bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of entanglement in interacting spin systems
Authors: Fazio R. , Macchiavello C.
Published: June 2022

We briefly review recent work on entanglement with particular emphasis on its behaviour in interacting spin systems. As already pointed out by several authors a general understanding of the properties of entanglement in condensed matter systems may lead to a deeper comprehension of both dynamics and thermodynamics of many‐body systems. After a brief resume of known means to identify and quantify entanglement, we take interacting spins on a network as an example. We briefly discuss critical properties of entanglement, if the system undergoes a quantum phase transition, and some aspects of its dynamical behaviour.
Spin & statistics in nonrelativistic quantum mechanics, II
Authors: Kuckert B. , Mund J.
Published: June 2022

Recently a sufficient and necessary condition for Pauli's spin‐statistics connection in nonrelativistic quantum mechanics has been established [1]. The two‐dimensional part of this result is extended to n‐particle systems and reformulated and further simplified in a more geometric language.
On the axioms of topological electromagnetism
Authors: Delphenich D.H.
Published: June 2022

The axioms of topological electromagnetism that were given by Hehl, Obukhov, and Rubilar are refined by the use of geometrical and topological notions that are found on orientable manifolds. The central problem of defining the spacetime electromagnetic constitutive law in terms of the geometrical and topological structure of the spacetime manifold is elaborated upon in the linear and nonlinear cases. The manner by which the spacetime metric might follow from the electromagnetic constitutive law is examined in the linear case. The possibility that the intersection form of the spacetime manifold might play a role in defining a topological basis for a nonlinear electromagnetic constitutive law is explored. The manner by which electromagnetic wave motion relates to the geometric structure is also discussed.
Darboux transformation for two‐level system
Authors: Bagrov V. , Baldiotti M. , Gitman D. , Shamshutdinova V.
Published: June 2022

We develop the Darboux procedure for the case of the two‐level system. In particular, it is demonstrated that one can construct the Darboux intertwining operator that does not violate the specific structure of the equations of the two‐level system, transforming only one real potential into another real potential. We apply the obtained Darboux transformation to known exact solutions of the two‐level system. Thus, we find three classes of new solutions for the two‐level system and the corresponding new potentials that allow such solutions.
Magnetic impurities in small metal clusters
Authors: Pastor G.M.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods.The singlet‐triplet spin gap ΔE shows a remarkable dependence as a function of band‐filling, cluster structure, and impurity position that can be interpreted in terms of the environment‐specific conduction‐electron spectrum. The low‐energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite‐temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite‐size equivalent of the Kondo effect is identified and its structural dependence is discussed.
Mirage phenomena in superconducting quantum corrals
Authors: Schmid M. , Kampf A.P.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

We investigate the local density of states and the order parameter structure inside an elliptic quantum corral on surfaces of isotropic and anisotropic superconductors. The Bogoliubov‐de Gennes equations are solved in the presence of non‐magnetic and magnetic impurities. We observe and discuss a variety of mirage and anti‐mirage phenomena, which specifically reflect the nature of the superconducting pairing state.
The Bose‐Hubbard model: from Josephson junction arrays to optical lattices
Authors: Bruder C. , Fazio R. , Schön G.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

The Bose‐Hubbard model is a paradigm for the study of strongly correlated bosonic systems. We review some of its properties with emphasis on the implications on quantum phase transitions of Josephson junction arrays and quantum dynamics of topological excitations as well as the properties of ultra‐cold atoms in optical lattices.
Quasiparticles in transition metals with strong local correlations: band formation and collective effects
Authors: Grewe N.
Published: June 2022

Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday

We address the question, whether low lying one‐particle excitations in the Fermi‐liquid phase of highly correlated electron systems can form well defined bands of nearly stable quasiparticles, and comment on features of a universal band picture for these systems. We outline how to derive a description of instabilities to magnetic, charged ordered or superconducting phases, which bears a close analogy to Stoner theory and lends itself to an interpretation in terms of quasiparticle bands and residual interactions at low temperatures. Concepts and problems are illustrated via calculations for some standard models of solid‐state theory using modern many‐body techniques like NRG, NCA and DMFT. Differences to conventional band structure theory are pointed out. We shortly comment on the relevance of these questions to the physics of inhomogeneous systems and small particles.
Sound in biased piezoelectric materials of general anisotropy
Authors: Declercq N.F. , Degrieck J. , Leroy O.
Published: June 2022

A theoretical model is presented that describes the propagation of sound in biased piezoelectric crystals of any kind of symmetry. The symmetry relations for the higher order material constants of trigonal 3m crystals, are calculated and listed in the appendix. The example of Lithium Niobate is highlighted, under influence of a bias pressure. The change of slowness (inverse velocity), because of this pressure, is calculated for every direction. Also the influence of stress on the acoustic polarization and the energy flow is outlined. Furthermore, the difference between the case where piezoelectricity is included and the case where it is omitted, is discussed. The description of changing slowness surfaces, because of a bias field, is not limited to homogeneous plane waves, but also inhomogeneous plane waves are taken into account.
Relativity and technology
Authors: Lämmerzahl C.
Published: June 2022

In this paper we first give a short outline of the principles and experimental status of tests of relativity, which indicates the huge still ongoing progress during the last years. Then emphasize is laid on the fact that relativity, either special or general, already enters a status of an applied technology in daily life. Examples are presented from positioning, metrology, earth sciences, and material sciences.
Cosmic black holes – from stellar to supramassive black holes in galaxies
Authors: Camenzind M.
Published: June 2022

The collapse of massive stars produces the most bizarre objects in the Universe. In the last ten years, astronomers have been successfully searching for real black holes in the Universe. Black hole astrophysics began in the 1960s with the discovery of quasars and other active galactic nuclei (AGN) in distant galaxies. Already in the 1960s it became clear that the most natural explanation for the quasar activity is the release of gravitational energy through accretion of gas onto supermassive black holes. The remnants of this activity have now been found in the centers of about 50 nearby galaxies. BH astrophysics received a new twist in the 1970s with the discovery of the X‐ray binary Cygnus X‐1. The X‐ray emitting compact object was too massive to be explained by a neutron star. Today, about 20 excellent BH candidates are known in XRBs. On the extragalactic scale, more than 100,000 quasars have been found in large galaxy surveys. At the redshift of the most distant ones, the Universe was younger than one billion year. The most enigmatic black hole candidates identified in the last years are the compact objects behind the Gamma‐Ray Bursters. The formation of all these types of black holes is accompanied by extensive emission of gravitational waves. The detection of these strong gravity events is one of the biggest challenges for physicists in the near future.
Quantum gravity: general introduction and recent developments
Authors: Kiefer C.
Published: June 2022

I briefly review the current status of quantum gravity. After giving some general motivations for the need of such a theory, I discuss the main approaches in quantizing general relativity: Covariant approaches (perturbation theory, effective theory, and path integrals) and canonical approaches (quantum geometrodynamics, loop quantum gravity). I then address quantum gravitational aspects of string theory. This is followed by a discussion of black holes and quantum cosmology. I end with some remarks on the observational status of quantum gravity.
The supersymmetric vistas of the supergravity landscape
Authors: Ortín T.
Published: June 2022

In the recent times a lot of effort has been devoted to improve our knowledge about the space of string theory vacua (“the landscape”) in order to find statistical grounds to justify how and why the theory selects its vacuum. Particularly interesting are those vacua that preserve some supersymmetry, which are always supersymmetric solutions of some supergravity theory. We are going to review some recent results on the problem of finding all the supersymmetric solutions of a supergravity theory. We will also review some interesting solutions that have been discovered using these methods.
The revival of cosmic strings
Authors: Sakellariadou M.
Published: June 2022

Cosmic strings are one‐dimensional topological defects which could have been formed in the early stages of our Universe. They triggered a lot of interest, mainly for their cosmological implications: they could offer an alternative to inflation for the generation of density perturbations. It was shown however that cosmic strings lead to inconsistencies with the measurements of the cosmic microwave background temperature anisotropies. The picture has changed recently. It was shown that, on the one hand, cosmic strings can be generically formed in the framework of supersymmetric grand unified theories and that, on the other hand, cosmic superstrings could play the role of cosmic strings. There is also some possible observational support. All this led to a revival of cosmic strings research and this is the topic of my lecture.
Inflationary cosmology and braneworld scenarios
Authors: Lidsey J.E.
Published: June 2022

Cosmology has undergone a significant advance in recent years both observationally and theoretically. New high quality data from a host of Cosmic Microwave Background and high redshift surveys has provided strong support for the inflationary paradigm, which postulates that the universe expanded exponentially fast when it was a fraction of a second old. A key question that has arisen is the nature of the underlying physics that drove such a phase of accelerated expansion. An exciting theoretical development has been the realization that the standard model interactions may be confined to a four–dimensional brane, whereas gravitational interactions may also propagate through the extra dimensions. The radical proposal of the ‘braneworld scenario’ is that our observable universe is a brane embedded in a higher–dimensional bulk. We will review some of the recent developments in this field.
Cosmological scaling solutions (and their applications to string scenarios)
Authors: de Carlos B.
Published: June 2022

In this review we will study the phase space of cosmologies consisting of a scalar field with an exponential potential and a barotropic fluid. This is a very simple system which, however, gives rise to many interesting solutions that can be classified according to the values of the parameters in the game, namely those that define the type of fluid and the steepness of the potential. We shall then pay particular attention to scaling solutions, where the scalar energy density tracks that of the fluid.

In the second part of this review we shall turn to specific models in order to apply the previous results. The goal is to study the dynamics of scalar fields in the Early Universe, and the framework to do so is different types of string compactifications. The corresponding scalar fields are then the so‐called moduli for which non perturbative potentials, of an exponential type, usually arise. We shall see how, contrary to previous expectations, the existence of scaling in this context allows these fields to dynamically stabilise at their tiny minima for a large fraction of initial conditions. This represents a further step in the quest for finding a suitable Particle Physics model compatible with the existing cosmology.
Universe scenarios from loop quantum cosmology
Authors: Bojowald M.
Published: June 2022

Loop quantum cosmology is an application of recent developments for a non‐perturbative and background independent quantization of gravity to a cosmological setting. Characteristic properties of the quantization such as discreteness of spatial geometry entail physical consequences for the structure of classical singularities as well as the evolution of the very early universe. While the singularity issue in general requires one to use difference equations for a wave function of the universe, phenomenological scenarios for the evolution are based on effective equations implementing the main quantum modifications. These equations show generic bounces as well as inflation in diverse models, which have been combined to more complicated scenarios.
Time evolution of relativistic d + Au and Au + Au collisions
Authors: Wolschin G. , Biyajima M. , Mizoguchi T. , Suzuki N.
Published: June 2022

The evolution of charged‐particle production in collisions of heavy ions at relativistic energies is investigated as function of centrality in a nonequilibrium‐statistical framework. Precise agreement with recent d + Au and Au + Au data at = 200 GeV is found in a Relativistic Diffusion Model with three sources for particle production. Only the midrapidity source comes very close to local equilibrium, whereas the analyses of the overall pseudorapidity distributions show that the systems remain far from statistical equilibrium.
The relativistic energy spectrum of hydrogen*
Authors: Marsch E.
Published: June 2022

The exact eigenfunctions of the spin‐orbit‐coupling operators for a relativistic binary system are calculated. Concerning the eigenvalue problem and the radial part of the wavefunction of the bound state, we provide corrections for our previous calculations [1] that contained some sign errors.
The posthumous impact of Paul Drude*
Authors: Cardona M. , Marx W.
Published: June 2022

In this study the long‐term impact of the works of Paul Drude has been analyzed by bibliometric methods. His overall citation impact and rank within the pre‐1910 authors in chemistry and physics has been determined. The time‐dependent number of mentions of his name, the overall citation impact and the citation numbers of single articles and books have been investigated. The impact time curves of his most frequently cited articles and books are presented and discussed. The scientific contributions of the most influential Drude works for solid state physics are analyzed, in particular their impact on recent research.
Ionics versus electronics, and the general case of mixed conductor *
Authors: Maier J.
Published: June 2022

The article emphasizes the importance of ion transport for solid state physics in view of the significance of ionic charge carriers for compositional changes and electrochemical applications, but also in view of their importance for defining the electronic charge carrier density. Special emphasis is given (i) to the mixed conductor as the general case which encompasses the pure electronic conductor and the pure ionic conductor as special cases, (ii) to the bridge between high temperature and room temperature situation and (iii) to the modern fields of interfacial ion transport and nano‐ionics.
Anomalous Hall effect in ferromagnetic disordered metals *
Authors: Wölfle P. , Muttalib K.A.
Published: June 2022

The anomalous Hall effect in disordered band ferromagnets is considered in the framework of quantum transport theory. A microscopic model of electrons in a random potential of identical impurities including spin‐orbit coupling is used. The Hall conductivity is calculated from the Kubo formula for both, the skew scattering and the side‐jump mechanisms. The recently discussed Berry phase induced Hall current is also evaluated within the model. The effect of strong impurity scattering is analyzed and it is found to affect the ratio of the non‐diagonal (Hall) and diagonal components of the conductivity as well as the relative importance of different mechanisms.
The Drude model in correlated systems *
Authors: Degiorgi L.
Published: June 2022

The Drude model provides a useful phenomenological approach for the discussion of the metallic properties in conducting materials, particularly from the perspective of their electrodynamic response. We first introduce the model and its generalization, which accounts for the frequency dependence of the scattering rate and effective mass of the quasiparticles. Three selected examples, from the optical research on the topic of strongly correlated metals, will illustrate the variety of issues and broad spectrum of informations, which can be addressed and achieved within this approach.
Eigentensors of the Lichnerowicz operator in Euclidean Schwarzschild metrics*
Authors: Martínez‐Morales J.L.
Published: June 2022

Properties of the eigentensors of the Lichnerowicz Laplacian for the Euclidean Schwarzschild metric are discussed together with possible applications to the linear stability of higher‐dimensional instantons. The main statement of the article is that any eigentensor of the Lichnerowicz operator in a Euclidean (possibly higher‐dimensional) Schwarzschild metric is essentially singular at infinity.
Strings and branes under microscope
Authors: Dzhunushaliev V.
Published: June 2022

It is shown that in the standard vacuum 5D Kaluza‐Klein gravity there exist wormhole‐like solutions which look like strings attached to two D‐branes. The asymptotic behaviour of the corresponding metric is investigated.
Scopes and limits of modality in quantum mechanics
Authors: Domenech G. , Freytes H. , de Ronde C.
Published: June 2022

We develop an algebraic frame for the simultaneous treatment of actual and possible properties of quantum systems. We show that, in spite of the fact that the language is enriched with the addition of a modal operator to the orthomodular structure, contextuality remains a central feature of quantum systems.
The gravitomagnetic clock effect and its possible observation
Authors: Lichtenegger H. , Iorio L. , Mashhoon B.
Published: June 2022

The general relativistic gravitomagnetic clock effect involves a coupling between the orbital motion of a test particle and the rotation of the central mass and results in a difference in the proper periods of two counter–revolving satellites. It is shown that at 𝒪(c‐2) this effect has a simple analogue in the electromagnetic case. Moreover, in view of a possible measurement of the clock effect in the gravitational field of the Earth, we investigate the influence of some classical perturbing forces of the terrestrial space environment on the orbital motion of test bodies along opposite trajectories.
Equations of motion for a (non‐linear) scalar field model as derived from the field equations
Authors: Kaniel S. , Itin Y.
Published: June 2022

The problem of derivation of the equations of motion from the field equations is considered. Einstein's field equations have a specific analytical form: They are linear in the second order derivatives and quadratic in the first order derivatives of the field variables. We utilize this particular form and propose a novel algorithm for the derivation of the equations of motion from the field equations. It is based on the condition of the balance between the singular terms of the field equation. We apply the algorithm to a non‐linear Lorentz invariant scalar field model. We show that it results in the Newton law of attraction between the singularities of the field moved on approximately geodesic curves. The algorithm is applicable to the N‐body problem of the Lorentz invariant field equations.
The self‐energy of the uniform electron gas in the second order of exchange
Authors: Ziesche P.
Published: June 2022

The on‐shell self‐energy of the homogeneous electron gas in second order of exchange, Σ2x = Re Σ2x (kF, k2 F/2), is given by a certain integral. This integral is treated here in a similar way as Onsager, Mittag, and Stephen [Ann. Physik (Leipzig) 18, 71 (1966)] have obtained their famous analytical expression e2x = (in atomic units) for the correlation energy in second order of exchange. Here it is shown that the result for the corresponding on‐shell self‐energy is Σ2x = e2x. The off‐shell self‐energy Σ2x (k, o) correctly yields 2e2x (the potential component of e2x) through the Galitskii‐Migdal formula. The quantities e2x and Σ2x appear in the high‐density limit of the Hugenholtz‐van Hove (Luttinger‐Ward) theorem.
Toward a nonlocal theory of gravitation
Authors: Mashhoon B.
Published: June 2022

The nonlocal theory of accelerated systems is extended to linear gravitational waves as measured by accelerated observers in Minkowski spacetime. The implications of this approach are discussed. In particular, the nonlocal modifications of helicity‐rotation coupling are pointed out and a nonlocal wave equation is presented for a special class of uniformly rotating observers. The results of this study, via Einstein's heuristic principle of equivalence, provide the incentive for a nonlocal classical theory of the gravitational field.
From RHIC to LHC: a relativistic diffusion approach
Authors: Kuiper R. , Wolschin G.
Published: June 2022

We investigate the energy dependence of stopping and hadron production in high‐energy heavy‐ion collisions based on a three‐sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies ( = 19.6–200 GeV) to Pb + Pb at LHC energies = 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.
Introducing relativity in global navigation satellite systems
Authors: Pascual‐Sánchez J.‐F.
Published: June 2022

Today, the Global Navigation Satellite Systems, used as global positioning systems, are the GPS and the GLONASS. They are based on a Newtonian model and hence they are only operative when several relativistic effects are taken into account. The most important relativistic effects (to order 1/c2) are: the Einstein gravitational blue shift effect of the satellite clock frequency (Equivalence Principle of General Relativity) and the Doppler red shift of second order, due to the motion of the satellite (Special Relativity). On the other hand, in a few years the Galileo system will be built, copying the GPS system unless an alternative project is designed. In this work, it will be also shown that the SYPOR project, using fully relativistic concepts, is an alternative to a mere copy of the GPS system. According to this project, the Galileo system would be exact and there would be no need for relativistic corrections.
Lanczos potential for the Gödel spacetime
Authors: Ahsan Z. , Caltenco J.H. , López‐Bonilla J.
Published: June 2022

We employ the local and isometric embedding of Riemannian spaces to construct one Lanczos potential in Gödel geometry.
The Einstein‐Elko system – Can dark matter drive inflation?
Authors: Böhmer C.G.
Published: June 2022

Recently, a spin one half matter field with mass dimension one was discovered, called Elko spinors. The present work shows how to introduce these fields into a curved spacetime by the standard covariantisation scheme. After formulating the coupled Einstein‐Elko field equations, the spacetime is assumed to be homogeneous and isotropic in order to simplify the resulting field equations. Analytical ghost Elko solutions are constructed which have vanishing energy‐momentum tensor without and with cosmological constant. The cosmological Elko theory is finally related to the standard scalar field theory with self interaction that gives rise to inflation and it is pointed out that the Elko spinors are not only prime dark matter candidates but also prime candidates for inflation.
Berry phase of two atoms in the same quantized light field
Authors: Liang M.‐L. , Zhang J.‐H. , Yuan B.
Published: June 2022

The Berry phase of two atoms exposed to the same quantized light field has been studied. The interaction between each atom and the light field obeys the Jaynes‐Cummings model. Due to the quantization of the light field, the interaction Hamiltonians for the two atoms interacting with the field do not commute with each other, which induces new parts in the Berry phase. Meanwhile, there appears a phase which doesn't exist in the classical regime and is purely induced by the field quantization.
Synergetic analysis of the Häussler‐von der Malsburg equations for manifolds of arbitrary geometry
Authors: Güßmann M. , Pelster A. , Wunner G.
Published: June 2022

We generalize a model of Häussler and von der Malsburg which describes the self‐organized generation of retinotopic projections between two one‐dimensional discrete cell arrays on the basis of cooperative and competitive interactions of the individual synaptic contacts. Our generalized model is independent of the special geometry of the cell arrays and describes the temporal evolution of the connection weights between cells on different manifolds. By linearizing the equations of evolution around the stationary uniform state we determine the critical global growth rate for synapses onto the tectum where an instability arises. Within a nonlinear analysis we use then the methods of synergetics to adiabatically eliminate the stable modes near the instability. The resulting order parameter equations describe the emergence of retinotopic projections from initially undifferentiated mappings independent of dimension and geometry.
A new look at the quantum mechanics of the harmonic oscillator
Authors: Kastrup H.A.
Published: June 2022

In classical mechanics the harmonic oscillator (HO) provides the generic example for the use of angle and action variables and I > 0 which played a prominent role in the “old” Bohr‐Sommerfeld quantum theory. However, already classically there is a problem which has essential implications for the quantum mechanics of the (φ,I)‐model for the HO: the transformation is only locally symplectic and singular for (q,p) = (0,0). Globally the phase space {(q,p)} has the topological structure of the plane ℝ2, whereas the phase space {(φ,I)} corresponds globally to the punctured plane ℝ2 ‐(0,0) or to a simple cone with the tip deleted. From the properties of the symplectic transformations on that phase space one can derive the functions h0 = I, h1 = Icos φ and h2 = ‐Isin φ as the basic coordinates on {(φ,I)}, where their Poisson brackets obey the Lie algebra of the symplectic group of the plane. This implies a qualitative difference as to the quantum theory of the phase space {(φ,I)} compared to the usual one for {(q,p)}: In the quantum mechanics for the (φ,I)‐model of the HO the three hj correspond to the self‐adjoint generators Kj, j = 0,1,2, of certain irreducible unitary representations of the symplectic group or one of its infinitely many covering groups, the representations being parametrized by a (Bargmann) index k > 0. This index k determines the ground state energy of the (φ,I)‐Hamiltonian . For an m‐fold covering the lowest possible value for k is k = 1/m, which can be made arbitrarily small by choosing m accordingly! This is not in contradiction to the usual approach in terms of the operators Q and P which are now expressed as functions of the Kj, but keep their usual properties. The richer structure of the Kj quantum model of the HO is “erased” when passing to the simpler (Q,P)‐model! This more refined approach to the quantum theory of the HO implies many experimental tests: Mulliken‐type experiments for isotopic diatomic molecules, experiments with harmonic traps for atoms, ions and BE‐condensates, with charged HOs in external electric fields and the (Landau) levels of charged particles in external magnetic fields, with the propagation of light in vacuum, passing through strong external electric or magnetic fields. Finally it may lead to a new theoretical estimate for the quantum vacuum energy of fields and its relation to the cosmological constant.
The radial wavefunction of a relativistic binary of two fermions bound by the Coulomb force
Authors: Marsch E.
Published: June 2022

The exact radial eigenfunctions of a relativistic binary atom bound by the static Coulomb force are calculated. We consider the two‐fermion Dirac equation for two distinguishable fermions (like, e.g., in positronium) including the static Coulomb potential but no radiative corrections. As shown in a previous paper and its addendum this problem can be solved exactly [1]. Here we provide the exact solution in terms of generalized hypergeometric functions for the radial eigenfunctions of the hamiltonian, which are determined through a matrix recursion relation. Also, an equivalent set of coupled first‐order, or uncoupled second‐order, differential equations that may be solved numerically is provided.
A case study of the Hirsch index for 26 non‐prominent physicists
Authors: Schreiber M.
Published: June 2022

Thehindex was introduced by Hirsch to quantify an individual's scientific research output. It has been widely used in different fields to show the relevance of the research work of prominent scientists. I have worked out 26 practical cases of physicists which are not so prominent. Therefore this case study should be more relevant to discuss various features of the Hirsch index which are interesting or disturbing or both for the more average situation. In particular, I investigate quantitatively some pitfalls in the evaluation and the influence of self‐citations.
Statistics of charge transfer through impurities in strongly correlated 1D metals*
Authors: Komnik A. , Trauzettel B. , Weiss U.
Published: June 2022

We review recent advances in the field of full counting statistics (FCS) of charge transfer through impurities imbedded into strongly correlated one‐dimensional metallic systems, modelled by Tomonaga‐Luttinger liquids (TLLs). We concentrate on the exact analytic solutions for the cumulant generating function, which became available recently and apply these methods in order to obtain the FCS of a non‐trivial contact between two crossed TLL.
Shot noise in non‐adiabatically driven nanoscale conductors*
Authors: Kaiser F.J. , Kohler S.
Published: June 2022

We investigate the noise properties of pump currents through molecular wires and coupled quantum dots. As a model we employ a two‐level system that is connected to electron reservoirs and is non‐adiabatically driven. Concerning the electron‐electron interaction, we focus on two limits: non‐interacting electrons and strong Coulomb repulsion. While the former case is treated within a Floquet scattering formalism, we derive for the latter case a master equation formalism for the computation of the current and the zero‐frequency noise. For a pump operated close to internal resonances, the differences between the non‐interacting and the strongly interacting limit turn out to be surprisingly small.
It's the coupling that creates resistance: Spin electronics in layered magnetic structures
Authors: Grünberg P.
Published: June 2022

Fast‐paced technological advancement is squeezing the data on computer hard disks ever closer together. For some ten years now, continuously shrinking and increasingly sensitive read/write heads are making use of the giant magnetoresistance (GMR) effect discovered in 1988. This term was coined for the effect that electric resistance of a magnetic layer system changes dramatically when the magnetization of the individual layers is reversed from antiparallel to parallel orientation. Very small external magnetic fields suffice to change the orientation and thus give GMR read/write heads their high sensitivity.
Max Planck – a life for thermodynamics*
Authors: Müller I.
Published: June 2022

Every problem that Max Planck approached during his long and distinguished career turned out, one way or another, to be motivated by thermodynamics and considerations of entropy. This was so, in particular, when Planck formulated the correct formula for the spectrum of black‐body radiation, whose interpretation made him the earliest pioneer of quantum mechanics. With his formulation of the third law of thermodynamics he gave the entropy a specific and definite value, which – to his own surprise – was closely related to the action quantum h, which we now call Planck's constant.
On the nature of thermodynamic extremum principles: The case of maximum efficiency and maximum work*
Authors: Jahnke T. , Birjukov J. , Mahler G.
Published: June 2022

Extremum principles are at the heart of theoretical physics. For a complete definition one does not only need to specify the variable to be extremized but also the respective functional space and its parametrization. Here we use a control‐theoretical approach to clarify the meaning of two maximum principles in the context of cyclic thermodynamic processes.
The Fokker‐Planck equation, and its application in plasma physics*
Authors: Peeters A.G. , Strintzi D.
Published: June 2022

In a classic paper Max Planck derived an equation, now known as the Fokker‐Planck equation, which plays a central role in the statistics description of many body problems. The equation is used in many branches of physics as well as chemistry and biology to describe a variety of different processes. In plasma physics, on which this paper concentrates, it forms the corner stone for the description of the Coulomb collisions. Furthermore, it is pointed out that also the so‐called quasi‐linear theory is closely related to the Fokker‐Planck equation.
Influence of light waves on the thermoelectric power under large magnetic field in III‐V, ternary and quaternary materials
Authors: Ghatak K.P. , Bhattacharya S. , Pahari S. , De D. , Ghosh S. , Mitra M.
Published: June 2022

We study theoretically the influence of light waves on the thermoelectric power under large magnetic field (TPM) for III‐V, ternary and quaternary materials, whose unperturbed energy‐band structures, are defined by the three‐band model of Kane. The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings in the presence of external photoexcitation. It has been found by taking n‐InAs, n‐InSb, n‐Hg1‐xCdxTe and n‐In1‐xGaxAsyP1‐y lattice matched to InP as examples that the TPM decreases with increase in electron concentration, and increases with increase in intensity and wavelength, respectively in various manners. The strong dependence of the TPM on both light intensity and wavelength reflects the direct signature of light waves that is in direct contrast as compared with the corresponding bulk specimens of the said materials in the absence of external photoexcitation. The rate of change is totally band‐structure dependent and is significantly influenced by the presence of the different energy‐band constants. The well‐known result for the TPM for nondegenerate wide‐gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions and this compatibility is the indirect test of our generalized formalism. Besides, we have also suggested the experimental methods of determining the Einstein relation for the diffusivity:mobility ratio, the Debye screening length and the electronic contribution to the elastic constants for materials having arbitrary dispersion laws.
Superluminal propagation of evanescent modes as a quantum effect
Authors: Wang Z.‐Y. , Xion C.‐D. , He B.
Published: June 2022

Contrary to mechanical waves, the two‐slit interference experiment of single photons shows that the behavior of classical electromagnetic waves corresponds to the quantum mechanical one of single photons, which is also different from the quantum‐field‐theory behavior such as the creations and annihilations of photons, the vacuum fluctuations, etc. Owing to a purely quantum effect, quantum tunneling particles including tunneling photons (evanescent modes) can propagate over a spacelike interval. With this picture we conclude that the superluminality of evanescent modes is a quantum mechanical rather than a classical phenomenon.
Effect of pure phase decoherence on entanglement teleportation
Authors: Ge M. , Zhu L.‐F. , Qiu Liang
Published: June 2022

We study entanglement teleportation in the two‐qubit XX Heisenberg model with pure phase decoherence taken into account. For some initial entangled states, pure phase decoherence has no effect on the teleported entanglement, while for others pure phase decoherence has a pronounced effect. In addition, entanglement sudden death happens in the latter case.
Universal tunneling time for all fields
Authors: Nimtz G. , Stahlhofen A.A.
Published: June 2022

Tunneling is an outstanding physical process. The observation that particles surmount a high barrier in spite of the fact that they don't have the necessary energy can not be explained by classical physics. However, this so called tunneling became allowed by quantum mechanics. Experimental tunneling studies with different photonic barriers from microwave frequencies up to ultraviolet frequencies point towards a universal tunneling time [1, 2]. Tunneling can be described by virtual, that is, by unobservable particles [3]. In the case of tunneling there is a virtual particle between the real incident and the real transmitted particles. Tunneling modes are solutions of the Schrödinger and of the Helmholtz equations. The most prominent example of the occurrence of tunneling modes in optics is frustrated total internal reflection (FTIR) at double prisms. In 1949 Sommerfeld [4] pointed out that this optical phenomenon represents the analogy of quantum mechanical particle tunneling. Recent experimental and theoretical data confirmed the conjecture that the tunneling process is characterized by a universal tunneling time presumably independent of the kind of field. The observed tunneling processes proceeded at a time of the order of magnitude of the reciprocal frequency of the wave packets.
Revival‐collapse phenomenon in the quadrature squeezing of the multiphoton Jaynes‐Cummings model with the binomial states
Authors: El‐Orany F.A.A.
Published: June 2022

In this paper we study the interaction between a two‐level atom and a quantized single‐mode field, namely, the Jaynes‐Cummings model (JCM). The field and the atom are initially prepared in the binomial state and the excited atomic state, respectively. For this system we prove that the revival‐collapse phenomenon exhibited in the atomic inversion of the standard JCM can be numerically (naturally) manifested in the evolution of the squeezing factor of the three‐photon (standard) JCM provided that the initial photon‐number distribution of the radiation field has a smooth envelope.
Four‐level systems and a universal quantum gate
Authors: Baldiotti M.C. , Gitman D.M.
Published: June 2022

We discuss the possibility of implementing a universal quantum XOR gate by using two coupled quantum dots subject to external magnetic fields that are parallel and slightly different. We consider this system in two different field configurations. In the first case, parallel external fields with the intensity difference at each spin being proportional to the time‐dependent interaction between the spins. A general exact solution describing this system is presented and analyzed to adjust field parameters. Then we consider parallel fields with intensity difference at each spin being constant and the interaction between the spins switching on and off adiabatically. In both cases we adjust characteristics of the external fields (their intensities and duration) in order to have the parallel pulse adequate for constructing the XOR gate. In order to provide a complete theoretical description of all the cases, we derive relations between the spin interaction, the inter‐dot distance, and the external field.
Particle production and nonlinear diffusion in relativistic systems
Authors: Wolschin G.
Published: June 2022

The short parton production phase in high‐energy heavy‐ion collisions is treated analytically as a nonlinear diffusion process. The initial buildup of the rapidity density distributions of produced charged hadrons within τp≃ 0.25 fm/c occurs in three sources during the colored partonic phase. In a two‐step approach, the subsequent diffusion in pseudorapidity space during the interaction time of τint≃ 7‐10 fm/c (mean duration of the collision) is essentially linear as expressed in the Relativistic Diffusion Model (RDM) which yields excellent agreement with the data at RHIC energies, and allows for predictions at LHC energies. Results for d+Au are discussed in detail.
Max Born and his legacy to condensed matter physics*
Authors: Cardona M. , Marx W.
Published: June 2022

After a presentation of Max Born's most salient biographical data, we discuss his contributions to science and science policy, with special emphasis on those related to condensed matter physics. Our discussion includes journal articles as well as books. The methodology used is both qualitative and quantitative, including number of items, number of formal and informal citations, and other bibliometric indicators such as the recently proposed Hirsch index (h‐index). The data are mainly based on the Thomson/ISI Web of Science (WoS) which covers a carefully selected set of the more prestigious journals dating back to 1900. Born's books and articles not published in the journals covered by the WoS can also be evaluated, provided they are cited within the WoS journals. Some anecdotic and historical details, which have come to the fore in the course of our bibliometric investigations, are included.
Interacting bosons in an optical lattice
Authors: Moseley C. , Fialko O. , Ziegler K.
Published: June 2022

A strongly interacting Bose gas in an optical lattice is studied using a hard‐core interaction. Two different approaches are introduced, one is based on a spin‐1/2 Fermi gas with attractive interaction, the other one on a functional integral with an additional constraint (slave‐boson approach). The relation between fermions and hard‐core bosons is briefly discussed for the case of a one‐dimensional Bose gas. For a three‐dimensional gas we identify the order parameter of the Bose‐Einstein condensate through a Hubbard‐Stratonovich transformation and treat the corresponding theories within a mean‐field approximation and with Gaussian fluctuations. This allows us to evaluate the phase diagram, including the Bose‐Einstein condensate and the Mott insulator, the density‐density correlation function, the static structure factor, and the quasiparticle excitation spectrum. The role of quantum and thermal fluctuations are studied in detail for both approaches, where we find good agreement with the Gross‐Pitaevskii equation and with the Bogoliubov approach in the dilute regime. In the dense regime, which is characterized by the phase transition between the Bose‐Einstein condensate and the Mott insulator, we discuss a renormalized Gross‐Pitaevskii equation. This equation can describe the macroscopic wave function of the Bose‐Einstein condensate in the dilute regime as well as close to the transition to the Mott insulator. Finally, we compare the results of the attractive spin‐1/2 Fermi gas and those of the slave‐boson approach and find good agreement for all physical quantities.
What is missing from Minkowski's “Raum und Zeit” lecture
Authors: Damour T.
Published: June 2022

This contribution tries to highlight the importance of Minkowski's “Raum und Zeit” lecture in a “negative” way, where negative is taken in the photographic sense of reversing lights and shades. Indeed, we focus on the “shades” of Minkowski's text, i.e. what is missing, or misunderstood. In particular, we focus on two issues: (i) why are Poincaré's pioneering contributions to four‐dimensional geometry not quoted by Minkowski (while he abundantly quoted them a few months before the Cologne lecture)?, and (ii) did Minkowski fully grasp the physical (and existential) meaning of “time” within spacetime? We think that this “negative” approach (and the contrast between Poincaré's and Minkowski's attitudes towards physics) allows one to better grasp the boldness of the revolutionary step taken by Minkowski in his Cologne lecture.
Nonlocal special relativity
Authors: Mashhoon B.
Published: June 2022

In the special theory of relativity, Lorentz invariance is extended in Minkowski spacetime from ideal inertial observers to actual observers by means of the hypothesis of locality, which postulates that accelerated observers are always pointwise inertial. A critical examination of the locality assumption reveals its domain of validity: it is true for pointwise coincidences, but is in conflict with wave‐particle duality. To remedy this situation, a nonlocal theory of accelerated systems is presented that reduces to the standard theory in the limit of small accelerations. Some of the main consequences of nonlocal special relativity are briefly outlined.
Electromagnetic energy and momentum in moving media
Authors: Obukhov Y.N.
Published: June 2022

The problem of the electromagnetic energy‐momentum tensor is among the oldest and the most controversial in macroscopic electrodynamics. In the center of the issue is a dispute about the Minkowski and the Abraham tensors for moving media. An overview of the current situation is presented. After putting the discussion into a general Lagrange‐Noether framework, the Minkowski tensor is recovered as a canonical energy‐momentum. It is shown that the balance equations of energy, momentum, and angular momentum are always satisfied for an open electromagnetic system despite the lack of the symmetry of the canonical tensor. On the other hand, although the Abraham tensor is not defined from first principles, one can formulate a general symmetrization prescription provided a timelike vector is available. We analyze in detail the variational model of a relativistic ideal fluid with isotropic electric and magnetic properties interacting with the electromagnetic field. The relation between the Minkowski energy‐momentum tensor, the canonical energy‐momentum of the medium and the Abraham tensor is clarified. It is demonstrated that the Abraham energy‐momentum is relevant when the 4‐velocity of matter is the only covariant variable that enters the constitutive tensor.
Resonance‐like Goos‐Hänchen shift induced by nano‐metal films
Authors: Gruschinski R. , Nimtz G. , Stahlhofen A.A.
Published: June 2022

The influence of nano‐metal films on the Goos‐Hänchen shift (GHS) is investigated. The films were deposited at the total reflecting surface of a perspex prism and had a sheet resistance varying between Z□ = 25 and 3 000 Ω. A resonance‐like enhancement of the shift and of the absorption is found for TE polarized waves, when the sheet resistance approached the value of the vacuum impedance. For TM waves the influence of the metal films on the GHS was marginal. The experiments were carried out with microwaves.