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J. E. Hirsch

Publications and source records attributed to J. E. Hirsch.

At least 109 records · Page 6Linked to original sources
arXiv2008

Hole superconductivity in Arsenic-Iron compounds

Superconductivity above 25K, and possibly above 40K, has recently been discovered in $LaO_{1-x}F_xFeAs$ and related compounds. We propose that this is another example of the mechanism of hole superconductivity at play. This requires the existence of hole carriers at the Fermi energy, which appears to contradict current observations. We propose that two-band conduction is taking place in these materials, that the negative ion $As^{-3}$ plays a key role, and that superconductivity is non-phononic and driven by pairing and undressing of heavily dressed hole carriers to lower their kinetic energy. We make several predictions of future observations based on our theory.

cond-mat.supr-con↗
arXiv2008

The missing angular momentum of superconductors

We point out that the Meissner effect, the process by which a superconductor expels magnetic field from its interior, represents an unsolved puzzle within the London-BCS theoretical framework used to describe the physics of conventional superconductors, because it appears to give rise to non-conservation of angular momentum. Possible ways to avoid this inconsistency within the conventional theory of superconductivity are argued to be farfetched. Consequently, we argue that unless/until a consistent explanation is put forth, the existence of the Meissner effect represents an anomaly that casts doubt on the validity of the conventional framework. Instead, we point out that two elements of the unconventional theory of hole superconductivity, namely that the charge distribution in superconductors is macroscopically inhomogeneous, and the fact that spin-orbit coupling plays an essential role, allow for a consistent explanation of the Meissner effect.

cond-mat.supr-con↗
arXiv2008

Electrodynamics of spin currents in superconductors

In recent work we formulated a new set of electrodynamic equations for superconductors as an alternative to the conventional London equations, compatible with the prediction of the theory of hole superconductivity that superconductors expel negative charge from the interior towards the surface. Charge expulsion results in a macroscopically inhomogeneous charge distribution and an electric field in the interior, and because of this a spin current is expected to exist. Furthermore, we have recently shown that a dynamical explanation of the Meissner effect in superconductors leads to the prediction that a spontaneous spin current exists near the surface of superconductors. In this paper we extend the electrodynamic equations proposed earlier for the charge density and charge current to describe also the space and time dependence of the spin density and spin current. This allows us to determine the magnitude of the expelled negative charge and interior electric field as well as of the spin current in terms of other measurable properties of superconductors. We also provide a 'geometric' interpretation of the difference between type I and type II superconductors, discuss the relationship between our model and Slater's seminal work on superconductivity, and discuss the magnitude of the expected novel effects for elemental and other superconductors.

cond-mat.supr-con↗
arXiv2007

Spin Meissner Effect in Superconductors and the Origin of the Meissner Effect

We propose a dynamical explanation of the Meissner effect in superconductors and predict the existence of a spin Meissner effect: that a macroscopic spin current flows within a London penetration depth $λ_L$ of the surface of superconductors in the absence of applied external fields, with carrier density = the superfluid density and carrier speed $v=\hbar/(4m_eλ_L$) ($m_e=$bare electron mass). The two members of a Cooper pair circulate in orbits of radius $2λ_L$ in opposite direction and the spin current in a Cooper pair has orbital angular momentum $\hbar$. Our description also provides a 'geometric' interpretation of the difference between type I and type II superconductors.

cond-mat.supr-con↗
arXiv2007

Does the h-index have predictive power?

Bibliometric measures of individual scientific achievement are of particular interest if they can be used to predict future achievement. Here we report results of an empirical study of the predictive power of the h-index compared to other indicators. Our findings indicate that the h-index is better than other indicators considered (total citation count, citations per paper, and total paper count) in predicting future scientific achievement. We discuss reasons for the superiority of the h-index.

physics.soc-ph↗
arXiv2007

Comment on Theory of spin Hall effect

Chudnovsky recently proposed (arXiv: 0709.0725) a beautifully simple mechanism for the intrinsic spin Hall effect involving an extension of the Drude model. We point out that an equivalent proposal was made by us in an alternative treatment of the problem in Phys.Rev. B60, 14787 (1999) (arXiv:cond-mat/9910408, reaching identical conclusions. The coincidence of both approaches supports their physical validity. The mechanism applies to the spin Hall effect in all metals and semiconductors and to the anomalous Hall effect in all ferromagnetic metals and semiconductors.

cond-mat.mes-hall↗
arXiv2007

Do superconductors violate Lenz's law? Body rotation under field cooling and theoretical implications

When a magnetic field is turned on, a superconducting body acquires an angular momentum in direction opposite to the applied field. This gyromagnetic effect has been established experimentally and is understood theoretically. However, the corresponding situation when a superconductor is cooled in a pre-existent field has not been examined. We argue that the conventional theory of superconductivity does not provide a prediction for the outcome of that experiment that does not violate fundamental laws of physics, either Lenz's law or conservation of angular momentum. The theory of hole superconductivity predicts an outcome of this experiment consistent with the laws of physics.

cond-mat.supr-con↗
arXiv2005

E=mc^2, ΔH = D(H-H)$, and the end of civilization

100 years ago Einstein discovered $E=mc^2$, the secret energy stored in ordinary mass. $ΔH = D(H-H)$ is the chemical energy released in chemical bond formation between two H atoms. The failure to recognize the enormously different energy scales in those two equations reflected in current events may start a chain reaction this very year, on the one-hundredths anniversary of Einstein's discovery, that leads to the end of civilization. Due to the confluence of a particular set of circumstances, this particular moment is more dangerous than any other in the history of nuclear weapons. Physicists have a special responsibility to do their utmost to prevent this from happening. This paper is a call to arms. A principle to underpin nuclear non-proliferation and enhance stability is advocated.

physics.soc-ph↗
arXiv2005

Pair production and ionizing radiation from superconductors

We show that an alternative theory of superconductivity recently proposed (theory of hole superconductivity) leads to the surprising consequence that real electron-positron pair production will occur for superconductors larger than a critical size. High frequency radiation with frequencies up to $0.511MeV/\hbar$ is predicted to be emitted from superconductors out of equilibrium. Attention to the possibility of harmful consequences is called for.

cond-mat.supr-con↗
arXiv2005

Spin currents, relativistic effects and the Darwin interaction in the theory of hole superconductivity

The existence of macroscopic spin currents in the ground state of superconductors is predicted within the theory of hole superconductivity. Here it is shown that the electromagnetic Darwin interaction is attractive for spin currents and repulsive for charge currents. It is also shown that the mere existence of spin currents implies that some electrons are moving at relativistic speeds in macroscopic superconductors, which in turn implies that the Darwin interaction plays a fundamental role in stabilizing the superconducting state.

cond-mat.supr-con↗
arXiv2005

Why holes are not like electrons. II. The role of the electron-ion interaction

In recent work, we discussed the difference between electrons and holes in energy band in solids from a many-particle point of view, originating in the electron-electron interaction, and argued that it has fundamental consequences for superconductivity. Here we discuss the fact that there is also a fundamental difference between electrons and holes already at the single particle level, arising from the electron-ion interaction. The difference between electrons and holes due to this effect parallels the difference due to electron-electron interactions: {\it holes are more dressed than electrons}. We propose that superconductivity originates in 'undressing' of carriers from $both$ electron-electron and electron-ion interactions, and that both aspects of undressing have observable consequences.

cond-mat.supr-con↗
arXiv2005

Explanation of the Tao effect

In a series of experiments Tao and coworkers\cite{tao1,tao2,tao3} found that superconducting microparticles in the presence of a strong electrostatic field aggregate into balls of macroscopic dimensions. No explanation of this phenomenon exists within the conventional theory of superconductivity. We show that this effect can be understood within an alternative electrodynamic description of superconductors recently proposed that follows from an unconventional theory of superconductivity. Experiments to test the theory are discussed.

cond-mat.supr-con↗
arXiv2004

Reply to "Comment on 'Charge expulsion and electric field in superconductors'"

I argue that the validity of the new electrodynamic equations for superconductors proposed in my paper can and should be decided by experiment. Furthermore I show that BCS theory is ambiguous in its prediction of screening of longitudinal electric fields and hence cannot be used to decide between the validity of my theory versus the conventional theory. I also give a physical argument for why screening of electric fields by superconducting electrons should be expected to be less efficient than that by normal electrons, as predicted by the new equations.

cond-mat.supr-con↗
arXiv2004

The fundamental role of charge asymmetry in superconductivity

Neither BCS theory nor London theory contain any charge asymmetry. However it is an experimental fact that a rotating superconductor always exhibits a magnetic field parallel, never antiparallel, to its angular velocity. This and several other experimental observations point to a special role of charge asymmetry in superconductivity, which is the foundation of the theory of hole superconductivity. The theory describes heavy dressed {\it positive} hole carriers in the normal state that undress by pairing and become light undressed {\it negative} electron carriers in the superconducting state. Superconductivity is driven by kinetic energy lowering rather than by electron-phonon coupling as in BCS. In quantum mechanics, kinetic energy lowering is associated with $expansion$ of the electronic wave function, and hence we predict: (1) Superconductors expel $negative$ charge from their interior which consequently becomes $positively$ charged; (2) Macroscopic electrostatic fields exist in the interior of superconductors always, and in certain cases also outside near the surface; (3) Macroscopic spin currents exist in the superconducting state; (4) Superconductors are 'rigid' with respect to their response to applied longitudinal electric fields. These predictions apply to all superconductors and are testable but are as yet untested. The theory predicts highest $T_c$'s for materials for which normal state transport occurs through $(positive)$ holes in $negatively$ charged anions.

cond-mat.supr-con↗
arXiv2004

Spin currents in superconductors

It is argued that experiments on rotating superconductors provide evidence for the existence of macroscopic spin currents in superconductors in the absence of applied external fields. Furthermore it is shown that the model of hole superconductivity predicts the existence of such currents in all superconductors. In addition it is pointed out that spin currents are required within a related macroscopic (London-like) electrodynamic description of superconductors recently proposed. The spin current arises through an intrinsic spin Hall effect when negative charge is expelled from the interior of the metal upon the transition to the superconducting state.

cond-mat.supr-con↗
arXiv2004

Electrodynamics of superconductors

An alternate set of equations to describe the electrodynamics of superconductors at a macroscopic level is proposed. These equations resemble equations originally proposed by the London brothers but later discarded by them. Unlike the conventional London equations the alternate equations are relativistically covariant, and they can be understood as arising from the 'rigidity' of the superfluid wave function in a relativistically covariant microscopic theory. They predict that an internal 'spontaneous' electric field exists in superconductors, and that externally applied electric fields, both longitudinal and transverse, are screened over a London penetration length, as magnetic fields are. The associated longitudinal dielectric function predicts a much steeper plasmon dispersion relation than the conventional theory, and a blue shift of the minimum plasmon frequency for small samples. It is argued that the conventional London equations lead to difficulties that are removed in the present theory, and that the proposed equations do not contradict any known experimental facts. Experimental tests are discussed.

cond-mat.str-el↗