Quasiparticles In Systems Research Articles

Nonequilibrium quasiparticle distribution in superconducting resonators: Effect of pair-breaking photons

Many superconducting devices rely on the finite gap in the excitation spectrum of a superconductor: thanks to this gap, at temperatures much smaller than the critical one the number of excitations (quasiparticles) that can impact the device’s behavior is exponentially small. Nevertheless, experiments at low temperature usually find a finite, non-negligible density of quasiparticles whose origin has been attributed to various non-equilibrium phenomena. Here, we investigate the role of photons with energy exceeding the pair-breaking threshold 2\Delta2Δ as a possible source for these quasiparticles in superconducting resonators. Modeling the interacting system of quasiparticles, phonons, sub-gap and pair-breaking photons using a kinetic equation approach, we find analytical expressions for the quasiparticles’ density and their energy distribution. Applying our theory to measurements of quality factor as function of temperature and for various readout powers, we find they could be explained by assuming a small number of photons above the pair-breaking threshold. We also show that frequency shift data can give evidence of quasiparticle heating.

Electrical Detection of Acoustic Antiferromagnetic Resonance in Compensated Synthetic Antiferromagnets.

Compensated synthetic antiferromagnets (SAFs) stand out as promising candidates to explore various spintronic applications, benefitting from high precession frequency and negligible stray field. High-frequency antiferromagnetic resonance in SAFs, especially the optic mode (OM), is highly desired to attain fast operation speed in antiferromagnetic spintronic devices. SAFs exhibit ferromagnetic configurations above saturation field; however in that case, the intensity of OM is theoretically zero and hard to be detected in well-established microwave resonance experiments. To expose the hidden OM, the exchange symmetry between magnetic layers must be broken, inevitably introducing remanent magnetization. Here, we experimentally demonstrate a feasible method to break the symmetry via surface acoustic waves with the maintenance of compensated SAF structure. By introducing an out-of-plane strain gradient inside the Ir-mediated SAFs, we successfully reveal the hidden OM. Remarkably, the OM intensity can be effectively modulated by controlling strain gradients in SAFs with different thicknesses, confirmed by finite-element simulations. Our findings provide a feasible scheme for detecting the concealed OM, which would trigger future discoveries in magnon-phonon coupling and hybrid quasiparticle systems.

A unified quasiparticle approach to the theory of strongly correlated electron liquids

Landau’s quasiparticle formalism is generalized to describe a wide class of strongly correlated Fermi systems, in addition to conventional Fermi liquids. This class includes (i) so-called marginal exemplars and (ii) systems that harbor interaction-driven flat bands, in both of which manifestations of non-Fermi-liquid behavior are well documented. Specifically, the advent of such flat bands is attributed to a spontaneous topological rearrangement of the Landau state that supplements the conventional Landau quasiparticle picture with a different set of quasiparticles, the so-called fermion condensate, whose single-particle spectrum is dispersionless. The celebrated Landau–Luttinger theorem is extended to marginal Fermi liquids, in which the density of the augmented quasiparticle system is shown to coincide with the particle density. On the other hand, the total density of a system hosting an interaction-driven flat band turns out to be the sum of the densities of the two quasiparticle subsystems: the Landau-like component and the fermion condensate. We demonstrate that within the framework of the scenario proposed, a long-standing problem faced by theories of D-wave superconductivity in cuprates, namely a consistent explanation of the so-called Uemera plot, can be naturally resolved.

Fuzzy dark matter dynamics and the quasi-particle hypothesis

ABSTRACT Dark matter may be composed of ultralight bosons whose de Broglie wavelength in galaxies is $\lambda \sim 1\, {\rm kpc}$. The standard model for this fuzzy dark matter (FDM) is a complex scalar field that obeys the Schrödinger–Poisson equations. The wavelike nature of FDM leads to fluctuations in the gravitational field that can pump energy into the stellar components of a galaxy. Heuristic arguments and theoretical analyses suggest that these fluctuations can be modelled by replacing FDM with a system of quasi-particles (QPs). We test this hypothesis by comparing self-consistent simulations of a Schrödinger field with those using a system of QPs in one spatial dimension. Simulations of pure FDM systems allow us to derive a phenomenological relation between the number of QPs that is required to model FDM with a given de Broglie wavelength. We also simulate systems of FDM and stars and find that the FDM pumps energy into the stars whether it is described by QPs or a Schrödinger field with the FDM adiabatically contracting and the stellar system adiabatically expanding. However, we find that QPs overestimate dynamical heating.

The Landau-level structure of a single polaron in a nanorod under a non-uniform magnetic field

Nanorod is a unique low-dimensional nanometer structure in which the Landau level arrangement of polaron is essential for understanding its quasiparticle system. However, the stability of the polaron level is susceptible to external factors, such as changing magnetic fields. In this manuscript, the Pekar variational method is employed to calculate the external magnetic field’s effect on the nanorod’s polaron Landau level. It was found that different magnetic fields have different effects on the polaron energy levels of the nanorod, which demonstrated that the external environment had critical effects on the polaron energy levels. This study provides a theoretical basis for regulating the interaction between electrons and phonons in low-dimensional nanomaterials.

Pgm: A Python package for free energy calculations within the phonon gas model

The quasi-harmonic approximation (QHA) is a powerful method that uses the volume dependence of non-interacting phonons to compute the free energy of materials at high pressures (P) and temperatures (T). However, anharmonicity, electronic excitations in metals, or both, introduce an intrinsic T-dependence on phonon frequencies, rendering the QHA inadequate. Here we present a Python code, pgm, to compute the free energy and thermodynamic property within the phonon gas model (PGM) that uses T-dependent phonon quasiparticle frequencies. In this case, the vibrational contribution to the Helmholtz free energy is obtained by integrating the vibrational entropy, which can be readily calculated for a system of phonon quasiparticles. Other thermodynamic properties are then obtained from standard thermodynamic relations. We demonstrate the successful applications of pgm to two cases of geophysical significance: cubic CaSiO3-perovskite (cCaPv), a strongly anharmonic insulator and the third most abundant phase of the Earth's lower mantle, and NiAs-type (B8) FeO, a partially covalent-metallic system. This is the oxide endmember of a recently discovered iron-rich FenO alloy phase likely to exist in the Earth's inner core. Program summaryProgram Title:pgmCPC Library link to program files:https://doi.org/10.17632/8rfw6syvzp.1Developer's repository link:https://github.com/MineralsCloud/pgmLicensing provisions: GNU General Public License 3Programming language: Python3Nature of problem: The classic quasi-harmonic approximation (QHA) method to compute the vibrational free energy does not apply to physical systems when phonon frequencies have an intrinsic and non-negligible temperature (T) dependence. Examples are anharmonic systems or metals with abundant electronic thermal excitations. Both cases introduce an intrinsic T-dependence on phonon frequencies.Solution method: The method implemented in pgm is based on the phonon gas model where the entropy is well defined for T-dependent phonon quasiparticle. The free energy is calculated by integrating the entropy, making it suitable for anharmonic systems or systems with extensive thermal electronic excitations affecting phonon frequencies. The static free energy, the vibrational density of states (VDoS), and the entropy are first computed on sparse T- and P-grids. The entropy is then suitably interpolated on denser user-specified grids for integration.Additional comments, including restrictions and unusual features: The package allows it to be run directly in the command line. It can also be incorporated into other programs. We implemented Just-in-time (JIT) compiling and parallel computing techniques [1] in pgm Python code to speed up the numerical calculation.

Polaron level spectrum in double-potential quantum wells

The description of macroscopic systems of quasi-particles is a bright spot in quantum physics, providing an accurate description of the physics development. The current study presents a theoretical study of the energy level spectrum of weakly coupled polarons in polar crystals (GaAs, PbSe, PbTe) in double potential quantum wells (parabolic and asymmetric Gaussian confinement potentials) using the linear combination operator and two simple unitary transformations. Rigorous electron-phonon coupling interaction results are obtained under the weak coupling limitation. The results indicate that the polaron energy is relatively lower than that of the electron and the coupling strength affects the energy difference between polaron and electron. The influence of quantum wells’ confinement potential on energy is also discussed. These findings provide the possibility for potential application of polaron.

Electric Field-Controlled Damping Switches of Coupled Dirac Plasmons.

For quasiparticle systems, the control of the quasiparticle lifetime is an important goal, determining whether the related fascinating physics can be revealed in fundamental research and utilized in practical applications. Here, we use double-layer graphene with a boron nitride spacer as a model system to demonstrate that the lifetime of coupled Dirac plasmons can be remotely tuned by electric field-controlled damping pathways. Essentially, one of the graphene layers serves as an external damping amplifier whose efficiency can be controlled by the corresponding doping level. Through this damping switch, the damping rate of the plasmon can be actively tuned up to 1.7 fold. This Letter provides a prototype design to actively control the lifetime of graphene plasmons and also broadens our horizon for the damping control of other quasiparticle systems.

Self-Trapping Phenomenon in an Exciton-Polariton System When the Lower Polariton Branch is Pumped by Two Laser Pulses with Close Frequencies

The dynamics of exciton-polariton states in a semiconductor microcavity is studied under pumping of the state corresponding to the lower polariton branch, taking into account single-mode and intermode elastic polariton-polariton interactions. In this case, pumping is carried out by two laser pulses with close frequencies. It is shown that at the initial phase difference equal to theta0=π/2, the regime of quantum self-trapping of exciton-polaritons is observed. Periodic and aperiodic modes of evolution of a system of quasiparticles are obtained. Keywords: exciton-polariton states, quantum self-trapping, periodic and apeiodic regimes.

Явление самозахвата в системе экситон-поляритонов при накачке нижней поляритонной ветви двумя лазерными импульсами с близкими частотами

The dynamics of exciton-polariton states in a semiconductor microcavity is studied under pumping of the state corresponding to the lower polariton branch, taking into account single-mode and intermode elastic polariton-polariton interactions. In this case, pumping is carried out by two laser pulses with close frequencies. It is shown that at the initial phase difference equal to θ_0=π⁄2, the regime of quantum self-trapping of exciton-polaritons is observed. Periodic and aperiodic modes of evolution of a system of quasiparticles are obtained.

Kinetic Description of Propagation of Quasiparticles Fluxes in Solid-state Structure

Within the framework of the kinetic theory, the interaction of systems of quasiparticles and the exchange of quasiparticles of different types between layers of a plane-parallel solid structure are taken into account. The reasons influencing the propagation of differential fluxes of quasiparticles near each boundary of the structure are indicated. These include not only the appearance of a force field, in particular, electric е∇φ(х) and thermal ∇Т(х), fields near the boundary in equilibrium and its modification when equilibrium is disturbed, but also a change in the coordinate and angular dependence of the relaxation length of fluxes le(x, k, Ω) in the same region. Some modification of the distribution of characteristic thermodynamic quantities in the inhomogeneous region of the layer in comparison with the homogeneous layer also affects the propagation of fluxes. The necessity of a self-consistent solution of the kinetic boundary value problem of the joint propagation of differential fluxes of quasiparticles-a system of equations and integral boundary conditions-is substantiated. Near the boundary and in another inhomogeneous region of the layer thickness, as well as in the thin layer as a whole, in quasiparticles systems, it is proposed to use a specific coordinate distribution of the flux density of thermodynamic quantities over the structure thickness, which is mutually self-consistent with the propagation of the corresponding quasiparticles fluxes. The main conclusion of this work: when developing modern multilayer solid-state structures, especially with thin layers, it is necessary to use the kinetic theory, which adequately takes into account the physical picture that occurs not only in homogeneous and inhomogeneous regions of the thickness of each layer, but also at all boundaries of the structure.

Thermomagnetic properties and Debye screening for magnetized quark-gluon plasma using the extended self-consistent quasiparticle model

The thermomagnetic behavior of quark-gluon plasma has recently received a lot of attention. In this work, we make use of the extended self-consistent quasiparticle model to study the thermodynamic properties of magnetized (2+1) flavor quark-gluon plasma. The system is considered as a non-interacting system of quasiparticles with masses depending on both temperature and magnetic field. This allows obtaining the equation of state of the system and the other thermodynamic properties such as the speed of sound. We use the extended self-consistent model to obtain the magnetization and show that QGP has a paramagnetic nature. In addition, we study the pressure anisotropy and calculate the transverse pressure. The obtained anisotropic pressure may be used in hydrodynamic studies of magnetized QGP produced in heavy-ion collisions. Finally, we examine the screening properties of magnetized QGP in the longitudinal direction by calculating the Debye screening mass.

Anomalous in-gap edge states in two-dimensional pseudospin-1 Dirac insulators

Quantum materials that host a flat band, such as pseudospin-1 lattices and magic-angle twisted bilayer graphene, can exhibit drastically new physical phenomena including unconventional superconductivity, orbital ferromagnetism, and Chern insulating behaviors. We report a surprising class of electronic in-gap edge states in pseudospin-1 materials without the conventional need of band-inversion topological phase transitions or introducing magnetism via an external magnetic type of interactions. In particular, we find that, in two-dimensional gapped (insulating) Dirac systems of massive spin-1 quasiparticles, in-gap edge modes can emerge through only an {\em electrostatic potential} applied to a finite domain. Associated with these unconventional edge modes are spontaneous formation of pronounced domain-wall spin textures, which exhibit the feature of out-of-plane spin-angular momentum locking on both sides of the domain boundary and are quite robust against boundary deformations and impurities despite a lack of an explicit topological origin. The in-gap modes are formally three-component evanescent wave solutions, akin to the Jackiw-Rebbi type of bound states. Such modes belong to a distinct class due to the following physical reasons: three-component spinor wave function, unusual boundary conditions, and a shifted flat band induced by the external scalar potential. Not only is the finding of fundamental importance, but it also paves the way for generating highly controllable in-gap edge states with emergent spin textures using the traditional semiconductor gate technology. Results are validated using analytic calculations of a continuum Dirac-Weyl model and tight-binding simulations of realistic materials through characterizations of local density of state spectra and resonant tunneling conductance.

Bose–Einstein condensation of quasiparticles by rapid cooling

The fundamental phenomenon of Bose-Einstein condensation has been observed in different systems of real particles and quasiparticles. The condensation of real particles is achieved through a major reduction in temperature, while for quasiparticles, a mechanism of external injection of bosons by irradiation is required. Here, we present a new and universal approach to enable Bose-Einstein condensation of quasiparticles and to corroborate it experimentally by using magnons as the Bose-particle model system. The critical point to this approach is the introduction of a disequilibrium of magnons with the phonon bath. After heating to an elevated temperature, a sudden decrease in the temperature of the phonons, which is approximately instant on the time scales of the magnon system, results in a large excess of incoherent magnons. The consequent spectral redistribution of these magnons triggers the Bose-Einstein condensation.

Atomic collapse in pseudospin-1 systems

We investigate atomic collapse in pseudospin-1 Dirac material systems whose energy band structure constitutes a pair of Dirac cones and a flat band through the conic intersecting point. We obtain analytic solutions of the Dirac-Weyl equation for the three-component spinor in the presence of a Coulomb impurity and derive a general criterion for the occurrence of atomic collapse in terms of the normalized strength of Coulomb interaction and the angular momentum quantum number. In particular, for the lowest angular momentum state, the solution coincides with that for pseudospin-1/2 systems, but with a reduction in the density of resonance peaks. For higher angular momentum states, the underlying pseudospin-1 wave functions exhibit a singularity at the point of zero kinetic energy. Divergence of the local density of states associated with the flat band leads to an inverse square type of singularity in the conductivity. These results provide insights into the physics of the two-body problem for relativistic quantum pseudospin-1 quasiparticle systems.

Cavity Quantum Eliashberg Enhancement of Superconductivity.

Driving a conventional superconductor with an appropriately tuned classical electromagnetic field can lead to an enhancement of superconductivity via a redistribution of the quasiparticles into a more favorable nonequilibrium distribution-a phenomenon known as the Eliashberg effect. Here, we theoretically consider coupling a two-dimensional superconducting film to the quantized electromagnetic modes of a microwave resonator cavity. As in the classical Eliashberg case, we use a kinetic equation to study the effect of the fluctuating, dynamical electromagnetic field on the Bogoliubov quasiparticles. We find that when the photon and quasiparticle systems are out of thermal equilibrium, a redistribution of quasiparticles into a more favorable nonequilibrium steady state occurs, thereby enhancing superconductivity in the sample. We predict that by tailoring the cavity environment (e.g., the photon occupation and spectral functions), enhancement can be observed in a variety of parameter regimes, offering a large degree of tunability.

Non‐Equilibrium Bose–Einstein‐Like Condensation

AbstractThe original Bose–Einstein condensation (BEC) was theoretically established in the 1920s, for the case of an ideal gas of boson particles (a consequence of the symmetry of the wave function). In the 1990s, it was realized in systems of atomic alkali gases. At the beginning of the 21st century, investigators considered its emergence in solid‐state matter, and a BEC‐like phenomenon was observed in the case of bosonic quasiparticles (elementary excitations in solids). Both types of BEC can occur in a condensation in conditions of thermodynamic equilibrium. A third type of what has been dubbed a BEC in non‐equilibrium conditions can occur in systems of bosonic quasiparticles (phonons, magnons, excitons); this phenomenon (which can be considered as cases of systems with complex behavior) follows after a certain threshold of intensity of an external pumping source is achieved. In this review, after brief comments on the two types of BEC in equilibrium, a description is presented on how a BEC‐like phenomenon arises in systems of quasiparticles that are driven away from thermodynamic equilibrium, and several examples are described. This description is given within a unique theoretical framework, and a comparison with experimental results is performed; in addition, the possible technological applications are outlined.

Fisher Metric for Diagonalizable Quadratic Hamiltonians and Application to Phase Transitions

We derive the extended entanglement entropy and the Fisher information metric in the case of quantum models, described by time-independent diagonal quadratic Hamiltonians. Our research is conducted within the framework of Thermo field dynamics. We also study the properties of the Fisher metric invariants to identify the phase structure of the quasi-particle systems in equilibrium.

Direct comparison of fractional and integer quantized Hall resistance

We present precision measurements of the fractional quantized Hall effect, where the quantized resistance in the fractional quantum Hall state at filling factor 1/3 was compared with a quantized resistance , represented by an integer quantum Hall state at filling factor 2. A cryogenic current comparator bridge capable of currents down to the nanoampere range was used to directly compare two resistance values of two GaAs-based devices located in two cryostats. A value of 1–(5.3 ± 6.3) 10−8 (95% confidence level) was obtained for the ratio (). This constitutes the most precise comparison of integer resistance quantization (in terms of h/e2) in single-particle systems and of fractional quantization in fractionally charged quasi-particle systems. While not relevant for practical metrology, such a test of the validity of the underlying physics is of significance in the context of the upcoming revision of the SI.

Effective approach for taking into account interactions of quasiparticles from the low-temperature behavior of a deformed fermion-gas model

A deformed fermion gas model aimed at taking into account thermal and electronic properties of quasiparticle systems is devised. The model is constructed by the fermionic Fibonacci oscillators whose spectrum is given by a generalized Fibonacci sequence. We first introduce some new properties concerning the Fibonacci calculus. We then investigate the low-temperature thermostatistical properties of the model, and derive many of the deformed thermostatistical functions such as the chemical potential and the entropy in terms of the model deformation parameters p and q. We specifically focus on the p,q-deformed Sommerfeld parameter for the heat capacity of the model, and its behavior is compared with those of both the free-electron Fermi theory and the experimental data for some materials. The results obtained in this study reveal that the present deformed fermion model leads to an effective approach accounting for interaction and compositeness of quasiparticles, which have remarkable implications in many technological applications such as in nanomaterials.