Is diamagnetism really acausal?

Fuente: arXiv
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Main Authors: Westerberg, Niclas, Barnett, Stephen M.
Format: Preprint
Published: 2025
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author Westerberg, Niclas
Barnett, Stephen M.
author_facet Westerberg, Niclas
Barnett, Stephen M.
contents Diamagnetism, in which the magnetisation in a medium opposes the direction of an applied magnetic field, is a weak but familiar effect in a wide class of materials. Being weak it is also a linear response to any applied field. The problem is that the existence of diamagnetism is in direct conflict with the requirements of causality as embodied in the familiar Kramers-Kronig relations. Nature does not care about our confusion and diamagnetism exists and physics is constrained by the requirements of causality (that effect cannot precede its cause). This puzzle has received intermittent attention from time to time, with a variety of arguments made to resolve the paradox. None of these, no matter how plausible, reveal the mechanism that resolves the existence of diamagnetism without sacrificing causality. The full resolution is presented in this letter.
format Preprint
id arxiv_https___arxiv_org_abs_2505_10612
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Is diamagnetism really acausal?
Westerberg, Niclas
Barnett, Stephen M.
Quantum Physics
Materials Science
Other Condensed Matter
Optics
Diamagnetism, in which the magnetisation in a medium opposes the direction of an applied magnetic field, is a weak but familiar effect in a wide class of materials. Being weak it is also a linear response to any applied field. The problem is that the existence of diamagnetism is in direct conflict with the requirements of causality as embodied in the familiar Kramers-Kronig relations. Nature does not care about our confusion and diamagnetism exists and physics is constrained by the requirements of causality (that effect cannot precede its cause). This puzzle has received intermittent attention from time to time, with a variety of arguments made to resolve the paradox. None of these, no matter how plausible, reveal the mechanism that resolves the existence of diamagnetism without sacrificing causality. The full resolution is presented in this letter.
title Is diamagnetism really acausal?
topic Quantum Physics
Materials Science
Other Condensed Matter
Optics
url https://arxiv.org/abs/2505.10612