Kosterlitz-Thouless Research Articles

Detection of Berezinskii–Kosterlitz–Thouless transitions for the two-dimensional q-state clock models with neural networks

Detection of Berezinskii–Kosterlitz–Thouless transitions for the two-dimensional q-state clock models with neural networks

Fazovye perekhody v chasovoy modeli s chislom sostoyaniy spina <i>q </i>= 5 na treugol'noy reshetke

The phase transitions and thermodynamic properties of the clock model with q = 5 spin states on a triangular lattice have been investigated using the Wang–Landau Monte Carlo algorithm. The phase transitions have been analyzed with the histogram method and the fourth-order Binder cumulant method. Two Berezinskii–Kosterlitz–Thouless phase transitions are shown to be observed in the ferromagnetic clock model, while a second-order phase transition has been detected in the antiferromagnetic clock model.

Non-spontaneous symmetry breaking, chaos, and universality in 2D superconducting phase transition

This research paper explores the intriguing phenomenon of the superconductor-metal–insulator phase transition in thin films, examining it from a theoretical standpoint. Our study revolves around the proposition that the process of U(1) symmetry breaking in the Landau–Ginzburg theory might not be entirely spontaneous. Building on this insight, we derive critical parameters characterizing the superconducting phase transition. Our findings demonstrate that the application of an electric field can effectively control the phase transition, leading to the suppression of the supercurrent at specific electric potential values, which is consistent with recent research. Furthermore, we have developed a robust relationship for the nonlinear resistivity that accurately simulates experimental measurements below the critical temperature. This derived relation adopts the form of logistic functions, providing a systematic framework to describe the system within the realm of chaos theory. Moreover, we establish a link with the Berezinskii–Kosterlitz–Thouless theory, highlighting the universality of the topological transition. However, this universality breaks down under the influence of multiple control parameters. To delve further into the underlying reasons for the collapse of universality, we turn to the study of Markus–Lyapunov fractals, which offers a deep understanding into the system’s behavior in the presence of varying external influences..

Role of Inter-site Hubbard Interactions in MnS Monolayer: DFT+U+V Investigation

The stable MnS monolayer was recently predicted using first-principles density functional theory (DFT) including Hubbard U (DFT+U) correction and Monte Carlo (MC) simulations. It is shown to exhibit an indirect band gap of 0.68 eV semiconductor with a high Neel temperature (T_N) of 720 K and an in-plane easy axis magnetic anisotropy energy (MAE). The considered on-site Hubbard U correction takes into account only the Mn (3d) localized nature. To correct the inter-site errors due to strong hybridization between bonded Mn (3d) and S (2p) states, the Hubbard +V inter-site parameter should be added to the calculations. In this study, the band gap of MnS is found to be increased to 1.24 eV (twice that for DFT+U) after considering the inter-site V correction (DFT+U+V). Since the MnS monolayer prefers an in-plane easy axis for the MAE, the estimated Berezinskii Kosterlitz Thouless transition (BKT) transition temperature is as high as 1667.8 K. The carrier mobility is calculated based on the deformation potential and effective mass and it is found that holes (2.12 〖cm〗^2 v^(-1) S^(-1)) are twice the size of these electrons (1.21 〖cm〗^2 v^(-1) S^(-1)). The results are expected to improve the potential of the MnS monolayers in multiple AFM spintronic device applications.

Characterization of Quantum and Classical Critical Points for an Integrable Two-Qubit Spin–Boson Model

The class of two-interacting-qubit spin–boson models with vanishing transverse fields on the spin-pair is studied. The model can be mapped exactly into two independent standard single-impurity spin–boson models where the role of the tunneling parameter is played by the spin–spin coupling. The dynamics of the magnetization are analyzed for different levels of (an)isotropy. The existence of a decoherence-free subspace, as well as of different classical regimes separated by a critical temperature, and symptoms of quantum (first-order and Kosterlitz–Thouless type) phase transitions in the Ohmic regime are brought to light.

The interplay between anomalous metallic and superconducting states tuned by disorder in thin flakes of Kagome metal KV3Sb5

Recently, V-based Kagome metals have attracted intense attention due to the coexistence of their topological nontrivial electronic structure, charge density wave, and superconductivity. Here, we report the fabrication and physical investigations of single-crystalline thin flakes of the Kagome metal KV3Sb5. For samples with a thickness of , Berezinskii–Kosterlitz–Thouless type behavior is revealed by the temperature dependent resistance and voltage–current data, which indicates the presence of two-dimensional superconductivity. Meanwhile, a temperature-independent resistance behavior is observed in a wide field region, supplying the hallmark of the anomalous metallic (AM) state. Importantly, by comparing the interplay between the superconducting and AM states of two samples with different levels of disorder, a striking competitive evolution with the external field between these two states is uncovered.

New analytical results in solid state physics using the Lambert W function

Analytical solutions in physics are always preferred for the sake of mathematical completeness. For this, using the Lambert W function, I derive closed-form analytical expressions for the equilibrium interionic distance in an ionic crystal, the formation energy of a vacancy in a crystal, the zero-temperature energy gap of a clean-limit superconductor and the critical Kosterlitz–Thouless temperature for the phase transition in 2D-XY model. Besides their theoretical interest, some of the present results suggest alternative experimental determinations of the relevant physical quantities. In addition, I similarly derive an explicit analytical formula based on the Lambert W function for a determination of the Boltzmann constant. This formula is proposed here as a theoretical basis for an experimental method to measure this constant. This method is suitable for undergraduate physics students.

Universal scaling of the dynamic BKT transition in quenched 2D Bose gases.

The understanding of nonequilibrium dynamics in many-body quantum systems is a fundamental issue in statistical physics. Experiments that probe universal properties of these systems can address such foundational questions. In this study, we report the measurement of universal dynamics triggered by a quench from the superfluid to normal phase across the Berezinskii-Kosterlitz-Thouless transition in a two-dimensional (2D) Bose gas. We reduced the density by splitting the 2D gas in two, realizing a quench across the critical point. The subsequent relaxation dynamics were probed with matter-wave interferometry to measure the local phase fluctuations. We show that the time evolution of both the phase correlation function and vortex density obeys universal scaling laws. This conclusion is supported by classical-field simulations and interpreted by means of real-time renormalization group theory.

Dynamic renormalization group analysis of the chiral smectic-C to smectic-C phase transition

The chiral smectic-C to smectic-C (SmC -SmC) phase transition has been studied using dynamic renormalization group (DRG) analysis. Langevin equations are derived from the nonlinear elastic model of the SmC -SmC phase transition. The DRG equations are derived. The DRG analysis predicts the Kosterlitz-Thouless transition at low frequency limit and Kardar-Parisi-Zhang (KPZ) fixed point. The DRG calculation confirms that the SmC -SmC phase transition belong to the KPZ universality class.

Disordering complexion transition of grain boundaries in bcc metals: Insights from atomistic simulations

Complexion transitions (CTs) of grain boundaries (GBs) have been a subject of extensive discussions in the last years, but many aspects of this phenomenon are still unclear. Here we studied temperature-induced disordering transitions of GBs in several body-centered cubic metals by means of classical atomistic simulations. Our study shows that gradual heating from room temperature to the melting temperature (Tm) leads to continuous disordering of the GB structure due to spontaneous formation of point defects in all studied metals. This disordering is accompanied by two CTs and exhibits analogies to transitions described by the Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young theory. The first CT occurs at temperatures of about 0.7Tm and is characterized by significant changes of mechanical and kinetic properties. The second CT at about 0.9Tm is a premelting transition when the GB order parameter becomes zero.

Kardar–Parisi–Zhang roughening associated with nucleation-limited steady crystal growth

The roughness of crystal surfaces and the shape of crystals play important roles in multiscale phenomena. For example, the roughness of the crystal surface affects the frictional and optical properties of materials such as ice or silica. Theoretical studies on crystal surfaces based on the symmetry principle proposed that the growing surfaces of crystal growth could be classified in the universal class of Kardar–Parisi–Zhang (KPZ), but experiments rarely observe KPZ properties. To fill this the gap, extensive numerical calculations of the crystal growth rates and the surface roughness (surface width) have been performed for a nanoscale lattice model using the Monte Carlo method. The results indicate that a (001) surface is smooth within the single nucleation growth region. In contrast, the same surface is atomically smooth but thermodynamically rough in the poly-nucleation growth region in conjunction with a KPZ roughness exponent. Inclined surfaces are known to become Berezinskii–Kosterlitz–Thouless (BKT) rough surfaces both at and near equilibrium. The two types of steps associated with the (001) and (111) terraces were found to induce KPZ surface roughness, while the interplay between steps and multilayered islands promoted BKT roughness.

Oscillating paramagnetic Meissner effect and Berezinskii-Kosterlitz-Thouless transition in underdoped Bi2Sr2CaCu2O8+δ.

Superconducting phase transitions in two dimensions lie beyond the description of the Ginzburg-Landau symmetry-breaking paradigm for three-dimensional superconductors. They are Berezinskii-Kosterlitz-Thouless (BKT) transitions of paired-electron condensate driven by the unbinding of topological excitations, i.e. vortices. The recently discovered monolayers of layered high-transition-temperature ([Formula: see text]) cuprate superconductor Bi2Sr2CaCu2O8+δ (Bi2212) meant that this 2D superconductor promised to be ideal for the study of unconventional superconductivity. But inhomogeneity posed challenges for distinguishing BKT physics from charge correlations in this material. Here, we utilize the phase sensitivity of scanning superconducting quantum interference device microscopy susceptometry to image the local magnetic response of underdoped Bi2212 from the monolayer to the bulk throughout its phase transition. The monolayer segregates into domains with independent phases at elevated temperatures below [Formula: see text]. Within a single domain, we find that the susceptibility oscillates with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up to [Formula: see text]. The finite modulation period, as well as the broadening of the peaks when approaching [Formula: see text] from below, suggests well-defined vortices that are increasingly screened by the dissociation of vortex-antivortex plasma through a BKT transition. In the multilayers, the susceptibility oscillation differs in a small temperature regime below [Formula: see text], consistent with a dimensional crossover led by interlayer coupling. Serving as strong evidence for BKT transition in the bulk, we observe a sharp jump in phase stiffness and paramagnetism at small fields just below [Formula: see text]. These results unify the superconducting phase transitions from the monolayer to the bulk underdoped Bi2212, and can be collectively referred to as the BKT transition with interlayer coupling.

Monte Carlo study of Potts versus Kosterlitz-Thouless transitions in a 2D generalized XY model

The generalized XY model has seen renewed interest recently. This model contains both the spin-spin exchange interaction and q-fold nematic interaction. Due to competition between these two kinds of interaction, the model exhibits a rich phase diagram with various phases and unusual phase transitions. Here, we perform an extensive Monte Carlo simulation for this model, focusing on the case of q=3, which corresponds to a three-fold nematic interaction. We use the correlation length to locate the phase transition lines, including the Kosterlitz-Thouless (KT) line, the 1/3 KT line, and the Potts line, which meet at the tricritical point. Further, the magnetic correlation length gives more insights into the tricritical region. Finally, it signifies an intermediate region starting from the tricritical point, where the transition line is neither of the same physics as the Pott transition below nor the KT transition far above the tricritical point.

Lieb-Schultz-Mattis, Luttinger, and 't Hooft - anomaly matching in lattice systems

We analyze lattice Hamiltonian systems whose global symmetries have ’t Hooft anomalies. As is common in the study of anomalies, they are probed by coupling the system to classical background gauge fields. For flat fields (vanishing field strength), the nonzero spatial components of the gauge fields can be thought of as twisted boundary conditions, or equivalently, as topological defects. The symmetries of the twisted Hilbert space and their representations capture the anomalies. We demonstrate this approach with a number of examples. In some of them, the anomalous symmetries are internal symmetries of the lattice system, but they do not act on-site. (We clarify the notion of “on-site action.”) In other cases, the anomalous symmetries involve lattice translations. Using this approach we frame many known and new results in a unified fashion. In this work, we limit ourselves to 1+1d systems with a spatial lattice. In particular, we present a lattice system that flows to the c=1c=1 compact boson system with any radius (no BKT transition) with the full internal symmetry of the continuum theory, with its anomalies and its T-duality. As another application, we analyze various spin chain models and phrase their Lieb-Shultz-Mattis theorem as an ’t Hooft anomaly matching condition. We also show in what sense filling constraints like Luttinger theorem can and cannot be viewed as reflecting an anomaly. As a by-product, our understanding allows us to use information from the continuum theory to derive some exact results in lattice model of interest, such as the lattice momenta of the low-energy states.

Magnetic-field-driven rise and fall of a bipartite entanglement in a spin-liquid phase of a spin-1/2 Heisenberg branched chain

The spin-1/2 Heisenberg branched chain with the unit cell composed of three spins in the main backbone and one spin at a side branching of one-dimensional chain is investigated with the help of density-matrix renormalization group (DMRG) and quantum Monte Carlo (QMC) methods. The DMRG simulations were employed to calculate zero-temperature magnetization curves and to construct the ground-state phase diagram, which is composed from four different ground states classified as gapped zero-plateau and one-half plateau phase, a gapless spin-liquid phase and a fully saturated phase. It is shown that the one-half magnetization plateau vanishes at the Kosterlitz–Thouless quantum critical point, which is wedged into a parameter space of the gapless quantum spin-liquid phase. The bipartite quantum entanglement between four distinct nearest-neighbor pairs of the spin-1/2 Heisenberg branched chain is quantified through the concurrence. It is found that the concurrence varies continuously within the quantum spin-liquid phase, where it may display a continuous rise, a continuous fall or eventually an intriguing rise-and-fall behavior. On the contrary, the concurrence is kept constant within two gapful zero- and one-half plateau phases. Temperature and magnetic-field dependencies of the magnetization and magnetic susceptibility computed within the QMC method uncover clear signatures of the quantum critical point at finite temperatures.

Statistical reconstruction of the GFF and KT transition

In this paper, we focus on the following question. Assume \phi is a discrete Gaussian free field (GFF) on \Lambda \subset \frac 1 n \mathbb{Z}^2 and that we are given e^{iT \phi} , or equivalently \phi \pmod{ {2\pi} T} . Can we recover the macroscopic observables of \phi with o(1) precision? We prove that this statistical reconstruction problem undergoes the following Kosterlitz–Thouless type phase transition: This statistical reconstruction problem is motivated by the two-dimensional XY and Villain models. Indeed, at low temperature T , the large scale fluctuations of these continuous spin systems are conjectured to be governed by a Gaussian free field. It is then natural to ask if one can recover the underlying macroscopic GFF from the observation of the spins of the XY or Villain model. Another motivation for this work is that it provides us with an “integrable model” (the GFF) that undergoes a KT transition.

Berezinskii—Kosterlitz—Thouless correlations in copper-based quasi-2D spin systems (Review Article)

We present an overview of selected copper-based quasi-2D square-lattice spin-1/2 materials with an easy-plane anisotropy, providing the possibility to study emergent Berezinskii-Kosterlitz-Thouless (BKT) correlations. In particular, in those materials with a comparatively small exchange coupling, the effective XY anisotropy of the low-temperature spin correlations can be controlled by an applied magnetic field, yielding a systematic evolution of the BKT correlations. In cases where the residual interlayer correlations are small enough, dynamical BKT correlations in the critical regime may be observed experimentally, whereas the completion of the genuine BKT transition is preempted by the onset of long-range order.

Observation of a magnetic phase transition in monolayer NiPS3

Monolayer magnet of $\mathit{XY}$ type composes a pivotal part of the two-dimensional magnetism. As an important suspected $\mathit{XY}$-type antiferromagnet, whether $1L \mathrm{NiP}{\mathrm{S}}_{3}$ exhibits magnetic order remains elusive. Herein by helicity-resolved Raman and ultrafast spectroscopy of $\mathrm{NiP}{\mathrm{S}}_{3}$ from bulk to monolayer, we find that $1L \mathrm{NiP}{\mathrm{S}}_{3}$ is magnetically ordered with a Berezinskii-Kosterlitz-Thouless (BKT) transition at ${T}_{\mathrm{BKT}}\ensuremath{\approx}140$ K. We have also performed large-scale density-matrix renormalization-group calculations to verify the ground state zigzag antiferromagnetic order and Monte Carlo simulation to confirm the BKT-transition temperature in $1L \mathrm{NiP}{\mathrm{S}}_{3}$. Our investigations establish $1L \mathrm{NiP}{\mathrm{S}}_{3}$ to be an $\mathit{XY}$ antiferromagnet with a relatively high-temperature BKT transition, providing an important platform for investigating complex couplings and topological excitations.

Flux-flow instability across Berezinskii Kosterlitz Thouless phase transition in KTaO3 (111) based superconductor

The nature of energy dissipation in 2D superconductors under perpendicular magnetic field at small current excitations has been extensively studied over the past two decades. However, dissipation mechanisms at high current drives remain largely unexplored. Here we report on the distinct behavior of energy dissipation in the AlOx/KTaO3 (111) system hosting 2D superconductivity in the intermediate disorder regime. The results show that below the Berezinskii Kosterlitz Thouless (BKT) phase transition temperature (TBKT), hot-spots and Larkin Ovchinnikov type flux-flow instability (FFI) are the major channels of dissipation, leading to pronounced voltage instability at large currents. Furthermore, such FFI leads to a rare observation of clockwise hysteresis in current-voltage characteristics within the temperature range TBKT < T < TC (TC is superconducting transition temperature). These findings deepen our understanding of how a BKT system ultimately transforms to a normal state under increasing current.

Two Types of Topological Kosterlitz–Thouless Phase Transitions in SmMnO3+δ Manganites, Driven by External Magnetic Field

Two Types of Topological Kosterlitz–Thouless Phase Transitions in SmMnO3+δ Manganites, Driven by External Magnetic Field