripe-related phenomena.
The low-dimensional s=1/2 compound (NO)[Cu(NO3)3] has recently been suggested to follow the Nersesyan-Tsvelik model of coupled spin chains. Such a system shows unbound spinon excitations and a resonating valence bond ground state due spin frustration. Our Raman scattering study demonstrates phonon anomalies as well as the suppression of a broad magnetic scattering continuum for temperatures below a characteristic temperature, T<T*=100K. We interpret these effects as evidence for a dynamical interplay of spin and lattice degrees of freedom that might lead to a further transition into a dimerized or structurally distorted phase at lower temperatures.
The frustrated isotropic $J_1-J_2$ model with ferromagnetic $J_1$ and anti-ferromagnetic $J_2$ interactions in presence of an axial magnetic field shows many exotic phases, such as vector chiral and multipolar phases. The existing studies of the phase boundaries of these systems are based on the indirect evidences such as correlation functions {it etc}. In this paper, the phase boundaries of these exotic phases are calculated based on order parameters and jumps in the magnetization. In the strong magnetic field, $Z_2$ symmetry is broken, therefore, order parameter of the vector chiral phase is calculated using the broken symmetry states. Our results obtained using the modified density matrix renormalization group and exact diagonalization methods, suggest that the vector chiral phase exist only in narrow range of parameter space $J_2/J_1$.
Here we study the emergence of different Symmetry-Protected Topological (SPT) phases in a spin-2 quantum chain. We consider a Heisenberg-like model with bilinear, biquadratic, bicubic, and biquartic nearest-neighbor interactions, as well as uniaxial anisotropy. We show that this model contains four different effective spin-1 SPT phases, corresponding to different representations of the $(mathbb{Z}_2 times mathbb{Z}_2) + T$ symmetry group, where $mathbb{Z}_2$ is some $pi$-rotation in the spin internal space and $T$ is time-reversal. One of these phases is equivalent to the usual spin-1 Haldane phase, while the other three are different but also typical of spin-1 systems. The model also exhibits an $SO(5)$-Haldane phase. Moreover, we also find that the transitions between the different effective spin-1 SPT phases are continuous, and can be described by a $c=2$ conformal field theory. At such transitions, indirect evidence suggests a possible effective field theory of four massless Majorana fermions. The results are obtained by approximating the ground state of the system in the thermodynamic limit using Matrix Product States via the infinite Time Evolving Block Decimation method, as well as by effective field theory considerations. Our findings show, for the first time, that different large effective spin-1 SPT phases separated by continuous quantum phase transitions can be stabilized in a simple quantum spin chain.
We report experimental and theoretical evidence that Rb$_2$Cu$_2$Mo$_3$O$_{12}$ has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin-$1/2$ chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a novel class of ferroelectricity induced by a vector spin chirality order.
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