Breakdown Of Time-reversal Invariance Research Articles

Comment on “Magnetic circular dichroism versus orbital magnetization”

In a recent article [Resta, Phys. Rev. Research 2, 023139 (2020)] it is argued, based on the dichroic sum rules derived from the modern theory of orbital magnetization, that the x-ray magnetic circular dichroism (XMCD) orbital magnetization sum rule is not providing an expectation value of the orbital angular momentum and of the orbital part of the magnetic moment, but a different quantity, also related to the breakdown of time-reversal invariance, but different. In this Comment, it is shown that this conclusion is incorrect, and that the XMCD sum rule, within its assumptions, delivers an essentially exact expectation value of the orbital angular momentum and of the orbital moment.

Dynamical breakdown of time reversal invariance and causality

Irreversibility and acausality of a sub-system are established in exactly soluble harmonic models with reversible and causal dynamics. It is shown that initial conditions, imposed on some dynamical degrees of freedom may break time reversal invariance for other degrees of freedom. This happens if observations carried out in any large but finite amount of time can not resolve the spectrum of the eliminated degrees of freedom, namely when the spectrum has a condensation point at the ground state. Acausality follows due to the dominance of the dynamics by almost time-independent modes.

Anomalous Nernst effect from a chirald-density-wave state in underdoped cuprate superconductors

We show that the breakdown of time-reversal invariance, confirmed by the recent polar Kerr effect measurements in the cuprates, implies the existence of an anomalous Nernst effect in the pseudogap phase of underdoped cuprate superconductors. Modeling the time-reversal-breaking ordered state by the chiral $d$-density-wave state, we find that the magnitude of the Nernst effect can be sizable even at temperatures much higher than the superconducting transition temperature. These results imply that the experimentally found Nernst effect at the pseudogap temperatures may be due to the chiral $d$-density-wave ordered state with broken time-reversal invariance.

Paramagnetic Meissner effect and time reversal non-invariance from spin polarization

We propose that recent experiments on the paramagnetic Meissner effect can be understood in terms of pairing fermion (quasiparticle) spin polarization. The polarization comes from the fact that for Coulomb Fermi systems the polarized state has lower energy than the unpolarized state due to the Coulomb interactions when the fermion density is small. With suitable surface topology the polarized spins cannot be screened by supercurrents inside a surface layer. The same theory explains also the double transition inUPt3and the observed breakdown of time reversal invariance associated with polarized spins. The low temperature Schottky effects seen in high-Tccases are also proposed to be caused by the polarization.

Effect of weak time-dependence of disorder on localization

The zero momentum divergence of the zero frequency Cooperon- (i.e. leading quantum-) correction to the dc-conductance of noninteracting electrons in a random potential is cut off when the random potential changes on a time-scale which is much larger than the electron mean free time. This is due to a breakdown of time-reversal invariance. As a consequence this system belongs to the unitary case concerning the Anderson transition.

Macroscopic T nonconservation: Prospects for a new experiment.

Breakdown of time-reversal invariance can be detected in macroscopic samples as a magnetic alignment along an electric field. It is shown that both fundamental and practical limits to the detection of this effect in paramagnets correspond to measurement of electron electric dipole moments down to d(e) of about 10 to the -28th e cm on 50-g quantities of EuS near its Curie point; this compares to the current limit of d(e) not greater than 10 to the -24th e cm. Strategies for still greater sensitivity are outlined.