Presence Of Frustration Research Articles

Structural magnetic glassiness in the spin ice Dy2Ti2O7

The spin ice compound Dy$_2$Ti$_2$O$_7$ is well-known to realise a three-dimensional Coulomb spin liquid with magnetically charged monopole excitations. Its fate at low temperatures, however, remains an intriguing open question. Based on a low-temperature analysis of the magnetic noise and diffuse neutron scattering under different cooling protocols, combined with extensive numerical modelling, we argue that upon cooling, the spins freeze into what may be termed a `structural magnetic glass', without an a priori need for chemical or structural disorder. Specifically, our model indicates the presence of frustration on two levels, first producing a near-degenerate constrained manifold inside which phase ordering kinetics is in turn frustrated. Our results suggest that spin ice Dy$_2$Ti$_2$O$_7$ provides one prototype of magnetic glass formation specifically, and a setting for the study of kinetically constrained systems more generally.

Exploiting localized transition waves to tune sound propagation in soft materials

Programmable materials hold great potential for many applications such as deployable structures, soft robotics, and wave control; however, the presence of instability and disorder might hinder their utilization. Through a combination of analytical, numerical, and experimental analyses, we harness the interplay between instabilities, geometric frustration, and mechanical deformations to control the propagation of sound waves within self-assembled soft materials. We consider levitated magnetic disks confined by a magnetic boundary in-plane. The assemblies can be either ordered or disordered depending on the intrinsic disk symmetry. By applying an external load to the assembly, we observe the nucleation and propagation of different topological defects within the lattices. In the presence of instabilities, the defect propagation gives rise to time-independent localized transition waves. Surprisingly, in the presence of frustration, the applied load briefly introduces deformation-induced order to the material. By further deforming the lattices, new patterns emerge across all disk symmetries. We utilize these patterns to tune sound propagation through the material. Our findings could open new possibilities for designing exotic materials with potential applications ranging from sound control to soft robotics.

Magnetoelectric and multiferroic properties of spinels

In the last two decades, significant progress has been made in combining ferroelectricity and magnetism in the same material. Usually, magnetism and ferroelectricity were thought of as independent phenomena. However, the discovery of spin-induced ferroelectricity with a strong coupling between magnetism and electric polarization is intriguing. Whether they interact non-trivially is determined by the symmetries of the crystal lattice and the appearing magnetic structure, which, in turn, depends on the nature of magnetic ions, their exchange, and anisotropic interactions, the presence of frustration, etc. Several structural families of compounds exhibiting magnetoelectric (ME) or multiferroic properties have already been reported. This paper gives an account of the richness of structure, magnetism, magnetoelectric and multiferroic properties of spinels. After presenting symmetry aspects of the crystal and magnetic structures of spinels related to these phenomena, we give several examples of magnetoelectric and multiferroic spinels explaining the relations between magnetism and electric polarization and discuss their future perspectives.

Interplay of mass imbalance and frustration in correlated band insulators

We report the emergence or broadening of exotic magnetic metallic phases upon explicit breaking of $SU(2)$ symmetry by introduction of mass imbalance in a variant of Hubbard model, known as the ionic Hubbard model in the presence of frustration at half-filling on a square lattice. The ionic Hubbard model has in addition to hopping($\sim t$) and onsite coulomb repulsion ($\sim U$), a staggered ionic potential ($\sim \Delta$) which breaks translational symmetry of the underlying lattice. In the low to intermediate ranges of $U$ and $\Delta$, we use unrestricted Hartree-Fock theory to construct the phase diagram in the $U-\Delta$ plane for a fixed mass imbalance($\sim\eta$). Where as in the limit where both $U,\Delta$ are comparable and much larger than the first $(\sim t_{\sigma})$ and second $(\sim t_{\sigma}')$ neighbor hopping amplitudes , we employ the technique of generalized Gutzwiller approximation and subsequently use renormalized mean field theory to construct the phase diagram for varying values of hopping asymmetry. In both cases, starting from a correlated band insulator with weak antiferromagnetic spin density wave order, if we tune $U/\Delta$, we observe the opening of novel magnetically ordered metallic phases such as spin imbalanced ferromagnetic metal, ferrimagnetic metal and antiferromagnetic half metal. We also study singlet superconductivity in the d-wave and extended s-wave channels in the strong coupling limit of this model in the presence of mass imbalance.

Nonlinear stability of stationary solutions to the Kuramoto-Sakaguchi equation with frustration

<p style='text-indent:20px;'>We study measurable stationary solutions for the kinetic Kuramoto-Sakaguchi (in short K-S) equation with frustration and their stability analysis. In the presence of frustration, the total phase is not a conserved quantity anymore, but it is time-varying. Thus, we can not expect the genuinely stationary solutions for the K-S equation. To overcome this lack of conserved quantity, we introduce new variables whose total phase is conserved. In the transformed K-S equation in new variables, we derive all measurable stationary solution representing the incoherent state, complete and partial phase-locked states. We also provide several frameworks in which the complete phase-locked state is stable, whereas partial phase-locked state is semi-stable in the space of Radon measures. In particular, we show that the incoherent state is nonlinearly stable in a large frustration regime, whereas it can exhibit stable behavior or concentration phenomenon in a small frustration regime.

PROFESSIONAL BURNOUT FACTORS IN PHYSICIANS OF POLYCLINICS

Introduction. The presence of burnout syndrome in health workers has an impact on the effectiveness of their professional activities. Objective. Identification of actors of burnout in physicians of polyclinic institutions. Materials and methods. The study involved 62 general practitioners from the polyclinic institutions of the city of Arkhangelsk. There were used such methods as “The questionnaire for burnout detection” (K. Maslach); questionnaire “ Attitude to work and professional “burnout” by V.A. Vinokur; test “11 personality factors”; technique “Coping behavior in stressful situations” by T.L. Kryukova; profile A. Meyer for the study of organizational conditions, job satisfaction and professional development; questionnaire on socio-demographic characteristics. Results. 72.5% of physicians were established to be characterized by a high level of professional burnout. The most significant contribution to the development of burnout is made by components such as low self-esteem of both overall health and adaptation, emotional exhaustion and professional perfectionism. Socio-demographic factors of burnout in physicians include: age (35 years), the lack of children, work experience in the specialty (average - 10 years), the number of received patients per day (up to 10 and more than 41 patient), the lack of additional work in the hospital; personal factors: the low level of the sensitiveness, moral flexibility, the use of emotionally-focused coping and search for social support; organizational factors: dissatisfaction with the content of professional activity, the presence of frustration at work, dissatisfaction with wages, lack of possibility of training and further professional development, as well as tiring working conditions. Conclusion. For 2/3 of physicians of polyclinic institutions show the high levels of burnout manifested by low self-esteem of both overall health and adaptation, emotional exhaustion and professional perfectionism. The appearance of burnout syndrome among physicians is influenced by socio-demographic, personal and organizational factors.

Robustness in the instability of the incoherent state for the Kuramoto-Sakaguchi-Fokker-Planck equation with frustration

We study the robustness in the nonlinear instability of the incoherent state for the Kuramoto-Sakaguchi-Fokker-Planck (KS-FP for short) equation in the presence of frustrations. For this, we construct a new unstable mode for the corresponding linear part of the perturbation around the incoherent state, and we show that the nonlinear perturbation stays close to the unstable mode in some small time interval which depends on the initial size of the perturbations. Our instability results improve the previous results on the KS-FP with zero frustration [J. Stat. Phys. 160 (2015), pp. 477–496] by providing a new linear unstable mode and detailed energy estimates.

Emergence of Phase-Locking in the Kuramoto Model for Identical Oscillators with Frustration

We present an exponential synchronization for the finite-dimensional Kuramoto model for identical oscillators under the effect of frustration. In the presence of frustration, the total phase balance law and gradient-flow structure are destroyed. Hence the gradient flow approach cannot be applied for the emergence of phase-locking, and the Lyapunov functional approach based on $\ell^2$-energy and phase diameter only show some results in a restricted set of initial configurations smaller than a half circle. In this paper, we show that an initial phase configuration whose order parameter is bounded below by some positive value, which is only depending on the size of frustration, leads to the complete phase synchronization or the bipolar state exponentially fast. This extends earlier results on the asymptotic phase-locking for the identical oscillators in which initial phase configurations are confined in a half circle.

Thermally stable multipartite entanglements in the frustrated Heisenberg hexagon

Thermally stable quantum states with multipartite entanglements led by frustration are found in the antiferromagnetic spin-1/2 Heisenberg hexagon. The model has been solved exactly to obtain all analytic expressions of eigenvalues and eigenfunctions. Detection and characterizations for various types of entanglements have been carried out in terms of concurrence and entanglement witnesses based on several thermodynamic observables. Variations of entanglement properties with respect to temperature and frustration are discussed. Even though the frustration opposes the bipartite entanglement, it favors the multipartite entanglement. Entangled states exhibit robustness against the thermal effects in the presence of frustration and they are found to survive at any temperature.

Magnetocaloric Effect and Frustrations in One-Dimensional Magnets

In this paper, we investigated the magnetocaloric effect (MCE) in one-dimensional magnets with different types of ordering in the Ising model, Heisenberg, XY-model, the standard, planar, and modified Potts models. Exact analytical solutions to MCE as functions of exchange parameters, temperature, values and directions of an external magnetic field are obtained. The temperature and magnetic field dependences of MCE in the presence of frustrations in the system in a magnetic field are numerically computed in detail.

Quantum phase transition as an interplay of Kitaev and Ising interactions

We study the interplay between the Kitaev and Ising interactions on both ladder and two dimensional lattices. We show that the ground state of the Kitaev ladder is a symmetry-protected topological (SPT) phase, which is protected by a $\mathbb{Z}_2 \times \mathbb{Z}_2$ symmetry. It is confirmed by the degeneracy of the entanglement spectrum and non-trivial phase factors (inequivalent projective representations of the symmetries), which are obtained within infinite matrix-product representation of numerical density matrix renormalization group. We derive the effective theory to describe the topological phase transition on both ladder and two-dimensional lattices, which is given by the transverse field Ising model with/without next-nearest neighbor coupling. The ladder has three phases, namely, the Kitaev SPT, symmetry broken ferro/antiferromagnetic order and classical spin-liquid. The non-zero quantum critical point and its corresponding central charge are provided by the effective theory, which are in full agreement with the numerical results, i.e., the divergence of entanglement entropy at the critical point, change of the entanglement spectrum degeneracy and a drop in the ground-state fidelity. The central charge of the critical points are either c=1 or c=2, with the magnetization and correlation exponents being 1/4 and 1/2, respectively. In the absence of frustration, the 2D lattice shows a topological phase transition from the $\mathbb{Z}_2$ spin-liquid state to the long-range ordered Ising phase at finite ratio of couplings, while in the presence of frustration, an order-by-disorder transition is induced by the Kitaev term. The 2D classical spin-liquid phase is unstable against the addition of Kitaev term toward an ordered phase before the transition to the $\mathbb{Z}_2$ spin-liquid state.

Thermodynamics of a bad metal-Mott insulator transition in the presence of frustration.

Thermodynamic properties of the Hubbard model on the anisotropic triangular lattice at half filling are calculated by the finite-temperature Lanczos method. The charge susceptibility exhibits clear signatures of a Mott metal-insulator transition. The metallic phase is characterized by a small charge susceptibility, large entropy, large renormalized quasiparticle mass, and large spin susceptibility. The fluctuating local magnetic moment in the metallic phase is large and comparable to that in the insulating phase. These bad metallic characteristics occur above a relatively low coherence temperature, as seen in organic charge transfer salts.

Divide and conquer the Hilbert space of translation-symmetric spin systems

Iterative methods that operate with the full Hamiltonian matrix in the untrimmed Hilbert space of a finite system continue to be important tools for the study of one- and two-dimensional quantum spin models, in particular in the presence of frustration. To reach sensible system sizes such numerical calculations heavily depend on the use of symmetries. We describe a divide-and-conquer strategy for implementing translation symmetries of finite spin clusters, which efficiently uses and extends the "sublattice coding" of H. Q. Lin [Phys. Rev. B 42, 6561 (1990)]. With our method, the Hamiltonian matrix can be generated on-the-fly in each matrix vector multiplication, and problem dimensions beyond 10^{11} become accessible.

Investigation of critical phenomena and magnetism in amorphous Ising nanowire in the presence of transverse fields

A cylindrical magnetic nanowire system composed of ferromagnetic core and shell layers has been investigated by using effective field theory (EFT) with correlations in the presence of transverse fields and surface shell amorphization. Both weak and strong exchange couplings at the core–shell interface have been considered. The main attention has been focused on the former situation where the system exhibits similar characteristic features with that observed in thin film and semi-infinite systems in which the surface effects are prominent. A complete picture of the phase diagrams and magnetization profiles has been represented and the effect of the surface shell amorphization on these properties has been discussed. Furthermore, we have investigated the ground state behavior of total magnetization mT curves and we have observed that mT curves exhibit highly non-monotonous and exotic ground states in the presence of frustration in the surface shell. We have also analyzed the necessary conditions for the occurrence of reentrant behavior in the system.

Anisotropic quantum quench in the presence of frustration or background gauge fields: A probe of bulk currents and topological chiral edge modes

Bosons and fermions, in the presence of frustration or background gauge fields, can form manybody ground states that support equilibrium 'charge' or 'spin' currents. Motivated by the experimental creation of frustration or artificial gauge fields in ultracold atomic systems, we propose a general scheme by which making a sudden anisotropic quench of the atom tunneling across the lattice and tracking the ensuing density modulations provides a powerful and gauge invariant route to visualizing diverse equilibrium current patterns. Using illustrative examples of trapped superfluid Bose and normal Fermi systems in the presence of artificial magnetic fluxes on square lattices, and frustrated bosons in a triangular lattice, we show that this scheme to probe equilibrium bulk current order works independent of particle statistics. We also show that such quenches can detect chiral edge currents in gapped topological states, such as quantum Hall or quantum spin Hall insulators.

ChemInform Abstract: Highly Frustrated Magnetism in Spinels

AbstractReview: 97 refs.

Adiabatic spin cooling using high-spin Fermi gases

Spatial entropy redistribution plays a key role in adiabatic cooling of ultra-cold lattice gases. We show that high-spin fermions with a spatially variable quadratic Zeeman coupling may allow for the creation of an inner spin-1/2 core surrounded by high-spin wings. The latter are always more entropic than the core at high temperatures and, remarkably, at all temperatures in the presence of frustration. Combining thermodynamic Bethe Ansatz with local density approximation, we study the spatial entropy distribution for the particular case of one-dimensional spin-3/2 lattice fermions in the Mott phase. Interestingly, this spatially dependent entropy opens a possible path for an adiabatic cooling technique that, in contrast to previous proposals, would specifically target the spin degree of freedom. We discuss a possible realization of this adiabatic cooling, which may allow for a highly efficient entropy decrease in the spin-1/2 core and help access antiferromagnetic order in experiments on ultracold spinor fermions.

Backflow correlations in the Hubbard model: An efficient tool for the study of the metal-insulator transition and the large-Ulimit

We show that backflow correlations in the variational wave function for the Hubbard model greatly improve the previous results given by the Slater-Jastrow state, usually considered in this context. We provide evidence that, within this approach, it is possible to have a satisfactory connection with the strong-coupling regime. Moreover, we show that, for the Hubbard model on the lattice, backflow correlations are essentially short range, inducing an effective attraction between empty (holons) and doubly occupied sites (doublons). In the presence of frustration, we report the evidence that the metal to Mott-insulator transition is marked by a discontinuity of the double occupancy, together with a similar discontinuity of the kinetic term that does not change the number of holons and doublons, while the other kinetic terms are continuous across the transition. Finally, we show the estimation of the charge gap, obtained by particle-hole excitations \`a la Feynman over the ground-state wave function.

The Berry phase in frustrated spin glass

The presence of disorders in frustrated spin glass offers conflict in spin ordering. As a result, the hopping electron is unable to complete a closed path. We have pointed out that a different kind of Berry connection is developed in a frustrated spin system. The developed Berry phase in the frustrated spin system departs from the usual solid angle, but the two are identical under special conditions. Further, the chiral change of helicity of a quantized spinor is prominent only in the presence of frustration. We show how the Berry phase is able to reveal the disordered character of systems such as spin glasses.

Frustrated Bose condensates in optical lattices

We study the Bose-condensed ground states of bosons in a two-dimensional optical lattice in the presence of frustration due to an effective vector potential, for example, due to lattice rotation. We use a mapping to a large-S frustrated magnet to study quantum fluctuations in the condensed state. Quantum effects are introduced by considering a 1/S expansion around the classical ground state. The large-S regime should be relevant to systems with many particles per site. As the system approaches the Mott insulating state, the hole density becomes small. Our large-S results show that, even when the system is very dilute, the holes remain a (partially) condensed system. Moreover, the superfluid density is comparable to the condensate density. In other words, the large-S regime does not display an instability to noncondensed phases. However, for cases with fewer than 1/3 flux quantum per lattice plaquette, we find that the fractional condensate depletion increases as the system approaches the Mott phase, giving rise to the possibility of a noncondensed state before the Mott phase is reached for systems with smaller S.